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Arctic sea ice / Re: MOSAiC news
« on: Today at 04:49:17 AM »
I went through the last 45 days of preprints at The Cryosphere journal looking for new Mosaic articles. There was a third one there, another N-ICE2015 piece now five years out, and quite a few others of interest to this and other Arctic forums, select ones below.

Most of the articles have quite readable sections, better than the abstracts. It's seldom a good idea to get too far from the mainstream in forum posts so these provide a good baseline for those wanting anchors to reality.
Never forget that extraordinary claims require extraordinary evidence. The burden of proof is always on the proposer; there is no burden of disproof on the non-believer.

Estimating statistical errors in retrievals of ice velocity and deformation parameters from satellite images and buoy arrays

Sea ice drifts under the influence of wind and ocean currents. Spatial gradients in the sea ice motion lead to distortion of the sea ice cover, termed deformation. The retrieval of sea ice drift vectors and deformation parameters from pairs or sequences of satellite synthetic aperture radar (SAR) images has gained increased attention during recent years because of the growing availability of suitable data.. Sea ice kinematics is also studied based on data from arrays of buoys or GPS receivers   which in addition can serve as reference in comparisons to motion vectors obtained from SAR images. The knowledge of spatially detailed motion and deformation fields is potentially useful in ice navigation to locate divergent or compressive ice areas, as complementary information for operational sea ice mapping, for validation of models for forecasting of ice conditions, and for assimilation into ice models.

Seasonal transition dates can reveal biases in Arctic sea ice simulations

Arctic sea ice experiences a dramatic annual cycle, and seasonal ice loss and growth can be characterized by various metrics: melt onset, breakup, opening, freeze onset, freeze-up, and closing. By evaluating a range of seasonal sea ice metrics, CMIP6 sea ice simulations can be evaluated in more detail than by using traditional metrics alone, such as sea ice area. We show that models capture the observed asymmetry in seasonal sea ice transitions, with spring ice loss taking about 1–2 months longer than fall ice growth. The largest impacts of internal variability are seen in the inflow regions for melt and freeze onset dates, but all metrics show pan-Arctic model spreads exceeding the internal variability range, indicating the contribution of model differences. Through climate model evaluation in the context of both observations and internal variability, we show that biases in seasonal transition dates can compensate for other unrealistic aspects of simulated sea ice. In some models, this leads to September sea ice areas in agreement with observations for the wrong reasons.

New insights into radiative transfer in sea ice derived from autonomous ice internal measurements

The radiative transfer of short-wave solar radiation through the sea ice cover of the polar oceans is a crucial aspect of energy partitioning at the atmosphere-ice-ocean interface. A detailed understanding of how sunlight is reflected and transmitted by the sea ice cover is needed for an accurate representation of critical processes in climate and ecosystem models, such as the ice-albedo feedback. Due to the challenges associated with ice internal measurements, most information about radiative transfer in sea ice has been gained by optical measurements above and below the sea ice. To improve our understanding of radiative transfer processes within the ice itself, we developed a new kind of instrument equipped with a number of multispectral light sensors that can be frozen into the ice. A first prototype consisting of a 2.3 m long chain of 48 sideward planar irradiance sensors with a vertical spacing of 0.05 m was deployed at the geographic North Pole in late August 2018, providing autonomous, vertically resolved light measurements within the ice cover during the autumn season. Here we present the first results of this instrument, discuss the advantages and application of the prototype and provide first new insights into the spatiotemporal aspect of radiative transfer within the sea ice itself. In particular, we investigate how measured attenuation coefficients relate to the optical properties of the ice pack, and show that sideward planar irradiance measurements are equivalent to measurements of total scalar irradiance.

Implications of surface flooding on airborne thickness measurements of snow on sea ice

Snow thickness observations from airborne snow radars, such as the NASA’s Operation IceBridge (OIB) mission, have recently been used in altimeter-derived sea ice thickness estimates, as well as for model parameterization. A number of validation studies comparing airborne and in situ snow thickness measurements have been conducted in the western Arctic Ocean, demonstrating the utility of the airborne data. However, there have been no validation studies in the Atlantic sector of the Arctic. Recent observations in this region suggest a significant and predominant shift towards a snow-ice regime, caused by deep snow on thin sea ice. During the Norwegian young sea ICE expedition (N-ICE2015) in the area north of Svalbard, a validation study was conducted on March 19, 2015, during which ground truth data were collected during an OIB overflight. Snow and ice thickness measurements were obtained across a two dimensional (2-D) 400 m × 60 m grid. Additional snow and ice thickness measurements collected in situ from adjacent ice floes helped to place the measurements obtained at the gridded survey field site into a more regional context. Widespread negative freeboards and flooding of the snow pack were observed during the N-ICE2015 expedition, due to the general situation of thick snow on relatively thin sea ice. These conditions caused brine wicking and saturation into the basal snow layers, causing more diffuse scattering and influenced the airborne radar signal to detect the radar main scattering horizon well above the snow/sea ice interface

Trends and spatial variation in rain-on-snow events over the Arctic Ocean during the early melt season

 Rain-on-snow (ROS) events can accelerate the surface ablation of sea ice, thus greatly influencing the ice-albedo feedback. However, the variability of ROS events over the Arctic Ocean is poorly understood due to limited historical station data in this region. In this study early melt season ROS events were investigated based on four widely-used reanalysis products (ERA-Interim, JRA-55, MERRA2 and ERA5) in conjunction with available observations at Arctic coastal stations. The performance of the reanalysis products in representing the timing of ROS events and the phase change of precipitation was assessed. Our results show that ERA-Interim better represents the onset date of ROS events in spring and ERA5 better represents the phase change of precipitation associated with ROS events. All reanalyses indicate that ROS event timing has shifted to earlier dates in recent decades (with maximum trends up to −4 to −6 days/decade in some regions in ERA-Interim), and that sea ice melt onset in the Pacific sector and most of the Eurasian marginal seas is correlated with this shift. There has been a clear transition from solid to liquid precipitation, leading to more ROS events in spring, although large discrepancies were found between different reanalysis products. In ERA5, the shift from solid to liquid precipitation phase during the early melt season has directly contributed to a reduction in spring snow depth on sea ice by more than −0.5 cm/decade averaged over the Arctic Ocean since 1980, with the largest contribution (about −2.0 cm/decade) in the Kara-Barents Seas and Canadian Arctic Archipelago.

Methane cycling within sea ice; results from drifting ice during late spring, north of Svalbard

Sea ice is an important component of the Arctic system playing a significant role for gas exchange between ocean and atmosphere. However, global warming has led to a sharp retreat of sea ice coverage in the Arctic Ocean during the last decades. During 2019 sea ice covered 4.15 million km2 in summer representing a decrease of 33 % compared to the 1981-2010 average (Perovich et al., 2019). The negative downward trend in Arctic summer sea ice coverage has been observed for more than 30 years. This tendency is expected to continue  over the next decades   including a cascade of possible associated effects. In particular, sea ice retreat may quickly induce enhanced methane (CH4) emissions into the atmosphere due to the loss of its barrier function
for sea-air gas exchange. Because the Arctic holds large natural sources of this highly potent
greenhouse gas, this effect has to be considered as positive feedback of global warming. Moreover, the resulting decreased temporal flux retention of methane under the ice reduces oxidation intensity to the less potent CO2

Seasonal changes in sea ice kinematics and deformation in the Pacific Sector of the Arctic Ocean in 2018/19

Arctic sea ice kinematics and deformation play significant roles in heat and momentum exchange between atmosphere and ocean. However, mechanisms regulating their changes at seasonal scales remain poorly understood. Using position data of 32 buoys in the Pacific sector of the Arctic Ocean (PAO), we characterized spatiotemporal variations in ice kinematics and deformation for autumn–winter 2018/19. In autumn, sea ice drift response to wind forcing and inertia were stronger in the southern and western than in the northern and eastern parts of the PAO. These spatial heterogeneities decreased gradually from autumn to winter, in line with the seasonal evolution of ice concentration and thickness. Areal localization index decreased by about 50 % from autumn to winter, suggesting the enhanced localization of intense ice deformation as the increased ice mechanical strength. In winter 2018/19, a highly positive Arctic Dipole and a weakened high pressure system over the Beaufort Sea led to a distinct change in ice drift direction and an temporary increase in ice deformation. During the freezing season, ice deformation rate in the northern part of the PAO was about 2.5 times that in the western part due to the higher spatial heterogeneity of oceanic and atmospheric forcing in the north. North–south and east–west gradients in sea ice kinematics and deformation of the PAO observed in autumn 2018 are likely to become more pronounced in the future as sea ice losses at higher rates in the western and southern than in the northern and western parts.

Clouds damp the radiative impacts of polar sea ice loss

Clouds play an important role in the climate system: (1) cooling Earth by reflecting incoming sunlight to space and (2) warming Earth by reducing thermal energy loss to space. Cloud radiative effects are especially important in polar regions and have the potential to significantly alter the impact of sea ice decline on the surface radiation budget. Using CERES (Clouds and the Earth's Radiant Energy System) data and 32 CMIP5 (Coupled Model Intercomparison Project) climate models, we quantify the influence of polar clouds on the radiative impact of polar sea ice variability. Our results show that the cloud short-wave cooling effect strongly influences the impact of sea ice variability on the surface radiation budget and does so in a counter-intuitive manner over the polar seas: years with less sea ice and a larger net surface radiative flux show a more negative cloud radiative effect. Our results indicate that 66±2% of this change in the net cloud radiative effect is due to the reduction in surface albedo and that the remaining 34±1 % is due to an increase in cloud cover and optical thickness. The overall cloud radiative damping effect is 56±2 % over the Antarctic and 47±3 % over the Arctic. Thus, present-day cloud properties significantly reduce the net radiative impact of sea ice loss on the Arctic and Antarctic surface radiation budgets. As a result, climate models must accurately represent present-day polar cloud properties in order to capture the surface radiation budget impact of polar sea ice loss and thus the surface albedo feedback.

A linear model to derive melt pond depth on Arctic sea ice from hyperspectral data

Melt ponds are key elements in the energy balance of Arctic sea ice. Observing their temporal evolution is crucial for understanding melt processes and predicting sea ice evolution. Remote sensing is the only technique that enables large-scale observations of Arctic sea ice. However, monitoring melt pond deepening in this way is challenging because most of the optical signal reflected by a pond is defined by the scattering characteristics of the underlying ice. Without knowing the influence of meltwater on the reflected signal, the water depth cannot be determined. To solve the problem, we simulated the way meltwater changes the reflected spectra of bare ice. We developed a model based on the slope of the log-scaled remote sensing reflectance at 710 nm as a function of depth that is widely independent from the bottom albedo and accounts for the influence of varying solar zenith angles. We validated the model using 49 in situ melt pond spectra and corresponding depths from shallow ponds on dark and bright ice Our results indicate that our model enables the accurate retrieval of pond depth on Arctic sea ice from optical data under clear sky conditions without having to consider pond bottom albedo. This technique is potentially transferrable to hyperspectral remote sensors on unmanned aerial vehicles, aircraft and satellites.

Surface-Based Ku- and Ka-band Polarimetric Radar for Sea Ice Studies Mosaic

To improve our understanding of how snow properties influence sea ice thickness retrievals from presently operational and upcoming satellite radar altimeter missions, as well as investigating the potential for combining dual frequencies to simultaneously map snow depth and sea ice thickness, a new, surface-based, fully-polarimetric Ku- and Ka-band radar (KuKa radar) was built and deployed during the 2019–2020 year-long MOSAiC International Arctic drift expedition. This instrument, built to operate both as an altimeter (stare mode) and a scatterometer (scanning mode), provided the first in situ Ku- and Ka-band dual frequency radar observations from autumn freeze-up through mid-winter, and covering newly formed ice in leads, first-year and second-year ice floes. Data gathered in the altimeter mode, will be used to investigate the potential for estimating snow depth as the difference between dominant radar scattering horizons in the Ka- and Ku-band data. In the scatterometer mode, the Ku- and Ka-band radars operated under a wide range of azimuth and incidence angle ranges, continuously assessing changes in the polarimetric radar backscatter and derived polarimetric parameters, as snow properties varied under varying atmospheric conditions. These observations allow for characterizing radar backscatter responses to changes in atmospheric and surface geophysical conditions. In this paper, we describe the KuKa radar and illustrate examples of these data and demonstrate their potential for these investigations.

Simulated Ka- and Ku-band radar altimeter scattering horizon on snow-covered Arctic sea ice Ku- and Ka-band Polarimetric Radar for Sea Ice Studies

Owing to differing and complex snow geophysical properties, radar waves of different wavelengths undergo variable penetration through snow-covered sea ice. However, the mechanisms influencing radar altimeter backscatter from snow-covered sea ice, especially at Ka- and Ku-band frequencies, and its impact on the Ka- and Ku-band radar scattering horizon or the "track point" (i.e. the scattering layer depth detected by the radar re-tracker), are not well understood. In this study, we evaluate the Ka- and Ku-band radar scattering horizon with respect to radar penetration and ice floe buoyancy using a first-order scattering model and Archimedes’ principle. Our simulations demonstrate that the Ka- and Ku-band track point difference is a function of snow depth, however, the simulated track point difference is much smaller than what is reported in the literature from the CryoSat-2 Ku-band and SARAL/AltiKa Ka-band satellite radar altimeter observations. We argue that this discrepancy in the Ka- and Ku-band track point differences are sensitive to ice type and snow depth and its associated geophysical properties. Snow salinity is first increasing the Ka- and Ku-band track-point difference when the snow is thin and then decreasing the difference when the snow is thick (> 10 cm). A relationship between the Ku-band radar scattering horizon and snow depth is found. This relationship has implications for 1) the use of snow climatology in the conversion of radar freeboard into sea ice thickness and 2) the impact of variability in measured snow depth on the derived ice thickness.

Arctic sea ice / Re: MOSAiC news
« on: September 19, 2020, 09:56:46 PM »
FOMO today: the last of the off-ship experimental equipment is being brought on board for a Sept 20th departure. The original plan called for Oct 15th but that was later changed to Oct 12th. They first set up on Oct 4th of 2019. They arrived at the North Pole on Aug 20th 2020and to their present floe shortly thereafter, so a month moored and a bare minimum of the freezing season sampled.

It may take them a while to reach the ice edge from where they are with helicopter fog, ice pressure and thickness hindering progress but open leads and intermediate concentration favoring it. The Polarstern can do some work while underway, notably surface water chemistry, disposable CTD casts and ice thickness measurements.

It's possible the ship will pause underway or near the ice edge to study the ice for a while. The return port is Bremerhaven as there are no more trip legs and no reason to meet up in Norway.

A truly massive logistical effort under trying conditions that they accomplished safely. It's too soon to say what scientific advances will come out of all the data collected (which launched buoys will continue for years). It seems like the primary focus was atmospheric boundary layer processes though of course they looked at everything imaginable.

As a guess: incremental improvement in many areas of our understanding of the Arctic but no real game-changers in terms of radical improvements to satellite interpretation or seasonal ice prediction from improved models.

Consequences / Re: The Climatic Effects of a Blue Ocean Event
« on: September 19, 2020, 07:30:44 PM »
Please keep comments appropriate to the "Climatic Effects of a Blue Ocean Event" forum. This is not a catch-all forum for climate change or climate policy discussion. 'Climatic' means inappropriate for local Arctic-only seasonal impacts which have their own forums.

Consider discussing and developing your favorite BOE climatic effect based on other recent scientific journal articles. Just making bald assertions or intuiting is not going to work quantitatively given the complexity of planetary climate systems. Try to see where a given subject is at. Full text can always be located at

Rightly or wrongly, the vast majority of climate science focuses on long-term build-up of greenhouse gases and their effects at NH mid-latitudes where most white people live and most of their food is grown. Rightly or wrongly, messaging is currently centered on CO2 levels and what can be done to reduce it (more trees, less beef consumption, fossil fuels, consumerism). All this is incredibly important but unacceptably off-topic given this forum's restricted remit.

The authors here framed their result in the above context, the trillion extra tons. Their calculated effect on annual heat retention alone is enough by itself to seriously undercut current global policy planning on climate change and to significantly offset benefits from planting trees, going vegan and riding wind-powered electric bicycles. Yes, lots of other feedbacks like ESAS methane could pile on but there are forums for those too.

My subsequent posts will be looking into the calculation itself and its reliability. Science does not arrive written on clay tablets. Already, an alternative method has been published. Those authors find less of an effect but actually their results still call for a massive effect (which they call 'modest'). Still, both calculations could be wrong or have too high a level of uncertainty to deserve concern priority.

To repeat, the loss of the planet's primary climate-buffering refrigerator (seasonal high latitude albedo) is only one aspect of downstream consequences of fractional loss of Arctic sea ice increasingly matching the insolation season.

BOE events do not happen overnight on Sept 14th but instead will have a long lead-up of increasing areas of low albedo open water, a much better match to peak insolation than mid-Sep dates which don't match at all. More sunlight absorbed means less reflected up and, after cloud and atmospheric processes, less incident sunlight escaping out to space. The papers under consideration look only at this: heat retained = TOE input - TOE output.

The three articles do not aspire to represent all downstream aspects nor to compare its impacts to all others; they merely assert it is large and real. If you find scientific errors missed by peer reviewers -- and that happens -- please document specifics. Alternatively, write a separate post based on different articles about your pet effect.
The first graphic is taken from a pair of easy-read classics by Perovich, Stroeve and others. They follow the solar insolation distribution during seasonal evolution of the surface, the complement of the Pistone 2019 independent top of atmosphere observations and projections.

Solar partitioning in a changing Arctic sea-ice cover
DK Perovich et al
Annals of Glaciology 52(57) 2011

"The daily values of albedo depend on the local onset dates of melt and freeze-up. The albedo sequence includes melt ponds, assuming they follow an evolution similar to that observed by Perovich and others (2002). Using the method of Markus and others (2009), daily averaged satellite passive microwave temperatures are used to map four onset dates for each grid cell for each year: early melt, full melt, early freeze-up and full freeze-up.

"Briefly, the melt season is determined using temporal changes in brightness temperatures at 37 GHz and temporal changes in the gradient ratio between 19 and 37 GHz

1. Before melt onset the snow albedo is 0.85.
2. At early melt the albedo decreases to 0.81.
3. Starting with full melt, there is a linear decrease to 0.71 in 15 days.
4. For the next 6 days, decrease from 0.70 to 0.50.
5. Albedo decreases by 0.0029 d–1 (but to no less than 0.2).
6. At early freeze-up set albedo to 0.46, representing some ponds freezing.
7. At full freeze-up, albedo increases by 0.026 per day to 0.85."

Increasing solar heating of the Arctic Ocean and adjacent seas, 1979–2005:
DK Perovich et al
Geophys. Res. Lett., 34(19), L19505. (10.1029/2007GL031480.)

The graphical time series will look at incipient fractional BOE: open water in the Arctic Basin at the time of maximum insolation (summer solstice, June 21). There is a surprising amount of open water already on that date and has been for years. However the AMSR2 record used is not long enough to distinguish trend from natural variability. That is a fool's errand anyway if the New Arctic is qualitatively different. However the unweighted locational average is still instructive.

The animation will show open water for the years 2013-20 (since 2012 data starts later). The second graphic will provide the average geographic distribution for open water for eight years on the solstice and later dates. A preliminary version gives the idea.

This average is calculated graphically to sidestep the flawed netCDF. Select open water blue in each year and color it 240 white (out of 256 pure white). If every year has open water at a given pixel location, then all the pixels will be 240 and the average atoo in the output graphic. If 7 years are open water, then 7/8 or 210 is the output, and so on down to 1/8 yielding 30, not quite black. 

Thus the average-graphic is strongly but accurately binned into a 8-10 colors (allowing a few extra for land and and pole markers. The image can then be recolored with any discrete palette without disturbing quantitative accuracy.

To weight recent years more heavily, their layer simply needs to be duplicated by the chosen weighting number.

Arctic sea ice / Re: MOSAiC news
« on: September 19, 2020, 01:57:09 PM »
The Mosaic expedition seems to be winding down/falling apart despite being scheduled to continue until Oct 12th. That's not unusual, the horse begins to gallop when it smells the barn.

It hasn't been made clear whether the 12th is the date when field equipment is borught in and the engines fired up or the date of arrival at the dock in Tromsø. The ice has been thickening but not to point where the return passage of a week would be hindered.

The ship's position is currently 89.1  110.7, quite close to the pole but some 2274km from port at 69.6 18.9 which would require about 100 hours of travel time in calm seas.

Ice movement yesterday continued to be extreme, or rather no one seemed to have suspected prior to the expedition what the new normal would be. The long lead re-opened again; it extends off the edge of the radar so 5km or more. The pack also has a bulk rotational component and that 179m broken-off floe pounding on the port side of the ship. This is surprising since the winds at their position have been brisk but not exceptional, below 10m/s.

Arctic sea ice / Re: MOSAiC news
« on: September 18, 2020, 11:37:28 AM »
Floe motion is as crazy as ever around the Polarstern's position of 89.1  107.4 despite mild winds of 4m/s and cold temperatures of -9.4ºC. Despite two weeks of increasing ice chaos documented on bow radar, there has been no mention to date of its effects on scientific equipment deployment on Follow  :) :) :) Mosaic.

Instead, various science for science sake studies on snow flakes and algae are described that seem like escapism. Thee could just as well have been done in the Baltic. It might have been better to have just concentrated on studies relevant to climate change. There's been almost no mention of that over the last year.

The six hour time series raises questions about whether distinct floes exist at this near-pole site. What's seen are blocks of ice joining up with other blocks of ice, then leaving for another. When that repeats, the block boundaries are often different with new fractures and leads as boundaries. Spatial constraints limit the options though so despite many breaks and rejoins the picture can eventual return to resemble to the start.

The notion of solid SYI ice blocks welded together into a matrix with weak intervening FYI freezes doesn't seem applicable. Without having the whole history of formation, how are floe boundaries defined if most are ever-changing composites?

Consequences / Re: The Climatic Effects of a Blue Ocean Event
« on: September 18, 2020, 10:45:24 AM »
Central Arctic?
That may refer to Region 11 of Masie map at NSIDC. These divisions are widely used but have no physical basis for basin boundaries and do not correlate well with ice age or thickness distributions.

Great to see Nico links and gerontocrat graphs; it's been a most excellent bottom-up effort. Earlier posts have said potential albedo doesn't take clouds into consideration. The Pistone papers are top-down, all about clouds, the satellites that observe them, and the sunlight coming in vs that decreasing portion lost to space under a growing fractional BOE trend and consequent greater adsorption, retention and redistribution of extra heat within the earth climate system.

With just scattered buoys and the occasional ship, given the rapidly changing cloud layers, phases  and fog we see all summer blocking WorldView and microwave observation of the surface, it's hard to convert potential into actual albedo without field observations and simplifying assumptions.

The evolving complexity over the summer of ice/snow surface reflectance/transmittance of incident sunlight and indeed measuring it over time but just over one sq km among millions has been a main focus of Mosaic and its buoys, towers, drones, balloons and aircraft as well as similar expeditions before it such as Sheba and N-ICE2015. These expeditions are funded because it is not yet feasible to calculate critical parameters ab initio or observe them from space.

Even open water varies a lot on its albedo according to capillary waves and sun angles. However the dramatic factor-of-ten difference between sea and ice albedos does allow estimation of the effect of an ever-encroaching fractional open water on the insolation season.

In terms of precipitation, wx-savvy posters sometimes differentiate rain vs snow using RAMMB. GFS/nullschool provides 3HPA, TPW and TCW channels for 3-hr accumulation, precipitable water in the air column, and total cloud water. Rain has a huge effect on albedo and its latent heat on snow/ice melt and thus on early attainment of open water so its future trend (and that of clouds under Arctic Amplification) is critical:

The impact of Arctic warming on increased rainfall
R Bintanja 2018

No one here has taken an interest in CERES which seems to be the satellite sensor scientists mainly use to characterize Arctic clouds and incoming storms. WorldView has recently added nine new cloud data layers; those too have not yet gotten a forum mention. Posts do frequently use the M3 13 11 (pink vie) on NOAA-20 VIIRS to see where clouds are not obscuring ice surface visibility.

The cloud layer is very complicated; it is not a binary topic of cloud vs not cloud or high vs low but many types and combinations with highly variable optical properties. Indeed when that Finnish firm Vaisala shared their lightening event database for the Central Arctic, it suggested far more convective thunderstorm weather occurs than anyone had imagined.

Interannual variations of Arctic cloud types in relation to sea ice
R Eastman 2009

Cloud radiative forcing of the Arctic surface:
The influence of cloud properties, surface albedo, and solar zenith angle
MD Shupe JM Intrieri 2004    Sheba and later Mosaic co-leader

Given the difficult of just monitoring albedo over a single ongoing melt season, one can wonder just how accurately the Pistone and Donohoe papers above can calculate loss of Arctic refrigerator effect as the fraction of early open water continues to grow. Encouragingly they come out with quite similar numbers despite very different approaches.

The latter paper sees a slightly lower effect, calling it 'modest' whereas in fact it is still catastrophic as in the Pistone papers.

As with ESAS methane, nobody wants to hear about albedo, better to err on the side of least drama, hundreds of examples documented by AbruptSLR on that forum.

Arctic sea ice / Re: Home brew AMSR2 extent & area calculation
« on: September 17, 2020, 01:45:33 PM »
using SIC LEADS (experimental) processing?
There's a lot of that going around but that region seems also lit up in the old AMSR2_UHH which does not have that processing so apparently is just a reduced sea ice concentration area (or passing weather artifact since persistence has not yet been established).

Meanwhile has CMEMS has released an amazing interactive product, sort of Mercator Ocean on steroids. Only a fraction of its available layers are shown in the screenshot below. The graphical slider is fully interactive so a particular lat lon can be followed for a whole year for SST, thickness, concentration etc.

As always, a slick display can get ahead of underlying data quality. And it's one thing to study the data at the site but another to port it away somewhere else. It needs its own tinyUrl generator like WorldView. The display cannot be rotated to Greenland down in situ. However this is a very rich site that we may need to use a lot.

SMOS-SMAP ice thickness is shaping up as colder temperatures settle in. It needs to be scaled up 130.07% to fit over AMSR2_AWI. Actually it needs to be redone entirely as an 8-bit color tiffs

Ascat is also looking better though not there yet. The url has been moving around but the link below is working (if you know the day-number(,

Consequences / Re: The Climatic Effects of a Blue Ocean Event
« on: September 16, 2020, 10:40:59 PM »
It's worth a look at what climate scientists have recently published specifically on the topic of large scale open water gain and consequent albedo loss has during an early fractional BOE summer because the extra heat kicks in immediately adding to the earth's heat imbalance.

A truly comprehensive bibliography is beyond the scope of a post: thousands of papers going back decades on the overall impact of arctic amplification or sea ice loss on the global climate, for example J Francis et al 2009 on "20th and 21st century Arctic cloud amounts in global climate models". or JE Overland et al 2016 "Nonlinear response of mid-latitude weather to the changing Arctic".

The K Pistone 2019 paper mentioned above is directly on-topic: sunlight that formerly bounced off the reflective ice back into outer space is greatly diminished during a near-BOE summer due to the dramatically decreased albedo of open water, greatly enhancing retained solar heat.

This heat will be redistributed across the whole climate system affecting many processes but the paper focuses solely on how much less solar energy goes back out to space. This is readily measurable over the Arctic.

An earlier 2014 paper by these same authors appeared in PNAS along with some later back-and forth based on a misunderstanding of Arctic-specific top-of-the-atmosphere albedo vs globally averaged vs surface.

Observational determination of albedo decrease caused by vanishing Arctic sea ice
K Pistone  I Eisenman V Ramanathan
PNAS March 4, 2014 111 (9) 3322-3326; open access
128 cites

A thoughtful technical paper discussing the two Pistone papers in detail appeared as Donohoe 2020 (with a Piomas co-author). After developing alternatives to perceived shortcomings, the authors conclude with a lower but similarly shocking estimate of the sea ice albedo loss effect (10-19% vs 25%).

K Pistone has four new above-cloud aerosol papers in 2020 but nothing further yet on BOE albedo. I have not yet checked on the two co-authors.

he Effect of Atmospheric Transmissivity on Model and Observational Estimates of the Sea Ice Albedo Feedback
A Donohoe E Wrigglesworth A Schweiger Philip J. Rasch
J. Climate (2020) 33 (13): 5743–5765.

Consequences / Re: The Climatic Effects of a Blue Ocean Event
« on: September 16, 2020, 09:37:06 PM »
Here I want to calculate a range of fractional BOE area values and display them over various common Arctic Ocean graphics in plausible areas and shapes for remnant ice. For example, what does two million sq km of ice look like up against the Canadian coast?

According to wikipedia, a polar cap area on a spherical earth (not quite our WGS84 ellipsoid) can be calculated by a simple formula given the radius of the earth and the latitude of the bottom of the cap. Having some target areas for BOE in mind, inverting the area formula will give the cap latitude yielding them.

The formula given is area = 2 pi r*r (1-cos (theta)) where theta is the polar angle included from the center of earth to the pole and to the bottom of the cap. This is not the latitude but rather its complement lat = 90-theta. Solving for theta for target area with the shorter polar radius of the earth taken as 6357 km amounts to finding a spreadsheet to provide the arccos function and convert radians to degrees:

90 - theta = 90- degrees(acos(1-(target area ÷ 2 *3.1416 * 6357 *6357)))

target area   cap lat
 500000   86.40
1000000   84.91
1500000   83.77
2000000   82.80
2500000   81.95
3000000   81.18
3500000   80.48
4000000   79.82
4500000   79.20
5000000   78.61

These need to be checked against a daily NSIDC matching area during late melt season (eg four million sq km but Greenland Sea and CAA unwelcome minor contributions) because the polar stereographic projection is not equal area -- the pole region is off by 5-6%. However for simply visualizing what remnant ice would look like, it is good enough.

The outcome shows the 85º latitude is convenient for BOE 1.0 as it comes provided on products such as AMSR1_UHH. The 80th parallel is similarly appropriate to the four million BOE 4.0. Elsewhere, the radius for the circle tool centered on the pole can be figured after pixels/degree are calculated from parallels provided or from known land latitudes such as the Bering Strait at 65.89°.

After drawing the polar cap out to the chosen radius in an auxiliary layer and filling it, the pixel count should be noted in the histogram tool. This will vary depending on the scale of the underlying image resource, eg OsiSaf, AMSR2_large, Mercator Ocean etc etc.

Next, the move and loop tools in Gimp freeware can be used to move the cap area to another location and to another shape while holding the pixel count at the histogram constant. For example, the fractional BOE area might adjusted so its bottom uses the upper contours of the CAA islands.

Some examples in a bit. The final shape favored will vary from person to person for each fractional BOE as the 2012-2020 shapes of remnant ice vary quite a bit.

Consequences / Re: The Climatic Effects of a Blue Ocean Event
« on: September 16, 2020, 06:15:54 PM »
One ice cube left = not a BOE
That is not how it is used in the scientific literature. There are a fair number of peer-reviewed articles on this very subject. They are primarily concerned with light energy reflected back into outer space, the loss of the Arctic as planetary refrigerator concept. This is a huge deal in itself, calculated below as a trillion tons of CO2 emission equivalent. (No one gives a hoot about local DMI 80N graphics.)

Radiative Heating of an Ice-Free Arctic Ocean
K Pistone I Eisenman V Ramanathan

During recent decades, there has been dramatic Arctic sea ice retreat. This has reduced the top-of-atmosphere albedo, adding more solar energy to the climate system. There is substantial uncertainty regarding how much ice retreat and associated solar heating will occur in the future. This is relevant to future climate projections, including the timescale for reaching global warming stabilization targets.

Here we use satellite observations to estimate the amount of solar energy that would be added in the worst-case scenario of a complete disappearance of Arctic sea ice throughout the sunlit part of the year. Assuming constant cloudiness, we calculate a global radiative heating of 0.71 W/m2 relative to the 1979 baseline state. This is equivalent to the effect of one trillion tons of CO2 emissions. These results suggest that the additional heating due to complete Arctic sea ice loss would hasten global warming by an estimated 25 years.

It is perhaps better to use BOE 0.0, BOE 0.5, BOE 1.0, BOE 2.0, BOE 3.0 etc according to what you intend as no one has the authority or scientific justification to declare a definition, though BOE 1.0 has traction on forums even though it lacks any grounding in physics.

However any choice is ill-posed. The problem, as @zlabe put it earlier, is we are really talking about the area and latitudinal timing of open water albedo vs insolation calendar. In other words, the energy retention integral over the whole summer season is growing worse as more ice is lost earlier. This extra retained heat will be redistributed somewhere within the climate system, the very last thing it needs right now.

This year was very bad by late July because of early open water, early melt and fire soot in terms of fractional BOE (the fraction of how bad it could possibly get, assuming some middle-ground cloud model).

I posted two graphics earlier that explain how to calculate this with two clicks (without dipping into math); no one had any interest either way.

Next post will show various BOE areas as polar latitudinal caps, then reshape and reposition with the Gimp loop and histogram tools, keeping pixel count constant. This has to be done separately for each projection scale, eg SMOS, OsiSaf, AMSR2 etc.

The word event suggests wrongly a single point in time, ie a day in mid-Sept when albedo is irrelevant. BOE is really about the albedo part of the energy budget of the entire high latitude season, the major modeling imponderable being cloud properties, snow cover and weather temperature distribution.

The land permafrost albedo is another huge consideration very much affected by Arctic Amplification. A BLE (bare land event) interacts strongly so it is difficult to carve out just an Arctic Ocean BOE from observation of overall extra solar energy retention from loss of northern latitude albedo.

Arctic sea ice / Re: MOSAiC news
« on: September 16, 2020, 02:55:26 PM »
The frenetic motion of floes continued for another day on Sept 15th. The bouncing floe within the open lead is 170x170m; the scale is 10m per pixel. Impacts on Mosaic operations remain undisclosed.

The Polarstern is represented by the gray ball; it is moored with its starboard bow against the ice (not shown as blocked from radar), so the bow is pointing east in the time series and ice motion below the ship is black (not visualized). The frames are 0.1 sec apart vs 6 hours apart on board so the motion is sped up 6*60*60*10 = 216,000 times, a lot but less than commonly done for Jakobshavn or Petermann glaciers.

The last frame is midnight on Sept 15th. The floe is at 89.1º latitude with air temperatures -4º, low enough to put a much-fractured ice skim on opening/closing leads. They do have kayaks on board but helicopter, fog permitting, is the main way to reach stranded equipment if indeed their specific floe is affected.

The winds at the ship have died down considerably from their peak of 16m/s but wind stress nearby can still propagate ice motion to their site.

The avi's frame of reference, while basically co-moving (lagrangian), has never been explained. The radar antenna rotates in a full circle, taking less than a minute to capture its scene. Of the 360 scenes taken per six hours, only one is retained for the shared video. The rest are shown on the bridge and also on meeting room monitors.

The bridge also has an instrument that measures ship heading, the angle between the mid-ship half-axial line and a line to north pole. (The magnetic pole cannot be used in the high Arctic.) This heading is shared to the radar display along with other parameters that have all been cropped out, with truncated 2dp lat lon and timestamp restored.

In production, each frame is rotated as specified by ship heading so north is always straight up the white scale bar. The ship is rigidly attached on its starboard side its floe by six sea anchors except when it breaks loose; anchors are checked and re-sunk daily as necessary.

The floe commonly rotates during the six hour gap between frames. This causes the 83º black-out area to rotate after correction to the fixed north pole heading. Recent months have seen a red ball added to each image to indicate the ship, rather than a more logical icon that shows bow and stern.

The center of the radar image (which verifies as a true circle) lies near the bottom of this red ball, NOT on its center. This is the location of the bridge mast on which the rotating radar is mounted several dozen meters above the water.

We do not know if the black-out area is symmetric with respect to the ship's long axis (perhaps because of intervening metal masts or smokestack); it may not extend to the experimental area to avoid rfi. If so, ice immediately port side is shown. The comparable radar on N-ICE2015 showed 360º.

The clumsy north icon obscuring the data is a recent add-on that serves no known purpose. It walks east and west without holding its lat lon, its position seemingly in accordance with blackout zone rotation.

Because the ship is so close to the pole, latitude lines converge rapidly. Only the white bar center goes straight up. Other latitude lines are straight but angled appropriately. The longitude lines are convex up and likely the expected arcs of circles.

The floe is mostly drifting along with the regional ice pack (which is known compact, ie at 100% sea ice concentration at 3x3 km resolution) but sometimes cohesive motion breaks down and floes in the scene have quasi-independent motions compatible with each other's constraints.

Motion of the Polarstern can be marked up within the video by tracking a lat lon intersection between frames. This gives jointed line segments and segmental mean velocities at six hour intervals. However GPS on ship and adjacent buoys are half-hourly or less with 4 dp precision, meaning a spreadsheet with a haversine column shows ship rotations and translations much better. as seen in uniq's many buoy products.

The speeds are rather high relative to those seen during the past year, over 1.2 km/hr for extended stretches. The Polarstern was subjected to a CCW gale force wind (small cyclone) during the affected period, likely responsible for the stress leading to the dramatic ice break-up motions.

The red bars on the buoy speed graphs show that six-hour sampling is not close enough to capture ups and downs in floe speeds whereas the half-hour buoy iridium call are satisfactory.

The buoy data is at the meereis gallery; the excel-ready haversine formula needs lat lon data in the first two columns; the csv speed file is attached.

=ACOS(COS(RADIANS(90-A2)) * COS(RADIANS(90-A3)) + SIN(RADIANS(90-A2)) *SIN(RADIANS(90-A3)) *COS(RADIANS(B2-B3))) *6356.752

Arctic sea ice / Re: MOSAiC news
« on: September 15, 2020, 03:57:16 PM »
The worst ice movement of the whole year-long expedition is happening. It is probably not a risk to the ship itself (though the rudder got rammed by a floe earlier) but puts experimental equipment out on the ice in jeopardy.

'Follow Mosaic' has not said if they can keep field work going safely under these conditions; in the past, great effort went into just keeping power lines out and sensors upright and running. Today's post is all about chlorophyll, fading light and zooplankton. The photo could be a week old for all we know.

It's hard to see the scientific value of sampling a hole or two over winter in an immense ocean; how long will biological data stay relevant in the fast-changing Arctic. Does AWI believe the coming BOE will bring a fisheries and fossil fuel bonanza? #53  diatom Melosira arctica

Arctic sea ice / Re: Home brew AMSR2 extent & area calculation
« on: September 14, 2020, 06:16:02 PM »
tiff can contain multiple 'pages' which might retain the lut
Right, worth exploring. Seems like we once had a WorldView url that showed its individual swaths and their timestamp. Given the rapid change in cloud cover, WV often has nasty swath lines and discontinuities when assembled into a full day. Be good synergy if we could get NOAA-20 VIIRS and AMSR2_AWI synched up.

I have never seen a step-by-step list of how to get from the satellite sensor's raw orbital data download to the first raster array (restricted to the Arctic).

There has been a race to the bottom in file formats to see who can provide the most incomprehensibly broad format prescription, for example geotiff and netCDF. They are really more like folders than files. Which is good because related information can't get separated but bad if web browsers and common software can't open them.

The question is inclusivity, how much of it the joe sixpack end user can see. NetCDF had a close call with oblivion -- one person makes Panoply happen, without it 99.999% of the world could not see climate model data. As mentioned, a single netCDF can store image sequences; Panoply is set up to animate and combine them.

The recent webp story is also interesting. It is a big improvement on gif89 in many ways (better compression, better color) but until all the major web browsers provided support, it couldn't really be used. Which is not to say forum software here will catch on soon.

Arctic sea ice / Re: MOSAiC news
« on: September 14, 2020, 05:10:17 PM »
FooW: consider the big picture
This is helpful. We are taken up documenting day to day noise but it is all happening for underlying climate change reasons.

The composite below looks at the position of the Polarstern relative to the North Pole, the AMSR2 pole hole of no data, the wind power density, the distance to the ice edge, and a cyclonic storm barreling up from the North Atlantic that has brought measurable precipitation (2nd image, 3hr accumulation).

The ship has been drifting rapidly and may reach the pole yet though the ice we wanted them to look at will have drifted away. They are currently 454 km away from the ice edge based on the pixel ratio for the pole to Morris Jesup. Note a strong wind is bearing down on a vulnerable region of ice north of SevZem which could still dramatically lower its concentration.

Both images benefit from a click. You are wasting your time on this forum if not looking beyond thumbnails. We cannot accurately downscale indexed color.

Arctic sea ice / Re: MOSAiC news
« on: September 14, 2020, 01:45:12 PM »
Somewhere up-forum, all the weather commentaries for the entire expedition was extracted into a flatfile database and a MS Word-type glossary system proposed to stub in the code lookups to eliminate tedious and error-prone code lookups. No one picked up that baton.

Meanwhile, the last three bow radar frames for the 13th show a very large lead opening immediately in front of the Polarstern's bow if not right under the ship. We have no better time resolution for the cycle of closed, open, closed than 12 hours but it may have been much shorter. The lead is 68m wide on average; 6 km of length is visible to the outer edge of the image. It is a rocker event, so more a pivot than a shear.

This may or may not have done any damage to gangways, ice anchors, cables and experimental set-ups. It's possible field work was ongoing despite the miserable weather and staff separated by open water from the ship. Radar coverage of the experimental area has been blocked out the entire trip whereas N-ICE2015 had full 360º coverage.

All we know for certain at this time is that 'Follow Mosaic' will downplay -- or not even mention -- the incident no matter how much damage it caused. Indeed the 13th on FOMO is all smiles on a nitrate survey on yet another idyllic day.

The ship is in a surprisingly active area of ice motion due to a small cyclone enveloping it so this event will not be the end of it.

Arctic sea ice / Re: Home brew AMSR2 extent & area calculation
« on: September 14, 2020, 03:37:57 AM »
New hot spot? The northern Laptev has perhaps not been told about the end of melt season, the gold line showing the week's shrinkage. The AMSR2_AWI are just coming in now as an afternoon assembly. It seems that the 14 hr am swaths did not quite add up to complete coverage often enough.

Monday morning: the archive is back to its twice-daily! The Beaufort Arm and northern Laptev remain active areas of intra-day change.

The orbital progression is shown below. It might make sense to make an avi using each consecutive pass as a frame. This might be useful to people wanting the very latest data (or recent time series) on just a specific area who don't need the whole Arctic Ocean build. That area might fall within a consistent repeat swath (or not).

Arctic sea ice / Re: MOSAiC news
« on: September 14, 2020, 02:07:09 AM »
In terms of correcting the full-time DWD meteorologist on board the Polarstern who entered that call on the hourly awiMet report going to ECMWF, not going to do that from where I sit in smokey Arizona.

The FOMO today seems to show an icebow flanking an air temperature inversion giving rise to a pronounced refracted solar mirage of a type commonly seen in the Arctic. The optics are discussed in the attached pdf.

Wayne, a member here who has lived many years in far north Nunavut, has written very extensively about these inversions and what they mean for conditions of the ice but on Neven's blog, not the forums.

But as you say, it's all going to change.

Arctic sea ice / Re: MOSAiC news
« on: September 13, 2020, 06:20:49 PM »
The bow radar has resumed! It seems that acquisition never stopped but perhaps transmission of files to shore has only now been possible.

This goes out 5km in all directions except towards off-ship experimental sites so is a bit hard to register with the recent drone overhead of Sept 6th which showed almost entirely experimental sites! They do not even have a phone cam strapped to the radar mast to time-lapse for a visible correlation. (This does not even require an app, they come capable.)

The first image below registers the drone with bow radar. FOMO does not share compass direction on the drone shot nor its time of day (often given ambiguously as 'ship time' rather than the UTC of the bow radar). The drone photo only goes out 3.3 multiples of ship length (~400m) and so has far greater resolution than the bow radar which goes out 5000 m but with only ~500 pixels for it.

At any rate, some incredible ice advection can be seen in the 6-hour frame rate of the mp4 below, as well as the usual opening/closing of leads. As the ice freezes, the bow radar shows more brittle fracture than the mushy scenes of quasi-independent floes from the Fram.

FOMO has not made clear whether power lines and fiber optic data lines are being run out to remote sensors (which are only 4-5 ship lengths away this time). Consequently it is hard to determine whether trails and lines have been disrupted by lead openings and floe shifts.

Fascinating though local ice motion may be visually, it is not at all clear how to describe it scientifically or compare year on year (ie is it fracturing more). After N-ICE2015, its (very different) bow radar was written up in highly obscure technical terms. The real goal is to correlate it with wind stress and mechanical strength of the ice so the latter tensor can be deduced over the whole pack (without a ship being there) since the wind and drag are known fairly well from reanalysis.;O=A

Arctic sea ice / Re: MOSAiC news
« on: September 13, 2020, 05:54:43 PM »
salinity/freshness of melt ponds varies
Right. It is not an either/or situation. Measured PSU (practical salinity units) can vary from near zero to 35 from pond to pond (ie fresh to brackish to salty) depending on drainage and connectivity to other ponds and open leads, possibly stratified by depth if dense brine channels become exposed. Brine is partially extruded upward onto newly formed ice -- it does not all sink out the bottom. Arctic FYI is generally too salty to supply drinkable melt water to humans. The city limit is 1000 ppm or about 1/35 of sea water.

Since only 10's of cm of very low snow-water-equivalent snow fell this year along the Polarstern's route and that rapidly redeposited in the lee of pressure ridges, it's clear that an observed landscape of meter-deep melt pond was not filled with snow melt but rather with in situ ice melt.

A whole lot more is written about summer melt ponds than about what happens to them over the winter and spring. In a scene like the north pole, half the August landscape was melt ponds -- and not superficial ones at that. It follows the SYI will be very pocketed with them in the spring. None of this shows up in 'volume' models.

Yes it all freezes but depending on how fresh, brackish or saline it was, it never really "becomes one" with the ambient ice that matured but never melted. The ice retains aspects of its history; it never becomes one big crystal. Melt ponds have been around since forever but the issue today is the extent of ice heterogeneity -- it's gotten much greater. None of this shows up in satellite altimetry. It's often assumed for convenience that the ice pack is in local buoyancy equilibrium but it isn't really.

Since the freezing/melting point changes with salinity from 0ºC to -1.8ºC, floes wilt melt unevenly given their embedded melt ponds and false bottoms. If a melt pond began as brackish or salty, it will develop its own brine; if it never established a drain, that brine may become trapped. Brine reaches its eutectic point at −21.2 °C at which point it is 23.3% salt by mass.

And don't be fooled by oceanography jargon. They'll talk about a giant pool of 'fresh water' in the Beaufort Gyre when in point of fact, there isn't any at all. The somewhat lower salinity equates to a certain volume of hypothetical pure fresh water needed to be added to the Beaufort Sea to lower the psu. But observed could equally well have been attained with brackish.

"Dimethyl sulfide (DMS) production in the northern Arctic Ocean has been considered to be minimal because of high sea ice concentration and extremely low productivity. However, we found DMS concentration (1–33 nM) in melt ponds on sea ice at a very high latitude (78°N) in the central Arctic Ocean to be up to ten times that in the adjacent open ocean (<3 nM). We divided melt ponds into three categories: freshwater melt ponds, brackish melt ponds, and open saline melt ponds. Melt ponds from each category had different formation mechanisms and associated DMS contents. Closed brackish ponds (salinity of >20) had particularly high DMS concentration. Water in brackish ponds was mixed with open ocean water in the past via a hole at the bottom of the floe that kept the pond open to the ocean; therefore, unlike freshwater melt ponds, brackish ponds became sites of DMS accumulation.!divAbstract high DMS

In sea ice, interconnected pockets and channels of brine are surrounded by fresh ice. Over time, brine is lost by gravity drainage and flushing. The timing of salt release and its interaction with the underlying water can impact subsequent sea ice melt. Turbulence measurements 1 m below melting sea ice north of Svalbard reveal anticorrelated heat and salt fluxes. From the observations, 131 salty plumes descending from the warm sea ice are identified, confirming previous observations from a Svalbard fjord. The plumes are likely triggered by oceanic heat through bottom melt. Calculated over a composite plume, oceanic heat and salt fluxes during the plumes account for 6 and 9 % of the total fluxes, respectively, while only lasting in total 0.5 % of the time. The observed salt flux accumulates to 7.6 kg m−2, indicating nearly full desalination of the ice. Bulk salinity reduction between two nearby ice cores agrees with accumulated salt fluxes to within a factor of 2. The increasing fraction of younger, more saline ice in the Arctic suggests an increase in desalination processes with the transition to the “new Arctic”. brine plumes by Svalbard

In the summer months, melt water from the surface of the Arctic sea ice can percolate down through the ice and flow out of its base. This water is relatively warm and fresh compared to the ocean water beneath it, and so it floats between the ice and the oceanic mixed layer, forming pools of melt water called under-ice melt ponds. Sheets of ice, known as false bottoms, can subsequently form via double diffusion processes at the under-ice melt pond interface with the ocean, trapping the pond against the ice and completely isolating it from the ocean below. This has an insulating effect on the parent sea ice above the trapped pond, altering its rate of basal ablation. under-ice melt ponds"

Arctic sea ice / Re: MOSAiC news
« on: September 12, 2020, 08:51:06 PM »
I couldn't find any specs on either drone (such as flight range, flight duration, maximal altitude and kg of payload). The big one has an utterly unsearchable name (Spectra) but appears to be made in India; I can only direct you to their marketing team for further information. However there are no prospects for autonomous flights over any sizable part of the Arctic.

The two working aircraft AWI is currently operating could do a whole lot more more. They don't need the Polarstern down below, being capable of stop-and-go landings for spot ice measurements as was done out of Alert (but not exactly disclosed).

This is very different situation from Greenland where the radar instrument builder required prompt and full public disclosure online of every track. Or NASA satellites -- imagine the uproar if they delayed fire weather release until every possible 2023 publications had been bagged.

Polar 5 is a DC-3 built in 1942 but refurbished as a Basler BT-67 after the AWI acquired the plane in 2007. Without payload, the flying range is around 3900 km, enough for instrumented  transects. Polar 6, another DC-3, was acquired by AWI in 2011. It is doing the thickness transects but not sharing anything about them.

In January 2005, Polar 4 was severely damaged during a rough landing at the British over-wintering station Rothera on the Antarctic Peninsula. It was impossible to repair the plane and now parts are in a museum. Since then, scientific and logistical tasks of polar flights have been performed by Polar 2. In February 1985, the Polar 3 was shot down by guerrillas of the Polisario Front over West Sahara. All three crew members died. It was on its way back from Antarctica and had taken off in Dakar, Senegal, to reach the  Canary Islands.

Arctic sea ice / Re: MOSAiC news
« on: September 12, 2020, 06:46:05 PM »
may be too harsh on mosaic. 98.8% of site visitors can't be bothered to look at ice thickness when spoon fed to them.
Yes but 99.8% won't provide feedback on an improved ice concentration product even when it is solicited. They would rather copy/paste obsolete extent data Provided by Authorities on an untended pipeline whose errors go unnoticed for years.

My sense is that buoy data needs a lot more edu: arrows drawn on stills, longer prose accounts of basics, fewer assumptions that such and such is obvious, tutorials even, sharing of explanations provided by buoy owners. Buoys have a history of bizarre malfunctions; people not specializing in them lack confidence in interpretation. No one ever errs on a forum by providing too much explanation: HL Mencken 1926

The buoys reporting over iridium, international blowback if they had sequestered or encrypted that data. Buoys just reporting over LAN, we don't know how many are not shared at the meereis gallery.

That bow radar was good sharing while it lasted. I don't have a problem with it being done so stupidly but rather with their refusal to fix it.

In terms of dumbing down lat lon to 1 dp, now that took active malice. but it was also stupid because the ship was visible to 4dp on daily high resolution satellite imagery.

After Oct 2019, they never systematically disclosed what sensors were working at what locations at what times, presumably to avoid embarrassment.

A lot of what they did was driven by institutional prestige considerations that trumped any thought of sharing, especially after that truth-telling BBC reporter.

The Polarstern had a 30 year history of publishing a weekly captan's blog. Like everything else not under direct control of PR officers, it had to go. Mosaic was too big; the tail began to wag the dog.

Negotiations before the trip: they got everyone to agree on a central data repository but the price for that was keeping it shut down until 2023 when all interest would be gone. The culture of leisurely publication is deeply entrenched; it's a good fit with scientific escapism and controversy avoidance.

In fairness, a lot of coupled observational time series like the one below do not lend themselves to sharing. The data needs calibration and review first. However there is a middle road not taken -- a full year in to the expedition, this is really the first we have heard about these fancy drones and their mission.

AWI is research foundation of about a thousand staff founded in 1980; it is not a university or educational facility but rather part of the broader Helmholtz Association. The present expedition fits into their organizational chart as shown below.

Arctic sea ice / Re: Home brew AMSR2 extent & area calculation
« on: September 12, 2020, 01:17:47 AM »
The Beaufort Arm is hard to figure. Going by GFS nullschool surface winds and forecast waves, it should have been long gone by now. But it isn't, at least on the experimental twice daily AMSR2_AWI -- the ice concentration mostly seems to be just rearranging itself. Worldview visible, shows some larger CAB floes in rubble.

 If small debris goes above and below 3.1 x 3.1 km AMSR2 pixels according to wind, wave and current aggregation and dispersion, that could lead to inconsistency in the imagery. Yet on the visible, clouds prevent regular quantitative assessment of the ice left.

Arctic sea ice / Re: MOSAiC news
« on: September 12, 2020, 12:36:46 AM »
Mosaic posted a beautiful photo of the new mooring site taken by a small drone on Sunday 06 Sept 2020. Since the Polarstern is 180m in length bow to stern, a grid of those specs can be put over the image to establish a distance scale of 2 pixels per meter.

However the drone was not directly overhead at the time of the photo because the more of the port than starboard side is shown (assuming the smokestack is centered amidship). As usual, all the Exif data has been stripped off the photo: we do not know time of day (sun angle), direction of north, nor height of the drone, nor nadir inclination of the camera.

The location of the Polarstern varied quite a bit that day, ranging from 88.7-8º  113.5-119.0º, so the lat lon at the time of the photo can only be estimated.

Consequently it is not possibly to orthorectify the photo for purposes of measure percent of melt pond area, leads and so forth. They've used Sentinel-2 in past months but that requires fog- and cloud-free conditions and decent sunlight at the time of overpass.

The new road system is visible but just barely. It heads out to 3-4 unlabelled gear depots where oceanographic and meteorological measurements are made. Some sites can be related to earlier ground-level scenes of sampling.

A curious feature of the photo: a swath 600 x 100 m just 'north' of the ship appears to show recent snow covering recently frozen melt ponds. The latter are visible after contrast enhancement. After that correction, the melt pond size and distribution appear fairly homogenous. They are in all stages of drainage and connectivity, well indicated by shades of blue. Black leads of open water and shattered ice cannot be interpreted without knowing how the ship approached the mooring site.

Mosaic's science communication through the ages:
Goethe 1774: Misunderstandings and lethargy perhaps produce more wrong in the world than deceit and malice do. At least the latter two are certainly rarer.

Heinlein 1941 "You have attributed conditions to villainy that simply result from stupidity."

Arctic sea ice / Re: MOSAiC news
« on: September 11, 2020, 10:58:25 AM »
Cold at the Polarstern, balmy in the Beaufort, Chukchi, ESS, Laptev, Kara and Barents.

The two adventurers had internet/sat phone the whole time and expert tech team support for it. Enough to send those pictures, receive weather forecasts and ice maps, have GPS lat lon and communicate with the rescue team on the rented icebreaker about the hopeless ice on the Svalbard side.

The Polarstern also has excellent internet according to the company that provided it with a new type of satellite. However they did not allow scientific staff to use it, only whatsapp on an outside stairwell and iridium if they bought a time card at the ship store.

There were apparently three reasons for this policy: AWI HQ wanted total control of PR messaging, a need for streaming home large data files, and enforcement of team interaction (rather than have everyone hunched over their laptop once back on ship).

Some participants brought their phones and recorded blogs, videos and stills for release on twitter once back home. Only 3-4 people have done that though, Lars K, M Shupe, S Hendricks and C Katlein being the best.

Arctic sea ice / Re: Home brew AMSR2 extent & area calculation
« on: September 11, 2020, 12:46:49 AM »
Disagree. These notions are not consistent with insolation diagrams, air temperatures at high latitude wx stations, geography of river discharge into the Arctic Ocean, measured spread of their freshwater plumes, observed daily surface salinity, 2020 melting degree day temperatures and long-modeled subsurface properties affirmed by moorings.

We are looking on this forum for an explanation of what visible, infrared and radar satellite imagery and drifting buoys have been showing for months above Greenland, Ellesmere and CAA which are nowhere near major rivers or their plumes yet the ice has been melted out to the point of oblivion by insolation and MDD this summer. We have direct confirmation from the captain of the transiting Polarstern.

Indeed the very thickest CAB ice evidently remains highly vulnerable to even a modest four-day cyclone well into September. That ongoing development worsened today and calls for an explanation, perhaps via new metrics along the lines jdallen put forth above in #3529 as the current ones are manifestly inadequate.

Mosaic described the ice encountered en route to the pole as 'porous'. That's not quite the same as permeability of ice in drainable melt ponds requiring freezing snow melt to plug. It sounds like extensive brine channel melt-out, perhaps taking out adjacent Ih crystalline ice and air bubbles along with it and so leaving floes severely structurally weakened with respect to high curl wind stress events.

There's a good account of Russian research on river plumes posted on 10 Sep 2020: these plumes are confined to peripheral seas and remain coastal behind islands. They account for ~75% of all river inflow into the Arctic. There is near-zero inflow for several thousand km (SevZem to SFJL to SV to Nares to western Banks Island. The influence of the McKenzie is limited to off-shore Beaufort as discussed here many times.

"The Ob, Yenisei and Lena rivers flow into the Kara and Laptev seas and account for about half of the total freshwater runoff to the Arctic Ocean. The total annual runoff from these three rivers is estimated at 2,300 cubic kilometers. The majority of this volume is discharged into the sea during the ice-free season, forming the Ob-Yenisei plume and the Lena plume, which are the largest in the Arctic and among the largest in the world ocean.

"River plumes are freshened water masses [river runoff mixing with ambient saltwater] that form near river mouths and spread at sea as a relatively thin surface layer. River plume dynamics are mostly determined by wind forcing and river discharge rate," explained Alexander Osadchiev, a co-author.

"In the absence of strong wind, the Coriolis force and density gradient between plume and  ambient seawater cause along-shore spreading of river plumes. That process induces a large-scale eastward freshwater transport that is observed in the Arctic Ocean along large segments of the Eurasian and AK/CA shores. 

The Ob-Yenisei plume spreads from the Kara Sea to the Laptev Sea through the Vilkitsky Strait, which is located between the Severnaya Zemlya archipelago and the Taymyr Peninsula. The Lena plume spreads into the East Siberian Sea through the Laptev and Sannikov straits.

"Continental runoff from the Ob and Yenisei accumulates in the Kara Sea during the ice-free season. Topographic barriers — the western coast of the Taymyr Peninsula and Severnaya Zemlya archipelago — hinder eastward spreading of the Ob-Yenisei plume to the Laptev Sea. This process occurs only as a result of very specific wind forcing conditions.

"On the contrary, the Lena plume is almost constantly spreading to the western part of the ESS as a large-scale water mass, forming a narrow freshened coastal current in the eastern part of this sea. Known as the Siberian Coastal Current, it is intensified by freshwater runoff from the large Indigirka and Kolyma rivers and flows farther eastward to the Chukchi Sea.

"Freshwater from the rivers flowing into the Arctic Ocean very slowly mixes with seawater so the large river plumes are very stable. Freshwater can spread eastward across hundreds of kilometers, forced by local winds."

Freshwater transport between the Kara, Laptev, and East-Siberian seas
A Osadchiev, M Pisareva, E Spivak, S Shchuka & I Semiletov
Scientific Reports v10 13041 (2020) free full

Arctic sea ice / Re: MOSAiC news
« on: September 09, 2020, 11:19:21 PM »
Taking pixel measurements on the above 11-buoy grid (final frame) and converting them to meters (at 3.26 m/pxl), the grid dimensions came out as shown below. (The x axis should have been rescaled to make it match the y.)

The animation above shows them to be stable in the short term, suggesting they are all embedded in the same floe (likely the same one as the Polarstern). They are not laid out in accordance to any strict geometrical pattern, probably because melt ponds and other irregularities precluded that.

The area came out to 282327 m^2 or about a fifth of a sq km. The situation mimics exactly what Krige had for boreholes in South African gold mining country so his method can be applied directly to whatever the buoys are measuring, ie the yellow below will get more nuanced coloring.

Arctic sea ice / Re: Home brew AMSR2 extent & area calculation
« on: September 09, 2020, 10:03:19 PM »
A fairly extensive and detailed new feature of mid-concentration ice has opened in the CAB well above Ellesmere in this morning's AMSR2_AWI. It was too foggy to confirm on WorldView but seems correlated with a rather localized cyclonic weather feature shown on nullschool at the time.

Given weather artifacts, this wouldn't be worth mentioning except for the appearance and unexpected persistence of the mega-crack along the CAA and the opening between Greenland and the North Pole. These showed how little we really know about the current condition of the ice, even within the CAB. If real, this feature will stay visible in future days.

We don't actually have a swath timing map to coordinate better with 3-hr GFS weather maps and other satellites. That conceivably could be derived from the orbital map for GCOM-C if that indeed is the satellite carrying the AMSR2 sensor that Jaxa data is taken from for AMSR2_AWI. The period is 140 minutes but how the final image is actually built may require QGIS.

update: uniq has found a clear channel in the visible that confirms the AMSR2_AWI concentration break-up, below enhanced and with land mask and distance scale. It's always a good idea to check all the visibles because they are at different times and the clouds sometimes clear. The nh_20200909PM_SIC has not yet come onto the AWI server but should also confirm; the AM/PM should be posted 12 hrs apart at predictable times but currently are not.

This was not an epic cyclone though it attained low gale force winds that persisted over 42 hrs. The CAB ice is really in a vulnerable state, far worse than anyone had imagined or modeled. Just like the NP at the time of the Polarstern transit.

Arctic sea ice / Re: MOSAiC news
« on: September 09, 2020, 07:25:12 PM »
It's turned significantly colder on the 38m mast at the current PS location. The only winds of consequence are westerlies off the AK coast that could still affect remnant ice in the Beaufort.

88.7  110.1 20-09-09 15:00  8 m/s  -7.6ºC

The polar night does not officially set in for another two weeks but daylight is winding down now. "Follow" is showing a snowy scene (depth not reported) but as usual we have no idea what we are looking at or when. There's no news at sea ice ticker and no announcement about the new buoy swarm at meereis.

It's too soon to say if significant science will emerge from all their efforts. While the original vision could not be executed, some of the ad hoc improvisation could have value.  However the inability to fly Polar 5&6 as scheduled was a huge loss in terms of broadening their observational swath..

They could not get timely permission from Canada, US, Denmark or Norway to fly ship-synchronized routes out of Alert, Thule, Nord or Longyearbyen as in past years. Those facilities have to maintain zero tolerance for covid19 introduction given everyone is confined in small places indoors with minimal medical support and difficult options for evacuation and site decontamination.

I wonder if Mosaic with be the last expedition of its type. While it's great to have a ship out there, the cost-effectiveness of new satellites, air-dropped buoys and undersea glider is increasing. A ship can carry large containers full of massive high tech gear but deploying it away from the diesel pollution envelope doesn't work out any more due to extreme ice mobility.

Societally, Nansen and Sverdrup were fully out of touch for three years; Dranitsyn lived in a floe tent for a year on canned food. Nowadays it's hard to find people willing to be offline for even a day despite sauna, pool, fresh cooked meals, two bars and dancing; this got them into 6 legs, attendant resupply complexity, and eventually third-round draft choices for technicians.

Arctic sea ice / Re: Home brew AMSR2 extent & area calculation
« on: September 09, 2020, 12:19:41 AM »
Below is an easy but accurate product to follow the 'end of the melting season' which is ill-posed because the various measures (volume, open water, area, extent) all behave differently according to location. For example, ice loss goes on 365 days a year in the Barents and certain Svalbard areas provided ice has blown in. Volume and extent aren't accurately known to begin with and have poorly known seasonally dependent errors.

The highest resolution product is the 3.125 km AMSR2 concentration product. While intermediate ice concentrations are sometimes not fully correctable for weather artifacts (ie have a white bias), that is not true at the open water end of the palette. AMSR2 has a consistent instrumental record back to 2012.

The best approach would be through the netCDF repository, perhaps making equal area maps and simply counting open water pixels. However not all the archives provide the necessary Geo2D files for this. An easier approach is just to count open water pixels in the polar stereographic projection  which is conformal so not equal area except at 70º.

This introduces small errors because there is hardly any open water pixels at the very highest latitudes that would significantly depart (by 5-6%) from equal area. Further, by comparing consecutive days, the relative error will be much smaller than the absolute error. It is only the former that matters for determining the minimum.

What's new this season is slightly better time resolution, 12-hour from AMSR2_AWI. And with that comes better coastal and ice edge determination relative to 24-hour because the somewhat scattered ice periphery tends to be in motion at the minimum.

However this archive has not quite settled down. For example the 0907 PM is nearly identical to the 0908PM, indicating an error. At color picker radius=0, open water is not quite increasing monotonically. It may be better to pick up all the dark pixels, say out to 16% concentration, to account for wind dispersal and small floes appearing and disappearing in the Beaufort. Next up: check these values in AMSR2_UHH!

Arctic sea ice / Re: MOSAiC news
« on: September 08, 2020, 10:37:26 PM »
A squadron of new Pbuoys in tight formation added tbuoys
What do you suppose the scientific objective is, releasing them so close together? The buoys could lie on a regular grid across their base floe and so sample a large area avoiding the potential bias from placing just one buoy at an convenient location by the ship. These buoys are likely to stay together over winter and well into next melt season since the floe will be getting thicker and more stable.

We can do the kriging from the buoy data if they don't get to it but it will need lots of dp or an accurate description from 'Follow' of grid dimensions and buoy numbering (don't hold breath). The output gives continuous values (raster image) interpolated from the initial number of input buoys.

Arctic sea ice / Re: MOSAiC news
« on: September 08, 2020, 09:41:44 PM »
year dates on the salinity graphic seem to be reversed
Good spotting! The dates are correct though. (It is easy to get them wrong in processing.) So it doesn't quite fit our presuppositions. SimonF92 offers a plausible explanation. It is instructive to see Mercator Ocean putting in observation instead of just modeling away on a trend narrative.

The two slides below show the surface salinity relative to the current AMSR2_AWI ice pack boundary, most of which is cut away in the first slide. Somehow MO has values for not directly observable salinity -- areas that have been under the ice pack for years and years, most notably the band between the NP and SV-FJL.

If their data can be believed, atlantification is much farther along than what one would guess from Atlantic Waters qua western boundary current + some tidal turbulence around the Yermak Plateau (eg Whaler's Bay). If so, there are issues to consider in slightly lower surface and bottom water freezing temperatures.
For every 5 psu increase in salinity, the freezing point decreases by 0.28 degrees C; thus, in polar regions with an ocean salinity of about 32 psu, the water begins to freeze at -1.8 degrees C -- NSIDC
The key Lind paper discussed in #1110 doesn't foresee total atlantification of the Barents until 2040; however the residual front between Arctic Ocean and North Atlantic waters is quite indistinct in the Mercator Ocean view of surface salinity. While it is somewhat more apparent in the 30m and 100m views, it seems a stretch to call this an effective halocline. With the ice pack edge so far away this year, it's unclear whether ice blown in will provide the necessary volume of fresh water melt to renew stratification.

Arctic sea ice / Re: The 2020 melting season
« on: September 07, 2020, 11:16:48 PM »
Actually the many Ascat animations posted earlier best capture the ice motion from Oct 15 to May 15, that's why we enhance them rather than use secondary low resolution products that don't allow ice feature tracking or delaunay shape change quantitation.

More recently, there's been some question of extraordinary melt atlantification of the Atlantic side (largely decoupled from shelf bathymetry) vs the wind simply blowing the ice pack north and west. The time series below suggests some of both but going by the arrows, feature conservation, lack of compactification and 5dp GPS of the newly moored Polarstern buoys, it was mainly just the wind.

Thus this is different from the massive opening north of Greenland which the Polarstern's captain correctly described as ice melt from the extraordinary heat wave (documented at Alert and Morris Jessup wx stations), rather than bulk pack advection towards the NSI creating open water gaps.

Regardless of how it got there, the largely unprecedented position of the ice pack today has many implications for the coming freeze season in terms of surface mixing of areas usually ice covered, possible lateral extension of long term atlantification, winter Fram export, and reduced Barents stratificational maintenance.

The Atlantic side has had a much more orderly progression than the Beaufort-Chukchi (which got just hammered in late July by an anti-cyclone). For clarity, the shrinkage is shown in a matched-pair palette created for this type of adjacency map at Colorbrewer2 (and used to good effect on NOAA-PSL maps). The AMSR2_UHH are set 4 days apart which surprisingly provides enough spacing. They are flipped horizontally so the two views face each other to bring matching areas visually closer.

Arctic sea ice / Re: MOSAiC news
« on: September 07, 2020, 09:17:04 PM »
FooW:that paper discusses conditions from about 3 yearsback before this summer's surge of Atlantic water. I would expect the Atlantification to get worse.
Right. It's not just Mosaic pushing scientific revelations about the current melting season out to 2023, most 'current' journal articles are 2-3 years  back. There's a terrible mismatch between the rapid rate of Arctic change, the needs of policy planners, and mechanisms for keeping scientific research up to date.

To take just two examples, the biggest news this melt season was shoaling of Atlantic Waters and erosion of stratification described in the two Polyakov papers. Those had 2020 submission dates, spent 8 months in peer review but actually analyzed mooring data from 2004-2018 with the main focus 2016-18.

So what happened in 2019 and 2020? We have near real time satellite coverage and weather reanalysis, so surface ice comings and goings, wind, sea surface temperatures and sea surface salinities along with their statistical anomalies.

What's missing is what we're mostly interested in: worsening conditions below the sea surface. Polyakov has given excellent interviews that clarify tipping point consequences but their impact is diminished by lack of current information. If it was an emergency back then, what is it now?

The main nrt update option seems to be the Mercator Ocean model. It's not at all clear what modern mooring tie points if any have been assimilated there. MO has salinities and temperatures at -30m and -100m but now farther back than 2019. Temperature anomalies are only available for the surface.

It's not correct to attribute the record position of the ice front on the Atlantic side to melt or specifically to atlantification induced melt. A lot of the 'melt' has just been displacement by the wind.

The Arctic will freeze over every year long after the first BOE
Substitute 'Barents' for 'Arctic' above? The Barents, some 1500 km farther north than the southern Chukchi, has been in near-total BOE year-round for decades.The northern third has ice cover in winter but it apparently none of it forms locally: it is all blown in from the Kara and Arctic Ocean.

The Barents Sea counterpart to the Polyakov papers is S Lind's 2018 review of Barents oceanography which finds an equally dire ongoing atlantification there but for data ending in 2016. It's been cited 131 times since but has not brought up to date.

The story there is fresh water from ice melt is needed to sustain stratification but it's not there any more in the necessary volume. The Barents is approaching terminal atlantification.

Arctic warming hotspot in the northern Barents Sea linked to declining sea-ice import
S Lind  R Ingvaldsen T Furevik

The Arctic has warmed dramatically in recent decades, with greatest temperature increases observed in the northern Barents Sea. The warming signatures are not constrained to the atmosphere, but extend throughout the water column. Here, using a compilation of hydrographic observations from 1970 to 2016, we investigate the link between changing sea-ice import and this Arctic warming hotspot.

A sharp increase in ocean temperature and salinity is apparent from the mid-2000s, which we show can be linked to a recent decline in sea-ice import and a corresponding loss in freshwater, leading to weakened ocean stratification, enhanced vertical mixing and increased upward fluxes of heat and salt that prevent sea-ice formation and increase ocean heat content. Thus, the northern Barents Sea may soon complete the transition from a cold and stratified Arctic to a warm and well-mixed Atlantic-dominated climate regime.

Arctic sea ice / Re: Home brew AMSR2 extent & area calculation
« on: September 06, 2020, 11:01:37 PM »
AMSR2_AWI continues to improve with the release of version 103 (though it's not 'there' yet). The new location for the twice daily files is provided below. The main change is explained in the ReadMe: the very latest sea ice concentration will appear at a fixed hour depending on your relative time zone. Rapid changes in concentration can be better resolved than with once-a-day products that use a full 24 hours of satellite swaths.

The winds have shifted to more off central Siberia and so differencing v103 shows that as the gold band in the upper Laptev. Surprisingly, these winds are not consolidating lower concentration ice as recognizable features persist for a week or more despite all the displacement on both OsiSaf light blue and AMSR2_AWI.

The product is generated twice daily for two different start times (filenames with AM or PM).

    [AM] ~22 UTC the day before until ~14 UTC. The AM product is available in the evening.

    [PM] ~10 UTC the day before until ~2 UTC. The PM product is available in the morning.

After about 16 hours the spatial coverage is almost complete. AM includes data mostly from before noon and PM after noon.

The advantage of this twice daily processing is A) a reduced latency and B) reduced time differences in the resulting ice concentration maps. A 24 hour difference as in traditional daily averaged products can cause displacement artifacts due to the ice drift. This effect can be observed along a moving ice edge which seems to be doubled in the 24 hours average.

The products so far often contain data gaps represented by gray swaths extending out from the pole hole (which never has data). These gaps can be repaired very simply as follows: open a time-ordered stack, switch mode to RGB, add a transparency alpha channel, select the gray, delete to let data from the immediately earlier file to show through, capture as a new layer, and merge down to retain file name. This can be done in one step if tiled. The dotted line in the illustrative image is not present in the actual repaired product. This process 'mixes' AM and PM but only to a very minor extent.

Arctic sea ice / Re: MOSAiC news
« on: September 06, 2020, 10:55:54 PM »
Quite a spectacular photo today of two Mosaic scientists measuring upward heat flux from 60m to the surface. The device isn't identified but is probably a Rockland vertical microstructure profiler (VMP-250 turbulence profiler) of the type used by I Fer in previously published field work, “On Thin Ice: Role of Ocean Heat Flux in Sea Ice Melt”.

It has a buoyancy collar and weight release mechanism that allows it to be operated in depth-to-surface mode. Various probes on the top measure shear, CTD and other properties need to determine upward heat flux towards the cap of relatively fresh water from melt pond run-off and bottom melt. Heat rising from depth is very important to the onset and extent of the freezing season.

The Arctic Ocean has more than enough heat (from incoming Gulf Stream water) to melt the entire icepack several times over. That water would not be significantly present  at the current location of the PS at the depth mentioned. However Atlantic Water has reached a depth of 80m inthe eastern European Basin according to an important recent mooring study by Polyakov et al.

Arctic sea ice / Re: MOSAiC news
« on: September 06, 2020, 12:41:16 AM »
It takes prolonged consistent wind to create motion and build any speed and once that motion is started, the mass of the flow creates a momentum that will maintain similar speed through wind speed fluctuations.
The rule of thumb is ice pack speed is 1% of a consistent wind speed. Those speeds and headings are listed (in m/s) for the whole expedition off a 38 m PS pole at sailwx or awiMet below. Pressure ridge keels erode very rapidly under water and would provide much less hydrodynamic drag now than initially. The opposite is true for late season aerodynamic drag in FYI.
This in not the idealized ice puck skating down a frictionless hockey rink — Newton’s first law does not apply, the pack quickly comes to rest if the wind dies down or reaches a terminal velocity if it persists.

Considerations of whole-pack cohesiveness (mechanical strength, center of mass, torque, rotation, deformability floe interdependence) come into play. Yet Uniq as notes on the melt forum "there's still some low concentration areas beyond the ice edge despite the constant 'compressional drift' [that evidently isn't happening even after 12 days].

The Polarstern is indeed a massively overwhelming sail that with winds abeam can rip out the six ice anchors and send the ship crashing through thinner ice, as the captain discussed at the October mooring.

The remarkable consistency is in direction, not so much in speed. The latter is quite variable and may have just sub-diurnal periodicity. As to your proposed sluggish response to changes in wind, can that be shown from the data for 2020T78_300234068529570_TS (which is on the same floe as the Polarstern)?

T78 reports every 30 minutes; there's reportedly an Obuoy reporting every 10 that would be better for accelerations (newtonian difference of velocity column). The maximum observed change in T78 velocity is -0.135 km/hr over a 30 minute interval and +0.127 km/hr for speed-up relative to a mean velocity of 0.487 km/hr.

For your convenience, I have added six columns to the original spreadsheet including an excel-ready haversine displacement formula based on the WGS84 earth radius. A column for wind speed at matching times needs to be added from the linked table.

=ACOS(COS(RADIANS(90-A2)) * COS(RADIANS(90-A3)) + SIN(RADIANS(90-A2)) *SIN(RADIANS(90-A3)) *COS(RADIANS(B2-B3))) *6356.752

Arctic sea ice / Re: MOSAiC news
« on: September 05, 2020, 09:09:15 PM »
Mosaic itself provides only the sketchiest details of the expedition written from the perspective of a future large format coffee table book. On past voyages, the Polarstern always posted a very informative weekly ship's log.

About 1% of the 600 scientists involved have supplemented 'Follow Mosaic' with blogs and twitter commentary, most notably the co-originator M Shupe. He posts quite regularly to the AGU and Cires sites, though often with a month's delay with undated pictures by others from the AWI photo gallery. The most recent is 8/4/20 but that was written on 9/17/20. He also posts youtubes that are basically zoom lectures on clouds, boundary layer processes and ice (not watched).

I extracted items of scientific interest from the AGU posts into 11 dense pages in the text attachment below, leaving out musings and miscellany. He is quite a good writer and openly discusses various problems they've had with abandoned and crushed equipment, lost data, flag litter, dirty ice (pebbles), lost weeks resupplying, and idling in the Fram. The blogs give a good sense of what it is like to be on such an expedition (minus inter-personal shipboard interactions).

Low-level mixed-phase clouds in a complex Arctic environment
R Gierens S Kneifel MD Shupe K Ebell M Maturilli U Löhnert
Atmospheric Chemistry and Physics doi: 10.5194/acp-20-3459-2020

Low-level mixed-phase clouds (MPCs) are common in the Arctic. Both local and large-scale phenomena influence the properties and lifetime of MPCs. Arctic fjords are characterized by complex terrain and large variations in surface properties. Yet, not many studies have investigated the impact of local boundary layer dynamics and their relative importance on MPCs in the fjord environment.

In this work, we used a combination of ground-based remote sensing instruments, surface meteorological observations, radiosoundings, and reanalysis data to study persistent low-level MPCs at Ny-Ålesund, Svalbard, for a 2.5-year period. Methods to identify the cloud regime, surface coupling, and regional and local wind patterns were developed. We found that persistent low-level MPCs were most common with westerly winds, and the westerly clouds had a higher mean liquid (42 g m−2) and ice water path (16 g m−2) compared to those with easterly winds.

The increased height and rarity of persistent MPCs with easterly free-tropospheric winds suggest the island and its orography have an influence on the studied clouds. Seasonal variation in the liquid water path was found to be minimal, although the occurrence of persistent MPCs, their height, and their ice water path all showed notable seasonal dependency. Most of the studied MPCs were decoupled from the surface (63 %–82 % of the time).

The coupled clouds had 41 % higher liquid water path than the fully decoupled ones. Local winds in the fjord were related to the frequency of surface coupling, and we propose that katabatic winds from the glaciers in the vicinity of the station may cause clouds to decouple.

We concluded that while the regional to large-scale wind direction was important for the persistent MPC occurrence and properties, the local-scale phenomena (local wind patterns in the fjord and surface coupling) also had an influence. Moreover, this suggests that local boundary layer processes should be described in models in order to present low-level MPC properties accurately.

Arctic sea ice / Re: MOSAiC news
« on: September 05, 2020, 07:24:00 PM »
The time series below looks at how the moored Polarstern responded to the long-running mild anti-cyclone from Aug 23rd on to Sep 4th, with speed and displacement determined from floe buoys by Uniq and applied wind stress provided by GFS-nullschool three times a day.

There's quite a bit of hourly variation in wind details so the PS drift is correspondingly complex, though the 122 km of net displacement is surprisingly uniform in direction. Thus predicting overall motion of the ice pack (or just shape of ice edge) is difficult even with a good weather forecast since neither ridge nor keel drag is known nor ice plasticity response to pressure.

As first shown, the wind series was reversed relative to drift time. This effect arises from gimp and imageJ using opposite time ordering conventions. The last frame shows a major directional shift in the wind, now down from central Siberia over the NSI, rather than curling down from SevZem as it has been doing.

Arctic sea ice / Re: Home brew AMSR2 extent & area calculation
« on: September 05, 2020, 03:13:36 PM »
The first image below overlays the thicker portion of SMOS-SMAP ice thinness of Sept 3rd over AMSR2_AWI of the same date. While this is 'too early' for this satellite product to approach its peak accuracy, it does seem that the >0.5m ice position correlates fairly well to where we think residual MYI CAB ice resides. Indeed, the thinner ice categories too are not at odds with AMSR2_AWI concentrations in areas of melting ice.

So SMOS-SMAP, as an accurate observational measurement of thin ice, is something to keep on eye on even in the pre-freeze season. It has one of the largest pole holes of no swath data which unfortunately includes the current location of the Polarstern. Ice models would do well just to ingest its daily thinnesses and focus on extending them.

The ship has drifted an amazing 122.4 km over the last 12 days under the persistent southerlies off SevZem in western Siberia. Those winds have now shifted to more off the New Siberian Islands, missing the PS position and no longer being orthogonal to the eastern Atlantic front.
88.7 120.8 20-09-04 10:00
87.7 105.5 20-08-23 04:00

The second image overlays OsiSaf motion on SMOS-SMAP for the same dates to show ice displacement vs thickness. The wind stress is applied quite unevenly and in an uncorrelated manner to ice thickness. OsiSaf is a lagging product that  takes two days of observation to develop a visible display even at 3x arrow exaggeration so it will be another day or two until it catches up with the change in wind.

On the technical side, a new AMSR2 paper has come out that may need assimilation into the AMSR2_AWI work-in-progress to map ice edges more accurately:

Assessment of AMSR2 Ice Extent and Ice Edge in the Arctic Using IMS
by Y Liu, S Helfrich, W Meier, R Dworak

This work assesses the AMSR2  ice extent and ice edge in the Arctic using the ice extent products of NOAA’s Interactive Multisensor Snow and Ice Mapping System (IMS) from the period of July 2015 to July 2019. Daily values and monthly means of four statistical scores (hit rate, false alarm ratio, false alarm rate, and Hanssen-Kuiper Skill Score*) over the Arctic Ocean show distinct annual cycles. IMS ice edges often extend further south compared to those from AMSR2, with up to 100 km differences over the Beaufort, Chukchi, and East Siberian Seas in August and September.

* True Skill Statistic or Hanssen-Kuiper skill score of 1965  is defined as “recall minus false alarm rate =TP/P-FP/N (or recall+specificity-1)”. Widely used to test performance of weather forecasts (McBride & Ebert, 2000) in place of the Heidke skill score of 1926.

Arctic sea ice / Re: Melt Ponds
« on: September 05, 2020, 02:50:30 PM »
Melt ponds are growing in importance as FYI increases its proportion yet it remains quite difficult to measure via remote sensing. The two papers below describe in great detail an effort to use multispectral sensors (RGB and beyond) from Sentinel-2AB for this purpose.
There's more to melt ponds than just surface area as that alone does not fully determine take-up of summer insolation because depth, volume, algae, pollutants, and salinity (ie freezing temperature) also have roles in the ever-evolving albedo.

Snow melt initiates pond formation but since there was so little during the Mosaic year and it so quickly blew into topographic lees, very little of summer melt pond volume arose from snow. The SWE (snow water equivalence) of dry cold snow after some abrasion is perhaps 10%, meaning a meter of snow drift could only furnish 10 cm of water.

To clarify, a melt pond forming on an extensive pressure ridge with containment topography could be a meter or two above sea level. If that developed a low drainage channel, the water would indeed drain out. However we are mostly concerned with flat first year ice with very modest freeboard so the doughnut model applies: incomplete pond drainage only to ambient sea level.

The substantial volume of water remaining will eventually freeze solid in winter modulo its brine exclusion, creating a massive inclusion within the hosting ice that will have various consequences for the following melt season, including more facile re-melt if fresher. Given less MYI and the sunny summer this year with extensive melt ponds even at the North Pole, this type of inclusion could be a goodly fraction of total ice volume.

The Bathymetry of Melt Ponds on Arctic Sea Ice Using Hyperspectral Imagery
M König,  G Birnbaum N Oppelt

Melt pond coverage, i.e., areal fraction of melt ponds on sea ice, depends significantly on sea ice surface topography which is in turn strongly influenced by deformation and aging processes, snow cover and ice permeability. Undeformed first-year ice is characterized by a homogenous snow cover enabling lateral spreading of shallow ponds, with pond depth mostly < 50 cm, and cover up to 80% of the ice surface. Multi-year ice shows a preexistent hummocky topography that controls snow depth distribution and lateral pond spreading, and a low permeability that retains meltwater at the ice surface.

Application of Sentinel-2 MSI in Arctic research: evaluating the performance of atmospheric correction approaches over Arctic sea ice
M König, M Hieronymi, N Oppelt

Multispectral remote sensing may be a powerful tool for areal retrieval of biogeophysical
parameters in the Arctic sea ice. The MultiSpectral Instrument on board the Sentinel-2
satellites of the European Space Agency offers new possibilities for Arctic research; S-2A
and S-2B provide 13 spectral bands between 443 and 2202 nm and spatial resolutions
between 10 and 60 m, which may enable the monitoring of large areas of Arctic sea ice. For
an accurate retrieval of parameters such as surface albedo, the elimination of atmospheric influences in the data is essential. We therefore provide an evaluation of five currently available atmospheric correction processors for S-2 (ACOLITE, ATCOR, iCOR, Polymer, and Sen2Cor).

Melt pond work at the Polarstern

Gerit Birnbaum and her team were able to document the waxing and waning of the meltwater ponds down to the nearest square metre, since during the helicopter survey flights over the ice, cameras recorded the size and shape of the individual ponds. Furthermore, based on the camera data, the researchers were able to determine the size distribution of the meltwater ponds, whether the ponds were interconnected, and how deep each one was. The average albedo (reflectivity) of the sea ice was also measured, while a laser scanner mapped its surface topography.

Knowing how early in the year the first ponds form, how large they become, and when they drain is essential in terms of predicting when in the summer the Arctic is likely to be ice-free for the first time. As a dark, sunlight-absorbing area, the network of meltwater ponds is a major factor in the Arctic sea ice melting more rapidly and extensively in summer than it has in the past.

Consequently, Birnbaum’s meltwater pond data gathered during MOSAiC will be used to support numerous scientific analyses. Some researchers are investigating whether the ponds on the MOSAiC floe and in its immediate vicinity are representative of the sea ice in the Central Arctic. At the same time, others are using data from the helicopter flyovers to assess how accurately the various satellite-based measuring systems capture the Arctic’s meltwater ponds.

One of these systems is MODIS, the Moderate Resolution Imaging Spectroradiometer, aboard the United States’ Terra and Aqua satellites. This summer, AWI sea-ice physicists plan to use MODIS data to painstakingly monitor sea-ice melting across the Arctic. To do so, they will use the satellite system to record where and when sea ice was present, in which areas it was covered with meltwater ponds, and where areas of open water formed.

Arctic sea ice / Re: Melt Ponds
« on: September 04, 2020, 06:45:59 PM »
Great to see this reinvigorated forum. Melt ponds have a lot of non-intuitive aspects. The article pair below is rather surprising for the late date of discovery within the century of melt pond study. With first year ice becoming ever more abundant and melt occurring perhaps earlier via Arctic Amplification, the intricate processes described below become ever more important.

Brine exclusion during FYI maturation ends up on the ice surface, in interior channels, and as non-buoyant water that sinks, affecting stratification and inhibiting later mixing. The Polarstern scientists are already skimming ice off the surface before lowering gear and seeing connecting currents.

In the North Pole region, with half the area in melt ponds, some measuring as deep as 1.5m, what fraction of the ice volume in December will be completely refrozen melt ponds rather than thermodynamic bottom ice? Some fraction will have drained and so have lower topography which might have consequences for re-formation via trapping in the following melt season.

Arctic melt ponds form when meltwater clogs ice pores
Pond formation mechanism previously unknown popular account

In 2014, Golden, along with study first author Chris Polashenski of the U.S. Army Corps of Engineers Cold Regions Research and Engineering Laboratory and colleagues traveled aboard the U.S. Coast Guard cutter Healy to the Chukchi Sea, between Alaska and Siberia, to investigate massive algae blooms below the ice, which had been first observed in 2011. As part of their study they needed to measure the permeability of the ice. Permeability is a measure of how well interconnected voids and channels within a material allow fluid to flow through.

Their first attempt involved drilling a hole in the ice down below the “freeboard level,” or water table, to see how quickly the water filled the hole back in.

“It filled up to the freeboard level in about a second and a half,” Golden says, indicating the ice was too permeable to make a measurement. Next, the team tried to add water to the hole to see how quickly the water level re-equilibrated to the freeboard level. They planned several attempts, and noticed that in the second attempt, the water level fell much more slowly than in the first attempt.

“And then the third time was the charm,” Golden says. The team poured water into the hole and the level didn’t go down at all. “We formed a melt pond!” he says.

Intrigued, the team tested different levels of water salinity in boreholes and used dyes to trace the progress of the water through the ice. The team used red and green food coloring from the Healy’s kitchen. All of their experimentation pointed to a clear mechanism for melt pond formation.

“The freezing point of the fresh meltwater from snow is zero Celsius,” Golden says. “But the ice itself is maybe -1 or -1.5. The freezing point of seawater is -1.8. So basically, you’re getting this infusion of fresh water and there’s enough cold there to clog up the pores. You’re lowering the permeability of the ice by this process of freezing freshwater plugs into the porous microstructure.” With lowered permeability, the meltwater can form a pool on top of the ice.

Percolation blockage: A process that enables melt pond formation on first year Arctic sea ice
Chris Polashenski  Kenneth M. Golden  Donald K. Perovich et al
16 January 2017 journal account

Melt pond formation atop Arctic sea ice is a primary control of shortwave energy balance in the Arctic Ocean. During late spring and summer, the ponds determine sea ice albedo and how much solar radiation is transmitted into the upper ocean through the sea ice. The initial formation of ponds requires that melt water be retained above sea level on the ice surface.

Both theory and observations, however, show that first year sea ice is so highly porous prior to the formation of melt ponds that multi-day retention of water above hydraulic equilibrium should not be possible.

Here we present results of percolation experiments that identify and directly demonstrate a mechanism allowing melt pond formation. The infiltration of fresh water into the pore structure of sea ice is responsible for blocking percolation pathways with ice, sealing the ice against water percolation, and allowing water to pool above sea level.

We demonstrate that this mechanism is dependent on fresh water availability, known to be predominantly from snowmelt, and ice temperature at melt onset. We argue that the blockage process has the potential to exert significant control over inter-annual variability in ice albedo

While optical properties of individual ponds vary, the areal fraction of the surface that the ponds cover is by far the most important aspect of pond formation in determining spatially averaged albedo and solar partitioning.

On first year sea ice, early in the melt season, pond coverage is largely controlled by a hydraulic balance of meltwater inflows and outflows and the bathymetry of the depressions available for this water to pool in. Limited outflow pathways result in an accumulation of meltwater above sea level and large pond coverage on undeformed ice.

.Later in the melt season, pathways for water to pass between the ice surface and ocean become relatively unrestricted, first through the formation of large drainage holes, and later through the onset of permeability through the ice matrix [Polashenski et al., 2012]. After large levels of permeability are established, pond coverage is controlled by the fraction of the ice surface situated below sea level ...[many more pages of detail]

Arctic sea ice / Re: MOSAiC news
« on: September 04, 2020, 01:42:22 PM »
The issue raised in the original post is that NOAA-PSL and Hycom models are making incompatible statements about regional ice thickness. One (or both) of them has to be wrong. DMI, Piomas and other thickness products do not make forward predictions and were not considered for reasons given many times by Oren.

Based on the brief and erroneous statement from the publicist back in Bremerhaven, 30 ice cores were collected and frozen for later lab studies. These ranged around 1.55m with very little scatter (10%), very similar to NOAA-PSL but well out of Hycom range.

Reading between the lines, the cores were collected at regular intervals along a transect: the newly established road system which goes out on level ice perhaps a km from the ship to sensor stations. Photos so far do not show notable ice jumbles or pressure ridges; cores there would be far more difficult to obtain and much thicker than reported. Melt ponds are not cored.

Mosaic has provided no information whatsoever about the site selected other than it had a lot to do with the time crunch of late arrival, match-up with their January drift location, floe stability and safety (0.7 m or more is sought). FYI, SYI, MYI ice? Nothing has been said about floe backtracking history.

Persistent thick fog may have prevented helicopter launch and so the taking of overhead photos. They did launch a drone but nothing from it has been shared. We do not know at this time whether melt ponds and rotten ice are as pervasive as at the North Pole.

How representative are these core thicknesses? Mosaic has seven methods for accurately measuring ice thickness: en route bow/side em, helicopter-flown em-bird, Polar 6 em-bird, sled em sensor, drilling for buoys, hole excavating for oceanography, and coring for biogeochemistry.

The first four can add up to tens of thousands of km of accurately determined ice thickness along swaths and rasters. None of this data has been disclosed nor will be disclosed prior to 2023. Mosaic did release various over and under camp maps for the first floe in November but in no case were thickness scales included or maps updated over the drift.

In summary, they have considerable context for the 30 core thicknesses but we do not. It's terribly naive to think site bias wasn't mitigated (how could they wring a publication out of the data?)

These models are not entirely ab initio physical theory but rather semi-empirical: before each day's recalc they are fed fresh weather, surface temperatures, ice edge location, ice concentration etc. Consequently they always get the current shape and overall drift of the ice pack correct as it's baked in.

Unobservable fields such as frictional drag of surface to wind and keels to ocean water can be inferred from observed response to recent wind. Indeed NOAA-PSL has separate graphics for them; Hycom provides rolling 30 days of which 24 are history that inform the 6 days of future.

In winter, they could (but don't) validate against SMOS/SMAP etc. However in summer months they have no sources of observed ice thickness to assimilate (though Polarstern weather and perhaps some buoy data is used right away in ECMWF). Consequently, the models have no way to control drift in thickness accuracy (except where it melts out to zero) until the fall sensor reset.

We do not run 'operational' forums here so rather than focus on futile forecasting, we can simply wait a week, see actually happens and try to understand why. However it does look like the persistent Siberian winds that began on Aug 23rd will continue a few more days and even worsen on Sept 6th,

Damaging swells remain on the table but so far no evidence for impacts on the ice pack has surfaced. The Beaufort arm is losing its loop but a patch may hold on through the season; the sheltered ice south of SevZem is finally dissipating.

The main story though changes in daily bulk movement of the ice pack to a squeeze against the CAA with reduced transgression on the Barents side. Hycom sees that as continuing through Sept 10th. We can revisit that prediction with AMSR2_AWI and Polarstern track at the time.

For now, from uniq's efforts, we have very accurate records of regional ice movement at the positions of ~50 individual buoys (these are sparse on the Siberian side). Buoys near the Polarstern show its track and recent variations in speed are shown below with 4 dp GPS precision. It can be followed loosely on the awiMet hourly report site.

Arctic sea ice / Re: The 2020 melting season
« on: September 03, 2020, 11:02:57 PM »
strongest winds are over ice; the fetch quite enough swells impacting ice pack
It's one thing to anticipate a significant swell but altogether different to show the swell had any significance.

Right now, 2100Z, the wind power density at the surface is about equally distributed over ice pack and open water on the Atlantic side north of SevZem, pushing the ice north and building swells nearly orthogonal to the ice edge (as seen by v102 of AMS2_AWI hollowed out of its highest concentration ice.

Since the air is still foggy and thick clouds remain above, it is not plausible that visible imagery of swell impact, if any, will be available. The Polarstern is a bit off to the side (green circle at 88.7  120.5) and so may see differential regional stress on the ice and so atypical displacement. The Beaufort is not participating at all in this prolonged event and indeed is seeing dispersion and a push west towards the Chukchi.

Suppose the swell does disrupt icepack floes 200 km in. How would that show up on AMSR2 microwave imagerymif the ice is still there but in smaller but still adjacent pieces?

This is an area of peripheral melt that has been ongoing for months -- if these small swell-broken pieces take a week to melt, how do we attribute the change to swell vs the usual lateral in-melt?

This is where the new 12 hour AMS2_AWI product might help by providing better temporal resolution. The swell scenario is not an edge progression but more of a simultaneity. However AMS2_AWI is not currently retro so the earlier events observed at sea cannot be revisited yet.

Arctic sea ice / Re: MOSAiC news
« on: September 03, 2020, 08:00:12 PM »
It's hard to get Arctic field research to adhere to any kind of plan. Mosaic has just had one bad thing happen after another, from not being able to find a suitable floe back in October, unexpectedly rapid TransPolar Drift, seven weeks lost in a resupply snafu, time and sensors wasted in the Fram, abandoned instruments lost to ice motion, more resupply and repositioning delays and the most scientifically damaging of all, loss of the Polar5 and Polar6 spring and summer overflight campaigns. press release

Had these synergistic transects been flown (for atmospheric measurements, pressure ridge and melt pond lidar and ice thickness) the swath of the Polarstern would have been greatly widened. However the Svalbard airport was shut down to non-Norwegian aircraft until just a few days ago. A fall campaign has been started; no information is available on number and routes of flights.

Arguably, the most important thing the Polarstern has done is set out more buoys along its route over and beyond the north pole. While some types of buoys can be air-dropped, others need to be set into place after drilling and confirmed to be working as designed (ie not going sideways through fractures in pressure ridge as was seen in underwater ROV scenes).

Quite a few buoys are currently active in the Arctic Ocean basin, mainly from non-Mosaic projects. Uniq has located a lot of them and plotted their recent drift paths; those are put onto yesterday's AMSR2_AWI below.

The buoy map can only be produced currently relative to the 0 meridian so the Greenland-down AMSR2_AWI has to be rotated 45º. Only the final frame of Uniq's gif is shown. The trick in producing readable text in the overlay is combining 'darken only' over the ice and 'lighten only' over open water.

It's difficult to apportion ice pack edge changes on the Barents side into melt and movement contributions.  No question, lateral melt momentum has been going on steadily for months but per GFS nullschool, persistent and consistent winds are blowing the whole ice pack towards Alaska.

The PS has been stably moored to its current floe since Aug 23 (after leaving the pole on the 19th). This floe has drifted north and east (larger lat and lon) since then. Over the last 11 days, the ship has moved 89.5 km for a speed of 0.324 km/hr without any indication of dimensional melt or compaction in its vicinity.

Presumably the ice edge has been moving north at an even faster nominal rate because of contribution of disappearing peripheral melt there. However subtracting two small numbers of pixel displacements is fraught with error.

The Polarstern is just one point. OsiSaf potentially offers speeds of ice passing by all its grid points. Below, I isolated one grid cell close to the ice edge and chained up arrows over 8 days to get displacement there. The data comes with a 3x vector exaggeration. It is shown together with a display of ship GPS on google earth, jagged because Mosaic cuts off 3 dp from what it shares.

Note this melt season will have exceeded 53% BOE for over a month this year (based on pixel counts on a non-equal area projection). The associated loss of planetary refrigeration is discussed quantitatively in K Pistone et al 2019 "Radiative Heating of an Ice-Free Arctic Ocean":

• The complete disappearance of Arctic sea ice would contribute an additional solar radiative heating of 0.71 W/m2 to the planet, equivalent to the radiative forcing from one trillion tons of CO2 emissions

• The added solar heating from complete Arctic sea ice loss would be an order of magnitude larger in the month of May than in the month of September

Arctic sea ice / Re: MOSAiC news
« on: September 03, 2020, 07:23:39 PM »
Finally, some ice thickness data at the new floe: 1.40 to 1.70 range from 30 ice cores near the ship. They are staying close by this time because of set-up time and past instability of remote floe sites.

It can be seen that Hycom is way off the mark, showing ice thickness of 0.7m and nothing even resembling observation within 500 km. However the forecast of ice motion over the coming week could still be on target.

NOAA-PSL is right on the mark with the correct thickness and an interesting shape for it. They use a goofy coordinate system with elliptical latitudes and curved meridians that is provincially AK-centric which cannot be rotated and rescaled to match conventional polar stereographic that everyone else uses. No netCDF is furnished. It has been like this for years; the site is unattended.

The tides and tidal currents at the current location are completely negligible. The issue for a solid week has been a strong persistent wind off Siberia that is quite noticeably moving the whole ice pack towards Banks Island. These winds can induce semi-diurnal near-inertial waves in the water that the public relations lady may be confusing with weak M2 lunar tides.

The photo shows decaying ice in an advanced state of melt. Freezing season is still several weeks off (especially in this non-stop fog) though one day they had to hand-skim ice off a melt pond in order to lower instruments.

Arctic sea ice / Re: Home brew AMSR2 extent & area calculation
« on: September 03, 2020, 06:07:38 PM »
The new AMSR2_AWI is up to version 102 today and has the early Sept dates but slightly changed per swath hour as noted in the new ReadMe.

Because the ice pack has been moving quite rapidly from SZ towards Banks for over a week, there are some distinct advantages to the 14 hour assemblies. Thus the 12 12 is probably more accurate than the 12 72 for now.

Hycom foresees ice pack motion continuing quite dramatically through Sept 9th. This is fully attributable to the persistent anti-cyclonic winds coming off central Siberia and the low mass of late season ice.

The pixel count of open water increases by about 10% over this time frame, an undetermined combination of melt, compaction and dispersion to sub-display resolution. There appears to be two fixed pivot points, one in the upper Fram and the other in the ESS at 80º 150º.

It can have some gaps in coverage (swath gray at the pole hole and periphery) just like we see with Ascat. These can be repaired by layering over the 72 hr, adding an alpha channel, selecting gray and deleting to let   the 72 show through but only where needed, then capture as 'new from visible'.

An example of v102 quality is attached below for Sept 2nd. The concentration palette has not changed. A small substitution palette is also included for those who wish to highlight specific ranges. Put a pair in the foreground/background and simply click on squares in the original palette (and thus image data) and fill.

Note individual remnant floes in the Beaufort can clearly be seen; the anomalous ice south of SevZem is finally dispersing/melting out.

The FAST product is generated twice daily for two different UTC start times: filenames with _00_ available in the afternoon or _12_ available in the morning

After 14 hours the satellite's spatial coverage is almost complete.  The twice daily (filname includes _12h) product has data gaps and errors due to weather and coastline effects.

The advantage of this twice daily processing is no time differences larger than 14 hours in swath assembly. The 24 hour difference in traditional daily averaged products can cause displacement artifacts due to ice drift. This effect can be observed along a moving ice edge which doubles up in the 24 hours average.

B) The CLEAN product takes into account the latest 72 hours of data indicated in the file name by _72h. The coastline is extended by about one grid cell and masks the frequently erroneous coastal overestimation of sea ice concentration.

Time-domain median- and latitude-dependent minimum-filtering reduces erroneous weather pixels. Moving isolated ice floes in open water are also removed by the filtering, a negative.
The grid cell size remains at 3.125 km though the image pixels are at an intermediate scale of 5.0 km

Arctic sea ice / Re: MOSAiC news
« on: August 29, 2020, 01:46:50 PM »
Another good source of information is the preprint page at The Cryosphere, conveniently reverse chronological.  A third Mosaic paper recently appeared there along with yet another from the predecessor cruise N-ICE2015. Overall though, a majority of Arctic sea ice papers are not based on either expedition.

Surface-Based Ku- and Ka-band Polarimetric Radar for Sea Ice Studies
J Stroeve et al

Experimental evidence for a universal threshold characterizing wave-induced sea ice break-up
J Voermans et al

Waves can drastically transform a sea ice cover by inducing break-up over vast distances in the course of a few hours. However, relatively few detailed studies have described this phenomenon in a quantitative manner, and the process of sea ice break-up by waves needs to be further parameterized and verified before it can be reliably included in forecasting models.

In the present work, we discuss sea ice break-up parameterization and demonstrate the existence of an observational threshold separating breaking and non-breaking cases. This threshold is based on information from two recent field campaigns, supplemented with existing observations of sea ice break-up. The data used cover a wide range of scales, from laboratory-grown sea ice to polar field observations. 

Trends and spatial variation in rain-on-snow events over the Arctic Ocean during the early melt season
T Dou et al

Rain-on-snow (ROS) events can accelerate the surface ablation of sea ice, thus greatly influencing the ice-albedo feedback. However, the variability of ROS events over the Arctic Ocean is poorly understood due to limited historical station data in this region. In this study early melt season ROS events were investigated based on four widely-used reanalysis products (ERA-Interim, JRA-55, MERRA2 and ERA5) in conjunction with available observations at Arctic coastal stations.

Our results show that ERA-Interim better represents the onset date of ROS events in spring and ERA5 better represents the phase change of precipitation associated with ROS events. All reanalyses indicate that ROS event timing has shifted to earlier dates in recent decades (with maximum trends up to -4 to -6 days/decade in some regions in ERA-Interim), and that sea ice melt onset in the Pacific sector and most of the Eurasian marginal seas is correlated with this shift.

There has been a clear transition from solid to liquid precipitation, leading to more ROS events in spring, although large discrepancies were found between different reanalysis products. In ERA5, the shift from solid to liquid precipitation phase during the early melt season has directly contributed to a reduction in spring snow depth on sea ice with the largest contribution in the Kara-Barents Seas and Canadian Arctic Archipelago.

Arctic sea ice / Re: MOSAiC news
« on: August 29, 2020, 12:46:11 PM »
Shupe posts a whole lot better information than AWI, also posts lectures
Right. Cires, AGU, Helmholtz, Ticker and scattered Twitter have provided occasional blog information of much better quality than the upbeat censored drivel coming out of AWI's Follow. It is most odd that these outside resources are scarcely mentioned or promoted on the Mosaic site.

Of the 600 scientists involved no more than 5-6 have made any effort whatsoever to communicate what really goes on in Polarstern research.

Mosaic is not interested in the current melt season or characterizing the overall state of the ice. The focus initially was directed entirely to a highly atypical pressure ridge, since disintegrated, that they settled on in desperation last October. That's been replaced by a one-off pressure ridge in a sea of melt ponds that cannot possibly provide year-long continuity.

The ship, in effect a gigantic polluted buoy, made good efforts to widen its swath of observation but even close-in, unexpected ice mobility made it all but impossible to keep equipment running and reporting. We have a good idea of overall drift from buoys but the bow radar picture of floes jostling and leads opening has not returned. This radar, essential to ship operations, is in good repair, just not being shared.

Another camper was killed by a three year old male polar bear in Svalbard. His mother and more recent cubs had recently been airlifted out of town. The victim was actually the manager of the barren Dutch facility and in his second season there. Six other campers witnessed the pre-dawn attack and were said hospitalized for shock.

The presence of two bears and persistent fog at the current location raise a number of issues about how researchers are being protected away from the ship; in the early months of the cruise, safety was taken very seriously.

Arctic sea ice / Re: MOSAiC news
« on: August 29, 2020, 01:55:22 AM »
A bit late, posted on aug17. Collecting buoys etc in the Fram strait
So once again, a bogus caption on a photo? They were not anywhere near the Pole on the 17th. Nor were they in the Fram but rather 86.8 12.3. Even the cheapest flip phone records time of photo on the photo.

AWI does provide a photo database for media but access requires a login that does not recognize the account you just created.  Sound familiar?
Jet stream important influence?
Of course in the big picture it's all tied together, though to date we appear no closer to reliable 5-day much less seasonal predictions than ever. Knowledge of the jet stream does not lead useful prediction of the surface winds that actually physically couple with the ice,.Especially this August, that would be a big leap given the jet stream's complex and semi-chaotic structure.

Rain, fog, melt pond and snow distribution: terribly important to the ice but where in the jet stream graphic (or any satellite product 42 years in) do I find reliable data for them at the scale we need? We have to get some better sensors out there; the Polarstern is not the answer.

Consequently, I would rather glance at nullschool 1000 hPa winds twice a day rather than read ungrounded weather speculation on the melt forum. And that is true too where I live, despite a full-time gov't Wx staff of seven, they cannot get a half day ahead on weather specifics such as rainfall.

So yes, maybe we can usefully do 2-3 days forward but really after-the-fact (yesterday) is the best option, if it is not a broad-brush climate forum. But frankly, given the importance of Arctic sea ice to the global climate system, the complete ignorance demonstrated on Aug 19th of the state of the north pole regional ice makes me wonder what they've been putting in the models all these years in place of observational fact. Having half the ice pack in melt pond doesn't matter?

But even with weather facts in hand, the explanation can elude us. Search 'arctic amplification' at google scholar. The top hit is a 2006 paper by MC Serreze and JA Francis called "The Arctic Amplification Debate". They could write a second paper with that same exact title today. The phenomenon has been under debate since 1969.

Arctic sea ice / Re: MOSAiC news
« on: August 28, 2020, 10:20:50 PM »
UC: Laptev more exposed to swells in coming days? cross-post melt forum?
Right, ice in the western Laptev ice appears more at risk from swells than that of the Beaufort though the latter is currently farther gone. The reach of the wind there is potentially 800 km or more, the speed is gale force at 15 m/s in places, the forecast calls for a few days of persistence, and the putative swells would hit head on.

That combination seems more than enough for a significant or even dramatic swell damage. While no one is out there to provide confirmation, if something significant does come to pass on satellite, swells should certainly be considered as candidate explanation. We don't have any real data on how common major swell events are; reports are entirely serendipitous.

People are welcome to cross-post to other forums or anywhere else on the internet -- and lay on their own interpretation. I recall that forum software will re-display images and animations just from its url, as wrapped with a 2nd row button above. The image does not need to be downloaded and re-uploaded.

There are two advantages to this: the image does not count towards the posting limit of 4, it can be reside in the middle of a text sandwich where it fits better rather than sit context-free on the bottom.

Below is a spectacular north pole ice photo I came across on a news site. It could be placed in any number of forums. Actually I am just trusting the caption; the photo is undated, has no lat lon nor  EXIF data. The Polarstern was at the pole on August 19th but Folke Mehrtens may not be the actual photographer as stated, she has been at the AWI's communications press office since 2008.

The second photo is on AWI media twitter so presumably is at the north pole as stated. It's very unfortunate that AWI does not put together a permanent gallery of properly labelled, dated and credited North Pole photos -- these will never be published or analyzed in a scientific journal but nonetheless are an important part of the record.

So many generic stock photos are shown, including by AWI, that the public never knows for sure when they are looking at the real thing.

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