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Messages - slow wing

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Arctic sea ice / Re: Latest PIOMAS update (January, mid-monthly update)
« on: January 20, 2021, 09:32:42 AM »
PIOMAS gridded thickness data was updated to day 15 (15th January). Volume calculated from thickness was 15.56 [1000km3], second lowest for that day of year.

Here is the animation for January so far.

Arctic sea ice / Re: The 2020/2021 freezing season
« on: December 25, 2020, 12:46:43 AM »
The mp4 below shows 84 days of the fall freeze season, from Oct 01 to Dec 23. Here SMOS was used at 132.24% enlargement to provide masks for land, open water and thin ice as Ascat alone has distracting artifacts there especially early in the season.

Note a white band of ice (an extended virtual buoy for tracking purposes) forms early on in the northern Laptev at the FYI/SYI edge (as it did last year) and will likely remain trackable until May. The overall pattern of ice movement here has been a squash towards Greenland and the CAA.

The physical explanation for the hundreds of km of white band remains elusive. Efficient scattering from low dielectric near-surface ice is typically seen in older ice that has lost its brine pockets. However Ascat's active microwave beam can also be reflected back from crumpled ice with right-sized debris particles. How and why this would form at the edge of SYI perhaps may require strong 'offshore' winds piling up newly formed ice. The area is inaccessible to ships and the feature may not be apparent at visible or infrared wavelengths anyway.

Other stably advecting Ascat features such the large dark elongated patch in the north Beaufort also lack interpretation. This area froze up very rapidly in patches per Smos-Smap and so may have incorporated extra near-surface salinity which would indeed make it appear darker.

Note too the unusual mid-December surge of ice west across the Chukchi to the shores of Chukotka; usually western Alaskan ice originating northeast of Banks Island turns north upon reaching the eastern Chukchi, perhaps riding Bering Strait inflows.

This can be attributed to the persistent anti-cyclone over the period 08-24 Dec 2020 that has brought clear skies and with it excellent Suomi band 15 views of heat loss from leads and their motion ( opens to a good palette set-up). As the large diameter anti-cyclone wandered across the Arctic Ocean towards the Kara side, winds often blew in the opposite direction of that needed for a return Gyre.

Export out the Fram has picked up but has the odd oblique meridional surge is from the central CAB rather than the usual zonal route between the pole and the SZ-FJL-Svalbard. This could have the effect of exporting older thicker ice but this year, as witnessed by the Polarstern, the ice between Greenland and the pole did not fit that description in September.

Arctic sea ice / Re: Latest PIOMAS update (December, mid-monthly update)
« on: December 21, 2020, 11:56:20 AM »
Total volume and regional differences with 2012 and 2016.

Arctic sea ice / Re: Latest PIOMAS update (December, mid-monthly update)
« on: December 20, 2020, 05:39:50 PM »
PIOMAS gridded thickness data was updated up to day 350 (15th or 16th December). Volume calculated from this thickness was 11.8 [1000km3], second lowest for day 350.

The animation for December sofar is attached.

Arctic sea ice / Re: Latest PIOMAS update (December)
« on: December 06, 2020, 03:00:10 PM »
PIOMAS gridded data was updated upto day 335, which is 30th Nov or 1st of December depending on your calendar. On day 335 volume, calculated from this thickness, reached 9/86 [1000]km3], which is the lowest value except for 2016.

Here is the animation for November.

Arctic sea ice / Re: Latest PIOMAS update (November mid-monthly update)
« on: November 18, 2020, 01:27:03 PM »
Cheers, Wipneus

Arctic sea ice / Re: Latest PIOMAS update (November mid-monthly update)
« on: November 18, 2020, 01:14:03 PM »
Thanks a lot Wipneus for your important work with PIOMAS data.
A few charts showing that 2020 is unfortunately still leading in the important places, though it lags the total behind 2016 mainly thanks to a 140k surplus in the Greenland Sea.
CAB and Pacific side rates of growth seems to be following in parallel to the slower years, such as 2016. In the Siberian side the rate of growth has been following the faster years, though on a very delayed curve. Hopefully by the next update 2020 will be firmly above 2016.

Click to enlarge.

Arctic sea ice / Re: Latest PIOMAS update (November mid-monthly update)
« on: November 18, 2020, 09:33:25 AM »
PIOMAS has updated the gridded thickness data to day 320 (16th or 15th of November). Calculated volume on day 320 was 8.07 [1000km3], second lowest, slightly over the 8.00[1000km3] in 2016 .

Here is the animation for November so far.

Arctic sea ice / Re: Latest PIOMAS update (Oktober, mid-monthly update)
« on: October 18, 2020, 07:02:21 PM »
Here are the volume and volume-anomaly graphs.

Arctic sea ice / Re: Latest PIOMAS update (Oktober, mid-monthly update)
« on: October 18, 2020, 06:59:10 PM »
PIOMAS has updated the gridded thickness data upto day 289 (15th or 16th of Oktober). Volume calculated from thickness on that day was 4.91 [1000 km3]. That is the second lowest value for day 289. The difference with the lowest (2012) is very small though.

Here is the animation for Oktober 2020 sofar.

Arctic sea ice / Re: The 2020/2021 freezing season
« on: September 19, 2020, 08:02:38 PM »
Animation of the annual max and min, from 1979 to present (click to play).

Arctic sea ice / Re: The 2020 melting season
« on: September 18, 2020, 07:33:35 PM »
This is the best thread on the Internet. Thanks, everyone.

Arctic sea ice / Re: The 2020 melting season
« on: September 17, 2020, 01:01:16 PM »
AMSR2: Some recent days of 2020 compared to 2012
Rough overlay of 2012 vs 2020 using awi amsr2 v103, aug20-sep15 (am/pm)

gimp grain extract, the years were slightly different sizes so there is a small scaling error

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: The 2020 melting season
« on: September 11, 2020, 05:25:02 AM »
I ask that you indulge my bathymetry-and-ice-distribution fixation one more time.  This gif is from images on the oden site.  I was not able to get images for the same date each year, so the images are from a day from each year during the first two weeks of September, showing the approximate ice extent minimum.  The thing that jumps out here for me is how different this year is from all the others in terms of the Atlantic front, as others have noted.  2020 melt has advanced into the deep basin of the Arctic Ocean in a manner that seems qualitatively different...   Retreating halocline?  Source:    Maps only go back to 2014, so no 2012.

Large gif.  Click to animate.  3 secs+ per image, a bit slow so features can be observed.

Arctic sea ice / Re: The 2020 melting season
« on: September 10, 2020, 01:53:49 PM »
Weekly sea ice losses from July 1st

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: MOSAiC news
« on: September 07, 2020, 05:16:51 AM »
It's about time for the temperatures to drop and the melt to slow down. The sun is close to the horizon at the pole. Temperatures have been in extra time for too long. Yes, excellent graphic.

The paper cited by A-Team is important. The Laptev sea is undergoing "Atlantification". Note that paper discusses conditions from about 3 years or more back before this summer's surge of Atlantic water. I would expect the Atlantification to get worse this fall and winter in response to the surge of Atlantic water.

Location number 10 on the figure of tides and tidal currents shows very weak tides and currents at the pole. That figure is relevant.

Also note that the GAC tapped into a small fraction of the heat in the Atlantic layer which used to be found at depths below 150m, before Atlantification set in. It takes a persistent very strong storm to mix up heat from that depth. This summer's cyclone didn't cause the extent of mixing caused by the GAC. I have not seen evidence that it mixed up water from the Atlantic water layer.

Arctic sea ice / Re: The 2020 melting season
« on: September 07, 2020, 03:33:33 AM »
Sentinel-1 animation of the Lincoln Sea. Nares Strait export has renewed since Aug 29th, with one of the large floes sloshing around for the last two months about to go out the door.


Arctic sea ice / Re: MOSAiC news
« on: September 07, 2020, 12:33:16 AM »
tbuoy update for those interested in data

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 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: Latest PIOMAS update (September 2020)
« on: September 03, 2020, 06:41:47 PM »
Volume and volume-anomaly graphs.

Arctic sea ice / Re: Latest PIOMAS update (September 2020)
« on: September 03, 2020, 06:39:21 PM »
PIOMAS has updated the gridded thickness data to day 244 (31 August or first of September). Volume calculated from thickness was 4.31 [1000 km3] which is third lowest for that day (behind 2012 and 2019).

Here is the August animation.

Arctic sea ice / Re: MOSAiC news
« on: September 03, 2020, 03:38:09 PM »


May I ask what the scale on the left is?

I'm really struggling to see where the base of the ice is!

Would the winter ice be more clearly defined as the freeze causes mixing, the water convecting below the ice layer? As the ice melts the heat is transferred by conduction, leading to a much smoother gradient.

Each value on the left is 2cm (there are sensors in a column every 2cm), so the difference between thermistor50 (Th50) and thermistor150 (Th150) is 1metre.

Heres a very quick image showing you the bottom (and why the temperature method wont work when its warm above the ice):

Arctic sea ice / Re: MOSAiC news
« on: September 03, 2020, 02:35:07 PM »
It is very easy to detect and perceive the bottom of the ice in the winter/spring due to the temperature gradient being positive from the top of the thermistor column to the bottom (very cold air: cold ice: warmer ocean).

Between us were setting the ice:ocean thermistor at the -1.8 to -2degC mark.

Unfortunately, during summer this temperature gradient becomes a U-shaped quadratic (warmer air: colder ice: warmer ocean) and eventually normalises to close to 0, which basically creates hell for analysis. Particularly given that the transition between ice and ocean at the bottom is probably muddied by supercooled water.

(the 2nd and 3rd figures represent different thermal conductivity sensors, you can just about perceive the bottom of the ice through summer)

Arctic sea ice / Re: The 2020 melting season
« on: September 02, 2020, 10:31:50 AM »
Today's daily images and animation. The loss on the Atlantic side is really beginning to stand out now.
As usual, there's a larger version of the animation on the twitter page.

Arctic sea ice / Re: The 2020 melting season
« on: September 02, 2020, 12:40:41 AM »

I’d hypothesize the major difference is that 2012 took some pretty extreme weather in a perfect setup to get where it was which also consequently released a lot of the absorbed energy possibly resulting in the 2013-2014 rebound. 2019 was not followed by a rebound and 2020 does not look quite likely to be either, so I think the difference lies in position regarding the overall trend, and the fact that this “extraordinary looking” melt season isn’t really all that out of the ordinary, especially compared to 2012 in its time. Next year could quite easily compound on this year further and maybe even pass 2012 while being plausibly expected instead of being a moonshot. The Arctic is much thinner and more fragmented while holding more thermal energy than before.

A very nice and concise summary of this year's melting season and what it may portend for the future. Thanks.

And it's not entirely over yet, when looking at the ECMWF forecast. That pressure gradient is going to do a real number on the ice north of Severnaya Zemlya. It's amazing what consistent weather can do in this final stage of a melting season that has seen a huge amount of melting momentum being built up. The only question left is how close 2020 can still get to 2012.

Keep those animations coming, everyone. Especially of the ice edge retreat/annihilation between 135° and 60° East. What a stunning sight that is. I think animations will be jaw-dropping by next week.

Arctic sea ice / Re: The 2020 melting season
« on: September 01, 2020, 08:34:09 PM »
That's really great BornFromTheVoid, many thanks.

A question, could you make a version that's much slower? And/or mark the loss per week with a colour? For me, that would mean even more information.
Your placing of dates and legenda & scale, and synchronising with the frames, and used font are also very good imo. You know your way around your tools :).
You have been a super visualizer and help for me.

Unfortunately I don't have time to do the animation this evening. But hopefully an image will suffice for now!

Arctic sea ice / Re: The 2020 melting season
« on: August 30, 2020, 11:34:04 PM »
Has anyone got any idea where I can read up the reasons for Arctic's Inverse stratification ?
Or can someone explain it here ?

Will try but am sure others can explain it better than I.  The simple explanation is that with a sufficient salinity difference and a temperature gradient that is not too great, cooler fresher water is less dense than warmer saltier water.  The arctic surface water is made fresher by precipitation, glacier runoff, iceberg and ice shelf melt water, river inflow (particularly over the shallow coastal shelf on the Siberian side) and also cycles of sea ice freeze and melt.

When seawater freezes it undergoes brine rejection as part of the crystallization process.  How this can be viewed is water molecules at the freezing point impact the undersurface of other water molecules that are frozen or freezing and some percentage (it is at the scale where quantum mechanics kicks in so the behaviour is statistical) surrender kinetic energy, stick and enter the solid state thus releasing latent heat.  Salt molecules are rejected in the process as not fitting into the crystalline structure.  However, as I understand it some slight amount of salt becomes trapped and encapsulated in freezing water particles and incorporated into the ice.  The rejected salt molecules create localized pockets of dense, very salty brine which rapidly sinks away into the depths.  The sea ice as a consequence is substantially freshened versus the water from which it formed.

When the sea ice subsequently melts the next melt season the resultant melt water creates a freshened lens of relatively cool less dense and salty water that floats on the warmer saltier currents below, much of which is North Atlantic surface currents that dive under the less dense Arctic Surface Water as they enter the Arctic proper, particularly once reaching the Nansen Basin which underlies the CAB on the Atlantic side where greater depth lends itself to more complex stratification.  A similar process occurs on the Pacific side to a lesser degree due to the narrowness of the Bering Strait.

As we are still undergoing a draw down of sea ice volume, freeze season extent is diminishing slower that melt season extent, and there is considerable ongoing glacier melt inflow, there is still plenty of freshened melt water each season to somewhat maintain the stratification.  The danger is that we will start to run out of non-Greenland glaciers at some point, the shallow Siberian side which is only 2% of Arctic water volume subsequently loses much of its freshening river and glacier inflow and these peripheral seas then see further extent and thickness reductions which lessens the brine rejection mechanism and a vicious feedback occurs where a saltier Arctic results in less sea ice formation, since saltier water freezes slower and at a lower temperature, which leads to a further increase in salinity and even less ice.  Looking at the pattern this year is worrying.

It gets worse, as I understand it the Arctic surface water in the CAB, specifically over the Amundsen Basin is only slightly less saline that the warmer Atlantic waters below which means it has always been on the razors edge of breaking down.  In the past this did not matter as the central arctic was proof against melting out.  But it is vulnerable, if it ever has a BOE it will start to mix with Atlantic surface water once no more fresh melt water is being added and that Atlantic water is much harder to refreeze.  That being said, we may see freshening of the CAB in the near term as more CAB melt starts to occur each year, delaying things a bit.  However models that suggest we may get a BOE every now and then in the future may be painting a too rosy picture.  BOEs likely create an environment that favors more BOEs, at some point it is probably a runaway phenomenon.

Arctic sea ice / Re: The 2020 melting season
« on: August 30, 2020, 12:35:28 PM »
Today's images and slow animation (big file).
The increased concentration, which is can be seen in the recent area values, are becoming more apparent

Arctic sea ice / Re: MOSAiC news
« on: August 28, 2020, 06:32:51 PM »
A few days of moderate surface winds are forecast at GFS, including easterlies along the Beaufort, a large but moderate anti-cyclone on the Laptev, and a commonly seen tight cyclone around Svalbard.

As a reminder, the bottom line is friction between local surface winds and ice roughness (respectively water) is what moves today's ice (makes waves). What the MSLP might be doing in the Azores over the next ten days, how the jet stream pattern could change far above as a consequence of fractional BOE, and whether ENSO will be trending in the eastern Pacific don't move ice. They might ultimately drive big-picture wind but predicting it below 2m isn't even an aspirational goal.

That friction is likely higher in the Beaufort because of exposed freeboard edges of dispersed floes. Thus a few days of persistent easterly wind may push much of what's left of the ice below the threshold of radar satellite visibility towards the warmer Chukchi. Waves are always a factor in late season but here long reach swells will not be a player.

The image below places these winds relative to the unfiltered 21:00 UTC of AMSR2_AWI (v101/nh_20200827_21_SIC_12h.tiff) by deleting the five highest palette ice concentrations (less likely to be affected by the winds) to let the 21:00 UTC of nullschool winds show through.

By changing the underlay, that could be visualized 2-3 days out but the problem is that the AMSR2 concentration overlay has no forward map. The difference between 24 hour 21:00's is already quite striking so the wind overlay on a fixed 21:00 of Aug 27 would rapidly become inexact.

Hycom does offer a forward map so AMSR2 could somehow be morphed along to follow its outline. More easily, the wind prediction could be shown behind deleted hycom open water. As interstitial noted, hycom's edge is way too far out. However those colors can be picked and filled with ocean gray.

The scale on nullschool was set to 2800 in its stereographic projection so rescaling by 141% matches it to AMSR2_AWI.

Note this new AMSR2 is unique among products used on the forum in that it is correctly constructed as an 8-bit color geo-located tiff, rather than 24-bit png, jpg, or ever-changing 8-bit gif89. Tiff specs are defined on page 23 of the 1992 defining document:

"Palette-color images are similar to grayscale images. They still have one component per pixel, but the component value is used as an index into a full RGB-lookup table." .

The particular tiff ColorMap used at AWI was laid out somewhere within the bundled file package as an ordered 3-column RGB list; a Baseline tiff reader such as ImageJ's then displays the color map tiles via the 'Edit Lut' command.

An ordinary full color image such as png can be changed to 8-bit color and saved as tiff but it won't have an orderly ColorMap as it is simply made from the highest frequency color usages. However as a csv file it can be sorted to order and loaded as the working LUT.

Arctic sea ice / Re: MOSAiC news
« on: August 28, 2020, 01:54:03 PM »
T78, nearest to PS, has been deployed on ice ~1.5m thick (~therm30-105). Nice to see some below zero air temps there.

Arctic sea ice / Re: MOSAiC news
« on: August 28, 2020, 01:35:18 PM »
Some new buoy data.

Arctic sea ice / Re: The 2020 melting season
« on: August 27, 2020, 09:30:00 PM »
I'm surprised no one has mentioned it yet, but today's the first somewhat clear view above Greenland in quite some time. It looks like export towards the Fram Strait has been almost completely severed off from the narrow triangle that forms on the Greenland's east shore.

The entire region just looks real unstable and fragile. With the upcoming strong winds projected to rip what's left into the Atlantic I think there's still some area to lose here.

Arctic sea ice / Re: 2020 Sea ice area and extent data
« on: August 27, 2020, 05:32:26 AM »
[ADS NIPR VISHOP (JAXA)] Arctic Sea Ice Extent.

August 26th, 2020:
     4,172,910 km2, a drop of -32,135 km2.
     2020 is 2nd lowest on record.
     Highlighted 2020 & the 4 years with a daily lowest min in Sept. (2012, 2019, 2016 & 2007).
     In the graph are today's 10 lowest years.

Arctic sea ice / Re: The 2020 melting season
« on: August 25, 2020, 10:39:15 AM »
The shape of this year's ice pack looks quite similar to that of 2012 (except for the big Beaufort bulge, off course), but it's shifted more to the 'left' on the Uni Bremen SIC map. This is bound to get more pronounced given the current weather forecast.

Arctic sea ice / Re: The 2020 melting season
« on: August 24, 2020, 03:22:26 AM »
A Worldview animation comparing the Beaufort on Aug7 and Aug23.
The ice has certainly been melting with significant open water showing between the floes, but in the race against time this ice can't clear out Chukchi-style before the minimum, barring some very extraordinary event (huge storm/persistent strong south winds/very late minimum).
Using the CT demarcation (Wipneus), NSIDC Beaufort area dropped from 170k to 117k during the similar period of Aug6-22, while UH AMSR2 area dropped from 250k to 137k.
Click to animate and enlarge.

Arctic sea ice / Re: The 2020 melting season
« on: August 23, 2020, 12:51:28 PM »
Updated version (improved colour scheme) of the comparison between the extent and concentration changes for the first 3 weeks of August.

Arctic sea ice / Re: Arctic Ocean salinity, temperature and waves
« on: August 21, 2020, 11:47:13 PM »
Arctic Ocean Moorings Shed Light On Winter Sea Ice Loss

The eastern Arctic Ocean's winter ice grew less than half as much as normal during the past decade, due to the growing influence of heat from the ocean's interior, researchers have found.

The finding came from an international study led by the University of Alaska Fairbanks and Finnish Meteorological Institute. The study, published in the Journal of Climate, used data collected by ocean moorings in the Eurasian Basin of the Arctic Ocean from 2003-2018.

The moorings measured the heat released from the ocean interior to the upper ocean and sea ice during winter. In 2016-2018, the estimated heat flux was about 10 watts per square meter, which is enough to prevent 80-90 centimeters (almost 3 feet) of sea ice from forming each year. Previous heat flux measurements were about half of that much.

"In the past, when weighing the contribution of atmosphere and ocean to melting sea ice in the Eurasian Basin, the atmosphere led," said Igor Polyakov, an oceanographer at UAF's International Arctic Research Center and FMI. "Now for the first time, ocean leads. That's a big change."

Typically, across much of the Arctic a thick layer of cold fresher water, known as a halocline, isolates the heat associated with the intruding Atlantic water from the sea surface and from sea ice.

This new study shows that an abnormal influx of salty warm water from the Atlantic Ocean is weakening and thinning the halocline, allowing more mixing. According to the new study, warm water of Atlantic origin is now moving much closer to the surface.

"The normal position of the upper boundary of this water in this region was about 150 meters. Now this water is at 80 meters,"
explained Polyakov.

A natural winter process increases this mixing. As sea water freezes, the salt is expelled from ice into the water. This brine-enriched water is heavier and sinks. In the absence of a strong halocline, the cold salty water mixes much more efficiently with the shallower, warm Atlantic water. This heat is then transferred upward to the bottom of sea ice, limiting the amount of ice that can form during winter.

Polyakov and his team hypothesize that the ocean's ability to control winter ice growth creates feedback that speeds overall sea ice loss in the Arctic. In this feedback, both declining sea ice and the weakening halocline barrier cause the ocean's interior to release heat to the surface, resulting in further sea ice loss. The mechanism augments the well-known ice-albedo feedback—which occurs when the atmosphere melts sea ice, causing open water, which in turn absorbs more heat, melting more sea ice.

When these two feedback mechanisms combine, they accelerate sea ice decline. The ocean heat feedback limits sea ice growth in winter, while the ice-albedo feedback more easily melts the thinner ice in summer.

"As they start working together, the coupling between the atmosphere, ice and ocean becomes very strong, much stronger than it was before," said Polyakov. "Together they can maintain a very fast rate of ice melt in the Arctic."

Polyakov and Rippeth collaborated on a second, associated study showing how this new coupling between the ocean, ice and atmosphere is responsible for stronger currents in the eastern Arctic Ocean.

According to that research, between 2004-2018 the currents in the upper 164 feet of the ocean doubled in strength. Loss of sea ice, making surface waters more susceptible to the effects of wind, appears to be one of the factors contributing to the increase.

The stronger currents create more turbulence, which increases the amount of mixing, known as shear, that occurs between surface waters and the deeper ocean. As described earlier, ocean mixing contributes to a feedback mechanism that further accelerates sea ice decline.

Igor V. Polyakov et al, Weakening of Cold Halocline Layer Exposes Sea Ice to Oceanic Heat in the Eastern Arctic Ocean, Journal of Climate (2020)

Igor V. Polyakov et al. Intensification of Near‐Surface Currents and Shear in the Eastern Arctic Ocean, Geophysical Research Letters (2020).

Arctic sea ice / Re: The 2020 melting season
« on: August 20, 2020, 08:28:32 PM »
Latest tomorrow a few guys and pals here have to read back a few weeks and re-consider their approach/attitude for the years to come, just one more drop like this while I think there will be many ( a few ) more to come.
All please remember that:
* It is ok to be wrong, it doesn't mean one is a denier or evil or stupid.
* A prediction that failed was not necessarily wrong. Random weather plays a big hand in the Arctic, it could be in retrospect that luck was what decided it.
* The season is not over until it is over, premature celebrations of being right can go wrong later.

Personally I've thought since the crazy July that this season had a good shot at records regardless of later weather, but it doesn't mean I don't respect those who thought otherwise, and I recommend all to do the same. (I don't mean the one or two cherry-pickers, I mean those who post in good faith).

Arctic sea ice / Re: The 2020 melting season
« on: August 19, 2020, 08:47:45 PM »
I am a very non-science based observer, but have lurked here for about 5 years with a few posts. The following may not hold water but what the hey -

I feel that the last fifteen years have truly changed the nature of arctic sea ice, but a lot of the systems and analysis was established as 'fact' before that change really manifested and to some degree it has yet to adjust. Pre-2007 the arctic sea ice remained 'land fast' even at minimum, but by 2012 the only connection to land was Greenland and the CAA islands. Since then even that connection has become intermittent and this year it has been almost non-existent for most of the summer.

The importance to me of the above is that pre2010 arctic ice movement except on the periphery was slow and measured - Ice forming on the Asian side took years to migrate toward Greenland where it either eventually exited the Fram/Nares or started to circle back toward Asia. Ice in the Beaufort got trapped into the gyre and circled back toward Greenland as multi-year ice.

This year looking at the speed with which Polarstern transversed from Asia to the Fram is a perfect illustration of the speed of arctic ice in this new era. Meanwhile no one really looks at the gyre because it is no longer a trap in which ice rotates year after year, but a transportation from the north of the CAA to oblivion for the remnants of 'older' ice. And with Greenland giving up its function as an anchor for the pack the other remnants of 'older ice' are moving towards the CAA and thence to their oblivion. The gyre is no longer tied to the Beaufort as peripheral ice movement but has in effect expanded to include the whole of the pack not destined for the Fram/Nares/Barents exit ramps.

The other aspect of this ice speed and the increased melt rate during melting seasons is that 'older' ice (I use quotes for a reason) is really limited to two year ice with maybe a few chunks interspersed that are older or formed from glaciers/collapsed ice shelves. Even the ice that is technically heading into a third winter this year has suffered so much top and bottom melt in its two summers that only a tiny fraction will be any thicker than the typical first year ice of 2000. And specific to the ice above Greenland - while this year may be extraordinary, the open water has been present for most of the past number of years so it was already fragmented and held together with a matrix of weaker ice. The disappearance of that ice was waiting for the right winds and temperatures and isolation which 2020 has provided.

Back to that second paragraph above - with a strong pack, slow movement and a melt season limited to the peripheral edges, extent with its simpler calculation was the best measure and quite accurate. As movement and melt increased, and the pack easily fragmented, area has become more accurate even with the calculation margins of error. The historic 'record' has validity, but at some point the extent measure becomes less and less relevant to the real life conditions. Additionally, volume measures (Piomas and others) are grounded in a 'solid pack' view of arctic ice and I believe struggle to deal with the 'real world' condition of the pack where 'thick ice' is actually a patchwork of loose flows held together by new and thin ice. Images from Polarstern seem to make this abundantly clear.

Updated volume and volume-anomaly graphs.

Arctic sea ice / Re: The 2020 melting season
« on: August 18, 2020, 05:47:25 PM »
9-day AMSR2 high-res false color animation. This format seems unsuited to animating, but I'll post it anyway. I may not do more.

large unoptimized GIF file. click to animate.

Arctic sea ice / Re: The 2020 melting season
« on: August 18, 2020, 03:51:23 PM »
I am impressed by the slow but relentless progress of the sea ice edge towards 85 North along the Atlantic Front, despite the ice being pretty much at 100% concentration.
The Nansen shelf break provides a handy static line to watch the ice edge retreat along the atl front. Other points of interest are the bathymetry north of Greenland and the yermak and chukchi plateaux.
Here using the development version of awi amsr2 overlaid onto gmrt bathymetry at 80% transparent. Open water has been set to fully transparent.
Scaling slightly out. Have to work on the number of colours used for gifs
Large file 9MB

Arctic sea ice / Re: MOSAiC news
« on: August 15, 2020, 10:35:33 PM »
Airborn Expendable Ice Buoy (AXIB)
An Air-Deployable Expendable Ice Buoy (AXIB) that can withstand multiple freeze-thaw cycles and operate equally well in ice prone ocean or fresh water. The AXIB can be dropped from an airborne platform, land on an ice surface, right itself to the vertical position, anchor and stabilize itself in the ice, withstand several freeze-thaw cycles and continue to transmit data while anchored to the ice or floating in the ocean. The unique hull design of the AXIB allows it to withstand multiple freeze-thaw cycles and continue to function. The AXIB is particularly well suited for deployment and utilization in any ice zone where repeated freeze-thaw cycles occur.

iabp buoy 300234065497190, north of Greenland. Drift speed and air temperature. Surface temperature and pressure are also available.

Arctic sea ice / Re: MOSAiC news
« on: August 15, 2020, 06:11:44 PM »
On our way north, we are now in colder waters ( colder than 1.4˚C) again (marked area). Before it was warmer than -1˚C. Click to enlarge.

Arctic sea ice / Re: Updating the ASIG
« on: August 14, 2020, 07:08:45 AM »
Neven can you please update said maps for the rest of 2019? This has been requested on the melting season thread.

Arctic sea ice / Re: The 2020 melting season
« on: August 09, 2020, 09:33:10 PM »
This remarkable freeze/melt cycle has been unfortunate but perhaps inevitable, putting us literally in uncharted waters with regards to massive climate change impacts.

It’s easy to forget, as the post-BOE forum properly notes, that once upon a time the Barents, Baltic, Bering, Baffin. Chukchi, and Kara hosted millions of sq km of year-round ice. (And that not so long ago, 1000 m thick ice gouged the Lomonosov ridgetop.) On 08 Aug 2020, 38% of the remaining ice (the Arctic Ocean basin, was open water. Vast areas of tundra are free of reflecting snow as well. We’re already well into BOE in most respects.

What’s going on at the moment is baffling, notably between Greenland and the north pole. It’s clear we don’t really understand the current physical state of the ice. Thus even if surface weather were predictable three days out, where things will end up by mid-October still remains up in the air.

However we do have a good grip on some of the pre-conditioning events that have brought the ice to its current state:

-1- The melt season really began in the previous freeze season, even earlier. Vast areas of surprisingly thin 0.3m ice remained in the Laptev when the Polarstern moored on Oct 4th. That and a slow start to freeze-up are documented by thousands of km of ship thickness transects with no graduating SYI floes thick enough to stand on for Mosaic. (T Krumpen

-2- The TransPolar Drift over winter, as accurately imaged in Ascat time series, bore little resemblance to recent years in two key respects: months of very rapid Fram-ward displacement and extensional engagement of ice to the pole and beyond. Often the ice drift is just circumpolar.

-3- The whole icepack does not rotate CW with the TPD but rather participation is demarcated by immense  curvilinear leads, newly visualized in a dockside posting by L Kaleschke and enhanced on the Mosaic forum by directional convolution. These fracture lines, coincidentally or causally, approximately delimit the puzzling openings to the pole above Morris Jesup. A lot of MYI ice between Greenland and the pole was fractured by lead formation.

-4- Missing this year was any significant CW rotational movement of thick ice out of the western CAB. While this ice has never moved further than a half gyre in the last ten years of tracking, commonly a strip of CAB ice moves to inevitable melt in the warmer open seas of the Chukchi (which might be called internal export).

-5- Export out the Fram was robust during the TPD, pushing everything ahead of a 500 km east-west line through the initial position of the PS to oblivion in the Greenland Sea. Behind this line, newly formed Laptev ice filled the growing open water gap to shore. However, since mid-May, export out the Fram, SV-FJL gap, Bering Strait, CAA garlic press and Nares have all been inconsequential (and will remain so, too little time is left).

-6- A record heat wave off Ellesmere in mid July coupled with persistent easterly winds melted vulnerable matrix ice joining floes, enabling churning of offshore ice into residual rubble. The observed movement to the west is not unusual but it was far more narrowly restricted to the CAA coast in past events. The main CAB ice pack, being no longer attached to coastal land or ocean bottom, might be set adrift to elsewhere by persistent winds from the south. We’ve not yet seen that game-changer.

-7- The Pacific-side cyclone centered on July 27th hit like a tornado at 75º/-160º decimating the ice, on Sentinel-1 and WorldView, making clear that error-prone thickness and area/extent whole-ocean numbers don’t capture key issues such as ice mechanical strength, internal pressure or response to stress.

Both the Chukchi and slow-melting Beaufort were pre-conditioned by dispersion for flash lateral and bottom melt after the storm; note insolation today at 75º surprisingly is still 64% the strength the week centered on solstice (4th image below) but has to get through clouds and escape low angle surface reflection.

Are these independent events or somehow consequent to a single master change (such as breakdown trend of equatorial heat gradient as manifested in the jet stream)? Yes to a certain extent but this view has to be distinguished from the slot machine model put forward by Csnavywx in #4662.

That is, the multi-decadal downward trend of ice has created a set-up for which a coincidental confluence of bad weather events over a single freeze/melt cycle sequentially sum to an ice disaster. Even bland weather from here to October may suffice for a seriously below-trend outcome. Regardless of how the season turns out, as @Zlabe notes, fractional BOE has gone on all summer.

The files below expand or animate with a click. File names explain the topic addressed. I thank uniquorn for valuable discussions. Clouds are removed by setting a sequential five day AMR2 stack to 'darken only' in gimp.

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