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A-Team

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Re: The 2020/2021 freezing season
« Reply #950 on: December 27, 2020, 01:57:08 PM »
Quote
white band: previous years yes/no/, where/when, other satellites
These are all useful avenues of investigation. The white band is not somehow 'inevitable' in C-band radar -- no one predicted its existence and no journal article describes or explains it, possibly because Ascat is seriously under-utilized and Sentinel-1AB is fairly new.

Looking back, the white band first appears in the Ascat archive at the end of August near the end of melt season at the seasonal marginal ice zone (MIZ), the transition zone between the ice pack and open Arctic. That cannot be the whole story because the Pacific half of the potential boundary zone doesn't form the white band. Some other tracker is needed there to mark the shape-shifting division between FYI and MYI ice over the freeze season.

The white band is initially far more extensive, forming a border from below the New Siberian Islands all the way around to Svalbard. Only the Laptev portion persists; the Atlantic side is still very subjected to wind effects in late December (uniq's AMSR2 gif above).

In the satellite archives we use, the visible is fairly literal (corrected reflectance) as is the infrared (offered in various false color palettes), not that different from the view out an airplane window with appropriate goggles.

Looking at Nasa's WorldView, there wasn't a clear enough day over the time and location window to determine whether or not the white band is visible at these wavelengths. The white band is not an open lead or polynya so not brighter/warmer in Suomi band15 infrared.

It is no coincidence that  Ascat and Sentinel-1AB both see the white band: they observe at very similar wavelengths of 5.7cm and 5.5cm (5.255 and 5.405 GHz, C-band in radar WWII terminology). Sentinel-1AB resolves much greater detail but coverage is episodic and difficult to tile.

The question is, can the white band be seen on the ground, with instrumented airplane flyovers, or in L-band or other radar products? In other words, the band's electromagnetic reflectance spectrum is key to determining what it is (or at least ruling out what it is not).

Microwave products like Smos are brought into visible 8-bit interpreted products after extensive processing algorithms. Smos looks at a longer wavelength of 21.4cm(1.4 GHz L-band) and can measure distance through the ice (of a half meter or less thickness) to sea water. The white band is not apparent; note though the archive provides only the highly processed view.

The white band cannot be seen in AMSR2, CMEMS, Piomas, Hycom, OsiSaf, SicLeads, Smap, Smos-Smap, Jaxa, cryosat2smos or other products.

Ascat brightness diminishes rapidly with near-surface ice and atmospheric path polarity (dielectric); older ice is farther along in brine exclusion so whiter. However this is not a good fit to the white band along the former MIZ unless that ice is somehow so crumpled that brine channels have already drained. Other forms of elastic scattering can relate to surface roughness or particle size relative to incident wavelength.

Only Ascat sticks to a literal beam reflectance (grayscaled 0-1 or σ⁰ backscatter, lower left corner scale in files). It was never intended for ice; the primary instrument justification has been ocean surface wind speed measurement at mid to low altitude.

We discovered here years ago that Ascat holds hidden treasures: after a series of photoshop-type contrast enhancements, the initially bland imagery can accurately display ice movement as well as regions of brine exclusion maturity (older thicker ice) and other persistent but unexplained interior features. There is no use of Ascat enhancement in the Arctic science community.

Yesterday's before and after are shown below, with emphasis on MYI. Movement of many of the ice substructures can be tracked for months, sometimes deforming but still persisting in time series, so not processing artifact. Click to see at full scale.

There's a lot more going on with the ice pack than just one-parameter thickness.
« Last Edit: December 27, 2020, 02:18:57 PM by A-Team »

A-Team

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Re: The 2020/2021 freezing season
« Reply #951 on: December 27, 2020, 05:48:07 PM »
Below is a quick wrap of the effect of the 08-26 Dec 2020 basin-wide anti-cyclone for the Lincoln Sea / Ellesmere Island area. (The effect on the Beaufort ice is shown over at the Mosaic forum.)

This is something we have seen many times before: the wind would like the ice to rotate with it about the center of the anti-cyclonic high but the shape of the Arctic Ocean basin is too small and asymmetric to accommodate CW rotation of the necessary diameter.

The ice then hits an unmovable object -- northernmost Ellesmere Island in the Cape Columbia / Ward Hunt Island / Cape Discovery area and shears repeatedly into very long arcs. In late December, the ice in the Lincoln Sea responded to stress by shearing transversely to the existing leads (inset on geology map), much like faulting in California earthquakes.

There's probably no long-term significance locally; it won't affect later opening of the Nares Strait and ice export. However, like MYI boundary tracking with the white band, it's part of understanding overall ice motion in the Arctic which is increasing as weaker FYI comes to dominate the overall ice pack.

The timing of ice disappearance cannot be figured from thermodynamics alone as ice breakup, swell damage, advection to warmer seas, and export out of the basin will play large roles in the end game. It looks now that 'Siberian side semi-BOE' will be a key intermediate because Arctic Amplification, Siberian weather and encroaching Atlantification are favorably asymmetric in that sense.
« Last Edit: December 27, 2020, 05:53:56 PM by A-Team »

Aluminium

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Re: The 2020/2021 freezing season
« Reply #952 on: December 28, 2020, 06:25:57 AM »
December 17-27.

2019.

uniquorn

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Re: The 2020/2021 freezing season
« Reply #953 on: December 28, 2020, 11:02:28 AM »
Thanks for the animation Aluminium.
Interesting that the Barents looks like it is freezing despite the southerly winds. Checking on nullschool, those surface winds leave the coast at -17C, rising to -5C as they cross mostly open water.
Sentinel S1B view of that area from polarview The wind driven ice edge is darker to the left, open water is bright to the far right. click for full res.

A-Team

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Re: The 2020/2021 freezing season
« Reply #954 on: December 29, 2020, 01:27:33 PM »
Fall freeze up to date, emphasis on MYI.

oren

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Re: The 2020/2021 freezing season
« Reply #955 on: December 29, 2020, 04:27:38 PM »
Thanks for this superb animation A-Team, it gives a lot of perspective about ice motion and development during the freezing season so far. It appears much of the ice north of Greenland was flushed down the exit, though luckily it wasn't the thickest surviving ice, which according to CS/SMOS was more to the west IIRC. It also appears most of the Beaufort Tail did not linger to strengthen the ice there for next year - some of it melted away and some was carried to the Chukchi and to quick demise in half a year.

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Re: The 2020/2021 freezing season
« Reply #956 on: December 29, 2020, 06:01:50 PM »
    Nice video A-Team.  That view makes me wonder if Nares export could become much more important in the next few years.  If open, it provides an exit route for what little remains of MYI.
 
    The Lincoln Sea ice does not look all that solid especially for this time of year.  While additional freeze will occur between now and March-April, does the animation provide any hint about how solid the Lincoln Sea ice is likely to be heading into the 2021 melt season relative to recent historical average condition?  And does my speculation about the degree of Lincoln Sea "solidity" having an effect on Nares export, and consequently also on the longevity of the heart of the remaining MYI, make any sense?  Maybe this belongs in the Stupid questions thread, but also useful to post it just below the animation to see what I'm referring to.  (note to others -- you need to double click to see the video in whole-screen mode).   The recurring mega-crack north of Greenland seems like it could be another important contributing factor to this scenario.
« Last Edit: December 29, 2020, 06:24:14 PM by Glen Koehler »

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Re: The 2020/2021 freezing season
« Reply #957 on: December 29, 2020, 10:28:53 PM »
Multi-year ice begets first-year ice.
I am an energy reservoir seemingly intent on lowering entropy for self preservation.

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Re: The 2020/2021 freezing season
« Reply #958 on: December 30, 2020, 07:59:18 AM »
December 17-27.

Thanks as ever, Aluminium.  The pronounced retreat of the ice front north of Svalbard so evident in your animation seems noteworthy to me.   From the start of November to the middle of December, your animations have shown the Atlantic ice edge to be either stable or advancing.  The ice remains in its retreated position N of Svalbard in the Dec 29 Bremen AMSR-2 image below.  I don't know how unusual this retreat is, but I have some questions...

-- Was this ice retreat wind-driven?  If so, then it indicates to me the ice front in that area was really fragmentary and weak in its nature in mid December. 
-- Was it due to ice pack rotation?  Unlikely, IMO, since it would seem the overall clockwise pack rotation would supply ice to this area, not remove it. 
-- Was it (gulp) melting?   We know an arm of the warm North Atlantic current loops north around Svalbard at this point.    If so, did this warm current recently pulse north at this point? 
-- Am I missing something here? 
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Re: The 2020/2021 freezing season
« Reply #959 on: December 30, 2020, 10:32:57 AM »
Fall freeze up to date, emphasis on MYI.
That is one of the best animations I've seen on this forum A-team. Thanks for that! Love the "dunk", or "hole in one" of a big chunk of ice into the McClure Strait. Absolutely perfect dunk...

Another thing I've noticed is that some of the ice got squeezed through a channel of the CAA. I think it is Borden Island that seems to act as a stop? I had noticed this already when I was looking at the 30 day Hycom model (gif), and to have that movement confirmed in your animation confirms it for me that this Hycom model is actually quite good. When it can model small details like that, I think we can trust that model when it comes to ice movement. I'm not sure about ice thickness, but ice movement surely is captured quite accurately by Hycom.

Does anyone feel an urge to put the Hycom model over your animation to compare them?

Here is the Hycom model for the full year. Notice the difference between last year an this year when the Gif comes to an end and starts again. There was way more thick ice last year around this time, and what's left this year is moving into next summer's melting areas...

I presume the ice is way more mobile now that the more solid MYI is almost all gone?

Edit:
The ice is younger and thinner then any other time in recent history. And this time of year it's also more windy. So thinner, younger, weaker ice + strong wind = much more mobility of the ice?

Is that correct?

Edit2:
I also think that when the ice is weaker, and more mobile, it will create more ridges. And ridges have a tendency to capture the wind better, which is another positieve feedback for ice movement?
« Last Edit: December 30, 2020, 08:00:45 PM by Freegrass »
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Re: The 2020/2021 freezing season
« Reply #960 on: December 30, 2020, 01:17:46 PM »
-- Was this ice retreat wind-driven?  If so, then it indicates to me the ice front in that area was really fragmentary and weak in its nature in mid December. <>
Yes. There are similarities with 2016. Note the refreeze south of the wind driven ice front (see #953 above)
Is it melting? In my view ice is always melting along much of the West Spitzbergen current. During most winters drift speed and thickness is enough that it is not visible from above except (imo) occasionally along the shelf break north of FJL.

amsr2-uhh comparison of 2020 and 2016, dec20-29

A-Team

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Re: The 2020/2021 freezing season
« Reply #961 on: December 30, 2020, 04:08:19 PM »
Quote
ice is always melting along much of the West Spitzbergen current. During most winters drift speed and thickness is enough that it is not visible from above
Right. OsiSaf quantitates ice displacements. Smos-Smap is in its element for sub-half meter ice thinness, showing Barents ice growth, shelf melt, and lee polynyas; pairing with AMSR2_UHH_3.125 concentration above might help disentangle these. Cryo2Smos has sub-optimal resolution but does ok. The effect of waves on the Barents MIZ ice has been the focus of a  neXtSIM improvement project, not yet in the CMEMS product.

https://www.researchgate.net/publication/338803774_Wave-sea-ice_interactions_in_a_brittle_rheological_framework 2020
https://tc.copernicus.org/articles/11/2117/2017/tc-11-2117-2017.pdf 2017

Wrapping the 'white band' discussion, a later Sentinel-1B extending farther east appears to show a series of three wave-deposited layers of MIZ onto SYI as the source; these ice fragments may be too fractured to retain brine pockets and so, lacking dielectric, effectively reflect Ascat's radar.
« Last Edit: December 30, 2020, 04:17:15 PM by A-Team »

A-Team

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Re: The 2020/2021 freezing season
« Reply #962 on: December 30, 2020, 09:17:58 PM »
Quote
Can thickness be shown simultaneously with sea ice concentration... are they always correlated?
On the Atlantic side corridor, the sea ice concentration can be put side by side with sea ice thinness or for that matter directly combined by the four overlay methods shown (Ismos-amsr2, smos:amsr2 grain merge; color, multiply).

Alternatively, Smos-Smap can be draped over AMSR_awi elevated per low values. However that isn't productive in this instance because the concentration values are poorly distributed, almost all being 0 or 100% where they can be reliably determined.

Experimental evidence for a universal threshold characterizing wave-induced sea ice break-up
J Voermans et al  Nov 2020
https://tc.copernicus.org/articles/14/4265/2020/

Waves can drastically transform a sea ice cover by inducing break-up over vast distances in the course of a few hours... We show that both field and laboratory observations tend to converge to a single quantitative threshold at which the wave-induced sea ice break-up takes place.

Wave–sea-ice interactions in a brittle rheological framework
G Boutin et al  Jan 2020
https://tc.copernicus.org/preprints/tc-2020-19/

The decrease in Arctic sea ice extent is associated with an increase of the area where sea ice and open ocean interact, commonly referred to as the Marginal Ice Zone (MIZ). In this area, sea ice is particularly exposed to waves that can penetrate over tens to hundreds of kilometres into the ice cover. Waves are known to play a major role in the fragmentation of sea ice in the MIZ... Here, we pair the spectral wave model WAVEWATCH III with the sea ice model neXtSIM, which includes a Maxwell-Elasto Brittle rheology... Focusing on the Barents Sea, we find that the decrease of the internal stress of sea ice resulting from its fragmentation by waves results in a more dynamical MIZ, in particular in areas where sea ice is compact. Sea ice drift is enhanced for both on-ice and off-ice wind conditions.

Interannual variability in Transpolar Drift ice thickness and potential impact of Atlantification
HJ Belter et al  22 Oct2020
https://tc.copernicus.org/preprints/tc-2020-305/tc-2020-305.pdf

Changes in Arctic sea ice thickness are the result of complex interactions of the dynamic and variable ice cover with atmosphere and ocean. Most of the sea ice exits the Arctic Ocean through Fram Strait, which is why long-term measurements of ice thickness at the end of the Transpolar Drift provide insight into the integrated signals of thermodynamic and dynamic influences along the pathways of Arctic sea ice. We present an updated time series of extensive ice thickness surveys carried 5 out at the end of the Transpolar Drift between 2001 and 2020. Overall, we see a more than 20% thinning of modal ice thickness since 2001.
« Last Edit: December 30, 2020, 10:21:52 PM by A-Team »

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Re: The 2020/2021 freezing season
« Reply #963 on: December 30, 2020, 09:26:12 PM »
-- Was this ice retreat wind-driven?  If so, then it indicates to me the ice front in that area was really fragmentary and weak in its nature in mid December. <>
Yes. There are similarities with 2016. Note the refreeze south of the wind driven ice front (see #953 above)
Is it melting? In my view ice is always melting along much of the West Spitzbergen current. During most winters drift speed and thickness is enough that it is not visible from above except (imo) occasionally along the shelf break north of FJL.
Thanks to you and A-Team.  I understand more now.  The current retreat N of Svalbard is a bit troubling but that 2016 animation you paired it with was downright scary.
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uniquorn

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Re: The 2020/2021 freezing season
« Reply #964 on: December 30, 2020, 11:11:02 PM »
awi amsr2 dec29-30

A very close look at the 3 wave layers in the white band (10MB for full res) dec30
16bit gimp to png
https://earth.esa.int/web/guest/missions/esa-operational-eo-missions/ers/instruments/sar/applications/radar-courses/content-2
Quote
Different surface features exhibit different scattering characteristics:
urban areas: very strong backscatter
forest: intermediate backscatter
calm water: smooth surface, low backscatter
rough sea: increased backscatter due to wind and current effects


The radar backscattering coefficient σ 0 provides information about the imaged surface. It is a function of:
- radar observation parameters:
(frequency f, polarisation p and incidence angle of the electromagnetic waves emitted);
-surface parameters:
(roughness, geometric shape and dielectric properties of the target).

Influence of frequency

The frequency of the incident radiation determines:
- the penetrationdepth of the waves for the target imaged;
- the relative roughness of the surface considered.

Penetration depth tends to be longer with longer wavelengths. If we consider the example of a forest, the radiation will only penetrate the first leaves on top of the trees if using the X-band (λ = 3 cm). The information content of the image is related to the top layer and the crown of the trees. On the other hand, in the case of L-band (λ = 23 cm), the radiation penetrates leaves and small branches; the information content of the image is then related to branches and eventually tree trunks.

The same phenomenon applies to various types of surfaces or targets (see the figure).

But it should be noted that:
- penetration depth is also related to the moisture of the target;
- microwaves do not penetrate water more than a few millimeters.

Influence of polarization
Polarization describes the orientation of the electric field component of an electromagnetic wave. Imaging radars can have different polarization configurations.

However, linear polarization configurations HH, VV, HV, VH are more commonly used. The first term corresponds to the polarization of the emitted radiation, the second term to the received radiation, so that XHV refers to X band, H transmit, and V receive for example.

In certain specific cases, polarization can provide information on different layers of the target, for example flooded vegetation. The penetration depth of the radar wave varies with the polarization chosen.

Polarization may provide information on the form and the orientation of small scattering elements that compose the surface or target.

More than one bounce of backscattering tends to depolarize the pulse, so that the cross polarized return in this case would be larger than with single bounce reflection.

Influence of roughness
Roughness is a relative concept depending upon wavelength and incidence angle.
A surface is considered "rough" if its surface structure has dimensions that are comparable to the incident wavelength.
« Last Edit: December 31, 2020, 12:37:28 AM by uniquorn »

A-Team

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Re: The 2020/2021 freezing season
« Reply #965 on: December 31, 2020, 01:21:46 PM »
On the best resolution PolarView offers for Sentinel-1AB, a single pixel is 41m wide, so the smallest object that can be seen. That scale can be taken from the distance between two parallels which is 111.11 km in this region. The three bands are then several km wide. These dimensions -- and the smallest visible particles -- are very much greater than the observing wavelengths which are 5 cm. For Mie scattering, they need to be comparable with something very extensive on the surface.

Winds in late August, a potential explanation for the hypothetical MIZ deposits on SYI, were strong, persistent and from the appropriate direction but not remarkable suggesting late melt season timing was important too. Between these bands on Ascat and sharp thickness shelving between FYI and SYI on neXtSIM, we are in good position to track that boundary into the next melt season.

uniquorn

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Re: The 2020/2021 freezing season
« Reply #966 on: December 31, 2020, 03:31:54 PM »
Here using the interferometry method to identify areas with more movement. Grey areas are relatively stationary with brighter and darker areas tending to move more. That FYI/SYI edge may always be under more stress than other areas. Continuous ridging?
Ascat day301-362 RGB composite from 1,2 and 3 day difference (grain extract in GIMP)
forgot this: <add 128 neutral gray to avoid negative color numbers> hence the very dark colours
« Last Edit: December 31, 2020, 05:22:18 PM by uniquorn »

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Re: The 2020/2021 freezing season
« Reply #967 on: January 01, 2021, 02:01:20 PM »
Quote
Despite the extreme sea ice extent recovery in late October early November, extent ended the year at 3rd lowest in the 42 year satellite record.
So we are back to win/place/show, or gold/silver/bronze...in the top three positions for smallness of ice. Sigh...
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Re: The 2020/2021 freezing season
« Reply #968 on: January 01, 2021, 07:22:39 PM »
It is interesting to note that one of the strongest non tropical storms is spinning in the gulf of Alaska with a pressure of 921mb!!! A wave height of 51ft was also measured. I have no idea if the waves will make it to the nice and affect it, but very interesting to see such a powerful storm.

Also, happy 2021 ya'll!
pls!

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Re: The 2020/2021 freezing season
« Reply #969 on: January 01, 2021, 08:55:34 PM »
2021 (end of 2020) appears to be starting off at about 5th lowest extent on record.
Prehaps even within the margin of error of the other lowest years (ie. very low)

http://nsidc.org/arcticseaicenews/charctic-interactive-sea-ice-graph

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Re: The 2020/2021 freezing season
« Reply #970 on: January 02, 2021, 12:10:16 PM »
A comparison of 2017, 2018 and 2020 freezing seasons using amsr2-uhh

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Re: The 2020/2021 freezing season
« Reply #971 on: January 02, 2021, 03:07:36 PM »
2020 extent at 2 week intervals, split into the freeze, melt, freeze periods.

Will add the gradual concentration change for the whole year in a day or 2

(large file, click to play)
I recently joined the twitter thing, where I post more analysis, pics and animations: @Icy_Samuel

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Re: The 2020/2021 freezing season
« Reply #972 on: January 02, 2021, 03:23:32 PM »
2021 (end of 2020) appears to be starting off at about 5th lowest extent on record.
Prehaps even within the margin of error of the other lowest years (ie. very low)

http://nsidc.org/arcticseaicenews/charctic-interactive-sea-ice-graph
There are several different data sets I believe Jaxa is third at end of year

Freegrass

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Re: The 2020/2021 freezing season
« Reply #973 on: January 03, 2021, 12:13:47 AM »
Can anyone explain the reason for that very salty patch in the Chukchi sea? Is that accumulating brine from the refreeze?
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Re: The 2020/2021 freezing season
« Reply #974 on: January 03, 2021, 07:04:00 AM »
I have no idea about the salinity in the Chukchi but it formed in December of 2017, 2018, 2019 and 2020. It also seems to dissipate by the end of January to mid February. Some of the bays on the pacific side tend to do something similar. Maybe some other shorelines in general. It looks to me to be no more than 4 salinity units. The only thing I can think of is what you said. Limited to shores that don't get flushed when Ice is forming?

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Re: The 2020/2021 freezing season
« Reply #975 on: January 03, 2021, 03:39:24 PM »
Satellite classification struggles for accuracy along the coast wherever a pixel's footprint includes shore, lagoons, estuaries, lakes, mires, seasonally changing unvegetated barrier islands, riverine inputs, stranded floes, brackish water ice and so on along with the targeted ocean. Neither ice concentration and ice thickness have currently attained winter maturation in this region of the Chukchi.

Mercator Ocean is a model to a large extent so it's not immediately clear where it is getting these higher readings nor whether there is any field observations that support them.
« Last Edit: January 03, 2021, 04:00:57 PM by A-Team »

uniquorn

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Re: The 2020/2021 freezing season
« Reply #976 on: January 03, 2021, 06:16:41 PM »
A possible candidate is upwelling.
http://oceanmotion.org/html/background/upwelling-and-downwelling.htm

Meanwhile in the Beaufort the warm layer is even thicker below whoi itp120
« Last Edit: January 03, 2021, 10:02:33 PM by uniquorn »

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Re: The 2020/2021 freezing season
« Reply #977 on: January 04, 2021, 01:01:33 AM »
...whoi itp120
That temperature profile is very, very strange, and quite disturbing.  Upwelling or intrusion from elsewhere, but strange, if not local, that a layer like that would slide along just under the top 25m of cold near-surface water.

The implied availability of local heat is significant.
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Freegrass

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Re: The 2020/2021 freezing season
« Reply #978 on: January 04, 2021, 02:12:34 AM »
It seems the question was way easier than the answer. If it was upwelling, then where does the salt water come from on the less salty Pacific side? That must be Atlantic water then that's upwelling, and that is either impossible, or a big problem...

Measuring errors that repeat themselves annually seem unlikely to me also, so I'm going with brine that is released by the refreeze of the Canadian side of the Bering sea that then enters the Bering strait as saltier water and reveals itself at the surface because of upwelling maybe?

Thanks for the answers! Even though the mystery remains...
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Glen Koehler

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Re: The 2020/2021 freezing season
« Reply #979 on: January 04, 2021, 03:21:44 AM »
...whoi itp120
That temperature profile is very, very strange, and quite disturbing.  Upwelling or intrusion from elsewhere, but strange, if not local, that a layer like that would slide along just under the top 25m of cold near-surface water.

The implied availability of local heat is significant.
     How close to the surface does the subsurface warm water become vulnerable to release to the surface from a strong storm? 

vox_mundi

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Re: The 2020/2021 freezing season
« Reply #980 on: January 04, 2021, 04:48:39 AM »
It might be related to this. The heat seems to upwell in the same general area. ...

Archived' heat has reached deep into the Arctic interior, researchers say

Quote


 Arctic sea ice isn't just threatened by the melting of ice around its edges, a new study has found: Warmer water that originated hundreds of miles away has penetrated deep into the interior of the Arctic.

That "archived" heat, currently trapped below the surface, has the potential to melt the region's entire sea-ice pack if it reaches the surface, researchers say.

The study appears online Aug. 29 in the journal Science Advances.

"We document a striking ocean warming in one of the main basins of the interior Arctic Ocean, the Canadian Basin," said lead author Mary-Louise Timmermans, a professor of geology and geophysics at Yale University.

The upper ocean in the Canadian Basin has seen a two-fold increase in heat content over the past 30 years, the researchers said. They traced the source to waters hundreds of miles to the south, where reduced sea ice has left the surface ocean more exposed to summer solar warming. In turn, Arctic winds are driving the warmer water north, but below the surface waters.

"This means the effects of sea-ice loss are not limited to the ice-free regions themselves, but also lead to increased heat accumulation in the interior of the Arctic Ocean that can have climate effects well beyond the summer season," Timmermans said. "Presently this heat is trapped below the surface layer. Should it be mixed up to the surface, there is enough heat to entirely melt the sea-ice pack that covers this region for most of the year."
  "Warming of the interior Arctic Ocean linked to sea ice losses at the basin margins" Science Advances (2018)
http://advances.sciencemag.org/content/4/8/eaat6773.





Over the period 1987–2017, total warm halocline heat content integrated horizontally over a region encompassing the BG has nearly doubled ... The capacity for sea ice melt of the additional heat content (the increase of ~2 × 108 J m−2 over 30 years) equates to a change of about 0.8 m in thickness, taking the latent heat of melting to be 2.67 × 105 J kg−1 and the density of sea ice to be 900 kg m−3.

Both increased temperatures and a thickening of the warm halocline layer [associated with spin-up of the Beaufort Gyre and accumulation of freshwater; see (1)] contribute to the observed heat content increase.

In the coming years excess BG halocline heat will give rise to enhanced upward heat fluxes year-round, creating compound effects on the system by slowing winter sea ice growth.
« Last Edit: January 04, 2021, 05:18:53 AM by vox_mundi »
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uniquorn

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Re: The 2020/2021 freezing season
« Reply #981 on: January 04, 2021, 11:50:07 AM »
Quote
It might be related to this. The heat seems to upwell in the same general area. ...

I probably shouldn't have posted those two together. I don't think that paper relates to upwelling. It is more about warming of the Pacific layer which currently remains trapped between the 'freshwater layer' and the Atlantic layer. According to the Arctic Monitoring and Assessment Program that layer has a residence time of ~10years.

Quote
<strange, if not local, that a layer like that would slide along just under the top 25m of cold near-surface water.>

It seems to be generally accepted that ocean layers can be at quite different temperatures without mixing if there is a large enough difference in salinity. That paper shows the increase in both temperature and area, though there must be a fair amount of interpolation based on scarce data.

Does it affect freezing/thickening? We are fortunate to have a cryosphereinnovation.com ice mass balance buoy co-located with whoi itp120. A great opportunity to study thickening as the buoys travel over the warmest area of the Pacific layer.

The ice thickness chart looks odd. The buoy is a 4m long tube. I think that it must have had a short melting experience (or some other trauma) and slipped further down the bore hole.

Further reading from https://advances.sciencemag.org/content/4/8/eaat6773
Quote
ACCUMULATION OF HEAT
Halocline ventilation

The source of the increased halocline heat content can be understood by first considering how the BG halocline is ventilated. The northern Chukchi Sea (NCS) region exerts major influence on the interior structure of the halocline; here, water masses with the salinity range of the warm halocline outcrop at the surface (11). In this region, which we define to be within 70°N to 75°N and 150°W to 170°W, and south of the 300-m isobath (Fig. 2E), water is pumped down from the surface (via the Ekman transport convergence as a result of the prevailing anticyclonic wind stress gradients) and transported laterally by the BG geostrophic flow into the interior gyre (9, 11). Observations suggest that the NCS is characterized by the strongest time-mean Ekman downwelling in the entire Canada Basin, with downwelling rates averaging around 20 m year−1, which corresponds to a vertical Ekman flux of around 0.05 Sv (1 Sv = 106 m3 s−1) for the region (12). This strong downwelling, associated with the region of maximum strength of the prevailing easterlies, takes place year-round with some interannual variability, but no significant trend over 2003–2014 [see Figs. 4 to 6 in (12)].

A major oceanographic feature of relevance in the NCS is a surface front in the vicinity of the Chukchi slope. The front marks the lateral transition between relatively warm (in summer/fall) and salty surface waters (and a deeper mixed layer) to the south, and cool and fresh surface waters (and a shallower mixed layer) to the north, toward the interior of the BG freshwater center. Water at the surface on the south side of the front is transferred below the mixed layer and into the interior halocline by subduction: vertical Ekman pumping plus lateral induction. It should be noted that there are likely other physical mechanisms at play in this important region that depend on the details of surface buoyancy forcing and sea ice state [for example, (13, 14)], local winds, and properties, dynamics, and stability of regional boundary currents [for example, (8, 15–17)]. The ventilation rate from this region (combination of Ekman downwelling and lateral induction) is estimated to be around 0.2 Sv (11). The cause of the warming halocline can be discerned by examining surface ocean temperatures over this region of maximum subduction, the portal for halocline ventilation.
« Last Edit: January 04, 2021, 12:04:42 PM by uniquorn »

A-Team

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Re: The 2020/2021 freezing season
« Reply #982 on: January 04, 2021, 12:55:06 PM »
Quote
It might be related to this. The heat seems to upwell in the same general area.
The Mercator Ocean salinity patch is 150 km up the coast and highly localized to shallow lagoon/barrier island regions, not associated with the Canadian Basin. The map under discussion is also showing dozens of other small hotspots like this along coastal regions of the Bering, Chukchi, Okhotsk seas and even Wrangel Island (also largely ringed by sand barrier island lagoons). It's not plausible that these all have different explanations (Occam).

We are not necessarily talking about actual observed salinity here (in winter?) but rather what the Mercator Ocean map is showing. The salinity scale is constantly changing with the date so going by colors can be very misleading; the constant-scale png lacks the enlargement capability. Possibly seasonal evaporative and brine exclusion processes are influencing the model.

It's never been clear how much of MO's maps are data driven, eg who is measuring daily salinity at 1000m under the millions of sq km central ice pack? However in this instance, given known winter flushing of hypersaline coastal lagoons, Mercator may be spot on.

Quote
The coastline of the Beaufort Sea comprises a series of lagoons that account for > 50 % of the land-sea interface. The lagoon ecosystems are novel features that cycle between “open” and “closed” phases (i.e., ice-free, and ice covered, respectively). In this study, we collected high-frequency pH, salinity, temperature, and PAR measurements in association with the Beaufort Lagoon Ecosystem LTER for an entire calendar year in Kaktovik Lagoon, Alaska. Flow channels between the land, Arctic lagoons and the ocean are ephemeral, causing the flow of water in and out of a lagoon to be intermittent, varying on short- and long-term time scales (Dunton et al., 2012; Kraus et al., 2008). These physical flow attributes result in highly variable salinity and temperature that range from fresh to hypersaline (0 to >45), and -2 C to 14 C, respectively (Dunton and Schonberg, 2006; Harris et al., 2017).
https://bg.copernicus.org/preprints/bg-2020-358/bg-2020-358.pdf
Below, first page from:
https://www.jstor.org/stable/1351734?seq=1
« Last Edit: January 04, 2021, 01:36:53 PM by A-Team »

interstitial

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Re: The 2020/2021 freezing season
« Reply #983 on: January 04, 2021, 02:12:07 PM »
Mercator offers two maps on their download page One has a scale optimized for the day and the other has a fixed scale that remains constant overtime.


From the model water temperatures on the surface are cooling when this occurs. This makes sense because the surface is freezing over near that time. This may not preclude warm water upwelling if it cools quickly when it reaches the surface.


I tried to draw a diagram but the result does not make sense to me. I don't understand something

A-Team

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Re: The 2020/2021 freezing season
« Reply #984 on: January 04, 2021, 02:29:02 PM »
Quote
Mercator offers two maps on their download page One has a scale optimized for the day and the other has a fixed scale that remains constant over time.
As I wrote in the post immediately above, the fixed scale png at Mercator Ocean is too small to show detail. It does not have the enlargement + or the full screen option. It follows that it is difficult to make time series of small features: the image is either too small or the salinity scale changes with each frame. There's no feasible way to adjust the scale later.

As noted many times previously, the salinity scale colors do not correspond to the map salinity colors. Nonetheless, the winter flushing of the 40 psu hypersaline coastal lagoons can still be seen in time series, even though the salinity cannot be read off accurately.

MO gifs are tricky to make but the outflow can easily be seen just clicking through the dates from 01 Dec 2019 on, notably 01-10 Jan 2020 of last year when the lagoon barrier is apparently breached. WorldView won't show this if the canned land mask layer is on. It might show in Band 15 (see https://go.nasa.gov/2X6roAf).  Sentinel-1B has occasional coverage of the sand barriers at high enough resolution to show breaches (eg https://tinyurl.com/yb2jjrmw).

Hycom salinity gifs do not have the resolution to show the feature. PSL does not have a salinity diagram despite having everything else. CMEMS has many salinity offerings but none that are current or adequately scalable.

The same timing of hypersaline lagoon breach and Mercator salinity out-surge would be another nail in a coffin that was already case-closed 40 years ago by onsite measurement.

Winter breaching of lagoon barriers is also a common phenomenon along the north California coast, for example Lake Earl, Stone Lagoon, Freshwater Lake, Humboldt Bay etc. To the extent these are not estuaries (river termini), salinity may increase notably during the following summer. These are not freeze-season related however like the AK and Russian cases.

I'm not sure why several people here keep posting off-topic diagrams.
« Last Edit: January 04, 2021, 04:00:20 PM by A-Team »

Freegrass

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Re: The 2020/2021 freezing season
« Reply #985 on: January 04, 2021, 02:39:26 PM »
The lagune theory seems plausible to me A-Team. I was actually looking at that but decided it was probably a flawed theory because I thought that salt would be flushed out during melting season and river run-off. I also thought that the tides are too insignificant there to add enough salt to those lagunes.

But as you pointed out, that thinking was wrong. Apparently there's a lot of salt in those lagunes, and their shallowness allows them to freeze over quickly.

Not sure how brackish the water up-river is, and if that plays a part in it as well? When the rivers freeze over, do they get saltier?

Another reason why I didn't post that theory was because I saw that the lagune was to the east from the salt patch. And so then I have to add my theory again that the Alaskan Coastal current must be getting saltier all along the coast because of those lagunes AND coastal refreeze? And maybe that area is unique in retaining more of that salty water?

Here's the Lagune on Google Earth.

Do we need to set up a new page for this Oren?
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uniquorn

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Re: The 2020/2021 freezing season
« Reply #986 on: January 04, 2021, 09:08:54 PM »
Comparison of whoi itp120 and 121 7m-200m temperature profiles. Small location inset.

For an older comparison, itp85 was deployed in 2014 with the profile ending in sep2 2015 so about 2/3 along the profile is roughly where itp120 is today and close to where itp121 was shortly after deployment.
« Last Edit: January 05, 2021, 01:50:16 PM by uniquorn »

Aluminium

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Re: The 2020/2021 freezing season
« Reply #987 on: January 05, 2021, 08:18:59 AM »
December 25 - January 4.

2019/2020

gerontocrat

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Re: The 2020/2021 freezing season
« Reply #988 on: January 06, 2021, 02:54:58 PM »
Could the SSW be a game changer for at least the rest of this month?

http://ds.data.jma.go.jp/tcc/tcc/products/clisys/STRAT/
Quote
A major stratospheric sudden warming (SSW) started in the Northern Hemisphere at 30-hPa around 4 January 2021.

Stratospheric Warming
   The Stratospheric Sudden Warming (SSW) is a phenomenon characterized by a rapid increase in polar temperatures in the stratosphere. The temperature increases more than a few dozen degrees in a few days in the boreal winter. In some cases the westerly polar night jet disappears and easterly winds appear during the warming. JMA is monitoring SSWs as one of the Regional Warming Centers. The warming is called a "Minor Warming", when the polar temperature increases more than 25 degrees in a period of a week or less at any stratospheric level. If the zonal mean temperature increases poleward from 60 degrees latitude and the net zonal mean zonal winds become easterly at 60 degrees latitude at 10 hPa (32 km) or below, it is classified as a "Major Warming".
« Last Edit: January 06, 2021, 03:00:55 PM by gerontocrat »
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Re: The 2020/2021 freezing season
« Reply #989 on: January 07, 2021, 04:32:44 PM »
A 42k daily sea ice area LOSS in the Kara Sea on 6 Jan is simply ridiculous

Looks like only 2016/2017 had a similar dip. It will be interesting how they compare in a while.
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Re: The 2020/2021 freezing season
« Reply #990 on: January 07, 2021, 05:21:15 PM »
A 42k daily sea ice area LOSS in the Kara Sea on 6 Jan is simply ridiculous

Looks like only 2016/2017 had a similar dip. It will be interesting how they compare in a while.

And 2012/2013 had a similar SSW with strong PV disruption although late January early February (remember the famous cracks of doom...)

Just purely speculating whether this will be a rebound year... most probably all of this may as well be sheer coincidental-

Freegrass

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Re: The 2020/2021 freezing season
« Reply #991 on: January 07, 2021, 06:52:10 PM »
How can this be a rebound year when all of the remaining MYI is now located in next seasons melting area?
« Last Edit: January 07, 2021, 10:11:40 PM by oren »
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Freegrass

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Re: The 2020/2021 freezing season
« Reply #992 on: January 07, 2021, 07:24:23 PM »
Has anyone ever seen a day in Januari without ice that's thicker than 1 meter along the Ellesmere coast?
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Freegrass

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Re: The 2020/2021 freezing season
« Reply #993 on: January 07, 2021, 07:36:46 PM »
HYCOM ice thickness on this day in 2016.

AMAZING REBOUND!

Not...
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Re: The 2020/2021 freezing season
« Reply #994 on: January 07, 2021, 10:47:59 PM »
How can this be a rebound year when all of the remaining MYI is now located in next seasons melting area?

Freegrass, I am just speculating. After all four out of 10 years from 2010 to 2019 might be considered rebound years.

But that you are, really, using HYCOM to refute my pure speculation... what about piomas, c2+cmos...

And anyways 2017 was record low volume by a extremely wide margin until May, and ended up being a pretty cold melting season.

Are you paying any attention?

kassy

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Re: The 2020/2021 freezing season
« Reply #995 on: January 07, 2021, 11:10:57 PM »
The whole concept of rebound year is useless. Yes maybe some measure may be bigger then last year but overall the volume goes down and the ice we have now is not the ice we used to have.

It is much weaker, remember the polar ice picture from last year?
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oren

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Re: The 2020/2021 freezing season
« Reply #996 on: January 08, 2021, 01:15:57 AM »
As far as I know Hycom is not comparable across the years from 2016 to 2020 as the model was changed in the interim.

Freegrass

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Re: The 2020/2021 freezing season
« Reply #997 on: January 08, 2021, 02:54:21 AM »
As far as I know Hycom is not comparable across the years from 2016 to 2020 as the model was changed in the interim.
That's a bummer...
What was the year it changed? Which years are we able to compare?
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oren

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Re: The 2020/2021 freezing season
« Reply #998 on: January 08, 2021, 01:05:39 PM »
It is okay to discuss rebounds, though don't expect them to be anything but short term. Still, the short term of Arctic sea ice is quite interesting, as evidenced by the popularity of the seasonal threads. OTOH I strongly doubt a rebound can be predicted so early with any skill.

To all, please avoid snarky comments. If your post has a personal element, delete that element, it's not adding anything useful except annoy or insult the person on the other side of the Internet.

Freegrass - my memory is short on details about Hycom, besides knowing that inter-year comparisons are problematic, but there was a Hycom thread where I think more info can be found.

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Re: The 2020/2021 freezing season
« Reply #999 on: January 08, 2021, 03:40:35 PM »
As far as I know Hycom is not comparable across the years from 2016 to 2020 as the model was changed in the interim.
That's a bummer...
What was the year it changed? Which years are we able to compare?
Hycom is meant to be accurate as possible on the day it is produced. For comparison purposes the focus is on doing things exactly the same measuring and processing data. When a new satellite goes up the focus is on the new satellite providing the same results for the same conditions. Even if that causes a bias in the current data as happens when better sensors are used. Hycom doesn't attempt this and in some cases a human analyst makes decisions that override the model. Generally speaking Hycom claims that comparisons over a month or two are reasonable but not year to year comparisons. They have a full time dedicated staff that makes tweaks frequently. They post generally what these changes are. These changes make the model more accurate on each day. The Hycom model is a global hybrid 3d model that uses higher resolution on more chaotic areas like near the ocean surface or near land. Where action tends to be uniform they use larger grid sizes. It also gives and receives input from an global atmospheric model. Hycom runs on a dedicated super computer designed for the task. If their is a problem with the run. They don't have time to rerun that day they have to limit it to an abbreviated run.

My point is that in my opinion it is more accurate for comparison purposes than any other source within stated accuracy. In order to validate that claim would take substantially more processing than running the model itself. Since the model requires a dedicated supercomputer that runs the model only somewhat faster than real time it seam unlikely that such would be done. Inconsistency is viewed as more suspect by scientists than systemic errors so I would lose the argument without proof. The magnitude of those errors is the most important factor. But the magnitude of inconsistency is much harder to prove. While I have spent considerable time looking at publicly available information on the subject I do not have enough information or experience with the model to truly know one way or the other.

Summery: Comparisons of Hycoms results are considered suspect beyond two months.