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Arctic sea ice / Re: Home brew AMSR2 extent & area calculation
« on: March 05, 2021, 07:28:30 PM »
UH AMSR2 extent in the Okhotsk sea. Very similar to 2014 and 2017 so far, though from a higher high.
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In the Atlantic Ocean, Subtle Shifts Hint at Dramatic Dangers
The warming atmosphere is causing an arm of the powerful Gulf Stream to weaken, some scientists fear.
By MOISES VELASQUEZ-MANOFF
and JEREMY WHITE
Dr. Broecker’s old schematics of the AMOC posit a neat warm current flowing north along the western edge of the Atlantic and an equally neat cold current flowing back south below it. In fact, says Dr. Lozier, that deeper current is not confined to the western edge of the Atlantic, but rather flows southward via a number of “rivers” that are filled with eddies. The network of deep ocean currents is much more complicated than once envisioned, in other words, and figuring out how buoyant meltwater from Greenland might affect the formation of cold deepwater has become more complicated as well.
This is the place scientists currently find themselves in. They suspect the AMOC can work like a climate switch. They’re watching it closely. Some argue that it’s already changing, others that it’s too soon to tell.
“There’s no consensus on whether it has slowed to date, or if it’s currently slowing,” said Dr. Lozier. “But there is a consensus that if we continue to warm the atmosphere, it will slow.”
2021-03-03T12:30:15,86.144000,-28.754640This can be located using the iwsviewer here (for a while)
QuoteIce north of Greenland perhaps missing the larger MYI component this year.Uniquorn, I wonder why the cracks are not visible on this DMI sentinel image taken the same day ?
a closer view with a bit less cloud
Sentinel-1 is the first of the Copernicus Programme satellite constellation conducted by the European Space Agency.[4] This mission is composed of a constellation of two satellites, Sentinel-1A and Sentinel-1B, which share the same orbital plane. They carry a C-band synthetic-aperture radar instrument which provides a collection of data in all-weather, day or night. This instrument has a spatial resolution of down to 5 m and a swath of up to 400 km. The constellation is on a sun synchronous, near-polar (98.18°) orbit. The orbit has a 12-day repeat cycle and completes 175 orbits per cycle.
Brightness Temperature (Band I5, Night)
Temporal coverage: 17 September 2017 - Present
The VIIRS Brightness Temperature, Band I5 Night layer is the brightness temperature, measured in Kelvin (K), calculated from the top-of-the-atmosphere radiances. It does not provide an accurate temperature of either clouds nor the land surface, but it does show relative temperature differences which can be used to distinguish features both in clouds and over clear land. It can be used to distinguish land, sea ice, and open water over the polar regions during winter (in cloudless areas).
The VIIRS Brightness Temperature layer is calculated from VIIRS Calibrated Radiances (VNP02) and is available from the joint NASA/NOAA Suomi National Polar orbiting Partnership (Suomi NPP) satellite. The sensor resolution is 375m, the imagery resolution is 250m, and the temporal resolution is daily.
it's a forecast to mar7Barents had a large drop.That is so weird. Looking at your Gif, it seems like the ice expanded a lot along the Novaya Zemlya coast. Where did the loss come from?
<>In reality I probably should have been more hands on<>It's predictably unreal
An ARGO float in the WSC north of Svalbard, which last reported in October, has woken up again!
Float ID 7900550.
Just a scratch of a halocline, and a 2-300m layer of Atlantic water still at ~2.5C.
Really pretty similar to some of the profiles from October, sans the halocline. Or rather, with the halocline being absorbed into the Atlantic layer.
Here we have 4m thick ice (or thicker) where thermistors 1 to 10 are clearly above surface so all or nearly all of the remaining sensors are in ice.
It's possible that thermistors 210-240 are in the ocean but look at the temps. Flat line from thermistor 140 onwards. The thick ice is still cooling.
It's weird that all these buoys are in place but in essence there is no good reliable way to find out where the ice ends and the water starts. There must be a better way than just thermistors with ambiguous results. An interesting engineering challenge, which I have no clue how to solve.Hopefully with all the equipment installed during the mosaic expedition someone is writing a paper on this. Otherwise we wait till 2023 for more detailed data....
<>How does this fit with the Heat120 data? Not well at all. However, has the ice really thickened to 2.74cm? Looking at CS2SMOS from your post, it seems very plausible.<>
The ice/ocean interface is estimated from temperature profiles alone since the winter sea-ice remains colder than the ocean. The ocean just below the ice is at or just above the freezing temperature (estimated from a near surface conductivity-temperature-depth (CTD) sensor see Koenig et al. [2016]). The method detects (1) the first sensor, downward of the snow/ice interface, with a temperature above the ocean freezing temperature and (2) the last sensor in the ice with a temperature below the mean ocean temperature by at least twice the ocean temperature standard deviation in that profile. The ice/ocean interface is then defined as half way between the last sensor in the ice and the first sensor in the ocean.edit: added buoy data for this paper N-ICE2015 SIMBA quality controlled and derived data
3.1.2. Interface between Ice and Ocean To identify the lower ice interface (ice-ocean interface), temperature profiles for the lower ice layer were obtained from some thermistors near the bottom of the sea ice. The seawater temperature was determined using the lower five thermistors, which generally had a negligible temperature gradient from the bottom of the sea ice. The points where the temperature profile of the lower ice layer intersected the ocean temperature were regarded as the ice-ocean interface (Figure 3b). The ice-ocean interface determined by the method of seeking described above had a good accuracy in winter or sea ice growth period. This method became unreliable in summer, especially in ice melting period when the temperature gradient across the lower interface weakened. In summer, the temperature profile of sea ice became non linear with a C-shaped curve. Then the lower ice interface was determined from the obvious inflection point in the vertical C-shaped ice temperature profile (Figure 3d). In winter,temperature profile of sea ice remained linear and temperature of the basal ice layer was colder than the upper ocean. There will be a sharp inflection point occurring at the interface. Thus, ice-ocean interface can be estimated from the vertical gradients of sea ice temperature profile.
<>Meanwhile JAXA extent is flatlining<>Just a touch of refreeze in Okhotsk so far. amsr2-uhh, feb1-22
Instrument experienced a dynamic event on 09/29/2020 which caused a downward shift in the rangefinder values and failure of the temperature string.
T84 also has additional deployment data but unfortunately a photo is not available. Thermistor 26 at surface, ice thickness 1.14m, Snow depth 0.03 m, so bottom of the ice at thermistor84. Similar analysis below with a closer look at temperatures near to -1.8C.
It's possible that drilling the deployment hole affects the results, allowing faster local melt that refreezes over time.
Well we have another chance to develop our thickness estimate algorithm soon. Core ice temperature is dropping to levels where we thought we had some reasonable estimates last year. I have doubts though.It's nice to have the actual thermistor air-snow and ice-water numbers at deployment.
Looking at T78 data the deployment report (1) states the ice was 1.52m thick with 2cm of fresh snow on aug23. Thermistor buoy sensors are 2cm apart so we can't really detect snow at that point but we are also given the sensor id of the air/snow interface as 33. Great. So the bottom of the ice on that day was at sensor 110.
The temperature profile then was almost flat by winter standards but a more detailed look shows the ice thickness quite well. (2)
Thermistors 33 and 110 have been marked roughly at the beginning of the animation(3) and again on nov22 when the temperature profile shows them clearly (with a short pause both times). There is not much additional thickening since then.
So my doubt is this. Did the ice melt quickly during end of august/september or has it been 1.5m thick and possibly porous all the time but took 3 months to cool down again?
added T78 drift path(4)
Looking at the animation, it appears like there was massive bottom melt, and then re-thickening.
This is what I would expect in general with the given temperature profile.
At first, ice top is warmer than at the bottom. This surely brings about bottom melt, as heat trickles from above and the salt water eats away from below, and I think would also depend on the rate of drag of the ice over the water.
The image from Aug 23 clearly shows ice-water interface at thermistor 110.
Next, the temp profile is flat. My understanding is that the bottom would still be melting, albeit at a much slower pace.
The image from Sep 13 seems to be the last day of top melt, as well as the ice having a cold core again (cold gradient from the middle to the bottom).
Eventually, the ice top is colder than the ice bottom, with a gradient appearing through the ice. From this point on the ice starts bottom freezing and it's easier to spot where the ice ends.
The image from Sep 21 in my opinion shows the ice-water interface at around thermistor 55.
The image from Oct 15 seems to show the ice-water interface at thermistor 70.
The end of the animation again shows the ice to exceed thermistor 110.
Admittedly these are just generalizations, since I can't put any quantitative expectations as to the rates of melting and freezing. The rates do depend on the steepness of the warm or cold gradient though. Therefore I would not expect a whole lot of bottom melting, also given the rather late date of deployment. However, eyeing the animation, it would appear as if the bottom melted all the way to thermistor 55. Some possible explanations:
* Bottom was higher than thermistor 110 to begin with, with 110 being some protruding edge. However, the animation data does support this initial placement for the ice-water interface.
* Melting did not actually reach thermistor 55, though I can't see any other explanation for the cold gradient ending where it ends on Sep 23, except that it was the ice-water edge.
* The ice was extremely mobile which enhanced bottom melt way beyond what the temp profile would suggest. This can be checked by looking at T78 drift.
* The ice has not cooled enough for the gradient to reach the ice-water interface.
* My intuition for rates of bottom melt is disconnected from reality (very probable).
All in all, a very interesting mystery, with wider implications. If indeed ice can bottom-melt so quickly at the end of the season, we are not so far away from blue ocean as the extent extrapolations seem to suggest.
regarding the dmi80 graph .. it is tracking perfectly the (stratospheric) rise this time in 2018 that coincided with the first great opening N. of Greenland . Deja vu ?NOAA-20 viirs brightness temperature has come back but it's too cloudy today. https://go.nasa.gov/2OZ85Iw
Where has the worldview of the winter Arctic gone since I recommended it a couple of days ago ? Too scary for us mere mortals to see ? .. or have we lost a precious resource ?
https://go.nasa.gov/2ONoaRl b.c.
So I ask the same question: what is the cause and what might be the effects, especially as 10 hpa temperatures have stayed down and 30 hpa temps have dropped as well?No idea but here is a comparison of 10hPa and 30hPa Zonal temps. 1979-2021 sep-feb.
http://ds.data.jma.go.jp/tcc/tcc/products/clisys/STRAT/
Satellite observations of thickness have severe deficiencies work is being done to improve their performance. At this point they are not very reliable at some observations.
Hycom is most interested in providing an accurate picture of current conditions and a short term forecast used for operating in the Arctic. The starting conditions are updated by any and all observations available. This includes the aforementioned satellites. As satellite thickness observations improve so will the daily starting point for Hycom model. The condition of ice at the north pole surprised researchers on the polar star but were consistent with the Hycom model.
HYCOM ice thickness paints a completely different picture. I know this has been discussed. But which one is the more accurate representation of thickness?Hold on. I'll get my augur and nip over and check.
Rationale
The European Space Agency’s (ESA) Earth Explorer SMOS satellite can detect thin sea ice, whereas its companion CryoSat-2, designed to observe thicker perennial sea ice, lacks sensitivity. Using these satellite missions together completes the picture of the changing Arctic sea ice and provides a more accurate and comprehensive view on the actual state of Arctic sea-ice thickness
interested in the movement of the zone of relative high Salinity/Temperature (Halocline?) upwards over the last years<<>>argo float 3901910 made it up the WSC north Svalbard branch during aug-dec 2018. Some posts about it here
There is a wealth of detailed studies, freely available here, mostly between circa 2014 and 2016, of the Sofia Deep, north of Svalbard. It is quite a large file with the start in french and then english.Handy to have all those studies in one file.
https://tel.archives-ouvertes.fr/tel-01721467/file/these_archivage_3003710o.pdf
The ocean interactions are very complex at this location. But I have attached a sample profile for winters 2014 to 2016 at approximately the same location as the float 7900550