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Carex

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Re: MOSAiC news
« Reply #1050 on: August 29, 2020, 01:53:15 PM »
A-Team, that first graphic in #1038 is excellent.  You'd get an A in graphics art class with that one.  A lot of information presented very clearly.  You earn a golden spyglass for peering through the fog.

uniquorn

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Re: MOSAiC news
« Reply #1051 on: August 29, 2020, 07:04:46 PM »
drift update. Two more buoys were deployed en route.

UCMiami

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Re: MOSAiC news
« Reply #1052 on: August 29, 2020, 07:18:50 PM »
uniquorn - interesting to see the divergence in drift between the southern most buoy heading in the general direction of the Fram, the second buoy headed perhaps toward the Nares or CAA and the others headed more toward the Beaufort. Those are of course pretty close to the prevailing current wind patterns, but the southern most buoy may be in more neutral wind and simply following 'least resistance' as more southerly ice is being pulled toward the Fram.

uniquorn

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Re: MOSAiC news
« Reply #1053 on: August 29, 2020, 07:39:11 PM »
The axib buoy was roughly 86N. Will run the iabp data and see how it compares. Most things north of Greenland end up in the Fram.

Here is the T78 thermistor string data. Perhaps it was deployed in a frozen melt pond.
edit:updated below
« Last Edit: August 30, 2020, 12:43:36 PM by uniquorn »

D-Penguin

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Re: MOSAiC news
« Reply #1054 on: August 29, 2020, 07:58:48 PM »
If an attempt is made to open a debate on the 2020 Melting Thread and its significance to future events, it is immediately swamped by postings commenting about weather forecasts, images from space and reference to the events of previous years.

Whilst I broadly agree with the points you raise I must also plead guilty to posting "images from space" in the 2020 Melting Season that reference "the events of previous years", not to mention "the ice between Greenland and the pole".
oooooooooooo   0000
What's not to like?
Absolutely nothing wrong. I find most of the comments, graphics and references interesting and informative. I just lament the lack of extended debate about the relativity and connectivity of current event postings to future events.

Perhaps, as an example, more comments about the picture you posted; why, how it relates to the present situation and what next?

I remember the 'old days' on the ASI Blog when a debate (exchange of ideas) on a particular topic might extend over a period of days or even weeks with a number of different contributors. The debate ended with either a consensus view having developed, an agreement to disagree or if the debate became acrimonious Neven would diplomatically end it with a few well chosen words.
« Last Edit: August 29, 2020, 08:04:16 PM by D-Penguin »
Remember...it's all about the Jet Stream you dummy...just a personal reminder!

uniquorn

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Re: MOSAiC news
« Reply #1055 on: August 29, 2020, 08:33:33 PM »
Debate is very welcome on this thread but please keep the mosaic project as the subject.
« Last Edit: August 30, 2020, 12:22:50 AM by uniquorn »

D-Penguin

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Re: MOSAiC news
« Reply #1056 on: August 29, 2020, 10:53:32 PM »
Debate is very welcome on this thread but please keep the mosaic project as the subject.

the axib buoy (..97190) is the most westerly.
apologies for the different orientation. I prefer greenland down but am still unable to rotate the land map
I wondered how I came to be posting on this thread then realized it was in response to a point made in a  posting from FOoW.

I do not know how to re-post my postings to a more appropriate thread but the point that you make is clear and fully respected.
« Last Edit: August 29, 2020, 11:00:06 PM by D-Penguin »
Remember...it's all about the Jet Stream you dummy...just a personal reminder!

uniquorn

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Re: MOSAiC news
« Reply #1057 on: August 30, 2020, 12:23:32 AM »
..
« Last Edit: August 30, 2020, 01:54:01 AM by uniquorn »

oren

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Re: MOSAiC news
« Reply #1058 on: August 30, 2020, 01:19:17 AM »
Indeed please stay on topic. D-penguin I can move said post(s) to another thread, just not sure where it fits.

D-Penguin

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Re: MOSAiC news
« Reply #1059 on: August 30, 2020, 01:28:41 AM »
Indeed please stay on topic. D-penguin I can move said post(s) to another thread, just not sure where it fits.
Nor do I - Perhaps The Forum?

Whatever you decide is fine with me.
Remember...it's all about the Jet Stream you dummy...just a personal reminder!

uniquorn

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Re: MOSAiC news
« Reply #1060 on: August 30, 2020, 01:52:58 AM »
the axib buoy (..97190) is the most southwesterly.
apologies for the different orientation. I prefer greenland down but am still unable to rotate the land map
I may have a solution for that

uniquorn

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Re: MOSAiC news
« Reply #1061 on: August 30, 2020, 12:49:25 PM »
thickness update from T78 (88N). Near surface temps above zero since aug25/26.  Possibly some bottom melt during that time.
note: lat/lon shown here is from the temp_proc file which often gives strange numbers. When plotting locations it is best to use the TS file.

updated below
« Last Edit: August 31, 2020, 08:58:09 PM by uniquorn »

oren

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Re: MOSAiC news
« Reply #1062 on: August 30, 2020, 12:58:25 PM »
It seems like about ~5 thermistors or 10cm of bottom melt over 6 days, which my intuition says is quite considerable for this date and latitude.

uniquorn

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Re: MOSAiC news
« Reply #1063 on: August 30, 2020, 05:28:09 PM »
Agreed, it looks like ~10cm, here is a close up. Maybe it's more ablation than melt.
Fomo confirming 1.5m thickness near PS

uniquorn

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Re: MOSAiC news
« Reply #1064 on: August 31, 2020, 08:42:34 PM »
Not too many of the original buoys in ice.

uniquorn

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Re: MOSAiC news
« Reply #1065 on: August 31, 2020, 08:59:33 PM »
T78 thickness update. Melt pond stays at 0C as surface temps drop below zero. More bottom melt.
Another 6cm? Needs confirmation tomorrow.
maybe 4cm

gif updated below
« Last Edit: September 01, 2020, 11:35:32 AM by uniquorn »

uniquorn

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Re: MOSAiC news
« Reply #1066 on: September 01, 2020, 11:43:19 AM »
I'm surprised by the data from T78. Thermistors 85-94 dropped to -1.5C in the last two days. That's 18cm. It's unclear from temperature alone whether this is ocean or 'rotten ice' but a few more days data should verify which is which.
It could be a good thing if the ice is cooling.
gif updated below
« Last Edit: September 02, 2020, 12:28:59 PM by uniquorn »

peterlvmeng

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Re: MOSAiC news
« Reply #1067 on: September 01, 2020, 12:07:08 PM »
I'm surprised by the data from T78. Thermistors 85-94 dropped to -1.5C in the last two days. That's 18cm. It's unclear from temperature alone whether this is ocean or 'rotten ice' but a few more days data should verify which is which.
It could be a good thing if the ice is cooling.

I tend to regard it as ocean. Maybe the Ekman pumping effect caused by weak storm?

uniquorn

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Re: MOSAiC news
« Reply #1068 on: September 01, 2020, 01:28:57 PM »
Thank you for the second opinion. That is worrying, -1.5C seems relatively warm beneath the ice at 88.3N
T78 drift, quite close to PS.
56 -- light freezing drizzle

SimonF92

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Re: MOSAiC news
« Reply #1069 on: September 01, 2020, 03:44:40 PM »
I'm surprised by the data from T78. Thermistors 85-94 dropped to -1.5C in the last two days. That's 18cm. It's unclear from temperature alone whether this is ocean or 'rotten ice' but a few more days data should verify which is which.
It could be a good thing if the ice is cooling.

Im still convinced salinity has a role to play at the ice:ocean interface thermistors
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oren

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Re: MOSAiC news
« Reply #1070 on: September 01, 2020, 06:20:10 PM »
The fresher the water the higher the temp at the interface.

FishOutofWater

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Re: MOSAiC news
« Reply #1071 on: September 02, 2020, 12:51:52 AM »
Juilenne Stroeve's research which is trying to use 2 satellite radar bands to separate measurements of snow depth and ice thickness makes sense, but it looks like the Polarstern took off at a critical time for studying the melting of snow and the beginning of melt pond season this spring.

This is a very frustrating story. My key take from it was, based on the photo, there was very little snow. What ever, they pretty much wasted the scientist's time as far as I can tell.
https://www.meereisportal.de/en/mosaic/driftstories/driftstory-07-the-importance-of-the-first-snowball/

A first taste of spring

The turning point came on 19 April in the form of a brief but massive inflow of warm air into the Central Arctic. Within the space of a day, the air temperature at the snow’s surface in the MOSAiC Ice Camp rose from minus 7.4 degrees to minus 0.2 degrees Celsius. The warm spell only lasted 24 hours, but it was enough to make a lasting change in the snow layer. “The warm air at the snow’s surface immediately brought the top third of the snow layer up to the melting point,” reports the scientist. Afterwards the entire snow layer froze again. But by that point, the warmth had already left its mark on the snow. “We assume that, in this brief warm phase, the first of many large snow crystals began to melt, changing their shape and becoming smaller, even though we couldn’t yet see these changes in detail in the overall snow cover,” says Arndt.

The only thing that could be seen with the naked eye was a clearly recognisable glazed layer. “From above, the snow looked as if the entire area was starting to melt. But in fact, following the inflow of warm air, the surface refroze and became reflective like a mirror,” the researcher reports.

The opportunity to personally experience such a warm spell in the Central Arctic was the highlight of the spring for Stefanie Arndt and the other researchers on board Polarstern. All the research groups intensified their measurements in order to document the effects of this event at all levels – from the atmosphere to the ocean. But it soon became clear: it would take more than just a brief influx of warmth to set off the melting season in the Central Arctic. It would take a special event – which occurred almost four weeks later, on 12 May.


This all sounds interesting except that anyone who has ever lived in a cold region for a winter knows that you can't form a snowball in cold dry snow. It doesn't take a physicist. That said, it all goes south from that point. Literally.

When the floes turn greyFreshly fallen snow crystals possess a multitude of tiny surfaces and edges. These reflect the sun-light so that to observers the snow layer appears white. But when the snow becomes warmer, the heat causes the various microstructures to melt into each other. The edges become rounder and the crystals clump together, creating sticky snow that can be formed into snowballs. “If this process continues for two to three days, the previously white snow turns grey, since the altered optical properties mean that it no longer reflects the entire spectrum of the sun’s rays. Instead, it absorbs more and more sunlight, causing the snow to become warmer and to melt further from within. It collapses and becomes wetter, turning into grey slush, and forming the first puddles of meltwater in depressions on the sea ice,” explains Stefanie Arndt.The onset of melting on the sea ice in spring also marks the end of the AWI ice-thickness meas-urements using the CryoSat satellite. When the snow is wet, the satellite’s radar signal is no longer reflected clearly enough. The researchers then have difficulty determining on the basis of the measurement data whether the signal has been reflected by a snow-and-ice layer, or by open wa-ter. They therefore discontinue the measurements during the summer.Unfortunately, in the third and fourth weeks of May, Stefanie Arndt was only able to observe the beginning of the snow melting from on board Polarstern. Due to the coronavirus pandemic, during this key phase for the sea-ice physicists the ship was on her way to Svalbard for a personnel rota-tion. By the time the ship returned to the MOSAiC floe, it was already mid-June.

Oops. In this case the Polarstern did not even serve as a giant polluted buoy. It went south at an absolutely critical time and abandoned what ever research might have been done. I feel sorry for the scientist in this story.




uniquorn

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Re: MOSAiC news
« Reply #1072 on: September 02, 2020, 12:35:31 PM »
T78 thickness update. There is still liquid water in the melt pond. Perhaps those 16cm at the bottom are rotten ice after all, or the salinity has dropped further. The temperature gradient is quite sensitive to surface temperature. It's probably not isolation this far north.

uniquorn

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Re: MOSAiC news
« Reply #1073 on: September 02, 2020, 12:48:27 PM »
I feel sorry for the scientist in this story.
All is not lost FOoW, we have 2 new snow buoys, S106 and S107

and a new thermistor buoy T81 which shows similar variable temperatures at the ice/ocean interface.

uniquorn

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Re: MOSAiC news
« Reply #1074 on: September 02, 2020, 04:54:22 PM »
drift update showing the new buoys. All the buoys north of 87N are heading for the CAA at the moment. P229 probably drifting to the Fram. click for motion

A closer look at the S and T buoys. S107 is about 460m from PS
> distHaversine(c(117.3566,88.4206),c(117.3602,88.4247)  )
[1] 456.5432

2020-09-02T06:01:00,88.4206,117.3566
 

SimonF92

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Re: MOSAiC news
« Reply #1075 on: September 03, 2020, 01:07:53 PM »
Once the ambient air temps get cold enough to not destroy our (imperfect) algorithm, ill update the code and start posting those thickness figures we were able to produce during the spring season
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slow wing

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Re: MOSAiC news
« Reply #1076 on: September 03, 2020, 02:04:09 PM »
T78, nearest to PS, has been deployed on ice ~1.5m thick (~therm30-105). Nice to see some below zero air temps there.

Really appreciating seeing actual experimental depth profile data, and very well presented, thanks uniquorn.

The top of the ice is easy to find. But what about the bottom?

I see the temperature remains constant with depth below thermistor 105. Is that definitive?

If it was just one snapshot at a fixed time then the profile could be consistent with some sort of 'freshwater lens' effect, where the gradient was due to increasing salinity with depth. So the actual boundary would not be definitive.

But is it because the gradient above 105 wiggles up and down slightly in time - indicating the better thermal conductivity of ice than of liquid water [UPDATE: ice is 2.2, liquid is 0.6 in MKS units -- not as big a ratio as I had thought], and so reacting more quickly to changes in air temperature - so it must be ice rather than water down to 105 and there is no freshwater lens to be seen at this location?

I think I have just convinced myself. Does that correspond to the actual physics as known by those familiar with this equipment?


Do any of these rigs ever show a freshwater lens below the ice? If not, is that not a real phenomenon in the Arctic?
« Last Edit: September 03, 2020, 02:09:22 PM by slow wing »

SimonF92

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Re: MOSAiC news
« Reply #1077 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)
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RoxTheGeologist

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Re: MOSAiC news
« Reply #1078 on: September 03, 2020, 03:12:38 PM »

Simon

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.



SimonF92

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Re: MOSAiC news
« Reply #1079 on: September 03, 2020, 03:38:09 PM »

Simon

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):
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A-Team

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Re: MOSAiC news
« Reply #1080 on: September 03, 2020, 07:23:39 PM »
Finally, some ice thickness data at the new floe: 1.40 to 1.70 range from 30 ice cores near the ship. They are staying close by this time because of set-up time and past instability of remote floe sites.

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

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

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

The photo shows decaying ice in an advanced state of melt. Freezing season is still several weeks off (especially in this non-stop fog) though one day they had to hand-skim ice off a melt pond in order to lower instruments.
« Last Edit: September 03, 2020, 07:36:06 PM by A-Team »

A-Team

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Re: MOSAiC news
« Reply #1081 on: September 03, 2020, 08:00:12 PM »
It's hard to get Arctic field research to adhere to any kind of plan. Mosaic has just had one bad thing happen after another, from not being able to find a suitable floe back in October, unexpectedly rapid TransPolar Drift, seven weeks lost in a resupply snafu, time and sensors wasted in the Fram, abandoned instruments lost to ice motion, more resupply and repositioning delays and the most scientifically damaging of all, loss of the Polar5 and Polar6 spring and summer overflight campaigns.

https://tinyurl.com/y5dyk83u press release

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

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

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

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

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

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

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

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

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

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

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

« Last Edit: September 03, 2020, 09:22:52 PM by A-Team »

UCMiami

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Re: MOSAiC news
« Reply #1082 on: September 03, 2020, 10:35:14 PM »
Great stuff A-Team.
While the core measurements are perhaps surprising, the fact that it took them quite a while to find a 'marginally good' flow to anchor to suggest to me that this flow may be an exception to the surrounding ice?

It is of course the issue with any measurements being physically taken anywhere but especially in such a mobile arctic ice pack - can it be extrapolated to an area much greater than the point at which it has been taken. Is this flow indicative of this section of the pack or it is exceptional. And with their stated limited area of measurements, it is more problematic than their earlier anchor flow.

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Re: MOSAiC news
« Reply #1083 on: September 04, 2020, 12:44:55 AM »
Great stuff A-Team.
While the core measurements are perhaps surprising, the fact that it took them quite a while to find a 'marginally good' flow to anchor to suggest to me that this flow may be an exception to the surrounding ice?

It is of course the issue with any measurements being physically taken anywhere but especially in such a mobile arctic ice pack - can it be extrapolated to an area much greater than the point at which it has been taken. Is this flow indicative of this section of the pack or it is exceptional. And with their stated limited area of measurements, it is more problematic than their earlier anchor flow.
Searching for a "good location to work on" is an extremely high bias. As before they searched for a location with thick enough ice to work on. They were looking for a while and settled on some ice thinner than they wanted. So they didn't waste more time. This was not a random sample. We should not expect models to predict random anomalies. It should predict systemic anomalies but not random ones.

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Re: MOSAiC news
« Reply #1084 on: September 04, 2020, 12:48:47 AM »
As was pointed out to me thickness is weighted by concentration so that should be factored in as well. Polersterns location does not appear to be at 100%.

binntho

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Re: MOSAiC news
« Reply #1085 on: September 04, 2020, 06:59:01 AM »
As was pointed out to me thickness is weighted by concentration so that should be factored in as well. Polersterns location does not appear to be at 100%.
Indeed. The claim that Hycom is "way off the mark" needs clarification. How long did it take them to find a floe thick enough for their needs? If the surrounding ice is made up of 1.5 meter thick large floes, how did Polarstern get there? I see nothing here that invalidates Hycom's estimate of 0,7m in this area.
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binntho

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Re: MOSAiC news
« Reply #1086 on: September 04, 2020, 07:02:44 AM »
And with some trepidation:

The tides and tidal currents at the current location are completely negligible.

but (red underline added) :
because a thing is eloquently expressed it should not be taken to be as necessarily true
St. Augustine, Confessions V, 6

slow wing

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Re: MOSAiC news
« Reply #1087 on: September 04, 2020, 09:02:21 AM »
Before it gets too far back, just want to say thanks very much for your detailed & very informative replies to my question on finding the ice bottom from the thermistor strings, SimonF92 and uniquorn.

I'm still digesting your replies & my understanding of the physical situation - things like the fresh water lens - definitely needs some revisions.

oren

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Re: MOSAiC news
« Reply #1088 on: September 04, 2020, 10:18:14 AM »
And with some trepidation:

The tides and tidal currents at the current location are completely negligible.

but (red underline added) :
But that is exactly why A-Team gave an alternative explanation:
The tides and tidal currents at the current location are completely negligible. The issue for a solid week has been a strong persistent wind off Siberia that is quite noticeably moving the whole ice pack towards Banks Island. These winds can induce semi-diurnal near-inertial waves in the water that the public relations lady may be confusing with weak M2 lunar tides.

binntho

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Re: MOSAiC news
« Reply #1089 on: September 04, 2020, 11:03:31 AM »
And with some trepidation:

The tides and tidal currents at the current location are completely negligible.

but (red underline added) :
But that is exactly why A-Team gave an alternative explanation:
The tides and tidal currents at the current location are completely negligible. The issue for a solid week has been a strong persistent wind off Siberia that is quite noticeably moving the whole ice pack towards Banks Island. These winds can induce semi-diurnal near-inertial waves in the water that the public relations lady may be confusing with weak M2 lunar tides.
<>
Yes, I could deduce the same from A-Team's terse statements (and did in fact deduce the same) but just saying things doesn't make them true.<>

I for one am not really able to see how consistent wind can be confused with tidal movement.

<Removed antagonistic language. O>
« Last Edit: September 04, 2020, 12:20:30 PM by oren »
because a thing is eloquently expressed it should not be taken to be as necessarily true
St. Augustine, Confessions V, 6

binntho

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Re: MOSAiC news
« Reply #1090 on: September 04, 2020, 01:05:12 PM »
And with some trepidation:

The tides and tidal currents at the current location are completely negligible.

but (red underline added) :
But that is exactly why A-Team gave an alternative explanation:
The tides and tidal currents at the current location are completely negligible. The issue for a solid week has been a strong persistent wind off Siberia that is quite noticeably moving the whole ice pack towards Banks Island. These winds can induce semi-diurnal near-inertial waves in the water that the public relations lady may be confusing with weak M2 lunar tides.
<>
Yes, I could deduce the same from A-Team's terse statements (and did in fact deduce the same) but just saying things doesn't make them true.<>

I for one am not really able to see how consistent wind can be confused with tidal movement.

<Removed antagonistic language. O>
You are going too far here Oren. What was so antagonistic other than that I dared to point a critical finger at A-Team?

I wrote a well considered and well written comment worth reading and sharing. If A-Team insists in making sweeping statements and not bothering to defend them, then I suggest that you start snipping him.
because a thing is eloquently expressed it should not be taken to be as necessarily true
St. Augustine, Confessions V, 6

A-Team

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Re: MOSAiC news
« Reply #1091 on: September 04, 2020, 01:42:22 PM »
The issue raised in the original post is that NOAA-PSL and Hycom models are making incompatible statements about regional ice thickness. One (or both) of them has to be wrong. DMI, Piomas and other thickness products do not make forward predictions and were not considered for reasons given many times by Oren.

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

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

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

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

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

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

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

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

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

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

We do not run 'operational' forums here so rather than focus on futile forecasting, we can simply wait a week, see actually happens and try to understand why. However it does look like the persistent Siberian winds that began on Aug 23rd will continue a few more days and even worsen on Sept 6th, https://tinyurl.com/y64busr6

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

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

For now, from uniq's efforts, we have very accurate records of regional ice movement at the positions of ~50 individual buoys (these are sparse on the Siberian side). Buoys near the Polarstern show its track and recent variations in speed are shown below with 4 dp GPS precision. It can be followed loosely on the awiMet hourly report site.
« Last Edit: September 04, 2020, 02:40:06 PM by A-Team »

FishOutofWater

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Re: MOSAiC news
« Reply #1092 on: September 04, 2020, 05:06:33 PM »
I suspect that all of the thickness models are wrong. PIOMAS is apparently wrong on the high side between Greenland and the pole. HYCOM is apparently wrong on the low side near the pole and probably in many other areas as well. And MOSAIC is giving us the mushroom treatment on the thickness measurements that they have made. Thanks, A-Team for parsing what MOSAIC's PR said between the lines. The confusion here was pretty much inevitable given the poor reporting by MOSAiC's PR officer. [A-Team quoted in blue]

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

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

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


The main tidal component is pretty close to zero at the pole. https://earth.esa.int/web/guest/missions/esa-operational-eo-missions/envisat/news/-/article/modelling-tides-in-the-arctic-ocean

Of course, there are other components, but they are amplified by being near land masses and submarine topography.
« Last Edit: September 05, 2020, 03:36:40 AM by FishOutofWater »

interstitial

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Re: MOSAiC news
« Reply #1093 on: September 05, 2020, 12:09:28 AM »

Fish out of water
Quote
It's terribly naive to think site bias wasn't mitigated (how could they wring a publication out of the data?)
I have no doubt that research papers will take appropriate steps to mitigate site bias or it won't be relevant. I am in no way saying their research will be faulty. I expect good research.
We do not have any research from the mosaic team yet only vague comments on what they are doing. When they say they are looking for a place that is thick enough to work on the ice safely that ice will be thicker than typical. I am sure they have good data on typical ice thickness but we do not. Once their paper are published we will have a much better information. If the purpose of those cores is to report on typical ice thickness I will be wrong. I was not aware of these cores. I don't know the purpose of their research. They could be choosing the thickest ice to measure for a reason. They may be interested in the evolution of ice that survives longer and want thicker ice. They could be looking for ice that shows ridging or a million other things.


ATeam
Quote
[/size]
Mosaic has provided no information whatsoever about the site selected other than it had a lot to do with the time crunch of late arrival, match-up with their January drift location, floe stability and safety (0.7 m or more is sought).

[/size]Exactly floe stability and safety mean they were looking for a thicker than average flow. They would not have to look for it if it was typical. The captain said he wanted 1.2 meter or thicker ice for safety. At least that was what someone wrote on one of these threads.

FishOutofWater

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Re: MOSAiC news
« Reply #1094 on: September 05, 2020, 03:51:07 AM »
I was quoting A-Team in blue or teal. I have been watching thickness models for years and I'm not convinced that any of them are accurately describing what has been happening to the Arctic sea ice. Hycom drops too quickly from 2m to 1m thickness, then takes forever to melt out. Of course, it all ends up corrected with the ice is completely melted out. PIOMAS makes the ice too thick between Greenland and the pole. The DMI model hasn't stood up to scrutiny here and I have spent little time with it. I haven't looked at the NOAA thickness model enough to comment.

Maybe the MOSAiC reports will end up in improved thickness models in 5 years. Maybe we'll have a blue ocean event in 5 years. What ever, I find the interface between the MOSAiC group and the rest of us to be unsatisfactory. Thanks to Uniquorn for plotting up the buoy data. That's helpful.
« Last Edit: September 05, 2020, 07:33:21 AM by FishOutofWater »

A-Team

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Re: MOSAiC news
« Reply #1095 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.
« Last Edit: September 05, 2020, 07:43:28 PM by A-Team »

UCMiami

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Re: MOSAiC news
« Reply #1096 on: September 05, 2020, 08:51:16 PM »
We tend to see wind speeds of 20 or 30 km/hr and imagine both immediate effect on ice and immediate response to fluctuations similar to how a small boat would respond in a lake. The reality is that the keel of an ice flow is huge, its wind profile is small, and its gross weight is significant. It takes prolonged consistent wind to create motion and build any speed and once that motion is started, the mass of the flow creates a momentum that will maintain similar speed through wind speed fluctuations.

Add to that most flows, and certainly the one the Polarstern is anchored to, are not located in open water but in close proximity to thousands of other massive flows - such a huge field that the winds affecting more distant flows may be completely different from those in closest proximity.

In fact given the obstacles to consistent speed and direction, the consistency exhibited by the buoys is quite impressive.

(Hadn't thought about this before, but the Polarstern must be creating quite a sail for the flow it is anchored to. It might represent 100% more wind resistance even to a very large flow. And I gues it is also creating a significant keel as well - 11.2m/40')

A-Team

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Re: MOSAiC news
« Reply #1097 on: September 05, 2020, 09:09:15 PM »
Mosaic itself provides only the sketchiest details of the expedition written from the perspective of a future large format coffee table book. On past voyages, the Polarstern always posted a very informative weekly ship's log.

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

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

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

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

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

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

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

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

https://blogs.agu.org/thefield/2020/08/08/postcards-from-a-formerly-frozen-icebreaker-part-46/
https://ciresblogs.colorado.edu/mosaic/2020/08/18/the-last-ice/



A-Team

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Re: MOSAiC news
« Reply #1098 on: September 06, 2020, 12:41:16 AM »
Quote
It takes prolonged consistent wind to create motion and build any speed and once that motion is started, the mass of the flow creates a momentum that will maintain similar speed through wind speed fluctuations.
The rule of thumb is ice pack speed is 1% of a consistent wind speed. Those speeds and headings are listed (in m/s) for the whole expedition off a 38 m PS pole at sailwx or awiMet below. Pressure ridge keels erode very rapidly under water and would provide much less hydrodynamic drag now than initially. The opposite is true for late season aerodynamic drag in FYI.
 
This in not the idealized ice puck skating down a frictionless hockey rink — Newton’s first law does not apply, the pack quickly comes to rest if the wind dies down or reaches a terminal velocity if it persists.

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

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

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

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

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

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

https://www.awi.de/fileadmin/user_upload/MET/PolarsternCoursePlot/psobsedat.html

https://data.meereisportal.de/gallery/
« Last Edit: September 06, 2020, 01:35:11 AM by A-Team »

OffTheGrid

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Re: MOSAiC news
« Reply #1099 on: September 06, 2020, 10:55:37 PM »
Got up to fifty kmph winds, with a rise of nearly a degree in temp in the last hour. Twice the windspeed gfs is claiming at 1000hpa or surface.
Raining it is suposed to be with above zero surface to 850 Siberian coast to near the pole.