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Messages - paolo

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1
Antarctica / Re: Pine Island Glacier (PIG) Calving and Discussion
« on: November 29, 2020, 05:55:30 PM »
I'm finishing the posts related to the history of the front line with the NIS.
There are two animations, one for the eastern part of the NIS and one for the western part (the northern part of the NIS, not covered by this post will be processed later).
As for the SWT Ice Rise I use images with an interval of 84 days, from 25/11/2019 to 07/11/2020.

You will notice :

> that also in this case the movements take place mostly during the southern summer (between the image of 25/11/2019 and the image of 11/05/2020) and are very limited during the winter (between the image of 11/05/2019 and the image of 07/11/2020)

> Eastern NIS front: there were calvings only towards the NMS (top right) and in the center (recent calving), the pinning point (bottom of the picture) clearly remained stable and the rest of the front advanced. We can thus consider this part, where the Larter Glacier is flowing and part of the Lucchitta Glacier is rather stable for the moment.

> Western Front: Here there have been important calvings, the NIS is losing support on the pinning point at the bottom of the image and the Domage Zones to the North (on the left in the image) are extending towards the sea. In the near future we can foresee a sharp retreat of the front with loss of contact with the northern part of the NIS (bottom left corner) which would remain anchored to its pinning points waiting to melt and detach towards the sea.

I added the commented image of the NIS that I had posted a year ago (I limited myself to adding the names of the two NIS glaciers)

Click to animate and enlarge images

2
Antarctica / Re: Pine Island Glacier (PIG) Calving and Discussion
« on: November 27, 2020, 09:08:16 PM »
Today I'm going to post :

> an animation related to the SWT front line history, same characteristics as the PIG front line history posted yesterday

> The last image of this animation to which I added comments on the foreseeable future for SWT in the coming years

> an animation related to the Ice Rise front line west of the SWT (and east of the Thwaites Glaciers). In this case I used images from 25/11/2019, 17/02/2020, 11/05/2020, 15/08/2020 and 07/11/2020, since changes in this area are much slower. The interval between images is therefore 84 days (except between 11/05 and 15/08 which is 96 days because of the missing image of 03/08).
We can notice :
>> that the movements of the front in this sector are concentrated in the period of the southern summer and autumn (between the image of 25/11/2019 and the image of 11/05/2020) and are practically absent in the following period (between the image of 11/05/2019 and the image of 07/11/2020)
>> that there are small tributaries with small advances and small retreats following calving, and that the front line has been stable during this year.
The stability of this Ice Rise, whose bottom is below sea level (except for a promontory to the west), and which is the left flank of the SWT, is important for the evolution of the SWT, whose health is declining : one can indeed foresee an increase in its speed and thus its thinning and the retreat of its grounding line which is not far from a more or less flat bed and frankly retrograde further west by rapidly descending to less than - 1000m (and I recall that the CDW has no problem to penetrate below the SWT, the bottom of the SWT being always less than -700m).  So it is to be followed, even if very spaced controls are enough. It will be necessary to follow especially the pinning points, in fact once lost there is a more pronounced retreat.
Be careful, this image is very long : 500 x 2000.

Click to animate and to enlarge the images.

3
Antarctica / Re: Pine Island Glacier (PIG) Calving and Discussion
« on: November 27, 2020, 12:04:24 AM »
In this post :

> The update of the animation of the history of the front line on the North side. It is the same format as last time, I limited myself to add the front line on 05/02, therefore before the big calving in February.

> An animation relating to the future iceberg in the north using one image every 48 days from 24/03 to 19/11. It can be seen that the situation is changing, even if slowly. In particular the central rift, named B in the last image of the animation, has widened significantly and there have been small extensions of rifts A (to the north) and B which are now slightly closer together. Rift C (in the south) has not changed. This iceberg will surely calve, but you have to be patient.

> A commented image relating to the evolution of the rifts in the NDDZ (North Downstream Damage Zone). The speed of the NEIS varies from a speed close to the PIG at NSM to 0 near the Ice Rise Evan's Knoll (grounding line). Now that the downstream NEIS is no longer under pressure from the PIG, the NEIS has likely accelerated and there has been a shift in the velocity gradient towards the Ice Rise and, as a result, a partial shift of the stress (PIG/NEIS) from the NSM to the grounding line on the Ice Rise Even's Knoll side. This should lead to a widening of the DZ

> The update of the animation of the history of the front line on the South side, in which I have integrated the front line on 05/02/2020.

Other history of the front line will follow (SWT,NIS)

Click to animate and enlarge.

4
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: November 24, 2020, 08:48:33 AM »
TM,
The confusion results from the fact that ASLR published only half of the figure, the half referring to the LIG simulation and forgetting the half relating to the RCP8.5 scenario. Below is the full figure

Click to enlarge

5
Antarctica / Re: Pine Island Glacier (PIG) Calving and Discussion
« on: November 21, 2020, 10:34:54 PM »
I think it was interesting to see (and follow) the behaviour of the last point of contact between the PIG and the SIS. Its resistance will determine the progress upstream of the damage zone.
Animation based on the images of 11/11 and 21/11

Click to animate

6
Antarctica / Re: Pine Island Glacier (PIG) Calving and Discussion
« on: November 21, 2020, 10:03:49 PM »
New high quality Sentinel2 image, I take this opportunity to show the rapid changes at the SIS and at the SSM (the SdDZ Damage Zone)

> animation based on the two images of 11/11 and 21/11 (10 days apart, homogeneous orbits), centred on the marginal rifts of the SIS. One can see the rapid changes not only in WmR4, but also in the other rifts, which will soon lead to calvings in this sector.

> animation based on the two images of 17/11 and 21/11 (4 days apart, the orbits are not homogeneous, but they show the speed of change), centred on the SSM and the SdDZ

Large images, click to animate

update: blocks B1, B2 and B3 move relative to the SIS (slightly)

8
Antarctica / Re: Pine Island Glacier (PIG) Calving and Discussion
« on: November 18, 2020, 09:10:35 PM »
My apologies, I had forgotten Sentinel2...  ::)

> An image of the SSM/SIS/SWT with the latest state of the SSM and the extension of WmR4 (click to enlarge)

> An animation to show the evolution between 11/11 and 17/11, even taking into account that a part of WmR4 was partially hidden by clouds the evolution seems obvious to me (click to animate)

9
Antarctica / Re: Pine Island Glacier (PIG) Calving and Discussion
« on: November 18, 2020, 03:57:37 PM »
I post an animation based on the SIS images of 06/11, 12/11 and 18/11 to show the rapid evolution of WmR4 (especially in the last 6 days).

Click to animate

10
Antarctica / Re: Larsen D
« on: November 13, 2020, 09:29:25 PM »
Interstitial,
I looked in Worldview which gives the speeds, but relative to 30/12/2011 and I find a maximum speed of 400 m/yr in the middle between Steele Island and Butler Island and 160 m/yr between Butler Island and Cape Mackintosh

"https://worldview.earthdata.nasa.gov/?v=-1795024.1235806216,913897.3490050219,-1598416.1235806216,1006313. 3490050219&p=antarctic&t=2011-12-30-T18%3A25%3A07Z&l=Coastlines,MEaSUREs_Ice_Velocity_Antarctica,MEaSUREs_Ice_Velocity_Greenland,Reference_Labels(hidden), Reference_Features(hidden),VIIRS_SNPP_CorrectedReflectance_TrueColor(hidden),MODIS_Aqua_CorrectedReflectance_TrueColor(hidden),MODIS_Terra_CorrectedReflectance_TrueColor(hidden)"

I checked the speed of a point between Steele Island and Butler Island, for which Worldview gives a speed of 280 m/yr in 2011, using the Sentinel2 images from 23/10/2019 and 17/10/2020 and I find, for the same point, a speed of 340 m/yr (± 12 m/yr taking 2 px as error).

Even if the oldest Sentinel1 image of the zone dates only from 09/07/2020 (120 days before the one of 06/11/2020), which makes a too narrow base to calculate speeds of a few hundred meters per year, I wanted to make a test anyway and, for this same point, I find a speed of 365 m/yr (happy coincidence, an error of only one pixel corresponds to an error of 60 m/yr!).

We can conclude that, at least for this point, there was a significant acceleration (25%).

For the moment no more detailed analysis, this sector does not fit, for the moment, in my schedule.

11
Antarctica / Re: Larsen D
« on: November 13, 2020, 03:29:56 PM »
Oren,
You will find enclosed :
> An animation with the two Sentinel1 images in their integrality with the scale and the indication lof two landmarks
> A simplified image of the Antarctic Peninsula with the two landmarks
> A detailed map of the Antarctic Peninsula

Click to enlarge and to animate the first image (very large images, to enlarge them completely click twice)

12
Antarctica / Re: Pine Island Glacier (PIG) Calving and Discussion
« on: November 13, 2020, 12:37:15 PM »
SSM: the calving scheduled in the Sentinel2 image comments has arrived tonight

13
Antarctica / Re: Larsen D
« on: November 12, 2020, 10:52:11 PM »
Interstitial,
Thank you, I had doubts myself, but it must be very thick, and almost simulates the appearance of an ice platform.
So I applied a very strict criterion, and I find a line parallel to the blue-coloured part in the Sentinel1 image (the displacement corresponding to the advance of the ice shelf).
Below is the result and you can see that this calving remains very impressive.

Click to enlarge

14
Antarctica / Re: Larsen D
« on: November 12, 2020, 07:56:28 PM »
Here is the history of the front lines of 06/11 and 12/11. I have differentiated a part that probably is not part of the ice shelf and is simply very thick sea ice (multi-year). I added the estimate of the area that calved.

click to enlarge

15
Antarctica / Re: Larsen D
« on: November 12, 2020, 05:30:45 PM »
The scale was displayed at the bottom left, next to the date, in the second image (post-calving image: 12/11). ;)

16
Antarctica / Larsen D
« on: November 12, 2020, 04:38:28 PM »
BIG calving at Larsen D !

Large image, click to animate

17
Antarctica / Re: Pine Island Glacier (PIG) Calving and Discussion
« on: November 12, 2020, 10:23:18 AM »
But we must not forget the two areas of damage, upstream : NuDZ and SuDZ.
Well that's a lot of pictures, but they were the first of the season and they were expected since a certain time.

Click to enlarge

18
Antarctica / Re: Pine Island Glacier (PIG) Calving and Discussion
« on: November 12, 2020, 09:53:18 AM »
Finally, two more images: the cR1 and the NSM

Click to enlarge

19
Antarctica / Re: Pine Island Glacier (PIG) Calving and Discussion
« on: November 12, 2020, 09:50:03 AM »
Finally a beautiful Sentinel2 image, not real novelties, just the clarity and precision of the images.
I start with the SSM, North and South side, SIS and SWT.

Click to enlarge

20
Greenland and Arctic Circle / Re: What's new in Greenland?
« on: November 12, 2020, 06:22:35 AM »
In reality the note on the image is poorly written, in fact are in blue not only the rivers feeding the lake, but also the rivers of the basin further north and flowing north, which intrigued everyone.
The images in the article are much clearer :

Click to enlarge

21
Antarctica / Re: Pine Island Glacier (PIG) Calving and Discussion
« on: November 10, 2020, 11:17:17 AM »
The low resolution image is not the best, but we can visualize a new calving at SSM, crumbling of the point (P3) at mR2 correspondence.

22
Antarctica / Re: Pine Island Glacier (PIG) Calving and Discussion
« on: November 09, 2020, 12:41:09 PM »
NSM
This year has been remarkable, in fact currently not only is the sea at the front not free, but there is no polynya, neither at the SSM, nor at the center, nor at the NSM.
I tried to make a small statistic of the state at the end of October from 2000 to 2020 based on the images of Worldview and I find :
> that the sea was completely free in a majority of the years: 2001, 2002, from 2008 to 2016 and 2019
> that apart from the year 2017, in which a major calving had just occurred and there was a narrow band of open sea between the PIG and the iceberg and for which one cannot thus establish the presence of polynyas, in all the other years there was always a polynya in the SSM and often a polynya in the NSM and/or in the center.
I recall that these polynyas are generated by the warmer water currents coming out below the ice shelf.
So, if the absence of open sea in front of the PIG is generated by the weather conditions of this southern spring, the absence of polynyas seems to indicate that the outgoing currents are weaker than usual (beyond the weather conditions) and therefore also the CDW is weaker than usual.
Before this end of October there were from time to time polynyas at the NSM and SSM, but very small and larger polynyas formed either in correspondence of the Ice Rise Evan's Knoll on the NIS side, or in correspondence of the SM (shear margin) between the SWT and the SIS, thus caused by outflows not related to the PIG.
I find this important and noteworthy.

Coming to what happened at the NSM on 07 and today I present an animation based on the images of 01, 06, 07 and 09 November (the images of 06 and 09 being at low resolution).
It can be noted that what happened on the 07th is a violent event which, among other things, moved the iceberg that I noted "A" by 2km and by turning it by 180° and apparently exploded the iceberg that I circled with red. The present debris was swept away, which produced a "polynya" effect, pushing it to invade the polynya in front of Evan's Knoll Ice Rise.  Needless to say, that day it was better not to be there. This calving did not correspond to the detachment of new pieces from the ice shelf, but interested the mix of icebergs that had formed at the NSM.
It seems that a new calving (still iceberg mixture) has just occurred (image of 09, to be confirmed with a better resolved image) which filled again the bay (no more open sea).

23
Antarctica / Re: Pine Island Glacier (PIG) Calving and Discussion
« on: November 01, 2020, 09:38:33 PM »
New Sentinel2 image, still clouds, but a a beautiful image of the SSM (SdDZ) and of the cR1 (not news compared to Sentinel1 images)

Scale at the bottom left of SdDZ image

Click to enlarge images

24
Antarctica / Re: Pine Island Glacier (PIG) Calving and Discussion
« on: October 19, 2020, 01:28:03 PM »
Thank you Oren,
Here is the new version (NSM and SSM) with the suggested improvements

Click to animate

25
Antarctica / Re: Pine Island Glacier (PIG) Calving and Discussion
« on: October 19, 2020, 12:21:21 PM »
As promised I am posting the history of the SSM in the new format. I will post the next update (NSSM and SSM) on 26/10 or the next day.

Fixed: My apologies, the order of the images was not good

Click to animate

26
Antarctica / Re: Pine Island Glacier (PIG) Calving and Discussion
« on: October 18, 2020, 11:00:34 PM »
I was looking for a good compromise to present the history (size and readability) and I think I found it. This is the result for the NSM. This is the history from 17/02 to 14/10, one front line every 12 days (NB the Sentinel1 images from 29/02 and 03/08 are missing)

If the result suits you it could become a regular post (every 12 days and with the SSM).

Click to animate

27
Antarctica / Re: Pine Island Glacier (PIG) Calving and Discussion
« on: October 15, 2020, 10:11:27 PM »
As second example of use of the Sentinel2 image of 12/10 I propose you the report on the current extension of the rifts cR1 and SmR2:
The first image gives an overview of these two rifts and I indicate the extension observed, see on this subject the two other images which are zooms on their terminal point. In the last few months they have extended and widened, but there is nothing catastrophic (at least for the moment).

On the other hand, I've been looking for other central rifts further north, but there don't seem to be any. However, the poor quality of the image doesn't allow me to make a decision, even if I'm beginning to think that the possible rifts seen in the Sentinel1 images don't exist (for the moment).

click to zoom in

28
Antarctica / Re: Pine Island Glacier (PIG) Calving and Discussion
« on: October 15, 2020, 09:47:09 PM »
I had judged the Sentinel2 image of 12/10 unusable because of its poor quality (see the first image), but I was wrong, it can be used.

Here is a first example with the SIS and its marginal fractures generated by the SWT action (second image). It shows that the WmR4 ([SIS] west marginal rift N°4), which we had seen appearing recently in the Sentinel1 images, and whose beginning, on the SWT side, appeared in an unmistakable and indisputable way only in the last images, is now very extended (more than 10km).

It seems that the part of the SIS related to T11, whose front is no longer constrained by the PIG, and which suffers on the flanks from the actions of the SWT and the PIG, has become unstable and that we may see it crumbling in the near future.

I also added, for comparison, yesterday's Sentinel1 image of this part of the SIS (third image; I noted on this image the probable extension of this rift), as well as the Sentinel2 image of 16/03 (fourth image) to give an overall view of T11 (note the two ices rumples that delimit it to the east and west).

  Apart from the first image the others are large and you have to click on them to zoom in.

29
Antarctica / Re: Pine Island Glacier (PIG) Calving and Discussion
« on: October 10, 2020, 12:45:22 AM »
The Sentinel2 images were not very good, but they show more details than the Sentinel1 images.

SSM: one can notice the complete fracture in the ice mélange of the SdDZ, it is parallel to the movement of the PIG and therefore there will be no resistance neither to the emptying of the DZ nor to the movement of the PIG. Consequently the rifts cR1 and smR2 should not change too much at the moment.
It will be to be followed, further upstream :
> if the last PIG/SIS shear point, currently upstream of A, will hold and for how long.
> the evolution of the SIS piece, noted A in the image, and see if it will detach from the SIS and if it will cross over, creating a point of resistence,
> if marginal rifts will open in the PIG in front of and upstream of A.

NSM: here again, it will be necessary to follow the last PIG/NE-IS shear point upstream of nmR1 and, downstream, the evolution of rifts in the NE-IS in front of the Ice Rise Evan's Knoll.

SWT: Another iceberg seems to be completely detached from the SWT and shows the state of decay of this part.

Click to zoom in

30
Antarctica / Re: Pine Island Glacier (PIG) Calving and Discussion
« on: October 08, 2020, 05:42:53 PM »
A small iceberg has calved on the SWT side (in the animation is identified by an arrow relative to its movement after calving)
This is the opportunity, while waiting for a Sentinel2 image, to present and name the multitude of marginal rifts caused by the shear between the SWT and the SIS. Remarkable is the EmR3 rift which opened recently and expanded rapidly.

It is also interesting to notice that now the SWT flow opens in a fan shape, the right side having a NE direction and the left side a N direction.  This being the cause of the (recent) opening of a longitudinal rift.

Conclusion: we can expect, in the next few months, a crumbling of the right side of the SWT.

Finally it is also interesting to notice the transversal rift that opened in the left part  (see the last image of the previous post)..

The animation uses the images of yesterday and today.

31
Antarctica / Re: Pine Island Glacier (PIG) Calving and Discussion
« on: October 07, 2020, 11:26:05 PM »
I take advantage of the fact that the Sentinel2 image of 21/09, which partially covers SWT, was clear to present some considerations on the DZ of SWT:

In the good old days, the PIG forced the SWT to rotate 120° around an Ice Rise and its left part was pushed against this Ice Rise. Sometimes, after the PIG (and the SWT) calving’s, the pressure was temporarily lacking and it could open locally some gaps between the SWT and the Ice Rise, but these openings were without tomorrow and the SWT then approached again to the Ice Rise => no DZ

Now no more PIG, the right side of the SWT has retreated a lot and now its movement is towards the North and tends to straighten up later on by powering up the SIS. In conclusion the left part is completely free, its movement is no longer parallel to the Ice Rise and the SWT is moving away from the Ice Rise => Opening a DZ
And already the Ice Rise it takes advantage of it to expand...

Since the speed with which the SWT moves away from the Ice Rise is maximum upstream, the DZ has started to open upstream to then extend downstream and soon it will be open to the sea. In this case the emptying will be slowed down by the fact that there is an Ice Rumple under the final part of the SWT (for this reason here the icebergs, once calved, wait a long time before moving away definitively), but the complete separation between the SWT and the eastern part of the Ice Rise can be considered as definitive.  In the same way it seems to me that the loss of the pinning point provided by the Ice Rumple with a front, for the SWT, further upstream is inevitable.
I find that we are witnessing a complete dismantling of the PIIS and that it proceeds quickly, too quickly...

You will find three animations:
The first one, very large to give an idea of the whole, contains the images spread out between the 21/10/2016 and the 21/09/2020 an image approximately every 6 months.
The other two limited to the period between 02/03/2019 and 21/09/2020 present two zooms on the DZ: one for the upstream part and the other for the downstream part.

Large images, click to animate


Added: SWT image with notations

32
Antarctica / Re: Pine Island Glacier (PIG) Calving and Discussion
« on: October 07, 2020, 03:54:47 PM »
As expected the last piece of the Cork3 calved with other icebergs behind (indicated with a star).
Animation based on the images of 01/10 and 07/10.

Click to animate

33
Antarctica / Re: Pine Island Glacier (PIG) Calving and Discussion
« on: October 02, 2020, 02:34:11 PM »
And animation on the NSM side, still with the images of 26/09 and 02/10.
No news, calving on the PIG side having already been communicated on 29/09. We can still note that the Ice Rise Evan's Knoll side rifts seem to widen.

34
Antarctica / Re: Pine Island Glacier (PIG) Calving and Discussion
« on: October 02, 2020, 01:42:47 PM »
Animation with the images of 26/09 and 02/10.

The iceberg A seems almost free and should calve soon.
Cork3c moves around a lot and its support is crumbling and, even if it is still linked to the SIS, it will soon be calving too.

Click to animate

added PS : and behind we don't see great resistance to calving, emptying of the DZ to be expected

35
Antarctica / Re: Halley base shut down and new crack in Brunt shelf
« on: September 29, 2020, 10:05:34 PM »
But we can do better, using Sentinel1 images directly without waiting for their publication on Twitter. Even better, given the season, we can use Sentinel2 images. ;)

Attached a zoom on the still intact part between the two rifts (today's image)

36
Antarctica / Re: Pine Island Glacier (PIG) Calving and Discussion
« on: September 29, 2020, 11:23:00 AM »
Micro calving on the NSM side, small crisis of jealousy for his big brother.
The bay between the PIG and the Ice Rise Evan's Knoll is not only getting deeper, it's getting wider.
Animation based on low resolution images of yesterday and today.

37
Antarctica / Re: Pine Island Glacier (PIG) Calving and Discussion
« on: September 28, 2020, 08:43:32 PM »
Clearly, I was speaking for the PIG, but for other ice platforms this link season/calving can clearly exist (action of melt water, see the classic example of the LarsenB; closer to the PIG, this may be the case in the future for the north side of the NIS).

38
Antarctica / Re: Pine Island Glacier (PIG) Calving and Discussion
« on: September 28, 2020, 06:28:56 PM »
Stephan,
I mentioned in my post the small icebergs of the DZ (Damage Zone) that were aggregated with P2 (I mention them as Ice mélange) and I evaluated them at 2.5km2.
Other calving’s in the SdDZ (Southern downstream Damages Zone) are inevitable, maybe the current front will last some ten days, but no more. And further upstream the structure of the icebergs of the DZ is less packed and the successive calving’s could be faster...
I became very pessimistic  :'(

39
Antarctica / Re: Pine Island Glacier (PIG) Calving and Discussion
« on: September 28, 2020, 04:55:35 PM »
SH,
I can't confirm your impression, indeed the two images in the animation, posted by Baking, don't have quite the same brightness and contrast (look at the darker structures in the image).
What I can confirm is that the two rifts: cR1 (the rift that was next to P2) and smR2 (the rift upstream of P2) are active rifts: in the month before this calving they have regularly widened and extended (with moderation)
As for the links you assume between season and calving, there have been none in the past and there are none now. But the season could be interesting: continuation of small calvings at the NSM and SSM and preparation for extended rifts across the PIG that may lead to larger calvings in the future. As I said above, I am waiting for the first clear Sentinel2 image to make a more accurate forecast.

40
Antarctica / Re: Pine Island Glacier (PIG) Calving and Discussion
« on: September 28, 2020, 03:26:04 PM »
A little analysis :
> Measurements: calved area 17km2, including 2.5km2 of ice mélages aggregated at P2 and that ,at the time of calving, detached from P2
> Ice Origin: Calved ice is part of the SIS ice aggregated at the upstream PIG.This ice, being part of the SSM, is thinner than the ice of the PIG and of the ice of T11.
This ice, being part of the SSM, is thinner than the ice of the PIG next door and the ice of T11
> Causes: the piles of icebergs between the SIS and the PIG that were pointing west/east and that contrasted with the advance of the PIG are probably the cause of the opening of the marginal rifts, and are therefore the main cause of the calving, but we must not forget the icebergs that were stuck downstream between the SIS and P2 and that pushed P2 northwards.  ;)

I, like everyone else, am looking forward to the first clear picture of Sentinel2 to discuss with you about what we can expect in the future.

41
Antarctica / Re: Pine Island Glacier (PIG) Calving and Discussion
« on: September 28, 2020, 12:41:04 PM »
And we even have a high-resolution image of P2's calving  8)

42
Antarctica / Re: Pine Island Glacier (PIG) Calving and Discussion
« on: September 28, 2020, 12:08:51 PM »
I modified the image of my previous post (2547), containing only the lines related to the main calvings, and replacing the front line on 20/09 with today's front line  ;)

click to zoom in

Image update: I had forgotten to change the date in the image
>:(

43
Antarctica / Re: Pine Island Glacier (PIG) Calving and Discussion
« on: September 28, 2020, 10:57:07 AM »
P2, arrivederci, aurevoir, aufwiedersehen, goodbye

44
Antarctica / Re: Pine Island Glacier (PIG) Calving and Discussion
« on: September 27, 2020, 11:32:30 PM »
You will find in this post:
> a history of the front for the southern half: an image containing the positions of the front between 17/02 and 20/09 by 12 days interval, but the positions of the front of 29/02 and 03/08 are missing (no PolarView image). The image is very busy, hence the use of a white background.
> an image containing only the lines related to major calvings, as well as the front line as of 20/09.
> an image containing only the positions of the front on 17/02 and 20/09 to highlight the totality of the losses
> an image containing only the positions of the front on 08/09 and 20/09 to highlight the changes that occurred during this last period Added: you can notice the speed of P2 as well as the mini calving on the SIS side.

click to zoom in


45
Antarctica / Re: Pine Island Glacier (PIG) Calving and Discussion
« on: September 26, 2020, 09:12:34 PM »
Oren,
History: cR1 before had been named ext smR1.  Indeed, it had been formed by extending the smR1 rift in the center (this rift became the north side of P2), but there had never been any connection of smR1 with the latter.
In May the existing tensions had found a weak point and a rift had opened (very abruptly) connecting smR1 with the front downstream of cR1 (this rift became the current front north of P2).
There was therefore a very resistant point between smR1 and cR1.
It is therefore possible that this point is still very resistant and in this case we will have to wait either that the part downstream of cR1 also calves, or that this point finally gives way, to be followed carefully ...

More info :
Maximum width of the rifts : cR1 : ~150m and smR2 : ~300m

46
Antarctica / Re: Pine Island Glacier (PIG) Calving and Discussion
« on: September 26, 2020, 01:09:25 PM »
This animation is based on high-resolution images of yesterday and today.
I wanted to show the differences that can exist between one image and the other because of the different orbits.
In our picture we can just see the "joint2" in today's image, joint that was very visible in yesterday's image. Hence the importance, as soon as possible, to check the images of other orbits.

In any case there is a joint between cR1 and the "rift of P2".
For the future there are two hypotheses: either cR1 reactivates and P2 remains attached to the piece of the ice shelf downstream of cR1, or there is an extension to the front of the "joint1" and in this case there is a much faster calving of P2.

To be followed carefully

47
Antarctica / Re: Pine Island Glacier (PIG) Calving and Discussion
« on: September 26, 2020, 01:29:54 AM »
Preamble: I must admit that the use of the term "Destruction Zone", which I had accepted, was a bit disturbing to me. After a first reading, diagonally (for the moment), of Stef Lhermitte et al. 2020, I found the term "Damage Zone", which seems to me better (and whose acronym is the same).
The other thing that disturbed me was the use only of the direction from the center of the Ice Shelf relative to the PIG, for example north side: NEDZ and NWDZ.
I propose to distinguish them by using the indications "upstream" and "downstream" (which really characterizes it), which gives: NuDZ, NdDZ, SuDZ and SdDZ.

About Stef Lhermitte et al. 2020, there are two sentences that leave me rather perplexed:
> “In the northern shear zone of PIG, on the other hand, the observed damage evolution is absent or lim-ited due negative maximum strain rates (Fig. 1A) that result in closing of crevasses and rifts.”
> "whereas the north-ern shear zone remained largely intact after the unprecedented retreat and disconnection from the northern PIG ice shelf in2015 (6)"
But it is true that this article was written in 2018 that for the PIG already seems so far away...
Indeed, as many have commented here, there is in fact a NuDZ and, as we have seen since the big calving in February, there is actually a NdDZ!

A few months ago we thought (we hope) that the very narrow NE-IS, supported by the Ice Rise Evan's Knoll, could provide, at least temporarily, a pinning point to the PIG. It seems that this will not be the case.

Analysis :
> the speed of the PIG is very high
> the NE-IS is fed by ice from the PIG basin which, to the right of the main flow, overflows an Ice Rumple and by a small tributary to the north.
> the ice of this ice shelf, in the strip near the NSM, moves parallel to the PIG with a very high velocity gradient
> downstream the NE-IS becomes very narrow

Currently this gives very high stresses with the PIG on the one hand and with the stationary ice of the Ice Rumble Evan's Knoll on the other hand.  And the remaining part of the NE-IS downstream of the separation with the PIG cannot provide support to the NE-IS upstream: the shock cannot be absorbed by deformation and it tends to break and calve.

And the NE-IS is a funnel and further upstream will widen which should make things worse.
I don't see what could prevent the NdDZ from gradually expanding upstream until it reconnects to the NuDZ. One can hope that this process will be slow (slower than at present), but it is only a matter of a few years.

And the speed of the PIG is likely to increase with the reduction of lateral stress, which is not conducive to stability.

Things are not better in the south, but this will be for another post.

click to zoom in

48
Antarctica / Re: Pine Island Glacier (PIG) Calving and Discussion
« on: September 25, 2020, 10:30:50 PM »
Baking,
I had had the same reaction, but I discovered afterwards that this transverse rift (towards the front) was already there on 20/09.
It seems to me, on the other hand, that on the 20/09 the rift of P2 stopped at this transversal rift and that it was not extended in the direction of the cR1 (central rift N°1), as it is currently the case.
It could well be that P2 will come off with a piece of the front ...

The almond is broken into two pieces.

There was a lot of movement to the south, even the ice mélange was moved, but I can't see what happened. I only found a very micro calving that can't be the cause, little mystery!

Because of the missing images in PolarView I made an animation based on the images of 20/09 and 25/09. So there are a lot of effects due to the different orbits.

49
Arctic sea ice / Re: The 2020/2021 freezing season
« on: September 25, 2020, 03:37:51 PM »
Thanks Aslan for the weather data which explains well the presence of snow/firnpack saturated with water even in today's image (almost the end of September)

By the way, a post by Mauri Pelto on the Leningradskiy Ice Cap (Svernaya Zemlya Archipelago) was recently released:
https://blogs.agu.org/fromaglaciersperspective/2020/09/14/leningradskiy-ice-cap-snowcover-vanishes-in-2020-more-thinning-svernaya-zemlya/

50
Antarctica / Re: Pine Island Glacier (PIG) Calving and Discussion
« on: September 23, 2020, 11:18:37 PM »
You will find in this post :
> a history of the front for the northern half: an image containing the positions of the front between 17/02 and 20/09 by 12 days interval, but the positions of the front of 29/02 and 03/08 are missing (no PolarView image). The image is very busy, hence the use of a white background.
> an image containing only the front positions on 17/02 and 12/03 to highlight the important calving that occurred shortly after the big calving in February.
> an image containing only the positions of the front on 17/02 and 20/09 to highlight the totality of the losses
> an image containing only the positions of the forehead on 08/09 and 20/09 to highlight the calvings that occurred during this last period. I have added the calving information for 21/09

More posts will follow

Click to zoom in

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