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Messages - paolo

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1
Antarctica / Re: Pine Island Glacier (PIG) Calving and Discussion
« on: December 01, 2020, 11:38:51 PM »
Today's Sentinel2 image is good, even if it is not perfect like the one of 11/21.
It allows me to present you two animations:
> the first one is related to the SIS being shredded by the SWT
> the second one is relative to the NdD and, more precisely, to its right flank which is cracking more and more.

Click to animate

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: 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)

6
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

7
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)

8
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

9
Antarctica / Larsen D
« on: November 12, 2020, 04:38:28 PM »
BIG calving at Larsen D !

Large image, click to animate

10
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

11
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

12
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

13
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).

14
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

15
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

16
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

17
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

18
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

19
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

20
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.

21
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  :'(

22
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.

23
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.

24
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)

25
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
>:(

26
Antarctica / Re: Pine Island Glacier (PIG) Calving and Discussion
« on: September 28, 2020, 10:57:07 AM »
P2, arrivederci, aurevoir, aufwiedersehen, goodbye

27
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


28
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

29
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/

30
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

31
Antarctica / Re: Pine Island Glacier (PIG) Calving and Discussion
« on: September 22, 2020, 10:41:48 PM »
New Sentinel2 image, but of terrible quality!
However the NSM and SSM are partially clear

A bad discovery at the NSM: the opening of rifts across the groundind line!

On the SSM side we can see very well, in the upstream and central parts, the separation between the two iceberg populations: PIG side and SIS side.

Click to zoom in

32
Antarctica / Re: Pine Island Glacier (PIG) Calving and Discussion
« on: September 20, 2020, 11:40:26 AM »
Animation with the images of 08/09 and 20/09, no alignment (so the movements are not relative, but absolute).
P2's calving should be soon  ::)
with other debacles from the SSM iceberg melange

33
Antarctica / Re: Thwaites Glacier Discussion
« on: September 15, 2020, 09:28:49 PM »
Thank you very much for the article, JCG

34
Antarctica / Re: Pine Island Glacier (PIG) Calving and Discussion
« on: September 12, 2020, 04:29:49 PM »
Some elements to complete and finalize this discussion:

Dimension at stake :
Sea ice: ~1m (the last place in the bay where the sea ice stabilizes and is no longer carried away, neither by the bay's current (turning clockwise) nor by the winds, being precisely the front of the PIG and it has only recently stabilized. The outgoing current, see below, can probably explain this.

Icebergs/Glacier: ~400m

Translated: an elephant and a small beetle

Clearly there is no possible comparison: when an iceberg is " ejected " by calving (expression of the existing tensions before calving which are released almost instantaneously), for it the sea ice does not exist.
Similarly, given its dimensions, if, following calving, it is no longer in static equilibrium and turns over.

On the other hand :
> the presence of sea ice can stop the movement of an iceberg more quickly than sea water alone
> a free iceberg surrounded by sea ice can be retained, even in the presence of currents or winds, if these are not too strong.


Warm current CDW :this enters the bay at depth (< -700m), reaches the grounding line, melts the PIG and comes out, passing under the glacier (and continuing to melt it), with water, whose temperature has dropped, but which is still warmer than sea water, which explains the formation of polynyas especially where it is stronger as in correspondence of the NSM, of the SSM and of the centre of the front (after the last big calving in February a new site appeared in correspondence of the Shear Margin between the SWT and the SIS).
This current is at its peak in autumn, but this is of no importance in relation to calvings. In fact its action, melting of the PIG, clearly has an influence on the dynamics of the glacier, but over the long term and not on a seasonal level.

To conclude, I would like to remind you, as Baking has already done, that the dynamics of the PIG is not currently linked to the seasons!

35
Antarctica / Re: Pine Island Glacier (PIG) Calving and Discussion
« on: September 08, 2020, 11:35:49 AM »
Cork3b has detached itself, waiting for P2 ...

36
Antarctica / Re: Pine Island Glacier (PIG) Calving and Discussion
« on: September 02, 2020, 08:19:21 PM »
PS: what is interesting is that the base of the Almond has been projected (hence a rotation of 90° degrees clockwise) which shows that a tension existed before calving.

37
Antarctica / Re: Pine Island Glacier (PIG) Calving and Discussion
« on: September 02, 2020, 08:12:05 PM »
What had to happen, happened  ;)

Almond, goodbye
The outermost piece of Cork3 (relative to the SIS) follows him.

Tomorrow's image will be interesting to see the latecomers who will follow them.

NB: The image is from the 02, but we don't have any images from the 01/09.

38
Antarctica / Re: Pine Island Glacier (PIG) Calving and Discussion
« on: August 26, 2020, 05:39:05 PM »
The emptying of the NSM continues (its speed is a bit worrying...)
Since the image of the previous calving was from 21/08 and therefore from a different orbit than the image of today and since the two images do not align as I would like (moreover today's image is a collage of two images) I will provide the two images separately.

Click to zoom in

39
Science / Re: Ocean temperatures
« on: August 21, 2020, 11:13:17 AM »
Hefaistos,

Retraction to: Nature https://doi.org/10.1038/s41586-018-0651-8, published online 31 October 2018.:
" Shortly after publication, arising from comments from Nicholas Lewis, we realized that our reported uncertainties were underestimated owing to our treatment of certain systematic errors as random errors. In addition, we became aware of several smaller issues in our analysis of uncertainty. Although correcting these issues did not substantially change the central estimate of ocean warming, it led to a roughly fourfold increase in uncertainties, significantly weakening implications for an upward revision of ocean warming and climate sensitivity. Because of these weaker implications, the Nature editors asked for a Retraction, which we accept. Despite the revised uncertainties, our method remains valid and provides an estimate of ocean warming that is independent of the ocean data underpinning other approaches. The revised paper, with corrected uncertainties, will be submitted to another journal. The Retraction will contain a link to the new publication, if and when it is published."

Change history :
"12 February 2020
The revised paper, with corrected uncertainties, mentioned in the Retraction, has now been published: Resplandy, L. Quantification of ocean heat uptake from changes in atmospheric O2 and CO2 composition. Sci. Rep. 9, 20244 (2019)."


You can find the article in its new version with the following link

https://www.nature.com/articles/s41598-019-56490-z

40
Antarctica / Re: Pine Island Glacier (PIG) Calving and Discussion
« on: August 15, 2020, 12:00:52 PM »
Mini calving at the MSM NSM, but this time the modalities are different: the calving is not "explosive", a sign that the tensions were small and therefore the icebergs were already almost separated.
The field of rifts is now very wide and this new regime could herald a further upstream migration from this area. The almost pinning point to the North is not very solid and our hopes that the northern front will resist for a while rest on it! To be followed with attention !

41
Antarctica / Re: Pine Island Glacier (PIG) Calving and Discussion
« on: August 10, 2020, 07:13:06 PM »
I'd like to make an update on the NSM.

I'll use yesterday's high-resolution image that I commented on.
In this image I have embedded an image with elevations, and thus thickness, (David E. Shean et al. 2019; data used first half of 2010) and velocities (WorldView 2011).

The NE-IS is fed upstream by a small tributary and, far to the east, by ice overflowing the Ice Rumples next to the PIG (north of the ZD). The ice of this IS is carried westward by the PIG and pushed towards the funnel between the Ice Rise Evan's Knoll and the PIG itself, where it recompacts.
This is the final part of the funnel that is visible in the image.
In the funnel the movement is parallel to the PIG and the speed gradually changes from zero, Ice Rise side, to that of the PIG itself, PIG side.
As for the thickness we can estimate it at 500m, see more.

Currently the movement of the PIG and the induced tensions lead to the opening of small marginal rifts in the NE-IS orthogonal to the PIG and the pieces of IS between two rifts are bent by the movement of the PIG until complete detachment and calving. This is the area indicated in red in the image (I also added a zoomed image of this area, image from the day before yesterday).
This area creates, PIG side, a shear force (even if relative), which ensures a progressive increase of the shear as we go upstream without abrupt increases.  As a result there is almost no formation of marginal rifts in the PIG (which is positive).
Downstream there is final detachment of the pieces of IS with dynamic calvings: rapid initial movement of the icebergs and in many cases, given their size, their turning over.
This field of rifts, as well as the calving front migrate upstream and nothing seems to be able to stop this process, the only thing that can be hoped for is that this process is as slow as possible.

Clearly upstream, where the funnel widens, the process can only accelerate and there will be reunification with the already existing ZD and thus a detachment of the NE-IS from the PIG. But this process is expected to take several years.
What could accelerate it is a collapse of the part of the NE-IS already detached from the PIG and which currently provides support to the NE-IS upstream: this part is under pressure from the NE-IS upstream but it should resist, moving without breaking, for some time.

Following the detachment of the PIG from the NE-IS there may be some mini calvings (PIG side), one has recently arrived, but they should remain anecdotal.

To the west, on the front line, the large iceberg left over from the big calving (see third picture), already half detached from the PIG, should resist for a while.Indeed the rifts indicated r1 and r2 in the image are widening contentedly but their progression is slow (there is no modification of the rifts r3 and r4). This calving should have no effect on the PIG.

Click to enlarge

42
Antarctica / Re: Pine Island Glacier (PIG) Calving and Discussion
« on: August 05, 2020, 11:15:52 PM »
No news on the PIG side.

So I post an animation of the SWT on the SIS side.
This animation, based on the high resolution images of 24/07 and 05/08, is aligned with the SIS, which highlights the movement of the SWT, or more precisely of its eastern part (which is the only one visualized in this animation), relative to the SIS.
I remind you that it is the part of the SWT that moves the fastest, the speed decreasing further west, to become very low at its western end, where Ice Rumples are located.

We can also notice the widening of the rifts in the SWT itself and in the SIS in front of it.
This leads to the possibility of future calvings on the SWT and on the SIS, the causes being the speed differential in the SWT itself and between the SWT and SIS.

Click to animate

43
Greenland and Arctic Circle / Re: Greenland 2020 Melting Season
« on: July 29, 2020, 10:12:55 PM »
This is the upper part of the glacier,
but where's the accumulation zone ? ! ? ! ?

 :'(  :'(

Click to zoom in

44
Antarctica / Re: Pine Island Glacier (PIG) Calving and Discussion
« on: July 29, 2020, 09:23:50 PM »
I wanted to add a lighter version:
with two intervals of 24 days: 17/02, 12/03 and 05/04,
and three intervals of 36 days: 05/04, 11/05, 16/06 and 22/07,
and adding little comments.

Click twice to zoom in



45
Antarctica / Re: Pine Island Glacier (PIG) Calving and Discussion
« on: July 29, 2020, 02:14:25 PM »
I am starting to catch up and you will find attached the history of the PIG calving front since the big calving of 09/02 based on the Sentinel1 images of 17/02 + n * 12 days (last image that of 22/07), the image of 29/02 being missing.
The calving front has been cut in two parts: North and South, they overlap and therefore give the global vision.
I give two versions: white background and Sentinel1 image of the 22/07.

click to zoom in

46
Antarctica / Re: Pine Island Glacier (PIG) Calving and Discussion
« on: July 23, 2020, 09:24:56 PM »
I can see you're an optimist:
The pinning point at the NSM has a certain solidity (over a few months for sure, over a few years to be confirmed), but it must absolutely not go upstream, the grounding line is moving away from the NSM upstream!
The pinning point at the SSM is the one I see very badly: after the last fractures, it is now well beyond T11 (and moreover the eastern part of T11 is less thick than the rest of T11). I don't feel that I trust too much the other components of the SIS upstream of T11. In my opinion it can withstand a few months, but not a few years.
To undo a glacier takes time, but at the moment the PIG seems to me in a very bad position and a retreat in the next few years seems inevitable.
I only ask to be reassured, but what I see does not reassure me in any way.

click to zoom in

EDIT: The only positive points are:
that in the North the NE-IS fracture, caused by the movement of the PIG, has gradually moved away from the Ice Rise, which may lead to a structure with some stability and at least partial closure of the rift zone...
and that in the South there have been, at least for the time being, no new marginal rifts in the PIG

47
Antarctica / Re: Pine Island Glacier (PIG) Calving and Discussion
« on: July 22, 2020, 05:05:24 PM »
A quick analysis of the PIG
NSM:
Mini calvings should continue, but the distance between the two edges should decrease, leading to temporary stabilization.
The recently opened rift has stabilized and tensions tend to move further upstream where another rift has widened. This process should continue and new rifts should open upstream as the PIG progresses. There should be no more than marginal rifts (at least for the time being). I have named this rift system nmR1.
Towards the front the block that had not calved in February should remain attached to the PIG, the two rifts, north and south (the latter is out of the picture) having not moved in the last few months.

We can timidly hope that this front will stabilize temporarily.

SSM :
Large calvings linked to the cR1, smR2 and new rifts are inevitable in the following months. Along the margin mini calvings should continue up to the shear margin of T11, as we have just sadly discovered.
The resulting pinning point is not very strong, let's hope that T11 behind supports it properly and holds as long as possible!

But, good news, for the moment no opening of the new marginal rifts in the PIG.

Conclusions:
It seems to me that the most critical point is the SSM, which is to be watched very carefully in the coming months.

click to zoom in

48
Antarctica / Re: Pine Island Glacier (PIG) Calving and Discussion
« on: July 22, 2020, 12:06:15 PM »
New calving at the NSM, animation based on the images of 10/07 and 22/07.

Click to animate

49
Antarctica / Re: Pine Island Glacier (PIG) Calving and Discussion
« on: July 09, 2020, 06:21:29 PM »
Not big news at the SSM, but the new rift has widened giving movement to the entire south side of P2.

At any given time calving of P2, Cork3 and Almand

12-day animation aligned with the PIG, which gives the movement of P2

Images très larges, click to animate

50
Antarctica / Re: Pine Island Glacier (PIG) Calving and Discussion
« on: July 06, 2020, 10:57:43 AM »
Oren,
Thanks for the encouragement.

> The Sentinel1 HR images I have available through PolarView are too inaccurate to allow efficient calculation using glacier details, but have the advantage of being available year-round and continuously, unlike Sentinel2 images which are only available in the austral summer and if clouds are absent. Sentinel2 images allow us to make more precise calculations and also give us directions, so they are complementary and I intend to take them into account next summer.

> The method is not automatic and requires a little work to build the image relative to the extension of the glacier:
>> extraction of the base image (between one base image and the other there are small shifts),
>> determination of the front line : determination to the nearest pixel is automatic, but it must be given the working area and in some cases (presence of sea ice) it must be very narrow.
>> for the number of pixels it is Gimp that does the calculation.
But I found an efficient and fast enough method

> The speed is already calculated systematically for all sectors and I automatically determine the sectors that have had a calving (comparison with a speed ceiling for the sector). You have understood what I meant when I said that a quantified calving follow-up can be implemented.

> For the Sentinel1 images, I use PolarView which does not give access to archives, they have to be stored at sois as I go along and my archives only go until 11/25/2019. But it still gives a period of 72 days before calving (until the image of 05/02/2020, the image of 31/12/2019 is missing). Indeed these images make it possible to calculate the speeds before calving, in a very particular context, an imminent calving (with, behind the forehead, rifts widening rapidly) and indeed it would be interesting to do so, especially since in this period we have Sentinel2 images which allow us more precise calculations and also give us the directions. I'll do it, it's only a question of time, you just have to be a little patient (it's not for today or tomorrow).

> For info: the strips are about 1910m high : in horizontal direction they are 1980m wide (20m less because of the pixel dedicated to the separation of the zones), but it should be taken into account that they are oblique.

> Further development, once there will be a standard presentation of the PIG: Now that the SIS is disengaged we can think of measuring the speeds by cutting the last area in strips and of course we can add a SWT analysis.

PS: Once the work on the speeds is underway, I will resume the publication of the historical data of the front by covering with two images the entire front.

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