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Messages - steve s

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1
Antarctica / Re: SH Polar Vortex
« on: July 14, 2019, 10:42:54 PM »
Images tell much. The jet varies. (Had to make them links)

First the southern polar jet - the "vortex" - at 10 hpa -- top of the atmosphere July 10,2016:
https://earth.nullschool.net/#2016/07/10/0700Z/wind/isobaric/10hPa/orthographic=-110.16,-91.63,314/loc=72.267,-53.020

Second, the more extensive 10 hpa jet July 10, 2019:
https://earth.nullschool.net/#2019/07/10/0700Z/wind/isobaric/10hPa/orthographic=-110.16,-91.63,314/loc=-1.100,-49.689

Third, for comparison, Greywolf's Is this real? of November 23, 2018:
https://earth.nullschool.net/#2018/11/23/0800Z/wind/isobaric/10hPa/orthographic=-110.16,-91.63,314/loc=138.580,-71.056

2
Antarctica / Re: Sea Ice Extent around Antarctica
« on: June 02, 2019, 01:43:52 PM »
Very interesting. And eyeballing the equation, a second order fit would look different. But ...

The parameters look as though the third and forth power terms contributed essentially nothing to the regression. But that could be an artifact of the size of the observations. Please scale the variables to one observation, say 2012 = 1, and rerun the regression so the parameters can be more readily interpreted.

BTW, the data has 8 digits, so the fourth power is 32 digits; least squares generates 64 digits during the calculation and then inverts the (in this case) 5x5 matrix. Normalizing the observations may be, statistically-speaking, interesting. 

3
Antarctica / Re: PIG has calved
« on: May 30, 2019, 04:01:54 PM »
The PIG may have thinned sufficiently to have become less brittle. Local crevasses may provide local stress relief, slowing the formation of full-width crevasses.     

4
Antarctica / Re: What's new in Antarctica ?
« on: May 02, 2019, 01:28:35 AM »
I am aware of the existing high thermal flows; I think of volcanism as a fast thermal flow. I'm naive here, as my posts probably show. Are you suggesting that the scenario projected by Larour, etc. would likely be interrupted by volcanic activity?

5
Antarctica / Re: What's new in Antarctica ?
« on: May 01, 2019, 10:25:11 PM »
Rox, are you suggesting that, if the authors are correct about the rebound mechanism, the ice volume loss outcome would be likely to be dominated by an increase in geothermal energy delivery to the Glacier? 

6
Antarctica / Re: What's new in Antarctica ?
« on: April 28, 2019, 11:19:26 AM »
From reply 467 on stabilizing Antarctic ice mass loss:

"As shown in Fig. 1, elastic uplift generated by a 2 km grounding-line retreat, modeled as loss of 100 m thick ice from a disk of 2 km radius, can reach 52 mm near the grounding line (centroid of the equivalent disk)."

In the quoted example the change in the slope due to grounding line retreat is 26 parts per million. That surface tilt is so slight that a drop of water might take a while to figure out which way was downhill on a flat piece of glass so tilted off the horizontal. Such a change in slope is well below the precision of current icestream bed slope measurements, so the hypothesis cannot be tested.

This seems at odds with the authors' claim:
"show a projected negative feedback in grounding line migration of 38% for Thwaites Glacier 350 years in the future, or 26.8% reduction in corresponding sea-level contribution."

Also, the analysis apparently also ignores bed roughness and MICI, for the glacier can be supported while it calves, and then can thin rapidly with fast grounding line retreat.

The authors spent more time on this than I have. Am I overlooking something basic?


7
Antarctica / Re: PIG has calved
« on: April 14, 2019, 07:02:40 PM »
I think I see distortions in the fresh snow beyond some of the visible cracks, implying they are growing rapidly.

8
Antarctica / Re: Thwaites Glacier Discussion
« on: March 22, 2019, 05:08:55 AM »
For a comparison with the previous post with respect to the retreat of the Thwaites Glacier's ice front, see the ice front on March 4, 2013 in the attached image. The variation in the pattern sea ice loss from year to year is a mystery to me.

9
Antarctica / Re: What's new in Antarctica ?
« on: January 19, 2019, 05:17:27 AM »
There is another factor in the formation of melt ponds: snow absorbs near infrared better than visible frequencies, but both penetrate the surface. Thus, even if the surface is kept below freezing, the temperature just below the surface can reach freezing with melting beginning there. That melting darkens the snow and changes the albedo. Then a broader spectrum is absorbed, increasing the melt, as discussed by Tealight.

10
Antarctica / Re: Antarctic Icebergs
« on: January 17, 2019, 06:37:29 PM »
The Thwaites' bergs seem to require time -- years -- losing depth in warm water before they are free to drift out to sea. I wish I had a better picture of the undersea topography relative to the existing sea ice and bergs. 

11
Iceberg b-35 (I think that's the number) has been grounded for the last couple of years, blocking movement of sea ice west of the Thwaites' tongue. It may be breaking up and starting to move, thereby allowing the crack to propagate to the west.


12
Antarctica / Re: Sea Ice Extent around Antarctica
« on: December 29, 2018, 01:57:12 PM »
The drop in sea ice began with a pretty dramatic step function, downward, when sea ice should have been growing.
...
A JAXA video of 8/1 to 9/17/16 (attached) shows the ice loss. Was there a time correlated weather event?
The thing is, most of the Antarctic sea ice is seasonal FYI, so the "memory" of the system is quite low, as opposed to the Arctic where MYI used to dominate and still has important buffering effects. Therefore a one-time crash should not have been felt two years after the event.
In addition, enhanced melting of the glaciers and ice shelves is expected to lead to freshening of the sea surface and growth in sea ice, as postulated by Hansen, so I don't think warming is to blame for the lack of sea ice. This is again very different from the Arctic due to having the continent in the middle, while Greenland melt runoff flows through Nares, Baffin and the Greenland Sea, all of which have strong southbound currents carrying the fresh water away from the main body of sea ice in the CAB.
I am also guessing the explanation has to do with wind patterns around Antarctica (or perhaps the monster El Nino of 2016) but this is far out of my league.

I quite agree. The step function has to reflect either a large scale change somewhere stabilized by a feedback from the Antarctic sea ice and waters; or another variable having changed elsewhere influencing condition massively. In either case, the cause is not local to Antarctica.

My main point is that we know when the shift occurred, although not why. And we also know that the shift took place in the middle of the Antarctic winter, a fact that seems to me likely to prove diagnostic.

13
Antarctica / Re: Sea Ice Extent around Antarctica
« on: December 29, 2018, 07:46:57 AM »
The drop in sea ice began with a pretty dramatic step function, downward, when sea ice should have been growing.

On 9/3/17 Tigertown posted a graph showing the drop:


A JAXA video of 8/1 to 9/17/16 (attached) shows the ice loss. Was there a time correlated weather event?


14
Antarctica / Re: Sea Ice Extent around Antarctica
« on: October 14, 2018, 08:50:34 PM »
I suspect the sea ice concentration has been low this year, causing the total volume of ice to remain low. At least, that is the way I've been reading the AMSR2 data. The link is to the current reported image:
https://seaice.uni-bremen.de/data/amsr2/today/Antarctic_AMSR2_nic.png

The low concentration probably allowed winds to repeatedly spread the ice. The temperatures remaining below freezing, new (but thin) ice would have formed soon after each breakup. The result would enlarge sea ice extent as measured. Obviously there are other assumptions involved -- including sea surface temperatures, outflows from glaciers, air temperatures near the surface, and cloud cover.

I expect a fast and large decline in extent during this Antarctic summer -- jf other things, such as temperatures, are similar to those of the last few years.

15
Antarctica / Re: PIG has calved
« on: October 07, 2018, 04:39:56 PM »
If I read the animation correctly, the SW tributary glacier is now forcing the cracking and the west side of the PIG is moving faster than the east side near the terminus. That newly enlarged and extended crack shown 5km from the terminus should speed up the tributary glacier's flow -- more so after it calves a berg or bergs.

This summer is likely to be interesting.

16
Antarctica / Re: PIG has calved
« on: September 30, 2018, 07:23:22 PM »
Thank you Grygory.

The low angle light shows many cracks extending almost all the way across the glacier. Apart from individual calving events, this seems to indicate a new widespread loss of stiffness for many kilometers upstream, and suggests the imminent loss of buttressing for the SW tributary glacier. 

17
Antarctica / Re: Sea Ice Extent around Antarctica
« on: September 06, 2018, 06:25:06 PM »
Is volume at an all-time low?

18
ASLR,

I understand the tectonics involved and think that the Thwaites Glacier is likely to have its melt accelerated by vulcanism, but I see no obvious case for more than a trivial direct influence of ice loss on magnetic reversal (at most). So I agree with RTG.

 

19
So where does loss of Antarctic ice come into play?

20
ASLR,

I'm not quite sure what light the magnetic field diagram is supposed to bring to the discussion. It seems to me the magnitude of the folds in the lines would be considerably less if the projection were less distorting; that the changes in the magnetic field might be an interesting note to your argument, but cannot be inferred from the diagram; and that the fold might cause the equivalent of Jupiter's Great Red Spot under different atmospheric conditions. However, I think RTG has a strong argument in the absence of a good theory -- correlations don't do much by themselves.

So, please elucidate a theoretical connection that will explain how the minor mass shift might be causal rather than coincident.
 

21
Pmt, I don't have a shot from last year, but I'd like to see one -- or better, a time series. The outflow seems to be more akin to a glacial belch. I've attached a June 3rd close up of the same area -- which shows a full sea ice coverage with the beginning of the melt out starting near the glacier.
 

22
ASLR,

1) The current pattern of melting does not match the heat pattern in the computer generated image of post 27; and
2) I do not remember a similar mid-winter sea ice pattern -- maybe a polynya -- in the past.

But i'm merely an interested amateur, finding it a disturbing coincidence when the nearby land seems to be rising faster than the ice above is melting.   

23
The Thwaites outflow seems to be increasing, and to be warm! , much of the near glacier waters are shown to be ice free - see the close up below.

Given ASLR's latest post, 2 above, perhaps the focus of the research should have been on the Thwaites, not the PIG.


24
Makes me wonder more about what's happening under the Thwaites. Sea ice concentration is much lower near its outflow than by the PIG. From NSIDC  for June 24th:


25
"ECS" refers to what?

26
Antarctica / Re: Sea Ice Extent around Antarctica
« on: January 30, 2018, 07:23:55 PM »
Ice melts from the edges, and there are many edges showing.



Strangely, sea ice near the Thwaites and Pine Island Glaciers is melting/breaking up much more slowly and to a smaller extent than in the last few years. I'm interpreting this as an indication that melt has accelerated under them, causing an increase in fresh water near the surface and thicker ice forming over the winter. Any body have evidence that might bear on this anomaly?

27
Antarctica / Re: Potential Collapse Scenario for the WAIS
« on: December 01, 2017, 10:30:54 PM »
ASLR,

The graph you show uses sea level rise on the y axis. Sea level rise seems irrelevant for this part of the discussion..

Your earlier image of the Thwaites profile indicates that by roughly the time the calving face retreats 20 km from the grounding line the cliff faces are high enough to spontaneously fail by their own weight -- no free water needed. So I do not see the need for hydrofracturing for a high speed of collapse, just a means of moving ice cubes out to sea. 

Keep up the good work,
Steve

28
Antarctica / Re: Potential Collapse Scenario for the WAIS
« on: December 01, 2017, 12:44:06 AM »
If one accepts that a rough glacial bed on a marine-terminating glacier reflects a lack of sliding erosion, the roughness also marks a region where during previous retreats ice cliff collapse was the dominant mechanism - not sliding nor creep.

I'm no specialist in this area, but the descriptions I've read of the models don't seem to take such bed changes into account as the local singularities they likely are.

Apropos the third diagram above, further retreat by the Thwaites Glacier can be expected to be through ICI starting almost immediately.

So why, ASLR, do you expect a delay to 2025+ and the action of "Super El Nino events"? Are you expecting a collapse of the Thwaites eastern ice shelf first?

29
Perhaps current basal roughness reflects past cliff fracturing with shallow bergs and little bed erosion. If so, rough beds may be a sign of rapid glacial retreat.

30
Antarctica / Re: Sea Ice Extent around Antarctica
« on: October 27, 2017, 11:24:53 PM »
Is there any time series tracking ice thickness or volume?

31
Antarctica / Re: PIG has calved
« on: October 16, 2017, 10:28:52 AM »
I agree, Shared Humanity. Beautiful.

32
From the paper:
"... the maximum possible erosion rate that could go undetected along our profiles is 500 mm a-1, far exceeding erosion rates reported for glacial settings from proglacial sediment yields, but substantially below subglacial erosion rates of 1000 mm a-1 previously reported from repeat geophysical surveys in West Antarctica."

The PIG has been transporting water under the ice for a long time. Given that fact, I find 20" per year -- 5 meters per decade -- of erosion of the bed to be rapid. It seems to me, admittedly poorly educated in this research area, that better instruments are needed before claiming minimal bed erosion.

33
Antarctica / Re: Sea Ice Extent around Antarctica
« on: September 08, 2017, 07:37:23 PM »
Not a surprising finding, ASLR; but there seems to have been a stair-step shift in sea ice extent, not the gradual change that article suggests. The cause of that step-wise shift begs explanation. We do not know whether the shift might repeat or the reason for its scale. Without gradualism, we are blinder than we knew.

34
Antarctica / Re: Sea Ice Extent around Antarctica
« on: September 07, 2017, 07:23:30 PM »
Last year's sea ice extent a perfect storm of coincidences? Then why does this year seem so similar? I find it much easier to imagine a single driver than the squared product of low probabilities.

35
Antarctica / Re: Sea Ice Extent around Antarctica
« on: September 03, 2017, 07:43:04 PM »
Oops I was misreading where months begin in your graph. The change began around or just after the beginning of September 2016 and took 10 days to 2 weeks to complete, as I now read the graph.

36
Antarctica / Re: Sea Ice Extent around Antarctica
« on: September 03, 2017, 06:35:20 PM »
Looks to me like the sea ice extent took a step downward in August 2016, and stayed down thereafter. An energy distribution change of some kind. What other event or events may be time correlated?

I wrote 'may' because the other events may be earlier or later due to transmission effects and the cause may be a separate matter, but the step nature of the shift is clear. The shift is as interesting a phenomenon as it is frightening.   

37
FT,

You do not seem to understand the material properties of ice and glaciers or the differences between ice shelves and glaciers. You set up straw men in situations that cannot exist and then talk of consequences that would be unlikely if they did exist. Study physics. Study ice. Learn about the ice topography of the Antarctic in more detail. And study the points that have been made in this thread for your benefit.

This website has some seriously competent glaciologists and few trolls. There is no ice conspiracy group here hiding a menace. 

38

1st, cascade structural failure of large body of ice, caused and triggered by ongoing (as we speak) weakening of the bottom parts of ice sheet(s), which is being melted by ocean water "from below", which is what one of links i gave in the 1st post is exactly about, and my primary concern for WAIS; and

2nd, possible "ice dam failure" event of gigantic proportions, resulting in _billions_ to _trillions_ of tons of ice and water flowing "down" from upper elevations all the way into the ocean, which is what the other link in the 1st post is about, and which is my primary concern (eventually) for EAIS.

The first fails on the basis of speed of propagation. Ice flexes and stretches. Then it has to travel to where it could displace water.

The second fails for two reasons. First because the antarctic has little suitable terrain:


Second because the wave front spreads out as it covers intercontinental distances. The mega-tsunami article does not mention major intercontinental impacts, other than leaving the possibility open for extraterrestrially-generated events.

39
Limitations on ice cliff height due to ice strength put an upper bound on possible energy delivery from a calving event. An ice dam collapse scenario can generate high forces in a channel due to gravity, which are the scenarios generating erosion features and depositing rocks at great heights (Missoula Floods, for example) but do not have much influence in open water.

Also consider that with any Antarctic event the wave front would expand over the long ocean distances, diminishing the impact on other continents.

I see no mechanism through which melting could generate much of an intercontinental tsunami. 

40
Antarctica / Re: Trends for the Southern Ocean
« on: April 12, 2017, 08:41:46 PM »
Best of luck, H.

Little on the news here, the US, about your extreme weather.

41
Antarctica / Re: Thwaites Glacier Discussion
« on: April 06, 2017, 04:22:26 AM »
Although this is awfully late in the year and new ice is forming, the calving activity on the Thwaites' tongue is continuing -- April 5th.

https://lance.modaps.eosdis.nasa.gov/imagery/subsets/?project=antarctica_regions&subset=Thwaites_Tongue.2017095.terra.250m

(Link provided because the image is not appearing inline in my browser window.)

42
Antarctica / Re: Thwaites Glacier Discussion
« on: March 24, 2017, 08:22:52 PM »
Looks like the Thwaites tongue is calving.



43
Antarctica / Re: Sea Ice Extent around Antarctica
« on: February 09, 2017, 07:37:42 PM »
Whether a new low or not, the number of square kilometers of multi-year sea ice has been drastically reduced; the remaining multi-year sea ice possibly drastically thinned; the surface waters warmed in preparation for the next freeze. Next year will probably be another low year.

The refreeze will start further south on average than most other years, so it might start early, although the warm waters probably mean at a slower than usual rate of progress.

44
Antarctica / Re: Melt water in Antarctica
« on: February 04, 2017, 08:44:35 AM »
A hypothesis about plume's visibility and shape -- no ice needed:

The third image shows an apparent outflow jet from the squared-off section of glacier. Rock flour scoured from underneath the glacier provides the visible silt. Then eddies and currents have spread the silt.

45
Antarctica / Re: Melt water in Antarctica
« on: January 23, 2017, 07:33:15 PM »
This striking melt pond across the center of the Amery Ice Shelf has had explosive growth the last ten days

http://go.nasa.gov/2iWj5W2

All those melt ponds and no sign any have formed moulins yet. Can anyone here estimate when we could expect those ponds to drain?

46
Antarctica / Re: PIG has calved
« on: December 11, 2016, 09:42:33 PM »
Tealight,

The dark areas look like places where snow bridges did not form or collapsed. I think the curved crevasses in the third image, with the obvious wind-formed ridges of snow crossing some crevasses, may show the main bridging process.

47
Antarctica / Re: PIG has calved
« on: August 03, 2016, 03:34:13 PM »
Looks to me as though a crevasse is extending toward the point of rotation and another is extending in a pattern that would separate the pinning point from the rest of the berg. Both crevasses are either racing thinning to free the berg by breaking it up, or they are products of thinning.

Any guesses as to when the berg will drift free?

48
Antarctica / Re: PIG has calved
« on: March 02, 2016, 09:28:43 PM »
ASLR: "... as it is probable that the keel of the iceberg is deep enough to also be impacted by the relatively warm CDW discharge shown in the first of my previous two images."

I'm confused by the first part of this comment. The berg's keel should be little deeper than the PIG's front. The second part may offer a clue. The berg's pinned, so return advective water might be a factor as it flows around the pin. There may be also orographic lifting of fluids over the eastern side of the berg, dependent on the local terrain, and about that I am ignorant. However the advective inflows must be west of the berg where the depths are greater for any of this to work out.

49
Antarctica / Re: PIG has calved
« on: March 02, 2016, 09:54:52 AM »
" ... the specific gravity of warm water is higher than of cold ... "

wait, what ?

Sorry I was imprecise Sidd. Fresh water's density is greatest at about 4 degrees C, so ice forms at the water's surface, where the water is at 0 degrees. Dissolved salt depresses the freezing point and increases the density, but leaves the general relationship unchanged.

Advective outflows, having lost heat to the ice, are less dense and above the inflows. The density change is due to both cooling and freshening.

The motion of the berg indicates that a large volume water is traveling at the top of the water column -- along the bottom of glacier. To my amateur eye, the strength of the outflow at the top of the water column seems either (1)  too great to be explained by melt-water alone (as ASLR's figure suggests is the case); or (2) the volume of melting is higher than seems to be indicated by apparent volume changes in the glacier.

50
Antarctica / Re: PIG has calved
« on: March 01, 2016, 10:09:33 PM »
Thanks ASLR.

I was originally thinking of tides being too weak. Now I realize that the specific gravity of warm water is higher than of cold, so the warm basal waters become an outflow river at the lower surface of the glacier. The strength of the flow (surprises me) is made visible by the ongoing separation between the berg and the glacier. 



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