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Lennart van der Linde

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Re: what's new in Greenland ?
« Reply #100 on: September 03, 2015, 07:52:40 PM »
Discussion paper by Mikkelsen et al on extreme GIS-runoff in 2012:
http://www.the-cryosphere-discuss.net/9/4625/2015/tcd-9-4625-2015.html

sidd

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Re: what's new in Greenland ?
« Reply #101 on: September 04, 2015, 02:17:27 AM »
I see Box is an author. The results show the firn layer is now saturated. Apart from the loss of the 3.6mm SLR buffer, so that all melt now discharges, i wonder about structural effects and cryohydrologic warming softening ice.

Every new result we see disquiets me.

skanky

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Re: what's new in Greenland ?
« Reply #102 on: September 15, 2015, 03:44:58 PM »
Don't know if this is the best thread for this, but ARS have a good interview with Marco Tedesco on the equipment they use to study Greenland:

http://arstechnica.co.uk/science/2015/09/tools-of-the-trade-when-your-trade-is-studying-the-greenland-ice-cap/


Laurent

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Re: what's new in Greenland ?
« Reply #103 on: October 27, 2015, 04:43:49 PM »
Greenland Is Melting Away
http://www.nytimes.com/interactive/2015/10/27/world/greenland-is-melting-away.html?_r=0
“No one has ever collected a data set like this,” Asa Rennermalm, a professor of geography at the Rutgers University Climate Institute who was running the project with Dr. Smith, told the team over a lunch of musk ox burgers at the Kangerlussuaq airport cafeteria.


Laurent

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Re: what's new in Greenland ?
« Reply #104 on: November 12, 2015, 09:37:03 PM »
Scientists say Greenland just opened up a major new ‘floodgate’ of ice into the ocean
https://www.washingtonpost.com/news/energy-environment/wp/2015/11/12/scientists-say-greenland-just-opened-up-a-major-new-floodgate-of-ice-into-the-ocean/
“Collapse of the entire basin is going to take a long time, it’s not going to happen tomorrow,” says Mouginot. “But it’s a process, when you start, it’s like Jakobshavn — [you don’t] see the glacier recovering from that.”

AbruptSLR

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Re: what's new in Greenland ?
« Reply #105 on: November 13, 2015, 06:12:04 PM »
Per the linked reference, ice mass losses (and associated loss acceleration rates) reported by the GRACE satellite when the measured losses are corrected for "land-ocean leakage effects":

Shuanggen Jin and Fang Zou (2015), "Re-estimation of glacier mass loss in Greenland from GRACE with correction of land-ocean leakage effects", Global and Planetary Change, doi: 10.1016j.gloplacha.2015.11.002


http://www.sciencedirect.com/science/article/pii/S0921818115301168

Abstract
The Gravity Recovery and Climate Experiment (GRACE) satellites can estimate the high-precision time-varying gravity field and the changes of Earth's surface mass, which have been widely used in water cycle and glacier mass balance. However, one of larger errors in GRACE measurements, land-ocean leakage effects, restricts high precision retrieval of ocean mass and terrestrial water storage variations along the coasts, particularly estimation of mass loss in Greenland. The land-ocean leakage effect along the coasts in Greenland will contaminate the mass loss signals with significant signal attenuation. In this paper, the precise glacier mass loss in Greenland from GRACE is re-estimated with correction of land-ocean leakage effects using the forward gravity modeling. The loss of Greenland ice-sheets is − 100.56 ± 8.86Gt/a without removing leakage effect, but − 171.56 ± 19.24Gt/a after removing the leakage effect from September 2003 to March 2008, which has a good agreement with ICESat results of − 184.8 ± 28.2 Gt/a. From January 2003 to December 2013, the total Greenland ice-sheets is losing at − 254.10 ± 6.90Gt/a from GRACE measurements with removing the leakage effect by 43.15%, while two-thirds of total glacier melting in Greenland is occurred in southern Greenland for the past 11 years. The secular leakage effects on glacier melting estimate mainly locate in the coastal areas, where larger glacier signals are significantly attenuated due to leaking out into the ocean. Furthermore, the leakage signals also have remarkable effects on seasonal and acceleration variations of glacier mass loss in Greenland. More significantly accelerated loss of glacier mass in Greenland is found by − 12.11 Gt/a2 after correcting leakage effects.
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sidd

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Re: what's new in Greenland ?
« Reply #106 on: November 13, 2015, 11:40:46 PM »
That Jin (2015) paper shows doubling in 7 years then for GIS mass waste.

sidd

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Re: what's new in Greenland ?
« Reply #107 on: November 15, 2015, 01:44:13 AM »
GRACE, from polarportal, Barletta's analyses i think.




alataristarion

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Re: what's new in Greenland ?
« Reply #108 on: November 20, 2015, 08:38:47 PM »
This is my first post, but I've been reading as a guest for a long time now. I hope this is the appropriate forum for this!

I've created an animation using the IceBridge bedrock data overlaid with the new image of the Sentinel data that A-Team. For me at least, this really helps highlight how the ice movement lines up with the underlying bedrock.

I find it particularly interesting that the NE Greenland Ice Stream moves quickly very near the deep bedrock canyon underlying the Storstrømmen glacier, and then stops. I wish the directional data on the ice movement were preserved, but if the ice is moving toward the canyon and then stopped by the pining of the islands near the calving face, it will be very interesting to see what happens if the calving face retreats northwest slightly.


Neven

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Re: what's new in Greenland ?
« Reply #109 on: November 24, 2015, 05:03:43 PM »
I've created an animation using the IceBridge bedrock data overlaid with the new image of the Sentinel data that A-Team.

Hi, alataristarion. Unfortunately your animation isn't playing (I fear because it's too big). Could you post another, slightly smaller one?
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alataristarion

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Re: what's new in Greenland ?
« Reply #110 on: November 24, 2015, 06:56:35 PM »
Absolutely! Here is one that is under 1MB, so hopefully it will play properly. I have the higher resolution version (and the source file) that I can email if anyone wants to look at them.

Neven

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Re: what's new in Greenland ?
« Reply #111 on: November 24, 2015, 07:36:20 PM »
Yup, that one works (when clicked). Thanks!
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Espen

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Re: what's new in Greenland ?
« Reply #112 on: November 24, 2015, 08:28:57 PM »
Absolutely! Here is one that is under 1MB, so hopefully it will play properly. I have the higher resolution version (and the source file) that I can email if anyone wants to look at them.

Great animation! ;)

Zachariae Fjord will be a serious contender to world largest fjord system title in the future, this now belongs to Scoresby Sund (a bit further south).
Have a ice day!

alataristarion

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Re: what's new in Greenland ?
« Reply #113 on: November 24, 2015, 10:04:14 PM »
Great animation! ;)

Zachariae Fjord will be a serious contender to world largest fjord system title in the future, this now belongs to Scoresby Sund (a bit further south).

Thanks!

I also like how this image makes clear what the rough structure of ice streams must have been during the last glacial maximum, in particular in Scoresby Sund and Disko Bay.

Does anyone know if there have been any sea floor cores drilled in Disko Bay? I would not be surprised to learn that there was once a Disko Bay Ice Shelf that was bifurcated around Disko Island like the Ronne-Filchner Ice Shelf in Antarctica, but I'd be interested to see if that has been confirmed scientifically.

oren

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Re: what's new in Greenland ?
« Reply #114 on: November 24, 2015, 11:30:11 PM »
Great animation indeed. And welcome to the forum as a poster.

Sleepy

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Re: what's new in Greenland ?
« Reply #115 on: November 25, 2015, 05:03:23 AM »
Does anyone know if there have been any sea floor cores drilled in Disko Bay? I would not be surprised to learn that there was once a Disko Bay Ice Shelf that was bifurcated around Disko Island like the Ronne-Filchner Ice Shelf in Antarctica, but I'd be interested to see if that has been confirmed scientifically.


Both of these mention MSM343300.
http://www.archipel.uqam.ca/6996/1/M13491.pdf
www.uib.no/sites/w3.uib.no/files/attachments/kelley_13.pdf
A quote from Kelley et al.
6. Conclusions
New 10Be ages from around Disko Bugt, western Greenland,
place the deglaciation of western Disko Bugt at 10.8  0.5 ka, with
the ice margin reaching the eastern coast of Disko Bugt near Ilulissat
at 10.1 0.3 ka and in southeastern Disko Bugt at 9.2  0.1 ka.
This chronology yields a retreat rate between w50 and 450 m a1
across central Disko Bugt. This rate indicates that w25% of the
overall retreat between the shelf edge and the current position
occurred in as little as 700 years. We suggest this retreat was the
result of internal ice dynamics acting upon an ice sheet driven out
of equilibrium by climatic factors. These findings further emphasize
the ability of marine sectors of ice sheets to change rapidly due to
ice dynamics in warming climates (e.g. Kjær et al., 2012). Our
chronology fills a gap in the current understanding of the early
Holocene behavior of the GrIS in Disko Bugt, and provides a dataset
that completes a history of a western GrIS margin spanning from
the continental shelf to the present ice position, and from the latest
Pleistocene through the Holocene.

Picture with locations from Kelley et al attached.

nukefix

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Re: what's new in Greenland ?
« Reply #116 on: November 25, 2015, 11:11:43 AM »
I find it particularly interesting that the NE Greenland Ice Stream moves quickly very near the deep bedrock canyon underlying the Storstrømmen glacier, and then stops. I wish the directional data on the ice movement were preserved, but if the ice is moving toward the canyon and then stopped by the pining of the islands near the calving face, it will be very interesting to see what happens if the calving face retreats northwest slightly.

Storströmmen has been slowing down, or at least ice has been piling up there according to altimetry. The Ice Velocity data does contain the direction so I expect it to be there once the S-1 Greenland-product is officially released by the project:

http://products.esa-icesheets-cci.org/

ps. Kick-ass animation, thanks!

alataristarion

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Re: what's new in Greenland ?
« Reply #117 on: November 25, 2015, 04:27:38 PM »
@Sleepy

Thanks! I have now fallen down a rabbit hole of research papers that will occupy me throughout the long Thanksgiving weekend here in the US.

@nukefix

That will be very interesting to see. And thanks!

Sleepy

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Re: what's new in Greenland ?
« Reply #118 on: November 26, 2015, 08:08:18 AM »
alataristarion, it's not a rabbit hole. It's more like passing the event horizon of a black hole, if one consider all of the papers out there associated with AGW.  ;D

I've tried to stop reading, but I can't.

A-Team

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Re: what's new in Greenland ?
« Reply #119 on: November 26, 2015, 04:39:59 PM »
Nice effort at overlaying surface velocity onto bedrock! Below are a couple of variations, first with blended frames of variable intermediate percentages and second similar but with color conflicts reduced by desaturating the bedrock layer.

These include the other glaciers of northern greenland. To optimize to NEGIS only and stay within our 700 pixel width, the second animation can be cropped, rotated sideways and enlarged to fit (3rd animation).

The NASA visualization center would do this differently: the bedrock DEM would be displayed in hill-shaded perspective grayscale with the speeds put on as an over-tint. This can be done in open freeware discussed on this forum but the catch will be finding the raw data, getting it out of its obtuse NSIDC storage format, cropping to the desired area, maybe exponentiating to get out of log compression, and recovering the grayscales that are needed for input to draped hill-shades.

In all this, it is crucial not to forget the actual resolution of the data and the associated error. In the words of R Feynman, it's easy to fool people and the easiest person of all to fool is yourself, as in the recent Zwally paper.

For example the bedrock had to be heavily kriged to interpolate from the sparse ice penetrating radar tracks which themselves have ~50 m error. The Sentinel velocity magnitudes -- well, you can see swath artifacts everywhere not to mention big blank places on the map.

Laurent

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Re: What's new in Greenland?
« Reply #120 on: December 10, 2015, 10:29:49 PM »
Greenland glaciers melt rate hits 9,500 year record
http://www.theecologist.org/News/news_round_up/2986640/greenland_glaciers_melt_rate_hits_9500_year_record.html

As Arctic Peoples at COP21 in Paris appeal for unity to halt global warming, writes Tim Radford, scientists report that Greenland's glaciers are now melting at a speed not seen since the last Ice Age almost 10,000 years ago.


The glaciers of Greenland are retreating two to three times faster now than at any time since the last Ice Age ended 9,500 years ago, according to new research.

The news comes as indigenous peoples from the northern polar region staged an Arctic Day at the COP21 climate change summit in Paris.

Leaders of Greenland peoples, the Nunavut region of Canada and the Inuit Circumpolar Council appealed to the governments of the world to unite to dramatically reduce greenhouse gas emissions and keep global warming to between 1.5C and 2C.

That is because the Arctic is now warming faster than almost anywhere else on Earth, and both human settlements and natural ecosystems are vulnerable.

That the Greenland glaciers are in retreat is itself not news. Satellite data and measurements on the ground have repeatedly confirmed the retreat of the glaciers, the loss of ice and the acceleration of flow. The Jakobshavn Isbrae glacier has even reached a speed of 17 kilometres a year.

Sediment cores

But US scientists report in Climate of the Past journal that the present rate of loss is without precedent.

They analysed sediment cores from a lake bed fed by two Greenland glaciers and built up a record reaching back nearly 10,000 years, charting the advance and retreat of the ice in response to natural cycles. And they found evidence of climate change triggered by the human combustion of fossil fuels imposed upon the natural pattern.

"Two things are happening", says one of the report's authors, William D'Andrea, a paleoclimatologist at Columbia University's Lamont-Doherty Earth Observatory.

"One is you have a very gradual decrease in the amount of sunlight hitting high latitudes in the summer. If that were the only thing happening, we would expect these glaciers to very slowly be creeping forward, forward, forward.

"But then we come along and start burning fossil fuels and adding carbon dioxide to the atmosphere, and glaciers that would still be growing start to melt back because summer temperatures are warmer."

The evidence lies in the erosion rates revealed by the lake silts. Colder climates mean more ice, which means heavier glaciers, which then grind and erode more rock. Cores of sediment preserve the annual record of seasonal change, and radiocarbon dating techniques can provide a calendar of melting and freezing periods.

The record reveals that erosion decreased 8,500 years ago, increased again, and then around 8,000 years ago the glaciers began almost to waste away. There was very little evidence of erosion, and the lake silt incorporated evidence that plants once bloomed around the lake.

Around 4,000 years ago, the glaciers grew again, and - with intervals of retreat - continued to grow until 100 years ago.

Pattern of retreat

Although the evidence comes from a small area confined to the southeastern part of Greenland, it remains a guide to the bigger picture. The same pattern of advance and retreat is matched by evidence from ocean sediments and cores of ice from Greenland and Baffin Island.

"This shows that there are internal responses within the climate system that can make glaciers grow and shrink on very short timescales", Dr D'Andrea says. "They're really dynamic systems, which we have not had much evidence for prior to this."

Greenland's minister of industry, labour, trade and foreign affairs, Vittus Qujaukitsoq, one the Arctic voices appealing for strong and effective action in Paris, said: "Greenland has an important responsibility in promoting international climate research.

"Greenlandic climate research combines international cutting-edge research with an Arctic human dimension. Our joint Inuit voice and our traditional know-how from across the Arctic should be heard and included in international policy-making."

A-Team

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Re: What's new in Greenland?
« Reply #121 on: December 11, 2015, 02:37:24 PM »
The article is open access:

Glacier response to North Atlantic climate variability during the Holocene
NL Balascio, WJ D'Andrea, RS Bradley
http://www.clim-past.net/11/1587/2015/cp-11-1587-2015.html

Kulusuk Lake is a small cirque 0.8 km2, 69 m depth in southeastern Greenland as shown in the first image. While the study is quite interesting, I wonder how safe it is to extrapolate to the whole of Greenland from this one particular lake (or rather its two tiny contributing glaciers) adjacent to a coastal ocean current. The glaciers themselves were not studied in tandem; no cores were taken; no ice-penetrating radar tracks are mentioned.

in many Northern Hemisphere regions glacier advances of the past few hundred years were the most extensive and destroyed the geomorphic evidence of ice growth and retreat during the past several thousand years. Thus, most glacier records have been of limited use for investigating centennial scale climate forcing and feedback mechanisms.

Here we report a continuous record of glacier activity for the last 9.5 ka from southeast Greenland, derived from high-resolution measurements on a proglacial lake sediment sequence. Physical and geochemical parameters show that the glaciers responded to previously documented NH climatic excursions, including the 8.2 ka cooling event, the Holocene Thermal Maximum, Neoglacial cooling, and 20th century warming.

... declining summer insolation caused long-term cooling and glacier expansions during the late Holocene [but] climate system dynamics resulted in repeated episodes of glacier expansion and retreat on multi-decadal to centennial timescales. These episodes coincided with ice rafting events in the North Atlantic Ocean and periods of regional ice cap expansion, which confirms their regional significance and indicates that considerable glacier activity on these timescales is a normal feature of the cryosphere. The data  indicate that recent anthropogenic-driven warming has already impacted the regional cryosphere in a manner outside the natural range of Holocene variability.

Bedrock erosion at the base of glaciers provides sediment supply for meltwater transport to proglacial lakes. In catchments where other sources of sediment are limited, such as from mass wasting or the release of stored sediment, there is a strong relationship between sediment properties and glacier size; large glaciers produce more minerogenic material than small glaciers. Measurements of physical and geochemical properties of proglacial lake sediments can therefore be used to reconstruct records of past glacier size.


The methods used these days to study sediment cores include scanning XRF for elemental analysis (xray fluorescence of K Ca Ti Mn Fe Zn Rb Sr in bedrock flour), magnetic susceptibility (proxy for changes in paleoclimate-driven depositional processes such as preferred orientation, distribution or shape of ferromagnetic or paramagnetic minerals associated with bottom currents, compaction, and deformation), net organic matter (whatever is burnt off at 4 hrs at 550ºC), and visual stratigraphy (gravelly sand, clayey silt, brown, organic sediment, laminated sand).

We'll see these same methods applied at this summer's study of Petermann Glacier to determine its comings and goings, though at the bottom of the fjord rather than in the context of a cirque lake.
« Last Edit: December 11, 2015, 05:06:23 PM by A-Team »

Lennart van der Linde

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Re: What's new in Greenland?
« Reply #122 on: December 17, 2015, 09:07:11 AM »
Kjeldsen et al 2015 on mass loss from GIS since 1900:
http://www.nature.com/nature/journal/v528/n7582/pdf/nature16183.pdf

Abstract
"The response of the Greenland Ice Sheet (GIS) to changes in temperature during the twentieth century remains contentious, largely owing to difficulties in estimating the spatial and temporal distribution of ice mass changes before 1992, when Greenland-wide observations first became available. The only previous estimates of change during the twentieth century are based on empirical modelling and energy balance modelling. Consequently, no observation-based estimates of the contribution from the GIS to the global-mean sea level budget before 1990 are included in the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Here we calculate spatial ice mass loss around the entire GIS from 1900 to the present using aerial imagery from the 1980s. This allows accurate high-resolution mapping of geomorphic features related to the maximum extent of the GIS during the Little Ice Age at the end of the nineteenth century. We estimate the total ice mass loss and its spatial distribution for three periods: 1900–1983 (75.1 ± 29.4 gigatonnes per year), 1983–2003 (73.8 ± 40.5 gigatonnes per year), and 2003–2010 (186.4 ± 18.9 gigatonnes per year). Furthermore, using two surface mass balance models we partition the mass balance into a term for surface mass balance (that is, total precipitation minus total sublimation minus runoff) and a dynamic term. We find that many areas currently undergoing change are identical to those that experienced considerable thinning throughout the twentieth century. We also reveal that the surface mass balance term shows a considerable decrease since 2003, whereas the dynamic term is constant over the past 110 years. Overall, our observation-based findings show that during the twentieth century the GIS contributed at least 25.0 ± 9.4 millimetres of global-mean sea level rise. Our result will help to close the twentieth-century sea level budget, which remains crucial for evaluating the reliability of models used to predict global sea level rise."

sidd

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Re: What's new in Greenland?
« Reply #123 on: December 18, 2015, 07:03:56 AM »
Thanks for the reference. I feel that Kjeldsen confirms what Enderlin proposed, that surface mass balance is driving Greenland mass waste. The thing is melting in place. We shall see if Greenland dynamic waste resurges, say in NEGIS, but i think we will see awful dynamic waste in Antarctica first.

A-Team

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Re: What's new in Greenland?
« Reply #124 on: December 18, 2015, 09:36:36 PM »
The Kjeldsen piece is open source thanks to a wonderful new policy adopted by Macmillan for across their scientific journal portfolio. This is html only, no pdf download without paying $6 to ReadCube. However -- and this astonished me -- full free access to figures at author-submitted size in permitted.

It's quite a decent article on the stereo photogrammetry processing side. It's not so surprising to see Melville Bay in far northwestern Greenland getting hammered. That area, despite its latitude, also jumps out on ocean current warming maps.

In terms of closing the sea level budget, that depends on the eye of the beholder (vis-a-vis Antarctica), be it that of the consensus or that of an obstinate 76-year old.

Here we calculate spatial ice mass loss around the entire GIS from 1900 to the present using aerial imagery from the 1980s. This allows accurate high-resolution mapping of geomorphic features related to the maximum extent of the GIS during the Little Ice Age at the end of the nineteenth century.

We estimate the total ice mass loss and its spatial distribution for three periods: 1900–1983 (75.1 ± 29.4 gigatonnes per year), 1983–2003 (73.8 ± 40.5 gigatonnes per year), and 2003–2010 (186.4 ± 18.9 gigatonnes per year). Furthermore, using two surface mass balance models we partition the mass balance into a term for surface mass balance (that is, total precipitation minus total sublimation minus runoff) and a dynamic term.

We find that many areas currently undergoing change are identical to those that experienced considerable thinning throughout the twentieth century. We also reveal that the surface mass balance term shows a considerable decrease since 2003, whereas the dynamic term is constant over the past 110 years.

Overall, our observation-based findings show that during the twentieth century the GIS contributed at least 25.0 ± 9.4 millimetres of global-mean sea level rise. Our result will help to close the twentieth-century sea level budget
« Last Edit: December 18, 2015, 10:00:13 PM by A-Team »

sidd

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Re: What's new in Greenland?
« Reply #125 on: January 05, 2016, 01:16:26 AM »
Firn is full, melt goes to ocean. This is why SMB began to dominate mass waste as Enderlin saw, no refreeze.


doi:10.1038/nclimate2899

Pmt111500

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Re: What's new in Greenland?
« Reply #126 on: January 11, 2016, 09:58:59 AM »
The wettest snow is most often found deeper in the springtime. It either reaches ground or if there's an ice layer it will float on that. One friend (regular icefisher though) once walked 2km in 20cm water/slush layer on ice (40cm) to get back on land. This is common knowledge that the surface granular snow/deformed icecrystals is pretty dry. It's still nice to have some numbers concerning Greenland about this aspect of regular spring runoff.
A quantity relates to a quantum like camel's back relates to camel's _______ ? (back, vertebra, vertebral tendon, spinal disc, paralysis)

A-Team

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Re: What's new in Greenland?
« Reply #127 on: January 11, 2016, 02:48:25 PM »
sidd is citing:

An improved mass budget for the Greenland ice sheet
E Enderlin
Geophys. Res. Lett., 41, 2014, doi:10.1002/2013GL059010
http://onlinelibrary.wiley.com/doi/10.1002/2013GL059010/pdf (paywalled, not on ResearchGate)

That paper has already been cited an astonishing 69 times (google-search with title in quotes). In fact Enderlin et al have a follow-up discussion paper now under contentious review which would bring in 2016 thinking. I actually prefer reading the back-and-forth with reviewers to reading a final published version (if there is one here).

The bottom line of these 70 papers? That seems a moving target but can't go on forever without some consensus being reached.

www.the-cryosphere-discuss.net/9/4661/2015

RC C1763: 'Review of Xu et al. (2015)', Anonymous Referee #1, 30 Sep 2015
  AC C2487: 'Response to referee#1 and updates', Zheng Xu, 14 Dec 2015 
 
RC C1925: 'Review of Xu et al.. (2015)', Anonymous Referee #2, 23 Oct 2015
  AC C2489: 'Response to referee#2 and updates', Zheng Xu, 14 Dec 2015
 
RC C2128: 'suggestions to improve clarity of GRACE vs IOM comparison', Anonymous Referee #3, 03 Nov 2015
  AC C2491: 'Response to referee#3 and updates', Zheng Xu, 14 Dec 2015
 
EC C2132: 'Major revisions required', Etienne Berthier, 03 Nov 2015
  AC C2493: 'rebuttal of the TCD paper " Improved GRACE regional mass balance estimates of the Greenland Ice Sheet cross-validated with the input-output method "', Zheng Xu, 14 Dec 2015

AbruptSLR

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Re: What's new in Greenland?
« Reply #128 on: January 18, 2016, 09:47:19 PM »
The linked (open access) reference discusses the use of GRACE to evaluate ice flow sensitivity in Greenland to climate change:

Schlegel, N.-J., Wiese, D. N., Larour, E. Y., Watkins, M. M., Box, J. E., Fettweis, X., and van den Broeke, M. R: Application of GRACE to the evaluation of an ice flow model of the Greenland Ice Sheet, The Cryosphere Discuss., doi:10.5194/tc-2015-224, in review, 2016.

http://www.the-cryosphere-discuss.net/tc-2015-224/


Abstract. Quantifying the Greenland Ice Sheet’s future contribution to sea level rise is a challenging task that requires accurate estimates of ice flow sensitivity to climate change. Forward models of ice flow dynamics are promising tools for estimating future ice sheet behavior, yet confidence is low because evaluation of historical simulations is so challenging due to the scarcity of highly-resolved (spatially and temporally) continental-wide validation data. Recent advancements in processing of Gravity Recovery and Climate Experiment (GRACE) data using Bayesian-constrained mass concentration ("mascon") functions have led to improvements in spatial resolution and noise reduction of estimated monthly global gravity fields. Specifically, the Jet Propulsion Laboratory’s JPL RL05M GRACE mascon solution (GRACE-JPL) now offers an opportunity for ice sheet model evaluation within independently resolved 300 km mascons. Here, we investigate how Greenland Ice Sheet mass balance captured through observations - GRACE-JPL - differs from that simulated by the ice flow model - the Ice Sheet System Model (ISSM). For the years 2003-2012, ISSM is forced with regional climate model (RCM) surface mass balance (SMB), and resulting mass balance is directly compared against GRACE-JPL within individual mascons. Overall, we find good agreement in the Northeast, Southwest, and the interior of the ice sheet, where mass balance is primarily controlled by SMB. In the Northwest, seasonal amplitudes match well, but trends in ISSM are muted relative to GRACE-JPL. In the Southeast, GRACE-JPL exhibits larger seasonal amplitude than that predicted by SMB while simultaneously having more pronounced trends. These results indicate that discrepancies in the Northwest are controlled by changes in ice dynamics that are not currently modeled by ISSM, i.e. transient processes driven by ice sheet hydrology and ice-ocean interaction, while discrepancies in the Southeast are controlled by a combination of these missing dynamics and errors in modeled SMB. Along the margins, we find that transient dynamics are responsible for consistent intra-annual variations in regional mass balance that ultimately contribute to the steeper negative mass trends observed by GRACE-JPL. Consequently, ice-ocean interactions and hydrologically-driven processes at relatively high (monthly-to-seasonal) temporal resolutions must be considered for improving upon ice flow models.
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AbruptSLR

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Re: What's new in Greenland?
« Reply #129 on: January 23, 2016, 05:57:37 PM »
The linked (open access) reference discusses the use of GRACE to evaluate ice flow sensitivity in Greenland to climate change:

Schlegel, N.-J., Wiese, D. N., Larour, E. Y., Watkins, M. M., Box, J. E., Fettweis, X., and van den Broeke, M. R: Application of GRACE to the evaluation of an ice flow model of the Greenland Ice Sheet, The Cryosphere Discuss., doi:10.5194/tc-2015-224, in review, 2016.


The process cited in the open access paper referenced below, should work well with the reference cited in Reply #128 (note overlap of Fettweis in the authorship)

Navari, M., Margulis, S. A., Bateni, S. M., Tedesco, M., Alexander, P., and Fettweis, X.: Feasibility of improving a priori regional climate model estimates of Greenland ice sheet surface mass loss through assimilation of measured ice surface temperatures, The Cryosphere, 10, 103-120, doi:10.5194/tc-10-103-2016, 2016

http://www.the-cryosphere.net/10/103/2016/

Abstract. The Greenland ice sheet (GrIS) has been the focus of climate studies due to its considerable impact on sea level rise. Accurate estimates of surface mass fluxes would contribute to understanding the cause of its recent changes and would help to better estimate the past, current and future contribution of the GrIS to sea level rise. Though the estimates of the GrIS surface mass fluxes have improved significantly over the last decade, there is still considerable disparity between the results from different methodologies (e.g., Rae et al., 2012; Vernon et al., 2013). The data assimilation approach can merge information from different methodologies in a consistent way to improve the GrIS surface mass fluxes. In this study, an ensemble batch smoother data assimilation approach was developed to assess the feasibility of generating a reanalysis estimate of the GrIS surface mass fluxes via integrating remotely sensed ice surface temperature measurements with a regional climate model (a priori) estimate. The performance of the proposed methodology for generating an improved posterior estimate was investigated within an observing system simulation experiment (OSSE) framework using synthetically generated ice surface temperature measurements. The results showed that assimilation of ice surface temperature time series were able to overcome uncertainties in near-surface meteorological forcing variables that drive the GrIS surface processes. Our findings show that the proposed methodology is able to generate posterior reanalysis estimates of the surface mass fluxes that are in good agreement with the synthetic true estimates. The results also showed that the proposed data assimilation framework improves the root-mean-square error of the posterior estimates of runoff, sublimation/evaporation, surface condensation, and surface mass loss fluxes by 61, 64, 76, and 62 %, respectively, over the nominal a priori climate model estimates.

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ms

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Re: What's new in Greenland?
« Reply #130 on: February 03, 2016, 05:55:09 PM »
I just saw this news (in danish).
http://videnskab.dk/miljo-naturvidenskab/oprab-til-alle-laenestolsforskere-esa-frigiver-satellitdata-over-gronland


A call to armchair-scientists, that ESA has launched a new home-page with data on the Greenland Ice sheet.

http://esa-icesheets-cci.org/

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Re: What's new in Greenland?
« Reply #131 on: February 03, 2016, 07:54:34 PM »
Make that http://esa-icesheets-cci.org/ as the 'h' didn't make it into the url.

sidd

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Re: What's new in Greenland?
« Reply #132 on: February 05, 2016, 12:08:42 AM »
MacGregor(2016) doi:10.1126/science.aab1702 "Holocene deceleration of the Greenland Ice Sheet"

indicates that a la Bamber in Antarctica, GRIS interior is also thickening. The MacGregor paper led to to a nice paper by the Paterson in 1991, and thence to a nice paper by the Alley in 1986 ... whereupon i ran out of time, so sad.

sidd

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Re: What's new in Greenland?
« Reply #133 on: February 05, 2016, 05:17:25 PM »
The article is an important follow-up on the MacGregor 2015 digest of Greenland isochrons. The illustrations are available in high resolution pngs from the UT press release, which also gives a good account of the paper.

http://www-udc.ig.utexas.edu/external/joemac/publications.html free full text
http://science.sciencemag.org/highwire/filestream/673104/field_highwire_adjunct_files/0/MacGregor.SM.pdf supplemental details
http://science.sciencemag.org/content/351/6273/562 paywalled commentary by CS Hvidberg
http://news.utexas.edu/2016/02/04/scientists-map-movement-of-greenland-ice-sheet-over-time-0
http://williamcolgan.net/blog/?p=247

Ouch: they had this ready about the same time as the isochron paper came out. Ten months in review is too long.
    Received for publication 23 March 2015.
    Accepted for publication 7 January 2016.

AUSTIN, Texas — Scientists have created the first paleo-velocity map that shows how the Greenland Ice Sheet has moved over time, revealing that ice in the interior is moving more slowly toward the edges than it has during the past 9,000 years.

Researchers said the findings don’t change the fact that the ice sheet is losing mass overall and contributing to sea level rise.

Along Greenland’s periphery, many glaciers are rapidly thinning. However, the vast interior of Greenland is slowly thickening.

The authors identified three causes for deceleration. First is that snowfall rates were generally higher during the past 9,000 years, second is the slow stiffening of the ice sheet over time, and third is the collapse of an ice bridge that used to connect Greenland’s ice across the Nares Strait to that of nearby Ellesmere Island. Of most interest were the last two.

“Like many others, I had in mind the ongoing dramatic retreat and speedup along the edges of the ice sheet, so I’d assumed that the interior was faster now too. But it wasn’t,” said MacGregor.

“The ice that formed from snow that fell in Greenland during the last ice age is about three times softer than the ice being formed today,” according to co-author William Colgan.

Because of this difference, the ice sheet is slowly becoming stiffer. As a consequence, the ice sheet is flowing more slowly and getting thicker over time. This effect is most important in southern Greenland, where higher snowfall rates have led to rapid replacement of ice from the last glacial period with more modern Holocene ice.

“But that didn’t explain what was happening elsewhere in Greenland, particularly the northwest, where there isn’t as much snowfall, so the stiffening effect isn’t as important,” said MacGregor.

The explanation of deceleration in the northwest lies in the collapse 10,000 years ago of an “ice bridge” across Nares Strait, which used to connect Greenland’s ice to that on Ellesmere Island. The collapse of the ice bridge at the end of the last ice age led to acceleration in the northwest, but the ice sheet has since returned to a slower pace.

“We’re saying that recent increases in snowfall do not necessarily explain present-day interior thickening,” said Colgan. “If you’re using a satellite altimeter to figure out how much mass Greenland is losing, you’re going to get the answer slightly wrong unless you account for these very long-term signals that are evident in its interior.”
« Last Edit: February 05, 2016, 09:13:43 PM by A-Team »

A-Team

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Re: What's new in Greenland?
« Reply #134 on: February 05, 2016, 08:54:52 PM »
The authors are going to keep us busy with 4 other related papers In various stages of publication:

Reeh thickening: Ongoing deglacial stiffening of the Greenland Ice Sheet
W Colgan, JA MacGregor, SB Simonsen and KK Kjeldsen
Geophysical Research Letters (unavailable at this time)
http://williamcolgan.net/blog/?p=247

A synthesis of the thermal state of the bed of the Greenland Ice Sheet
JA MacGregor, MA Fahnestock, GA Catania, A Aschwanden, GD Clow, W.T. Colgan, S.P. Gogineni, M. Morlighem, S.M.J. Nowicki, J.D. Paden, S.F. Price and H. Seroussi
Journal of Geophysical Research Earth Surface (unavailable at this time)
http://ig.utexas.edu/2015/12/09/utig-at-agu/
https://cires.colorado.edu/news/events/events/cryospheric-and-polar-processes-seminar2/?eID=380

Annual Greenland accumulation rates (2009-2012) from airborne snow radar
LSKoenig, A Ivanoff, PM Alexander, JA MacGregor, X Fettweis, B Panzer, JD Paden, RR Forster, I Das, JR McConnell, C Leuschen and P Gogineni
Cryosphere Discussions
http://wwwthe-cryosphere-discussnet/tc-2015-211/

Deep radiostratigraphy of the East Antarctic plateau: connecting Dome C and Vostok ice core sites
MGP Cavitte, DD Blankenship, DA Young, DM Schroeder, F Parrenin, E Le Meur, JA MacGregor and MJ Siegert
Journal of Glaciology (accepted for 2016 #2915; unavailable at this time)
https://earth.stanford.edu/radio-glaciology/radar-sounder-data-analysis

sidd

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Re: What's new in Greenland?
« Reply #135 on: February 05, 2016, 09:01:52 PM »
I shall watch JGR for the digest of thermal state of GIS bed, that seems important to understand.

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Re: What's new in Greenland?
« Reply #136 on: February 06, 2016, 01:15:43 PM »
watch JGR for the digest of thermal state of GIS bed, that seems important to understand.

Right. That and the status of basal till are the missing pieces. MacGregor 2016 above only went down to the 9000 kyr isochron which might be only the top quarter of ice thickness in central Greenland; MacGregor 2015a had no widespread isochrons to work with below 91 kyr and used a depth-age formula to locate Eemian. That paper deliberately sidestepped Greenland's basal deformations.

I was not thrilled with MacGregor 2015b per se but it likely lays the technical groundwork for the bed thermal synthesis paper we're awaiting (which will also sidestep the major deformation areas but probably still trip over the cryptic ones). They cannot get at till with radar yet seismic is terribly restricted with no prospects for islandwide coverage.

Radar attenuation and temperature within the Greenland Ice Sheet
JA MacGregor, J Li, JD Paden, GA Catania, GD Clow, MA Fahnestock, SP Gogineni, RE Grimm, M Morlighem, S Nandi, H Seroussi and DE Stillman
Journal of Geophysical Research Earth Surface, 120, 983–1008 2015b
http://www-udc.ig.utexas.edu/external/joemac/pdf/MacGregor_2015_JGR_2.pdf

'Reeh thickening' plays an important role in the current paper. That has not surfaced before in the forums though it is covered in early editions of Cuffey and Paterson's textbook, not so much in the current. Oddly we were just talking about Paterson's 'soft ice' of the last glacial and legacy effects of temperate paleo-firn described by Luethi around Swiss Camp a few days ago in the NEEM forum.

It's all part of 'ice sheets have long memories'. It simply doesn't work to pull an era like the Eemian out of its context, saying the CO2 and solar were such-and-such yet this that and other didn't happen so let's all drive Hummers. See https://en.wikipedia.org/wiki/Hysteresis

The second image from MacGregor 2016 shows ice thickness in Greenland 9000 years ago. Here snow and firn are converted to their ice thickness equivalent. The data for this map were determined MacGregor 2015. The authors deserve high marks both for high quality images (import into ImageJ for full resolution) and public access to them.

MacGregor 2016: The millennial-scale evolution of GrIS rheology can partly explain this response. Ice deposited during the last glacial is approximately three times less viscous (“softer”) than ice deposited during the Holocene1. To explain observations of subtle thickening (1 cm per) at DYE-3, Reeh2 hypothesized that, as softer LGP ice is buried by stiffer Holocene ice, the GrIS interior will thicken (hereafter referred to as “Reeh thickening”).

Reeh thickening is distinct from that induced by increased accumulation rate, decreased rate of firn densification, post LGP isostatic adjustment, or horizontal deceleration due to other poorly constrained mechanisms (e.g., increasing basal friction). By continuity, it follows that this transient viscosity change would also have caused the GrIS interior to decelerate after deglaciation....

Corroborating and expanding upon Reeh’s original hypothesis, we suggest that downward advection of the LGP-Holocene transition partly explains the subtle deceleration we infer in the interior of the southern GrIS. The dynamic consequences of this effect are predicted to have in creased nonlinearly within the GrIS interior during the Holocene and to continue for tens of millennia.


1. Why ice-age ice is sometimes “soft”
WSB Paterson 1991 (doi:10.1016/0165-232X(91)90058-O  cited 121 times)  full text still paywalled

Data on the mechanical properties, texture, fabric, and impurity content of ice deposited during the last glaciation are reviewed. The conclusions are: (1) Chloride and possibly sulphate ions, in concentrations high relative to those in Holocene ice, impede grain-boundary migration and grain growth so that the crystals remain small. (2) Such ice, in shear parallel to the ice-sheet bed, develops a strong, near-vertical, single-maximum fabric. (3) This fabric favours further deformation and this, in turn, further strengthens the fabric and keeps the crystals small. (4) This is why the strain rate in ice-age ice, in simple shear, is some 2.5 times that in Holocene ice at the same stress and temperature. (5) Ice-age ice under other stress systems, such as ice in roughly the upper 60% of the ice thickness, in bedrock hollows, at a stationary ice divide, in ice streams and in ice shelves, will not have enhanced flow. (6) An anisotropic flow relation must be used for detailed modelling of polar ice sheets.

2. Was the Greenland ice sheet thinner in the late Wisconsinan than now?
Niels Reeh
Nature 317, 797 - 799 (31 October 1985); doi:10.1038/317797a0
http://www.nature.com/nature/journal/v317/n6040/abs/317797a0.html full text still paywalled

Ice of Wisconsinan origin which constitutes the basal layers of the ice caps in arctic Canada and Greenland flows three to four times more readily than the Holocene ice above. A model based on simple ice sheet profile theory is set up for the thickness response of the interior ice sheet regions to the progressive thinning of this soft layer. The model is applied to calculate the thickness response of the Greenland ice sheet at the locations Dye 3 and Crête, and of the Devon Island ice cap in arctic Canada. It is concluded that the mechanism contributes significantly to the thickness change of the Greenland ice sheet, presently at a rate of about 1 cm yr−1 and that this rate of change will persist potentially over thousands of years to come. As regards the Devon Island ice cap, most of the estimated 15% thickness increase has already been accomplished. A further consequence is that in the late Wisconsinan, ice thicknesses of the interior regions of the Greenland ice sheet were likely to have been no greater and possibly even less than at present, in spite of the larger geographical extent of the ice sheet. It is argued that the glacial-interglacial cycles of accumulation rate and ice temperature are likely to enhance this ice thickness variation.
« Last Edit: February 06, 2016, 03:02:51 PM by A-Team »

Sigmetnow

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Re: What's new in Greenland?
« Reply #137 on: February 15, 2016, 04:07:03 PM »
Hurricane force storm developing just south of Greenland.  Very strong flow of warm air with a second, intensifiying system.

https://www.facebook.com/NWSOPC/posts/1007203242671740

Bottom image is surface air temperature with wind direction and speed.
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AbruptSLR

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Re: What's new in Greenland?
« Reply #138 on: February 29, 2016, 06:45:10 PM »
The linked reference documents a positive feedback mechanism between Arctic sea-ice loss and increased surface melting of the Greenland Ice Sheet:

Jiping Liu, Zhiqiang Chen, Jennifer Francis, Mirong Song, Thomas Mote and Yongyun Hu (2016), "Has Arctic sea-ice loss contributed to increased surface melting of the Greenland ice sheet?", Journal of Climate, doi: http://dx.doi.org/10.1175/JCLI-D-15-0391.1

http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-15-0391.1

Abstract: "In recent decades, the Greenland ice sheet has experienced increased surface melt. However, the underlying cause of this increased surface melting and how it relates to cryospheric changes across the Arctic remain unclear. Here we show that an important contributing factor is the decreasing Arctic sea ice. Reduced summer sea ice favors stronger and more frequent occurrences of blocking-high pressure events over Greenland. Blocking highs enhance the transport of warm, moist air over Greenland, which increases downwelling infrared radiation, contributes to increased extreme heat events, and accounts for the majority of the observed warming trends. These findings are supported by analyses of observations and reanalysis data, as well as by independent atmospheric model simulations using a state-of-the-art atmospheric model that is forced by varying only the sea ice conditions. Reduced sea ice conditions in the model favor more extensive Greenland surface melting. We find that a positive feedback between the variability in the extent of summer Arctic sea ice and melt area of the summer Greenland ice sheet, which affects the Greenland ice sheet mass balance. This linkage may improve the projections of changes in the global sea level and thermohaline circulation."
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Laurent

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Re: What's new in Greenland?
« Reply #139 on: March 04, 2016, 11:41:25 AM »
Greenland's ice melt accelerating as surface darkens, raising sea levels
http://www.theguardian.com/environment/2016/mar/03/greenland-ice-sheet-melting-global-warming-feedback-loop

The research, published in the European Geosciences Union journal The Cryosphere, looked at satellite data from 1981 to 2012. The drop in reflectivity from 1996 was probably due to a change in atmospheric circulation that favoured warmer, moist air from the south. The scientists found there was no significant increase in soot from forest fires since 1997 to explain the darkening of the surface.

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Re: What's new in Greenland?
« Reply #140 on: March 06, 2016, 03:38:10 AM »
It looks like Sentinel 2A will will finally acquire images from Greenland. It will start on the 12th March with Greenland's east coast and the south-centre on the 14th of March.

I can't wait to finally get High-res images  :D

The Acquisition Plans can be downloaded here:
https://sentinel.esa.int/web/sentinel/missions/sentinel-2/acquisition-plans

The final images will be available at:
https://scihub.copernicus.eu/

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Re: What's new in Greenland?
« Reply #141 on: March 06, 2016, 02:00:58 PM »
finally get Sentinel 2igh-res images... Acquisition Plans can be downloaded here:
https://sentinel.esa.int/web/sentinel/missions/sentinel-2/acquisition-plans
Yes, Sentinel 2 will be a great addition -- some of the longer wavelength bands are more interesting than those of Landsat. We don't know yet how useful these will be on the Greenland ice sheet. The 10 m resolution will also be a big plus for marine terminating glaciers. That link is a big improvement over slow, futile searches at their data portal.

My sense is that the Greenland glaciological research community has not been able to communicate their scientific interests to the Sentinel 2 committee. (The ESA overall is quite hostile to end-user feedback.) I could not imagine worse orbital choices than the ones that they are making available initially. What exactly do they expect to see in early March in the center of the ice sheet with visible and near IR?

Tealight

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Re: What's new in Greenland?
« Reply #142 on: March 06, 2016, 03:16:07 PM »
(The ESA overall is quite hostile to end-user feedback.) I could not imagine worse orbital choices than the ones that they are making available initially. What exactly do they expect to see in early March in the center of the ice sheet with visible and near IR?

Yeah their products are very unfriendly to small end users. I did send them an email a while ago, suggesting to allow downloads of individual tiles instead of these huge stripes. Most of us are just interested in a few square kilometer and not half of the continent. This could reduce the download size from 7-10Gb to just 1Gb, which also reduces the load of their servers.

Laurent

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Re: What's new in Greenland?
« Reply #143 on: April 01, 2016, 01:16:00 PM »
More Greenland melt under cloudy conditions
http://jasonbox.net/more-greenland-melt-under-cloudy-conditions/

Not an April 1 joke: Our new study reveals that under warm and wet conditions, atmospheric heat can melt the lower 1/3 of the Greenland ice sheet more than under sunny conditions. This was especially so during the 2012 heat wave when a record warm North America loaded the air with heat and moisture that drifted to Greenland.

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Re: What's new in Greenland?
« Reply #144 on: April 01, 2016, 04:22:57 PM »
Yeah ESA products are very unfriendly to small end users. I did send them an email suggesting to allow downloads of individual tiles  . Most of us are just interested in a few square kilometer and not half of the continent.

Just so it is on this thread too, little people can now grab just band 4 (red) with most of the benefit but none of the fou fou. It is 130 MB rather than 8300 MB which is 1.5%. Still, the micro preview is useless and does not indicate if your site is clouded over (scene percent is unsatisfactory). It is truly mystifying why they worry over another 100 KB in a multi GB context.

After much wrestling with their crazy-long file names that should have been in metadata like Landsat, the download drops the scene's date, time and location! So over time you will accumulate many dozen B04.jp2's that you better manually fix at the time of acquisition.

Once having drilled into the AWS file system to say the Jakobshavn calving front, it appears possible to keep the tab open and check daily or so for new scenes, then do a quickie download of band 1 (4 MB) for a cloud check or more ambitiously band 5 (33 MB) before bothering with the 10 m bands (2,3,4,8). It takes three bands to make 'true color', not of much use on ice sheets unless there's melt. Band 4 has a better histogram in shadowed regions.

These AWS bands are 16-bit jpeg2000 (jp2) but they will unfortunately open in most desktop software, without warning, as 8-bit. However all initial operations (contrast stretching, gamma, rotation, re-sizing) need to be done at 16-bit. The attached image shows the degradation of the image/histogram when processed at 8-bit.

It is very expensive to design, build, launch and support satellites, so it makes no sense to discard image quality by sloppy processing at the very end. Around here we say, "you don't put a two dollar saddle on a million dollar mule."

http://sentinel-s2-l1c.s3-website.eu-central-1.amazonaws.com/#tiles/22/W/EB/2016/3/26/0/
http://forum.arctic-sea-ice.net/index.php/topic,154.msg72793.html#msg72793
« Last Edit: April 01, 2016, 04:30:33 PM by A-Team »

Martin Gisser

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Re: What's new in Greenland?
« Reply #145 on: April 02, 2016, 01:03:41 AM »
After much wrestling with their crazy-long file names that should have been in metadata like Landsat, the download drops the scene's date, time and location! So over time you will accumulate many dozen B04.jp2's that you better manually fix at the time of acquisition.
Wow. Sounds like Microsofty stone age. What system is doing this?
(Your reply could help me deciding: I'm thinking of getting me some new Computer thing. But I'm so thoroughly fed up with stupid design and never fixed elementary bugs. I've meanwhile quit on German IT industry. Maybe I even quit serious private useage, because the stuff seems getting hopeless. (What I'm using right now is even worse than Windoze 93 on an Intel 486. Feels not even like a Turing machine anymore...))

(...)
Around here we say, "you don't put a two dollar saddle on a million dollar mule."
Seems like classic business administration going on. They can formally work numbers, but lack any understanding. The numbers are in tidy boxes. Outside those boxes the numbers have no dimension, no strategical or any other value. Billions in this box, peanuts in the other. The good German MBA keeps them strictly separate, for anything else would require creative thinking. This is taboo when dealing with money numbers. -- Heck, why a two dollar saddle? Lets do it without because the corresponding box is almost empty. -- I've seen Software sellers trying to do without software engineers.


« Last Edit: April 02, 2016, 01:13:17 AM by Martin Gisser »
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AbruptSLR

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Re: What's new in Greenland?
« Reply #146 on: April 04, 2016, 03:47:12 AM »
Rignot et al (2016) provides news measurements that many marine-terminating glaciers in Greenland has deeper water depths than previously realized; which could contribute to the relatively early acceleration of some of these glaciers with continued global warming:

E. Rignot, I. Fenty, Y. Xu, C. Cai, I. Velicogna, C. Ó Cofaigh, J. A. Dowdeswell, W. Weinrebe, G. Catania & D. Duncan (25 March 2016), "Bathymetry data reveal glaciers vulnerable to ice-ocean interaction in Uummannaq and Vaigat glacial fjords, west Greenland", Geophysical Research Letters, DOI: 10.1002/2016GL067832


http://onlinelibrary.wiley.com/doi/10.1002/2016GL067832/full

Abstract: "Marine-terminating glaciers play a critical role in controlling Greenland's ice sheet mass balance. Their frontal margins interact vigorously with the ocean, but our understanding of this interaction is limited, in part, by a lack of bathymetry data. Here we present a multibeam echo sounding survey of 14 glacial fjords in the Uummannaq and Vaigat fjords, west Greenland, which extends from the continental shelf to the glacier fronts. The data reveal valleys with shallow sills, overdeepenings (>1300 m) from glacial erosion, and seafloor depths 100–1000 m deeper than in existing charts. Where fjords are deep enough, we detect the pervasive presence of warm, salty Atlantic Water (AW) (>2.5°C) with high melt potential, but we also find numerous glaciers grounded on shallow (<200 m) sills, standing in cold (<1°C) waters in otherwise deep fjords, i.e., with reduced melt potential. Bathymetric observations extending to the glacier fronts are critical to understand the glacier evolution."
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A-Team

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Re: What's new in Greenland?
« Reply #147 on: April 04, 2016, 11:37:25 PM »
This being Rignot's 4th substantive article for 2016 -- it is a full-time job just reading them. This one is the overview of west-central Greenland glaciers; we've been discussing the expanded version of Store Glacier over on that and the Jakobshavn forums. Basically these glaciers cannot be meaningfully modeled without this better data.

The article doesn't say who did the extraordinary graphics. I have not had a chance to see what is in th 100 m geotiff file  available at ess.uci.edu/group/erignot/node/1535

Atmospheric Chemistry and Physics Ice melt, sea level rise and superstorms: evidence from paleoclimate data, climate modeling, and modern observations that 2 °C global warming could be dangerous
James Hansen · Makiko Sato · Paul Hearty · Reto Ruedy · Maxwell Kelley · Valerie Masson-Delmotte · Gary Russell · George Tselioudis · Junji Cao · Eric Rignot · Isabella Velicogna ..

Bathymetry data reveal glaciers vulnerable to ice-ocean interaction in Uummannaq and Vaigat glacial fjords, West Greenland.
E. Rignot · I. Fenty · Y. Xu · C. Cai · I. Velicogna · C. Ó Cofaigh · J. A. Dowdeswell · W. Weinrebe · G. Catania · D. Duncan
 Geophysical Research Letters

A constitutive framework for predicting weakening and reduced buttressing of ice shelves based on observations of the progressive deterioration of the remnant Larsen B Ice Shelf
Chris Borstad · Ala Khazendar · Bernd Scheuchl · Mathieu Morlighem · Eric Larour · Eric Rignot

Modeling of Store Gletscher's calving dynamics, West Greenland, in response to ocean thermal forcing
M. Morlighem · J. Bondzio · H. Seroussi · E. Rignot · E. Larour · A. Humbert · S. Rebuffi

AbruptSLR

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Re: What's new in Greenland?
« Reply #148 on: April 05, 2016, 01:11:26 AM »
This being Rignot's 4th substantive article for 2016 -- it is a full-time job just reading them.

For those who do not need another full-time job, Rignot provides a nice overview of his many faceted (but interconnected) interests in the linked video of his AGU Dec 2015 presentation:

https://www.youtube.com/watch?v=3p9uRxX95f4
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

sidd

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Re: What's new in Greenland?
« Reply #149 on: April 06, 2016, 12:56:17 AM »
"The reconstruction of subglacial thermal conditions suggests that about half of the north-central GIS is now resting on a thawed bed ... "

Nice paper, I attach Fig. 3. Illuminates the question "Why NEGIS ?" and the basal melt in NEEM, and perhaps some basal melt refreeze structure. Also, now i have a strange urge to look at the interior pics of Greenland from Sentinel ...

doi: 10.1038/NGEO2689