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Author Topic: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland  (Read 794022 times)

TenneyNaumer

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1200 on: January 21, 2016, 05:44:12 AM »
You know, there is still some serious mass balance loss going on today in almost the same locations.  This can't be normal in January.  Or rather, this can't have been normal in January.  We are in the no-analogue world.

Jim Hunt

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1201 on: January 21, 2016, 10:09:07 AM »
It is actually raw Brightness Temperature on Band 32 (11.770-12.270 µm)

Where can one lay one's hands on band 32 data? My first port of call is Worldview, which seems to show only band 31. This is from the 14th.

P.S. I added a version with a severely squashed palette:
« Last Edit: January 21, 2016, 12:37:32 PM by Jim Hunt »
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Jim Hunt

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1202 on: January 21, 2016, 10:17:35 AM »
Why don't we just assume that a strong storm blew out of the Fjord

As you may have gathered, that is currently my default position! What hard evidence is there to the contrary? Quoting Mauri:

Quote
We had questioned if the plume had any sediment origin initially. Its widespread nature and persistence suggested not.  Aeration was another suggestion.  Jason Box suggests that the opaque water plume leading to the developing polyna is driven by the strong offshore winds and the opaque whitening is capillary waves on the sea surface.

Keep an eye on the bottom right corner of this animation to see what AMSR2 reveals:
« Last Edit: January 21, 2016, 12:07:19 PM by Jim Hunt »
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A-Team

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1203 on: January 21, 2016, 02:27:17 PM »
The image below is a alternatively processed version of Jim H's Aqua 14 Jan 16 image above that brings out contrast patterns within the fjord and Diskp Bay (whose physical interpretation is up for grabs).

Strong wind, somehow hurricane related, works for me. It seems though 'strong' could be put into better context by examining historical weather records. Was this event unusual for peak wind speed, or strong wind x duration on a one year scale? Fifty year scale?

Wind direction of east to west (down-fjord) means a longer reach and so an impact that builds. A very common weather pattern is the wind diverted around Disko Island (1320+ m peaks) causing very strong emergent jets in the Jakobshavn and Uummanaq fjord systems. The 4th image shows peak WPDs on the 12th. I got these by pecking largish looking numbers around on the nullschool graphic for the biggest numbers rather than pulling the actual maximums from nullschool's  sources (GFS, NCEP, US NWS).

Nullschool offers something called WPD or 'instantaneous wind power density' of interest to wind turbine siting. I backed up their calendar date through to Jan 1 and captured the WPD levels at the site shown (green circle) for 1000 hPa as WPD is not provided for Sfc (surface) out to the 20th. This could be animated for two weeks centered around the event. For what it's worth, the big wind day for January was the 12th.

To animate nullschool, say over two weeks wind and WPD at 5 atmospheric isobars, I looked at the underlying javascript to see if the overly large controller could be down-sized so it interfered less with the globe display. If you do that, the issue is that the scene has to viewed online to get the js to download the data generating the display to your drive. We could pursue this further over at Developer's Corner if people are interested (though it might be better just to request a fix from C Boccario).

Alternatively, it is feasible in the situation here (14 days x 2 overlays x 5 isobars = 140 whole-window screenshots followed by batch mode cropping and resizing in Gimp) to just 'do it' in ten minutes or so. For say the surface winds over the course of a year Jakobshavn to Uummannaq, script a crawl. Some people would script an all-purpose crawl through all possible combos and then discard the ones that weren't specific to the immediate project, Or serve the massive pre-compute as a database resource. It would save some wear and tear to build a controller interface that ouput a fit-for purpose crawl.
« Last Edit: January 22, 2016, 12:42:23 PM by A-Team »

Andreas Muenchow

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1204 on: January 21, 2016, 07:24:27 PM »
@ Jim Hunt:

1. Beautiful movie of the ASMR data that actually made me think of a second, perhaps more dominant process to flush out fjords ... strong winds ALONG the Greenland coastline will move surface ice and water OFF-SHORE perpendicular to the winds as a result of balance between friction (surface wind/ice stress) and the Coriolis force (earth rotation). Note that the ice along the entire Greenland coast in the movie moves off-shore about the same time that we see the large plume off Disko Bay. For this "upwelling circulation" we will need an atmospheric low pressure system in the center of Baffin Bay. Such a low pressure system relative to the high pressure over the Greenland ice sheet will result in a large down-glacier wind as well. At the 1-10 km scales of glaciers and fjords, the latter process often dominates, however, at the larger 10-100 km scale of coastal waters, the former process dominates.

2. I download (and subsequently process) all available 36 MODIS channels via wget at NASA's ocean data site:

wget -r -nd -l1 --no-check-certificate http://oceandata.sci.gsfc.nasa.gov/cgi/getfile/$name.L0_LAC.bz2

where the variable $name is a text string such as T2016015151000 for a Terra image from 2016, year day 015 at 15:10 UTC. The LAC indicates 1-km data for all 36 channels while a HKM would represent 7 channels at 500-m and QKM represents 2 channels at 250-m resolutions. More details, codes, and pointers are at

http://muenchow.cms.udel.edu/MODIS/index.html
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A-Team

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1205 on: January 21, 2016, 08:34:26 PM »
Quote
I do not think that convection of an entire fjord and adjacent coastal areas are possible given the very strong vertical stratification that dominates most fjords in Greenland
Probably the case though there's almost no CTD data for stratification or bathymetry for that matter in the Jakobshavn fjord cited in the three most recent Holland papers. They've been reduced to dives of instrumented seals and Inuit anecdotes about lengths of fishing line needed to catch flounders. Non-unique AirGrav inversions? Let's not go there.

Uummannaq is much better off but only due to the 2015 papers of Rignot, but those are one-off casts and not even a seasonal time series. Large and frequent backwards rolling calving events, as well as copious seasonal meltwater jetting out the bottom surely affect stratification more at Jakobshavn than at these second-tier glaciers. However we have no idea where the melt season actually left things.

There's convective mixing and then there's turbulent mixing and just plain old mixing. The issue with moving lots of very bulky icebergs seen in Sentinel down-fjord raises the question of where the replacement water is coming from. Some of these icebergs are well over 100 m in height, reaching reach a km or so below the surface. We are talking thousands of cubic km of displaced water if these bergs are blown 70 km out to the sill.

Replacement water could just flow in from around the sides, keeping stratification in place. However the width of these bergs is not conducive to that so considerable replacement water will well up from depth. Will this denser water subsequently return quietly to its place in the water column without leaving some mark on stratification (in the absence of turbulent flow)?

Once upon a time, on a planet far far away, I worked on these very same Navier–Stokes equations in the context of an object's sedimentation velocity through a cesium chloride density gradient. Hydrodynamic drag has been a huge subject in engineering for centuries (towing barges?) or for that matter towing icebergs to LA to provide fresh water (El Nino proving a total bust).

We know a fair amount about the shape of these particular bergs (they're rectilinear slabs, initially) which greatly affects numerical modeling. However their down-fjord velocity is poorly known and unsatisfactorily bounded by satellite returns. We're not really in a position to compare before/after CTD casts for lack of befores. We learned last August that the scientific community does not maintain any records on Jakobshavn. This leaves low-resolution satellite monitoring of the fjord surface and weather reanalyses, suggesting the event will never be well-characterized observationally at depth.

With respect to the relative importance -- or even synergy -- of along-coast winds vs the sustained high energy along-fjord bursts observed on the 7th and 12th, again we need to look at rarity of this event vs frequency of the respective meteorological conditions. Alternatively such events might not be so rare but instead conditions were just favorable this time around for observing the effects.

Forget the Azores, western Greenland's big day with Hurricane Alex was earlier, on the 12th (according to 30 days of GFS at nullschool). The 7th was also noteworthy in Uummannaq Bay but for reasons unrelated to the hurricane.
https://en.wikipedia.org/wiki/Hurricane_Alex_(2016)
« Last Edit: January 22, 2016, 12:58:07 PM by A-Team »

Jim Hunt

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1206 on: January 21, 2016, 09:10:25 PM »
Beautiful movie of the ASMR data that actually made me think of a second, perhaps more dominant process to flush out fjords ... strong winds ALONG the Greenland coastline will move surface ice and water OFF-SHORE perpendicular to the winds as a result of balance between friction (surface wind/ice stress) and the Coriolis force (earth rotation).

Thanks for your kind words. I'll need to think about the mechanism you describe for a while though, being a bear of very little brain!

Thanks too for the MODIS info. I've taken the liberty of reproducing it over on the Developers Forum, where hopefully it will be easier to find than in here:

http://forum.arctic-sea-ice.net/index.php/topic,1468.0.html
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Iceismylife

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1207 on: January 21, 2016, 09:41:06 PM »
...

@Johnm33: I am not sure I can follow this. Why should there be a giant lake in the Greenland basin? To all I know that is almost 100% ice there.
Melt water lakes drain to the bedrock.  So in the melt zone you should have fresh water on bedrock and sediments.  Not all of that would nicely find its way to the sea in an orderly fashion.  With the calving face retreating you could have an unplugging of the drainage system.

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1208 on: January 21, 2016, 09:57:57 PM »
Plinius "@Johnm33: I am not sure I can follow this. Why should there be a giant lake in the Greenland basin? To all I know that is almost 100% ice there."
 I guess I'm suggesting that we have to consider the possibility that some of the areas showing mass loss may have reached the point where surface melt no longer freezes when it hits the bedrock, and that since it won't support the ice it migrates slowly either into the central basin, where it may yet freeze, or to the coast, at unseasonal times. The drainage basin of Jakobshavn looks a particularly likely candidate.

compare to http://sites.uci.edu/morlighem/files/2014/11/products_bed.jpg once there's a disconnect between ice and bedrock tides and high pressure systems will influence flows.
What are the odds that winds and tides both played some part in this event. Lets move over to http://forum.arctic-sea-ice.net/index.php/topic,1465.msg68618.html#msg68618 .

LRC1962

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1209 on: January 22, 2016, 12:17:18 AM »

@Johnm33: I am not sure I can follow this. Why should there be a giant lake in the Greenland basin? To all I know that is almost 100% ice there.
Check this: http://www.dailykos.com/story/2015/9/22/1421761/-Sudden-drainage-via-massive-chasm-of-Subglacial-lakes-in-Greenland-described-as-catastrophic
You will find that indeed Greenland subglacial lakes do exist, but they also can drain very fast and then refill.
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Laurent

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1210 on: January 22, 2016, 10:22:23 AM »
I wonder if this "katabatic" winds or pressure systems (high or low) may put some pressure on these internal lakes ? Does the ice is compressible (slightly) so the top surface above the lakes would put a pressure on the lakes below ?

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1211 on: January 22, 2016, 10:56:29 AM »
I believe this is negligible. The weight of the ice and the internal pressure is so much higher than any changes in atmospheric pressure.

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1212 on: January 22, 2016, 11:13:17 AM »
Your certainly right if you think of a column of ice and the lake below, but if the lake is not far from the surface (10, 30 meters) and stretch is volume on a big surface compare to the surface above...? especially if the ice is more fragile due to firn over-soaked by water.

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1213 on: January 22, 2016, 07:39:28 PM »
Your certainly right if you think of a column of ice and the lake below, but if the lake is not far from the surface (10, 30 meters) and stretch is volume on a big surface compare to the surface above...? especially if the ice is more fragile due to firn over-soaked by water.
That water tends to find a crack and head to the bottom.  The water on the bottom is governed by the glacial dynamics not so much the wind.

Where the surface lakes sit is in standing waves over the moving ice.

Jim Hunt

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1214 on: January 23, 2016, 12:59:07 PM »
For this "upwelling circulation" we will need an atmospheric low pressure system in the center of Baffin Bay. Such a low pressure system relative to the high pressure over the Greenland ice sheet will result in a large down-glacier wind as well.

Another piece of the puzzle? Here's the GFS 2016-01-12-06Z SLP forecast for 12:00
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Andreas Muenchow

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1215 on: January 23, 2016, 02:45:00 PM »
Whow ... those are two very strong pressure systems with the first (low-pressure) over Baffin Island and the second (high pressure) over Greenland. The winds aloft are clockwise around the High and counter-clockwise around the Low. So that gradient in the center of Baffin Bay implies a strong (geostrophic) wind from south to north aloft. Winds near the surface always veer a bit to the left of the winds aloft or, in our case from High to Low pressure.

This trashes my idea of along-shore winds causing off-shore motions of ice and surface waters, because for that to happen I need a winds that come from the north and blow along Greenland's West Coast to the south. It is the same type of "upwelling" that causes beaches along Central California and Oregon to be so cold and rich fisheries and wildlife.

If the earth's rotation is not important (it is dominant in the above arguments), then this flow from High to Low pressure is balanced by acceleration that speeds it up until bottom friction kicks in to slow it down.

So, the plot thickens. [It also shows that professors typing too fast do get things wrong ... what I need in my argument is a High in the center of Baffin Bay - not a Low - to get those coastal winds from north to south along West Greenland.]
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Andreas Muenchow

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1216 on: January 23, 2016, 02:58:40 PM »
Sorry for the double posting, but this map (it is actually a movie) suggests that the "polar vortex" (Low pressure over the Arctic Basin) split into two segments on Jan.-13 with one centered over Hudson Bay and the second over northern Norway, e.g., http://wxmaps.org/pix/NHanim.html

Edit: My weather station on Petermann Gletscher at this time had air temperatures rise to -8 C from the more usual -40 C, e.g., http://ows.udel.edu/data/test.dat with temperature in column-3 and format explained at http://ows.udel.edu/data/read.me ... I really have to pay closer attention to larger scale patterns.
« Last Edit: January 23, 2016, 03:16:30 PM by Andreas Muenchow »
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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1217 on: January 23, 2016, 05:00:20 PM »
Further to my prior Reply #1188 relating the Jakobshavn to the Byrd response to ice-bed uncoupling (including from an influx of basal meltwater), Hughes et al 2016 present a state-of-the-art discussion of such matters on the progression/acceleration of marine glacial flow/retreat with continued global warming.  The authors also relate their findings to other critical marine glaciers in both Greenland and Antarctica.  The two attached images relate ice-bed uncoupling for Jakobshavn and to the Jakobshavn Effect, respectively.

Hughes, T., Sargent, A., Fastook, J., Purdon, K., Li, J., Yan, J.-B., and Gogineni, S.: Sheet, stream, and shelf flow as progressive ice-bed uncoupling: Byrd Glacier, Antarctica and Jakobshavn Isbrae, Greenland, The Cryosphere, 10, 193-225, doi:10.5194/tc-10-193-2016, 2016


http://www.the-cryosphere.net/10/193/2016/


Abstract. The first-order control of ice thickness and height above sea level is linked to the decreasing strength of ice-bed coupling along flowlines from an interior ice divide to the calving front of an ice shelf. Uncoupling progresses as a frozen bed progressively thaws for sheet flow, as a thawed bed is progressively drowned for stream flow, and as lateral and/or local grounding vanish for shelf flow. This can reduce ice thicknesses by 90 % and ice elevations by 99 % along flowlines. Original work presented here includes (1) replacing flow and sliding laws for sheet flow with upper and lower yield stresses for creep in cold overlying ice and basal ice sliding over deforming till, respectively, (2) replacing integrating the Navier–Stokes equations for stream flow with geometrical solutions to the force balance, and (3) including resistance to shelf flow caused by lateral confinement in a fjord and local grounding at ice rumples and ice rises. A comparison is made between our approach and two approaches based on continuum mechanics. Applications are made to Byrd Glacier in Antarctica and Jakobshavn Isbrae in Greenland.



Our ice-sheet modeling approach is based on the first-order dependence of ice-sheet thickness on the strength of ice-bed coupling, such that ice 3000m high and 4000m thick at an interior ice divide can lower to 100m high and 1000m thick when ice margins become afloat, and lower further to 30m high and 300m thick at the front of calving ice shelves, a 99% reduction of ice elevations, all due to reduced ice-bed coupling. We began by quantifying ice-bed uncoupling as an increase in thawed fraction f of the bed for sheet flow, of floating fraction phi of ice for stream flow, and of unbuttressed fraction phiO of ice for shelf flow. Our treatment is holistic in the sense it provides smooth transitions from sheet flow to stream flow to shelf flow for steady-state conditions along surface flowlines.

We compared our treatment for ice sheets with two treatments based on continuum mechanics, one by Schoof and
Hindmarsh (2010) and one by Pattyn (2003). All three treatments avoided flow “laws” and sliding “laws” of dubious reliability for sheet flow. We substituted respective upper and lower yield stresses applied to cold ice over a frozen bed and to temperate ice sliding over bedrock and/or deforming till for sheet flow, with cold ice above temperate basal ice in ice streams and ice shelves. Schoof and Hindmarsh (2010) introduced “slip” and “no-slip” interfaces at the bed linked to separate deviator stress tensors that can be applied to sheet, stream, and shelf flow. Pattyn (2003) reduced basal drag as a frozen bed thaws. His approach can also be applied to sheet, stream, and shelf flow.


Our results for both Byrd Glacier and Jakobshavn Isbrae are compatible with basal buoyancy fraction phiB = phiphiO in Table 2 used to quantify a hypothetical “life cycle” of ice streams. The product of fraction phi linked to ice-bed uncoupling and fraction phiO linked to ice-shelf unbuttressing is maximized when surface meltwater floods the bed under an ice stream, and when its buttressing ice shelf shelf disintegrates. Hughes (1986) postulated these two processes, augmented by other processes, are sufficient to collapse marine portions of an ice sheet, and to that extent contribute to Termination of glaciation cycles lasting approximately 90 000 years during the Quaternary Ice Age in which we now live. He called this the Jakobshavn Effect because all the processes were active for Jakobshavn Isbrae. Contributing processes include additional surface melting when crevasses are ubiquitous, analyzed by Pfeffer and Bretherton (1987), warm ocean water entering Jakobshavn Isfjord, reported by Holland
et al. (2008) and restricted flow of outlet glaciers in curving and branching fjords like Jakobsahvn Isfjord (Pfeffer
et al., 2008).
We conclude the Jakobshavn Effect may have a long-term impact in Greenland if global warming allows these processes to migrate northward, causing successive ice streams to surge, thereby completing their life cycles. Some processes are already appearing in ice streams draining the east, west, and northwest parts of the Greenland Ice Sheet (Rignot and Kanagaratnam, 2006). Schoof (2010) shows how ongoing acceleration and thinning of Jakobshavn Isbrae reported by Joughin et al. (2014) could continue for a century. Various paths can be taken by phi and phiO in Table 2 during a life cycle, including reversals, as documented by Engelhardt and Kamb (2013) for Kamb Ice Stream. Hughes (2011) used Table 2 to determine where major Antarctic ice streams are in their life cycles today. When the Jakobshavn Effect is nearly simultaneous for many ice streams, Table 2 can be used to identify stadials and interstadials within Quaternary glaciation cycles, and to account for Terminations of cycles, all linked to global sea level (Denton et al., 1986) and the Jakobshavn Effect.


These ice streams bracket ice-bed uncoupling ranging from no surface meltwater lubricating the bed and a massive buttressing ice shelf for Byrd Glacier to massive surface meltwater lubricating the bed and an ice shelf that has recently disintegrated for Jakobshavn Isbrae.


Today, Byrd Glacier has low values of phi and phiO, but both values are substantially higher for Jakobshavn Isbrae. For Byrd Glacier we temporarily increased phi when two subglacial lakes at its head drained rapidly in 2006–2007 (Stearns and others, 2008). For Jakobshavn Isbrae, we set phiO = 1 when its buttressing ice shelf suddenly disintegrated in 2002 (Thomas, 2004).



Warming in high polar latitudes can, in principle, trigger a succession of positive feedback mechanisms called
the Jakobshavn Effect (Hughes, 1986). Buoyancy fraction phiB combines the two dominant mechanisms: reduced icebed coupling when surface meltwater floods the bed under an ice stream and reduced ice-shelf buttressing when an ice shelf disintegrates beyond the ice stream. For Greenland, the Jakobshavn Effect would move northward along the east and west coasts, affecting all calving ice streams. For Antarctica, it would affect the northernmost ice streams, which are primarily in East Antarctica, but also ice streams entering the Pine Island Bay polynya in West Antarctica (Hughes, 1987, 2011; Pingree et al., 2011)."
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AbruptSLR

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1218 on: January 24, 2016, 03:11:54 PM »
While I do not doubt that downslope winds had a major role in the recent seaward displacement of the Ilulissat Isfjord ice mélange, I note that climate change is a "wick problem" where simple answers are not always adequate; which is why I believe that a discharge of basal meltwater might have contributed to that seaward displacement (note by Muenchow's analysis the northward offshore winds [southerlies] & the Coriolis Effect should have pushed ocean currents into Ilulissat fjord thus resisting the seaward movement).

In this regard, I note that while basal meltwater seal near the grounding line of Jakobshavn may be weak and episodic, as relatively warm ice creeps (& flows like honey) the seal should regularly reform, no matter how many times the seal is temporarily broken.  The first image shows that basal meltwater leakage is a regular characteristic of Jakobshavn, and the second image shows that this leakage contributes water circulation vertically along the calving face which degrades the ice and contributes to accelerated calving events as demonstrated by Rignot et al.

Lastly, while every case is different, I attach the third image showing that a subglacial lake (circa 2011) near the southern base of the Thwaites Ice Tongue, may have contributed to the 2012 surge of the Thwaites Ice Tongue, by rapidly draining.
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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1219 on: January 24, 2016, 11:23:52 PM »
The water temp at the bottom of the glacier if it is at the local freezing is below the freezing point at the surface.  So a large rapid release of fresh water would form ice crystals in the liquid as it rose to the surface.  Was it this "slush" that was seen in the radar returns?

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1220 on: January 26, 2016, 04:39:50 PM »
Here's S-1 IW from 22.1.2016 for a change in 10m pixel size UTM...the ice-stream seems to be in a stable state at its receded location, no signs of imminent calving events visible.

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1221 on: January 26, 2016, 05:25:14 PM »
I have to disagree here:
Here's S-1 IW from 22.1.2016 for a change in 10m pixel size UTM...the ice-stream seems to be in a stable state at its receded location, no signs of imminent calving events visible.

Click on image to animate!

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« Last Edit: January 26, 2016, 05:30:16 PM by Espen »
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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1222 on: January 26, 2016, 06:00:37 PM »
Looks like it just calved before the image on the 22nd...therefore it looks so clean. With a wider image it would be interesting to see how far some recognisable icebergs travelled in those 12 days..

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1223 on: January 26, 2016, 06:10:43 PM »
And it is remarkable how much action is seen at the Northern Branch?
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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1224 on: January 26, 2016, 06:17:52 PM »
Quote
With a wider image it would be interesting to see how far some recognisable icebergs travelled in those 12 days...
remarkable how much action is seen at the Northern Branch?
Indeed, before/after might allow us to assign icebergs to either the main south channel or the north branch of that channel (which has become consistently uncorked). It's no problem matching up bergs 12 days apart if they are in both images.

I suppose the smooth icebergs (black in Espen's original, white as reprocessed below) represent calved material that has flipped on the side. If they stay right side up, that presents a rough crevassed layer to radar (so white above, black in image below).

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1225 on: January 26, 2016, 07:00:37 PM »
And it is remarkable how much action is seen at the Northern Branch?
Did that change from frozen to fluid?

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1226 on: January 26, 2016, 07:58:31 PM »
It looks like "our" Island separating the Northern branch from the Southern channel, probably got a family member in the middle of the northern branch:

Did you notice the fish mouth shape of the other island?
« Last Edit: January 26, 2016, 08:06:16 PM by Espen »
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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1227 on: January 26, 2016, 08:39:06 PM »
I stumbled upon this gem while hunting down data for a project I'm working on. It's a satellite photo from the now declassified ARGON mission in May 1962.

Credit to Dr. Ken C. Jezek and Ph.D. Guoqing Zhou (Byrd Polar Research Center of The Ohio State University).

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1228 on: January 26, 2016, 08:49:39 PM »
I stumbled upon this gem while hunting down data for a project I'm working on. It's a satellite photo from the now declassified ARGON mission in May 1962.

Credit to Dr. Ken C. Jezek and Ph.D. Guoqing Zhou (Byrd Polar Research Center of The Ohio State University).

Yes very interesting, thanks! The year 1962 also correspond to this image:
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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1229 on: January 26, 2016, 09:16:26 PM »
I stumbled upon this gem while hunting down data for a project I'm working on. It's a satellite photo from the now declassified ARGON mission in May 1962.

Credit to Dr. Ken C. Jezek and Ph.D. Guoqing Zhou (Byrd Polar Research Center of The Ohio State University).

Yes very interesting, thanks! The year 1962 also correspond to this image:

That is a cutout from a much larger mosaic. The full images show the entire island. Petermann, Humboldt, and many other regions have good shots. Unfortunately 79N and Zachariae are obscured by clouds.

I didn't realize anything this old existed. So I imagine that there are others who are unaware of them as well.

https://nsidc.org/data/docs/daac/nsidc0118_greenland_disp.gd.html
« Last Edit: January 26, 2016, 09:42:49 PM by jimbenison »

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1230 on: January 30, 2016, 03:02:55 PM »
Espen

As I watch the most recent animation From Jan 10 through Jan 26, My gaze is again drawn to the north wall of the south branch. (I know. My fixation continues.) One of the most interesting features is the pronounced slump of the ice sheet just south of the island that splits the north and south branches. It appears as the ice breaks away from the quickly retreating calving face, it collapses and then grounds itself on the shallow sea bed below. This now grounded, fractured ice then waits to be pushed off the sea bed into the deep water under the main ice stream. This would suggest that sufficient bottom melt has occurred and has resulted in this portion of the ice sheet to now float over the shallow sea bed beneath it. Is this interpretation correct?

The same phenomenon seems to be revealing itself just south of the newly emerging island along the north face.

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1231 on: February 03, 2016, 07:48:07 AM »
Would love to see what you guys think of the changes to the eastern sides of the north and south branches.  Hasn't the eastern side of the south branch sort of "crept up the hill" and now the south branch is much wider?

http://ocean.dmi.dk/arctic/images/MODIS/Disko/20160202TERR.jpg

which is also interesting in light of this:

http://ocean.dmi.dk/arctic/images/MODIS/Disko/20160201rs02.ASAR.jpg

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1232 on: February 03, 2016, 03:12:42 PM »
Hasn't the eastern side of the south branch sort of "crept up the hill" and now the south branch is much wider?

Isn't Espen's animation (post 1223) clear enough for you on this? Seems to me there is a big step back after the island, widening the South branch as you suggest. I assume bright swathes of white indicate where the ice starts gaining height and it is just floating melee in that stepped back area. Let me know if you think I am wrong which is entirely plausible.

There seems little difference between
http://ocean.dmi.dk/arctic/images/MODIS/Disko/20160104s01a.ASAR.jpg
and
http://ocean.dmi.dk/arctic/images/MODIS/Disko/20160128s01a.ASAR.jpg
at the calving areas. 10 Jan event brightened channel and it has largely remained that way - not sure if that means anything. I am unable to see any effect at calving area and behind that.

Any guesses for how big the island is or how far back the calving front will move by Oct/Nov this year, or any other date for which you would want to hazzard a guess?

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1233 on: February 03, 2016, 03:26:42 PM »
Sunlight has returned to Ilulissat Isfjord, and Worldview now shows images from Suomi as well as Aqua and Terra:

http://GreatWhiteCon.info/resources/arctic-sea-ice-images/winter-2015-16-images/#Jak

The "coastline" doesn't seem to be in quite the right place though!
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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1234 on: February 03, 2016, 09:02:05 PM »
Crandles
"Any guesses for how big the island is or how far back the calving front will move by Oct/Nov this year, or any other date for which you would want to hazzard a guess?"
The island, I just wish we had the rest of Greenland in such detail.

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1235 on: February 03, 2016, 09:38:55 PM »
Quote
Sunlight has returned to Ilulissat Isfjord
The first Landsat-8s came on day 43 and day 40 in previous years. I'm curious though about what will be new and different with Sentinel 2 which also will be imaging in the visible, though with different bands. These have been offered at the data hub for some time but not for winter Greenland. Ten meter at R,G,B is quite a bit different from 30 m of Landsat (though color has limited use on an ice sheet).

There is no panchromatic band like the 15 m Landsat. There could be an advantage to principle component analysis on the R,G,B with the first component a rough counterpart to panchromatic. These files are going to be 9x the size of Landsat RGB though for the same size scene so unless ESA allows a crop-specified download, this isn't going to happen on a home computer.
« Last Edit: February 03, 2016, 09:45:21 PM by A-Team »

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1236 on: February 04, 2016, 03:28:52 AM »
Nope. I'm gonna go out on a limb and speculate that the northeastern edge of the south branch has collapsed even more.  The southern edge is bound by solid rock, looks like.

Hasn't the eastern side of the south branch sort of "crept up the hill" and now the south branch is much wider?

Isn't Espen's animation (post 1223) clear enough for you on this? Seems to me there is a big step back after the island, widening the South branch as you suggest. I assume bright swathes of white indicate where the ice starts gaining height and it is just floating melee in that stepped back area. Let me know if you think I am wrong which is entirely plausible.

There seems little difference between
http://ocean.dmi.dk/arctic/images/MODIS/Disko/20160104s01a.ASAR.jpg
and
http://ocean.dmi.dk/arctic/images/MODIS/Disko/20160128s01a.ASAR.jpg
at the calving areas. 10 Jan event brightened channel and it has largely remained that way - not sure if that means anything. I am unable to see any effect at calving area and behind that.

Any guesses for how big the island is or how far back the calving front will move by Oct/Nov this year, or any other date for which you would want to hazzard a guess?

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1237 on: February 04, 2016, 01:51:45 PM »
Quote
out on a limb ...  northeastern edge of south branch has collapsed even more
I would think that the northeastern edge of south branch has been bottled up for some centuries, if not millennia, by buttressing by Jakobshavn Isbrae (main south branch). However the whole Greenland ice sheet has been creeping slowly forward during that time. So by now a lot of ice above the NE edge has become unstable (ready for a way out) since the main calving front has retreated.

In fact the situation may be turned around at the flow junction: ice from the NE edge is interfering to some extent with ice coming down the main channel. However there is not enough volume here to plug up the whole south fjord.

Here there is a need for a continuously updated online animation of the calving front as that gives the best sense of what is going on. However I don't foresee the scientific community providing this resource.

Quote
Any guesses for how far back the calving front will move by Oct/Nov 2016?
In terms of specific predictions from published models, this is getting into The Emperor Has No Clothes. My guess is this year will get interesting --  a record retreat though only a few km towards the 76º elbow, nowhere near around the bend and not a wholesale collapse though more ice will be free to come in from both sides.

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1238 on: February 05, 2016, 05:37:43 PM »
Here is what seems to be a rather nice airplane photo from the south taken by Tim Bartholomaus on an unknown date. It was posted by UT in the context of the slowing flow of interior Greenland during the Holocene. It needs a click to display at full size. The second images shows how the flow has changed (middl frame) between 9000 years ago and today.

The magenta line shows the boundary beyond which the flow could no longer be measured at 9000 kyr because of deteriorating isochrons. Thus the flow change can't be measured beyond this line either, leaving the coastal and calving front vicinity undetermined.

http://news.utexas.edu/2016/02/04/scientists-map-movement-of-greenland-ice-sheet-over-time-0
« Last Edit: February 05, 2016, 05:51:28 PM by A-Team »

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1239 on: February 06, 2016, 12:36:13 PM »
JIIslands by crandles57, on Flickr

What do you think of possible island locations/size/shape?

Image is
http://lance-modis.eosdis.nasa.gov/imagery/subsets/?subset=Arctic_r02c02.2016036.terra.250m

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1240 on: February 06, 2016, 02:33:56 PM »
Here is what seems to be a rather nice airplane photo from the south taken by Tim Bartholomaus on an unknown date. It was posted by UT in the context of the slowing flow of interior Greenland during the Holocene. It needs a click to display at full size. The second images shows how the flow has changed (middl frame) between 9000 years ago and today.

The magenta line shows the boundary beyond which the flow could no longer be measured at 9000 kyr because of deteriorating isochrons. Thus the flow change can't be measured beyond this line either, leaving the coastal and calving front vicinity undetermined.

http://news.utexas.edu/2016/02/04/scientists-map-movement-of-greenland-ice-sheet-over-time-0

That photo could not possibly give a better visual image of the rapid retreat of the north wall of the south branch. I don't believe you should actually describe this as a widening of the south branch. It is a calving front on its own and appears to be retreating rapidly, faster than the south branch which is likely due to the ice sheet moving more slowly here.

I would expect this new calving front to rapidly take on the appearance of the north branch and since the shallow sea extends much farther inland than where the north branch has formed, I would expect it to eventually dwarf the north branch calving face in size.
« Last Edit: February 06, 2016, 02:42:15 PM by Shared Humanity »

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1241 on: February 06, 2016, 02:48:13 PM »
Jakobshavn is preparing for a small calving:

Please click on image to enlarge and animate!
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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1242 on: February 06, 2016, 05:28:42 PM »
Nice chunk fell of the northeast, too.

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1243 on: February 06, 2016, 09:41:10 PM »
February caving at JI ... can we trust ecovery to get this right?

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1244 on: February 06, 2016, 09:52:44 PM »
February caving at JI ... can we trust ecovery to get this right?

Ecovery LLC Loxley, AL
www.ecoveryllc.com/
We at Ecovery are proud of our efforts to keep E-Scrap from going to landfills across this country. We look forward to exploring our options for synergy with your… 

ecovery: Return to Wellness
https://www.eains.com/work/
Fresh Outlooks for Return to Work Programs. What is ecovery? ecovery is Eastern's innovative, holistic program to help return injured workers to wellness and ...

ecovery blogging service. recover your free time with ecovery. simply send a topic and our inhouse experts will post blog in your name  ...
https://wsww.weblogforu.com

ecovery Low-Energy Kitchens
www.ecoveryinnovations.com/
Ecovery Innovations was launched in 2012 to provide energy saving products that lower carbon emissions and operating costs to the food and hospitality ...


They are all copy cats, I registered ecovery.com in 1998, together with a recycling concept for one way drink containers (cans, PET, glass etc.)

At that time the value of aluminium from cans alone in the US was worth more than 2 billion dollars a year, the value added services in the concept is far bigger!

« Last Edit: February 06, 2016, 10:22:34 PM by Espen »
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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1245 on: February 07, 2016, 12:55:01 AM »
Jakobshavn is preparing for a small calving:

Please click on image to enlarge and animate!
Looking at the animation it looks like the calving pushed of a chunk of ice off of the side wall.  That chunk looks to have been a free floating ice shelf.  Shared Humanity likes to look there.  Or not on second thought it looks like it just triggered a calving.

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1246 on: February 10, 2016, 10:12:38 PM »
The 2016 Landsats have arrived. But so has a cloud bank.

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1247 on: February 11, 2016, 07:14:16 AM »
Here is what seems to be a rather nice airplane photo from the south taken by Tim Bartholomaus on an unknown date. It was posted by UT in the context of the slowing flow of interior Greenland during the Holocene. It needs a click to display at full size. The second images shows how the flow has changed (middl frame) between 9000 years ago and today.

The magenta line shows the boundary beyond which the flow could no longer be measured at 9000 kyr because of deteriorating isochrons. Thus the flow change can't be measured beyond this line either, leaving the coastal and calving front vicinity undetermined.

http://news.utexas.edu/2016/02/04/scientists-map-movement-of-greenland-ice-sheet-over-time-0

That photo could not possibly give a better visual image of the rapid retreat of the north wall of the south branch. I don't believe you should actually describe this as a widening of the south branch. It is a calving front on its own and appears to be retreating rapidly, faster than the south branch which is likely due to the ice sheet moving more slowly here.

I would expect this new calving front to rapidly take on the appearance of the north branch and since the shallow sea extends much farther inland than where the north branch has formed, I would expect it to eventually dwarf the north branch calving face in size.

Yes to all of the above. And great photo.

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1248 on: February 11, 2016, 10:05:21 PM »
Another calving seen on Worldview between yesterday and today.

Edit:  I zoomed in, looks like a big one.
FNORD

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1249 on: February 11, 2016, 10:35:54 PM »
Yes that is a real big one, and it makes the end of calving seasons, now it is a year around business.

It is a 6 - 7 on the Jakobshavn scale, is my immediate unqualified estimate.
« Last Edit: February 11, 2016, 11:09:08 PM by Espen »
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