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George Ph notes: "A new James Hansen paper with 12 co-authors... Lots of press reporting, not one person links to or quotes from the article.' Because no one has seen the article. They screwed up royally by sending out the press release without an embargo contingent on article release. It is not available at Hansen's scholarly publication sites nor at ResearchGate. It is supposed to be released sometime "this week" at ACPD; by then the media cycle will have moved on, way on. We'd all be hollering foul play if the Southern Corp does this with Willie Soon's Nov 2015 paper. The link to the paper should be:
Toggle Commented Jul 22, 2015 on Junction June 2015 at Arctic Sea Ice
"Else we'd have problems of the Mississippi completely freezing over to the mouth, like it did in 1912." Actually in that year it didn't. Nor in any other year in recorded history. The surface froze down to the mouth of its confluence with the Ohio River in Jan 1912 which is still a thousand miles (1600 km) north of the mouth of the Mississippi River at the Gulf of Mexico. Downstream ice jams are not unusual at bridge pilings and piers at the latitude of St. Louis. This ice originates far to the north, not locally; the river continues to flow underneath.
"Nor does this explain current happenings in the Arctic." I re-processed the 19 Jul 15 Bremen AMSR2 that NeilT mentions above ... it's instructive what all poleward incursions into sea ice concentration are there but cannot be seen in the original.;topic=165.0;attach=18517;image
"My image processing pipeline uses ImageMagick. Can ImageJ2 likewise be used in "batch mode"? Doing everything manually would take forever" Yes, ImageJ has a macro recorder. So you just walk through enhancement steps one time and save as a menu tool. Then just apply the tool to a target folder, no need to open all the files, no need to learn or view a scripting language. See the ImageJ forum,165.msg57298.html#msg57298 However ImageMagick surely has this too, perhaps less conveniently. It also has the particular 'exponentiate image' command I used on the U Hamburg images (and much more, see The issue here really is what overall enhancements are fit for purpose. Here 'exp' works to exaggerate the low end of AMSR2 ice concentration. It's far from a unique way of over-weighting weak pixels but does not destroy pointwise data integrity the way contrast enhancement would. It's harmless in the sense of being invertible by 'log'. Both exp and contrast are fit for purpose if that is education or early alert to change. However exp is also suitable for building a tool that detects and measures swell damage to Beauford sea ice. That is, most of the time there won't be a research ship stationed there so we have to work with online products. WaveWatch III provides swell and wave data north of the Bering Straits while nullschool and others provide wind and cyclonic pressures, what's left is to determine the aftermath. Since that is initially floe size reduction, to the degree that shows up at all, it will be in more faint blue pixels of the Hamburg maps on the windward side. With an event strongly suspected, it is then feasible to dig into their raw x,y numbers. You have a good start on this at and associated links.
Nice work, Jim. To draw out the contrast between weaker blues and background white, I exponentiated the palette using a command over in ImageJ2, as explained in that developer forum.;topic=165.0;attach=18437;image
And what exactly will Wadhams do the Bering Sea this September? At $50,000+ per day for the Sikuliaq, there has to be a plan. And that plan has to have been in a grant application. And those have be to in the public domain, this is not something that ONR fwould put on ice (classify) … Mmmm, google search could hardly miss on ‘sikuliaq + wadhams' … ok here it is, Wow, 57 pages, 20 co-authors, journal quality. This is a must-read for folks posting on Arctic sea ice prediction. Sea State and Boundary Layer Physics of the Emerging Arctic Ocean The Office of Naval Research initiated a Department Research Initiative (DRI) titled Sea State and Boundary Layer Physics of the Emerging Arctic Ocean. The central hypothesis of the ‘Sea State’ DRI is that surface waves now have a much greater role in the contemporary Arctic Ocean. Indeed, the entire Arctic Ocean in summer may soon resemble a marginal ice zone (MIZ), where waves propagate through the ice pack and affect the evolution of sea ice over large scales. This large-scale pattern feeds back, as wave generation is controlled by the amount of open water fetch. At smaller scales, waves and ice interact to attenuate and scatter the waves while simultaneously fracturing ice into ever changing floe size and thickness distributions. Further complicating these processes are forcing by winds and surface fluxes from the ocean to the atmosphere, which are expected to increase with heightened storm activity in the region. The marginal open seas provide new opportunities and new problems. Navigation and other maritime activities become possible, but waves, storm surges and coastal erosion will likely increase. Air–sea interactions enter a completely new regime, with momentum, energy, heat, gas, and moisture fluxes being moderated or produced by the waves, and impacting upper-ocean mixing. Science objectives: • Develop a sea state climatology for the Arctic Ocean • Improve wave forecasting in the presence of sea ice • Improve theory of wave attenuation/scattering in the sea ice cover • Apply wave–ice interactions directly in integrated arctic system models • Understand heat and mass fluxes in the air–sea–ice system The DRI will focus on arctic conditions during the late summer and early autumn, especially the freeze-up of the Beaufort and Chukchi seas, to capture the strongest storms and maximum open water. This focus also complements the Marginal Ice Zone DRI (MIZ-DRI) that is studying the summer breakup and ice retreat. Field observations will be collected primarily during a cruise in the fall of 2015, supplemented by long-term moorings and autonomous platforms….
Toggle Commented Jul 12, 2015 on PIOMAS July 2015 at Arctic Sea Ice
>> "a poof! and it's all gone year" or PW's forecast That's my view as well. Swells from a bad cyclone when all the weather ducks have been in a row and it's in a sudden death spiral. Jim, not noticed PMs, maybe better if they blinked incessantly. Right now I am tied down with peak-season Greenland. Or rather, tied down trying to get Espen tied down on one of the large floating laboratories in the fjord to sample Jakobshavn ice calvings. I’ve added the 2009 article you cite above from your excellent web resource. Co-author MG Asplin cites this paper in both the 2012 and 2014 incident reports provided above. (I always read backwards from the most recent!) Surely the Sikuliaq needs a press officer onboard blogging the September trip — you would be eminently well-qualified. Have you asked? “What makes Sikuliaq unique is that it can operate year-round in first-year ice,” Oliver said, “and even some multiyear ice.” He declined to call it an icebreaker, preferring ice-capable. With half the heft and horsepower of the Healy, Sikuliaq doesn’t have the muscle to go through heavy ice packs, he said. Nonetheless, it can work in the Bering Sea in winter and in Arctic and Antarctic waters in summer. The Sikuliaq will be particularly adept at maneuvering in marginal ice zones where you have leads and broken floes, Oliver said. Enhanced maneuverability is made possible by the ship’s propulsion system (azimuthing Z-drive). “It has no rudders, no conventional shafting or screws,” Oliver explained. The system is called. [Oliver was commanding officer on the Healy.] By the way, I applaud what you, Chris, Temmey, Scribler, Wipneus and others are doing on the web sites side, even though in a parallel troll-free universe it could simply be assimilated into factual wikipedia page updates. Methane … the more coverage on that the better. The CO2 modellers are dead wrong here. Mocking and suppression of Shakhova and Semileto’s research, while citing bogus paleo — this has no place in science. One of the CO2 fellow-travellers (sputniks) started a prominent article saying the Siberian tundra holes smelled like methane [which of course is odorless, just look at the formula]. How can someone at this level of incompetence even begin to model free radical photochemistry in the upper atmosphere under changing conditions?!? That’s scattering theory on top of rather serious quantum chemistry kinetics. This is by far the most difficult area in climate science. … (Perennial pack ice in the southern Beaufort Sea was not as it appeared in the summer of 2009)
Toggle Commented Jul 12, 2015 on PIOMAS July 2015 at Arctic Sea Ice
I also took a good look at the dissertation focus, career track, ~230 publications and 40 years of Arctic field expeditions of P Wadhams. In a nutshell, quite extraordinary. Indeed, decades of research in mathematical physics of wave-ice interaction is especially timely, given the newly extended wind reach in the late-season Arctic Ocean and consequent far-reaching swell penetration, fragmentation of pack ice and enhanced lateral melt, none of which is in Piomas or any of the others. Maybe read the articles below? I’m very familiar with PNAS articles published by formerly distinguished but currently demented or self-deluded Academy members seeking to bask once again in the public limelight. Daft does not seem applicable here (though we're all headed there). I see a fair amount of commentary bordering on outright ad hominem coming from programmers with zero qualifications in ice physics and no first-hand observation of the Arctic. Chasing down the worst of these, where Wadhams is quoted as saying his Arctic predictions are “not based on physics”, is quite different in full context. This is humor, intended to put modellers in a hissy fit. There is value in expert judgement and let's face it, very few have the expertise of Wadhams. To appreciate the unanticipated effect of swells on ice, see: (Implications of fractured Arctic perennial ice cover on thermodynamic and dynamic sea ice processes 2014) (Fracture of summer perennial sea ice by ocean swell as a result of Arctic storms 2012) (In situ measurements of an energetic wave event in the Arctic marginal ice zone 2015) (Fracture of summer perennial sea ice by ocean swell as a result of Arctic storms 2014) (Observations and analyses of an intense waves-in-ice event in the Sea of Okhotsk 2003) (Wave Propagation in a Solid Ice Pack) (A prognostic model of the sea ice floe size and thickness distribution 2015)
Toggle Commented Jul 12, 2015 on PIOMAS July 2015 at Arctic Sea Ice
>>"OK, this is it. I am calling #FAIL on PIOMAS' volume numbers." By way of meta-analysis, I looked at the forward citations of the key Piomas papers and ordinary text search peer-reviewed articles mentioning ‘Piomas’ at both google and google-scholar. Here I was especially looking for how scientists with alternative or competing versions of ice volume viewed Piomas. The short answer: lots of citing articles in the 2012-15 window and all of them neutral or favorable. Piomas is taken seriously and has a good level of acceptance within the scientific community. However, that doesn't mean Piomas absolute, relative, or year-on-year differential volumes corresponds to, much less adequately characterizes, the ice encountered when a ship is out there. Indeed, every account I've see seems to be in outright contradiction, both for thickness encountered and more importantly quality of that ice, not just for Piomas but all the ice forecasts. Some of these accounts are anecdotal but others are from heavily instrumented oceanographic research vessels and qualified observers. Perhaps ships that observe the expected don't bother to report it. Surely ship tracks are sparse compared to satellite and not random transects. Still, reading account after account after account of flat-out contradictory observations on ice thickness and especially strength, it seems to me Piomas etc are not adequately characterizing Arctic ice. Yes, it is difficult to find measures that characterize ice resiliency but restricting to what is observable from satellites or calculable from models is just not working. I foresee some serious surprises -- on the downside of ice persistence.
Toggle Commented Jul 12, 2015 on PIOMAS July 2015 at Arctic Sea Ice
Now we have 5 of the 9. And this June issue was so perfectly timed for the coming melt season. This journal imposes a $2960 supplemental charge for each article, should its authors want it to be open access, even though that involves no additional costs nor lost revenue for the journal. That is on top of the base cost and ~$1000 per article color printing supplemental. For an issue entirely organized by the submitters and reviewed by unpaid volunteers! A seamless approach to understanding and predicting Arctic sea ice in Met Office modelling systems. Helene T Hewitt et al
Toggle Commented Jun 10, 2015 on What it's all about at Arctic Sea Ice
"It's a pity about all the paywalls though, Jennifer Francis excepted" I think we can agree $29 x 9 is over the top for the public to see what their public money has funded for public employees. I have been pinging them via Research Gate for reprints, recommended. Ronald Kwok has helpfully sent a pdf (3rd link below) that I believe will work for everyone -- it is a substantial paper on a topic of great interest to us, "Variability of Arctic sea ice thickness and volume from CryoSat-2". It would be great if Chris or others can review this over at one of the forums (not sure what best spot for it is). So far we have 4 of the 9. Towards Quantifying The Increasing Role Of Oceanic Heat In Sea Ice Loss In The New Arctic This paper summarizes our present understanding of how heat reaches the ice base from the original sources – inflows of Atlantic and Pacific Water, river discharge, and summer sensible heat and shortwave radiati ve fluxes at the ocean/ice surface – and speculates on how such processes may change in the New Arctic. 1) improved mapping of the upper and mid - depth Arctic Ocean, 2) enhanced quantification of important process, 3) expanded long - term monitoring at key heat - flux locations, and 4) development of numerical capabilities that focus on parameterization of heat flux mechanisms and their interactions.
Toggle Commented Jun 9, 2015 on What it's all about at Arctic Sea Ice
The article above was just one of nine in a quite interesting symposium published at Research article: Arctic sea ice trends, variability and implications for seasonal ice forecasting Mark C. Serreze, Julienne Stroeve September Arctic sea ice extent has a strong downward trend with a detrended 1 year lag autocorrelation of essentially zero. We argue from a stronger albedo feedback, a longer melt season, the lack of especially cold winters that the downward trend itself is steepening. The lack of autocorrelation manifests both the inherent large variability in summer atmospheric circulation patterns and that oceanic heat loss in winter acts as a negative (stabilizing) feedback, albeit insufficient to counter the steepening trend. There remains an inherent limit to predictability owing to the largely chaotic nature of atmospheric variability. Research article: Variability of Arctic sea ice thickness and volume from CryoSat-2 R. Kwok, G. F. Cunningham We present our estimates of the thickness and volume of the Arctic Ocean ice cover from CryoSat-2 data acquired between October 2010 and May 2014. Average ice thickness and draft differences are within 0.16 m of measurements from other sources (moorings, submarine, electromagnetic sensors, IceBridge). The choice of parameters that affect the conversion of ice freeboard to thickness is discussed. Estimates between 2011 and 2013 suggest moderate decreases in volume followed by a notable increase of more than 2500 km3 (or 0.34 m of thickness over the basin) in 2014, which could be attributed to not only a cooler summer in 2013 but also to large-scale ice convergence just west of the Canadian Arctic Archipelago due to wind-driven onshore drift. Review article: A seamless approach to understanding and predicting Arctic sea ice in Met Office modelling systems Helene T. Hewitt, Jeff K. Ridley, Ann B. Keen, Alex E. West, K. Andrew Peterson, Jamie G. L. Rae, Sean F. Milton, Sheldon Bacon Recent CMIP5 models predict large losses of summer Arctic sea ice, with only mitigation scenarios showing sustainable summer ice. Sea ice is inherently part of the climate system, and heat fluxes affecting sea ice can be small residuals of much larger air–sea fluxes. Analysis of energy budgets in point to the importance of early summer processes such as clouds and meltponds in determining both the seasonal cycle and the trend in ice decline. Forecasting on time scales from short range to decadal might help to unlock the drivers of high latitude biases in climate models. Research article: Regional variability in sea ice melt in a changing Arctic Donald K. Perovich, Jacqueline A. Richter-Menge The amount of surface melt and bottom melt that occurs during the summer melt season was measured at 41 sites over the time period 1957 to 2014. There are large regional and temporal variations. Combined surface and bottom melt ranged from 16 to 294 cm, with a mean of 101 cm. The mean ice equivalent surface melt was 48 cm and the mean bottom melt was 53 cm.… Under current conditions, summer melting in the central Arctic is not large enough to completely remove the sea ice cover. Research article: Factors affecting projected Arctic surface shortwave heating and albedo change in coupled climate models Marika M. Holland, Laura Landrum Changes in the surface sea ice properties are associated with an earlier melt season onset, a longer snow-free season and enhanced surface ponding. Because many of these changes occur during peak solar insolation, they have a considerable influence on Arctic surface shortwave heating that is comparable to the influence of ice area loss in the early twenty-first century. As ice area loss continues through the twenty-first century, it overwhelms the influence of changes in the sea ice surface state, and is responsible for a majority of the net shortwave increases by the mid-twenty-first century. Research article: Sea-ice thermodynamics and brine drainage M. Grae Worster, David W. Rees Jones As the summertime extent of sea ice diminishes, the Arctic is increasingly characterized by first-year rather than multi-year ice. It is during the early stages of ice growth that most brine is injected into the oceans, contributing to the buoyancy flux that mediates the thermo-haline circulation. Current operational sea-ice components of climate models often treat brine rejection between sea ice and the ocean similarly to a thermodynamic segregation process, assigning a fixed salinity to the sea ice, typical of multi-year ice. However, brine rejection is a dynamical, buoyancy-driven process and the salinity of sea ice varies significantly during the first growth season. As a result, current operational models may over-predict the early brine fluxes from newly formed sea ice/ Review article: Recent changes in Antarctic Sea Ice John Turner, J. Scott Hosking, Thomas J. Bracegirdle, Gareth J. Marshall, Tony Phillips In contrast to the Arctic, total sea ice extent across the Southern Ocean has increased since the late 1970s. However, this net increase masks regional variations, most notably an increase (decrease) over the Ross (Amundsen–Bellingshausen) Sea. Sea ice variability results from changes in atmospheric and oceanic conditions. T former is thought more significant since there is a high correlation between anomalies in the ice concentration and the near-surface wind field. The Southern Ocean extent trend is dominated by the increase in the Ross Sea sector, where it is significantly correlated with the deepening the Amundsen Sea Low. Research article: Evidence linking rapid Arctic warming to mid-latitude weather patterns Jennifer Francis, Natasa Skific see above
Toggle Commented Jun 8, 2015 on What it's all about at Arctic Sea Ice
A new 01 Jun 15 article on the wavier jet stream by Dr. Francis is quite readable; free full text at: Evidence linking rapid Arctic warming to mid-latitude weather patterns Jennifer Francis, Natasa Skific Philosophical Transactions of the Royal Society A. The effects of rapid Arctic warming and ice loss on weather patterns in the Northern Hemisphere is a topic of active research, lively scientific debate and high societal impact. The emergence of Arctic amplification—the enhanced sensitivity of high-latitude temperature to global warming—in only the last 10–20 years presents a challenge to identifying statistically robust atmospheric responses using observations. Several recent studies have proposed and demonstrated new mechanisms by which the changing Arctic may be affecting weather patterns in mid-latitudes, and these linkages differ fundamentally from tropics/jet-stream interactions through the transfer of wave energy. In this study, new metrics and evidence are presented that suggest disproportionate Arctic warming—and resulting weakening of the poleward temperature gradient—is causing the Northern Hemisphere circulation to assume a more meridional character (i.e. wavier), although not uniformly in space or by season, and that highly amplified jet-stream patterns are occurring more frequently. Further analysis based on self-organizing maps supports this finding. These changes in circulation are expected to lead to persistent weather patterns that are known to cause extreme weather events. As emissions of greenhouse gases continue unabated, therefore, the continued amplification of Arctic warming should favour an increased occurrence of extreme events caused by prolonged weather conditions.
Toggle Commented Jun 8, 2015 on What it's all about at Arctic Sea Ice
In some ways, they are just kicking the can down the road by saying this particular melt lake didn't initiate a hydro-fracture on its own, but needed an established moulin nearby to buckle the melt lake region via hydrostatic pressure from underneath. How then did that first moulin form with nothing to trigger IT? It seems hydro-fractures can and do form on their own, as indeed proposed in ref 8 cited by this paper (1973, J Weertman). So how many ab initio moulins form each year and are they limited/favored by increasing elevation? As CB notes above, rapid draining is unfavorable for Greenland melt in three ways: first, the meltwater quickly exits the glacier without warming up the interior via latent heat, second by helping establish efficient sub-glacial tunneling that will prevent later melt water from jacking up other melt lakes and third, providing widespread sliding lubrication. Retained meltwater that warms either surface firn or the deep interior, (exacerbating creep) would contribute more to overall acceleration of the ice sheet. The question is how this stacks up compared to early season inefficient drainage lubrication from melt lake drainage. Note non-subscribers have free access to full size figures and legends -- open in new browser tab or you will just get a thumbnail. It is a very nice study in terms of quantitating tensional changes during the event.
Walls slowly closely in ... a refreshing change from frog in stove pot. Not to worry: 316,205,000 anti-anxiety drug prescriptions in 2013 in the US alone; in order of popularity Xanax, Zoloft, Celexa, Prozac, Ativan, Desyrel, Lexapro, Cymbalta, Wellbutrin XL, Effexor ER, Valium, Paxil. And that is just a start on soothing medications in daily use. It will take an impactful event to rouse them. If that.
That's great that the Arctic Sea Ice Blog can send a reporter to AGU 2014. Reporter Steve Bloom is quite right -- any time 22,000 attendees hold forth at a 3-4 day meeting, there will be a firehose of information (pumping out meltwater in this case). The AGU youtube channel is below. These are no real substitute for the ppts used in actual talks. These are in the public domain in some meaningless sense but good luck getting ahold of them. The Greenland news conference featured two very recently published papers that we've discussed over on the forum. These are both available as free full text. The PNAS one is at:
Toggle Commented Dec 18, 2014 on In the meantime: CryoSat at Arctic Sea Ice
Steve, that would be fantastic if you could attend. I'm thinking of swinging by myself. They don't seem to be providing live or archival session video even though the Moscone Center is well set up for that. I'm not seeing presenter slides or posters yet but it may be too soon for their posting. I expect them to approve your application without any fuss but we could even pass the paypal hat for a normal attendee fee. (If I donate even a penny to that, I would expect you to summarize the 23,000 submitted abstracts and run between all the Greenland sessions even if concurrent.) Regular: Full Meeting $425 Senior (65): Full Meeting $215 Additional friend guest $35 + AGU membership $50 (some full text journal access) Actually, the AGU has a very fast and effective search tool and I have already read through all 454 Greenland talks (ditto the Chamonix conf). This was very worthwhile and I recommend it to everyone for their areas of interest. Please note many of these abstracts will never result in a published paper. Some will be, but changed unrecognizably. A few are already old news. However on the whole, this will us a fantastic head's up on what is the works for 2015 publication. Please do not clog up the forums merely pasting abstracts. We can all go to the AGU site. Please post only if you can 'add value' in some way.
Toggle Commented Oct 28, 2014 on PIOMAS October 2014 at Arctic Sea Ice
Another fantastic year of coverage of this ongoing debacle, Neven! Given a flock of coal mine canaries -- some coughing and wheezing from aspergillosis, others staggering from mycoplasma, the remainder feverish with canary pox or spitting up blood from airsac mites -- I suppose we could argue over which will be first to fall off its perch. I still favor Arctic sea ice as being the first to go. However it's fair to say that greenhouse gas increase, atmospheric moisture content, Arctic shelf methane release, ocean acidification, sea level rise (WAIS ice shelf collapse, Greenland melt acceleration), ocean current rearrangement, stationary weather patterns (jet stream slowing and dipping) and so forth have their place already among the sick canaries. They'll be falling off the perch the way things are going.
Toggle Commented Sep 7, 2014 on PIOMAS September 2014 at Arctic Sea Ice
Blaine, a lot of good points. Briefly, we've moved over to the forum and I'm on my 5th post there. The Joughin article is based almost entirely on analysis of proprietary TerraSar imagery. You and I do not have access to it, neither did the referees. There is no way anyone can reproduce the figures when underlying data and methods are not provided. The best we can do is reverse-engineer figures -- count pixels in photoshop to re-create the missing numerical data and dissect their underlying DEM file (the Cresis ftp link above) which I did over at the forum in the course of making a bedrock flythru. The Gogineni group drastically binned the bedrock depth data, eg -1512 to -1103 navy blue, -1103 to -819 mid-blue, -819 to -535. That's why you can't resolve the colors. There's arguably heuristic value to these illustrations -- they get the main idea across without burdening the reader with scientific detail on troughs, pinning points and sills along the bottom of the channel. The temptation on a coordinate system is to take a central flowline of the main ice stream, because the best data comes from flight lines that follow it and velocities and mass fluxes are naturally measured across surfaces orthogonal to the velocity field. Earlier flights went after overall Greenland bed topography so rectangular grid lines made more sense. However there are problems using an ephemeral surface feature to define coordinates. This flowline may or may not lie over the lowest point in bedrock. Joughin uses the long-gone calving front of 2003 as origin of coordinate system origin and not quite a central streamline -- figure 1 starts out as an oblique line, changes to a curve, then cuts cross-channel between M9 and M10. It's also tempting to run the coordinate system through emplaced instrumentation, though that too is ephemeral. Because the ice stretches, they need both Eulerian and Lagrangian reference frames here. The latter means GPS or theodolite targets going along for the ride. Along-track coordinates could have been correlated to lat,lon but that was not done as a Fig.3 scale. So we have to put km coordinates along the photo track or determine from the DEM where the trough lies relative to the calving front on the image. I can't get too exercised over older inaccurate depth profiling when both IceBridge and the new radar drone are out there now updating glacial thinning (the part above sea level) and determining fine-grain features of channel bedrock (needed to model resistance flow). Inverse methods, deducing the bottom from deformations on the ice stream surface, have severe limitations as Sidd discusses over at the main Jakobshavn forum. There have to be consequences of something this massive and moving so rapidly while making a 43º turn. A huge new issue, freeze-on of meltwater leading to drastic deformations of overhead ice stratigraphy, may also be applicable to Jakobshavn.
Espen, agree it's better to consolidate these over in your Jakobshavn forum. However my registration there is hopelessly screwed up and there's no email for a forum admin. I'll see if Neven can help. Yes indeed, a century of observations on Jakobshavn Isbrae ... and it takes awhile even to digest the 2013-14 journal articles on it. Awright, I've finally managed a decent correlation map of bedrock depth with surface imagery: This represents a kridged CReSIS 2008 digital elevation map (from pdf after unzipping: rescaled 4.167:1 to overlay the 30 meter 24 June 14 Landsat-8. It is the DEM thought best by Joughin et al 2014. The transparency is set to ~30% so that ice stream features show through. The animation pauses at the last frame but will loop again. The big hole (~1300 m below sea level) co-locates with a standing wave feature in the surface imagery. Coincidence? You'll see something very similar as an ordinary river passes over a pothole.
So folks don't have to wrestle with a gigabyte images at 12 bit resolution, here is a piece of the 15 m Landsat-8 band B8 (panchromatic) of 24 June 14, namely LC80832332014175LGN00 as provided by I normalized and equalized the contrast histogram within ImageJ at 16 bit depth before export to your 8 bit monitor. Espen has posted 30 m bands 2,3,4 with a calving front comparison over at the forum. Even with 15 meter pixels, there's no forewarning of the next big calving event. The front is about to enter the narrow part of the ice stream.
Below is a schematic cutaway in longitudinal profile of how Jakobshavn Isbrae ice sits over bedrock. More realistically it would show meltwater along the bottom and perhaps deep erosional till cut from headwalls in the trough bottoms (per Tremoran above) as well as temperature and ice rheology profiles. Ice stratification layers may also deformed on Jakobshavn, though not to the extremes seen on Petermann or nearby Epiq. We need Andy Lee Robinson again to illustrate this properly: If the ice were taken away, the remaining glacial valley would be U-shaped in cross-sectional profile, other than some possible bumps (local pinning points that retard glacial advance). The bedrock form does not resemble a valley cut by a river because river longitudinal profiles do not have sills and troughs except at plunge pools, the counterpart of glacier overdeepenings. The next image shows the actual bed profile determined by ice-penetrating radar, as well as the position of the centerline of the calving front in recent years (from Joaghin 2014 linked above). Note the graphic shows the terminus retreating out of a -1300 m trough to the next sill at -950 m below sea level. There's an even deeper trough farther inland. The position of the terminus relative to the deep trough may explain the speed-up in recent years to a certain extent, indeed this year's early retreat to an approaching sill. That sill may diminish future warming of the base from waters of Baffin Bay. So well do we really know the bedrock profile? Here Gogineni himself says ice-penetrating radar is not reliable on narrow fast-moving ice streams. Echoes from the bed can be masked by surface debris and watery inclusions volume scatter. Trailing radar antenna wires on P3's cannot provide the optimal 14 and 35 MHz probes. The bigger problem though has been mis-interpretation of bottom freeze-on and consequent upward deformation as side-scatter from hills. This was recently disproven by gravity measurements showing no Greenland rock (2.67 gm/cm^3) in the vicinity. Meanwhile, Kansas group has developed a greatly improved instrument, a drone with antennas embedded in the airframe. This is capable of flying on a 5m grid cross-track, enabling 2D synthetic aperture radar, as described in a free article in the March 2014 issue of IEEE Geoscience and Remote Sensing. They've announced a field deployment on Jakobshavn Isbrae for this summer. Meanwhile Operation IceBridge flew straight up the channel this spring presumably for the same purpose. These two efforts should result in a greatly improved understanding of this ice stream's stratigraphy and so predictions of its future retreat and attributable sea level rise.
Nukefix has posted some early ESA Sentinel-1 polarized radar imagery of Epiq Sermia and nearby glaciers to the north (described at Glacier's perspective). The graininess can be removed either by Fourier frequency splitting, followed by blurring of the high frequency component (Gimp --> G'MIC) or by wavelet decomposition with discard of first level or two (Gimp --> Filters --> Generic). HH and VV are nearly identical, as can be seen from grain extract after RGB decomposition. It's not entirely clear what the polarizations tell us about ice properties per se. This resolution will allow us to follow calving at Jakobshavn Isbrae at 6-12 day repeat intervals. The imagery is free and puts us back in the ball game. Here we'll want to make a rolling RGB 'interferometric' animation to see which parts of Jakobshavn ice stream are moving at which relative velocities. The position of the calving front has been vacillating in accord with the trade-off between westward glacier advancement and eastward calving loss. So far, the calving front has not ventured up the narrow ice stream channel as it did last fall. Espen posted a very nice image for June 24 at the forum. (To recover individual frames, open animation in a separate tab, save, open gif in Preview or Gimp as layers.)
TL;DR: Landsat-8 is unsuitable for calving front time series. Very helpful link to June Landsat-8 acquisition schedule, Wipneus. Despite being a small ~5km feature, the Jakobshavn calving front is situated very unfavorably with respect to orbital scenes. The corners of path 7, row 11 appear in the middle of this scene; note the apparent drift. Tomorrow 24 June may provide the long-awaited updates to 10 June. Then again the calving front could be covered by a small cloud like yesterday. row path scene 10 11 LC80100112014175LGN00 83 233 LC80832332014175LGN00 Here (path, row) appear between LC80 and the date (day 175) in the scene names. LC80 and LGN00 (Landsat Global Network) do not seem informative. The SvalSat ground station in Svalbard will be receiving (10,11) and (83,233). Maybe.
Here is the latest synthesis of ice-penetrating radar bedrock recent analysis (free) from Gogineni and coworkers. Here I wanted to see at a glance what was below sea-level. However the authors provided a jpg'ed tinted and tilted shaded relief, causing the color key to get out of synch with the image itself. The second slide shows a cure for this: pass to HSV color space and toss the S and V components. Then return to RGB and additively color-pick the key to create a mask for the land above sea level. I made the mask slightly translucent. The bedrock under Jakobshavn Isbrae has numerous ups (sills) and downs (overdeepenings) along its course. Calving depends to a considerable extent on the position of the front relative to this profile.