Jakobshavn has proven too complex to experimentally characterize or productively model so we're stuck with observation.
In the Jan 2016 paper below, just listing the dozen weakly motivated assumptions and poorly constrained experimental quantities and reviewing the ever-changing historic explanations make it clear that continuum mechanics has nothing to offer Jakobshavn at this time.
Indeed, watching the first motion animation in #1273, the disconnect between daisy world and actual ice stream is so extreme
I wonder if we even want to talk about the same glacier. However it is the real Jakobshavn and its future behavior that concerns us. There was no guidance in this paper nor any testable predictions.
Maybe that's just as well. Modelling of El Nino tele effects ran afoul of 'primum non nocere' this year, the predictions being worse than worthless, were actually harmful from a planning perspective.
Crandles and Oren ask us (#1234 #1275) to predict the Oct 2016 calving retreat line and year-on-year ice discharge isopleths. These won't be provided in the scientific literature as models cannot see even 8 months out. The discharge line has never been determined even though it is more important overall than fluctuations of the calving front.
To find all the ice that will make it out to the fjord this year requires line integrals of the seasonally-varying velocity field along flow lines -- the groundwork for that has only been laid at Zachariae by the Rignot group.
However we can estimate this for Jakobshavn by carefully watching the 2015 Landsat summer animation, ie watch a blob, see if it goes into the sea, if not follow a feature closer in on the flow line, if so follow one farther upstream, mark the limiting point, repeat on a nearby flow line, connect the dots.
This is not thrown off, like velocity, by thinning or crevasse widening towards the front and gives ice volume discharged integrating the bounded area over the bedrock DEM.
Your predicted maximal calving front retreat might be drawn over the first 2016 Landsat of the year or the 27 Feb 16 high resolution Sentinel, with one eye of course on the maximal retreat line history during the grounded era (post-2004).
The issues here are whether the retreat will be greater than the usual 1-2 km, whether the retreat line will again be lopsided (asymmetric about the central flow line), whether the north side of the south branch will have a substantive impact, and whether there will be a repeat of last August's massive event.
The latter scenario has serious potential for unwelcome outcomes. Interpreting dark as smooth, light as rough in Sentinel 1A images (first image below), these consistently show highly crevassed ice extending back from the calving front well past the elbow, eventually transitioning to two dark streams of the principal ice streams.
The question is, how deep do these crevasses go today and how far back? Looking at oblique air photos, the surface ice appears in total shambles: not orderly sheared crevasses but randomly shattered brittle ice that couldn't adapt to newly higher velocity with viscous deformation.
If this shattered ice extends deeper down and farther back than before, then the unprecedented calving event of mid-August 2015 could be a harbinger of things to come this summer.
Basal resistance for three of the largest Greenland outlet glaciers
DR Shapero IR Joughin K Poinar M Morlighem F Gillet-Chaulet
http://onlinelibrary.wiley.com/wol1/doi/10.1002/2015JF003643/full
Resistance at the ice-bed interface provides a strong control on the response of ice streams and outlet glaciers to external forcing, yet it is not observable by remote sensing. We used inverse methods constrained by satellite observations to infer the basal resistance at Jakobshavn, Kangerdlugssuaq, and Helheim [which account for 40% of excess discharge from the GrIS].
In regions of fast ice flow and high driving stresses, ice is often assumed to flow over a strong bed. We found, however, that the beds of these three glaciers provide almost no resistance under the fast-flowing trunk. Instead, resistance to flow is provided by the lateral margins and stronger beds underlying slower-moving ice upstream.
The mechanistic explanation of fast flow at Jakobshavn has changed over the years from (1) vertical shear in ice flowing over a strong bed resisting horizontal sliding of ice above it, (2) to a transition from no-sliding to fast-sliding regime over a weak bed of a deep, narrow trough, to (3) resistance to flow from lateral margins with an inconsequental role for the downstream bed though a stronger bed underlying slower-moving ice upstream. Fast flow in Greenland has been attributed more to internal deformation, facilitated by high strain heating that softens the ice, with the beds supporting a large proportion of the driving stress.
