The Parallel Ice Sheet Model pism0.6 is an open source, parallel, high-resolution ice sheet model. Features:
|Changing basal conditions during the speed-up of Jakobshavn Isbræ, Greenland|
|investigators:||M. Habermann, M. Truffer, and D. Maxwell|
We use a Tikhonov inverse method, with PISM's SSA as a forward model, to invert for basal conditions from surface velocity data throughout a well-observed period (1985, 2000, 2005, 2006 and 2008) of rapid change. Ice-softness, model norm, and regularization parameter choices are justified using the data-model misfit metric and the L-curve method. The sensitivity of the inversion results to these parameter choices is explored. We find a lowering of effective basal yield stress in the first 7 km upstream from the 2008 grounding line and no significant changes higher upstream. The temporal evolution in the fast flow area is in broad agreement with a Mohr–Coulomb parameterization of basal shear stress, but with a till friction angle much lower than has been measured for till samples. The lowering of effective basal yield stress is significant within the uncertainties of the inversion, but it cannot be ruled out that there are other significant contributors to the acceleration of the glacier.
Only fixes and improvements that should not break existing functionality are included in this release. We recommend updating from v0.6 unless you have a good reason against it. Upgrade by doing “git pull” in the PISM source tree. (Or get a new tagged “.tar.gz” or “.zip” at github.com/pism/pism/releases.) Then do “make install” in the build directory.
For a full list of changes since v0.6, please see https://github.com/pism/pism/blob/stable0.6/CHANGES.md
Send email to email@example.com for help with any version of PISM.
In a just-published Nature Climate Change article, Potsdam Institute for Climate Impact Research authors Matthias Mengel and Anders Levermann use PISM to define the “ice-plug” which, if removed from the coastal ice in the Wilkes Basin of East Antarctica, would initiate irreversible retreat of the grounded ice in that basin. The modeled retreats, which occur on a time scale of a few thousand years, generate 3–4 m of sea level rise from the region surrounding the basin. Thus this basin is a potential “tipping-point” ice sheet configuration, in additional to the better-known West Antarctica configurations.
For the PISM user this paper is an indication of its ability to model an ice sheet region (hashed in figure) at high resolution across a range of ice dynamics parameters and climate forcing choices.
This Science Daily news item quotes the authors about this work.
PISM is jointly developed at the University of Alaska, Fairbanks (UAF) and the Potsdam Institute for Climate Impact Research (PIK). UAF developers, who are in the Glaciers Group at the GI, are supported by NASA's Modeling, Analysis, and Prediction and Cryospheric Sciences Programs (grants NAG5-11371, NNX09AJ38C, NNX13AM16G, NNX13AK27G) and by the Arctic Region Supercomputing Center.