Documentation for PISM, a parallel Ice Sheet Model

NEWS: New PISM user help email: uaf-pism@alaska.edu

The Parallel Ice Sheet Model pism0.7 is open source and capable of high resolution. It is widely adopted as a tool for doing science. Features include:

PISM Application of the Month

December 2016

During the Last Glacial Maximum (LGM), glaciers in the Alps reached a maximum extent well-beyond their current coverage (red line). This study models the ice cap using PISM and parameterized forms of the uncertain LGM precipitation pattern. Constraints on the model come from geomorphological reconstruction of ice extent based on interpretation of moraines, trimlines and erratic boulders. The model is forced using different temperature cooling and precipitation reduction factors. Use of the present-day precipitation pattern leads to a systematic overestimation of the ice cover on the northern part of the Alps relative to the southern part. A more severe decrease in precipitation in the north was required to reproduce the LGM extent. This result supports a southwesterly advection of atmospheric moisture to the Alps, sustained by a southward shift of the North Atlantic storm track during the LGM.

2016/12/12 12:50 · Ed Bueler

Latest News

PostDoc in ice sheet and climate modelling at AWI Bremerhaven, Germany

The Paleoclimate Dynamics section at Alfred-Wegener-Institut invites applications for a position as a

PostDoc scientist

with a background in ice sheet or climate modelling for the DFG-project “Global sea level change since the Mid Holocene” (SPP 1889).

Background and tasks:

The aim of this project is to study the evolution of polar ice sheets of the last 6000 years and to estimate the role of climate – ice sheet interactions. Combining climate and ice sheet simulations of different resolution, the project particularly focusses on the ice sheets' mass balance and on ice shelf – ocean interactions under natural and anthropogenic climate change.

The postdoc’s duties will include set-up, supervision, and analysis of climate and ice sheet (PISM) simulations as well as publication in peer-reviewed journals.

Requirements:

The successful candidate should have a PhD in glaciology, atmospheric sciences, oceanography or related sciences and should have a background in either ice sheet or climate modelling.

The position is limited to 3 years, starting August 1st, 2016 or later. The salary will be paid in accordance with the German Tarifvertrag des öffentlichen Dienstes (TVöD Bund), salary level 13. The place of employment will be Bremerhaven.

For further information:

http://www.awi.de/nc/en/work-study/jobs/job-offer/detail/jobs/postdoc-scientist-section-paleoclimate-dynamics.html

2016/06/15 07:49 · Ed Bueler

PISM stable/dev and PETSc 3.7

PETSc 3.7 was released on April 25, 2016. We are currently working on making PISM compatible with PETSc 3.7 and will announce it here as soon as possible.

In the meantime, please install petsc 3.6.4 from here. PISM version 0.7 (stable0.7 branch) works with any PETSc 3.5.X and higher.

2016/04/27 08:54 · Andy Aschwanden

Greenland outlet glacier flow modeled the right way

Today's publication of Aschwanden et al. (2016) in Nature Communications is certainly a milestone in PISM development. However, it is also a milestone in ice sheet modeling generally. Here's why.

The paper is based on PISM simulations with grid resolution down to 600 m over the entire Greenland ice sheet. To start, each of an initial ensemble of 14 lower-resolution (1500 m) experiments has a single ice-sheet-wide value for all parameters. The best of these, in an ice-sheet-wide measure, is re-run at the 600 m resolution and various coarser resolutions. The quality of this flow model for 29 outlet glaciers is assessed; each outlet glacier sees the same physics. The main result is that the majority of the outlet glaciers show strong correlation between modeled and present-day-observed velocity, when it is compared along cross-flow and near-ocean profiles.

Before this paper one might suppose, based on the most prominent literature on the subject, that a detailed, measurably-accurate, outlet-glacier-resolving model of the present-day velocity of an entire ice sheet was dependent both on removing shallow assumptions from the stress balance and on tuning a very large number of basal parameters. Both of these “required” properties would be very bad news for the prospect of using ice sheet simulations to do science! On the one hand, Stokes models are computationally-expensive, while on the other hand only present-day, and not past or future, data are available to set all these basal parameters through inversion.

Such a pessimistic view turns out to be substantially false. Aschwanden et al. (2016) show that four things do matter: (i) an accurate map of bedrock topography, (ii) a stress regime in which viscous membrane stresses are part of the balance with basal sliding resistance, (iii) an energy-conservation-driven basal stress model derived (conceptually) from a model of a wet, pressurized, deformable basal layer, and (iv) high model resolution over all areas of the ice sheet where sliding is possible and/or steep/rough basal topography exists.

NASA IceBridge missions, and the mass-conserving-bed technology of Morlighem et al (2014), are shown by this paper to represent major progress on item (i). Items (ii) and (iii) are properties of the PISM continuum model, and item (iv) of its implementation as parallel-scalable software. Certainly all of these “things that matter” are improvable. More-complete stress balances and the use of inversion of present-day velocities will both be essential to improvements. The main idea remains, however: if the modeled flowing ice has the right bottom geometry, and if the dynamical model has certain key features, then the resulting dynamics are already inside the ballpark!

This research has been featured in Alaska's largest newspaper, the Alaska Dispatch News.

2016/02/01 11:49 · Ed Bueler

PISM team

PISM is jointly developed at the University of Alaska, Fairbanks (UAF) and the Potsdam Institute for Climate Impact Research (PIK). For more about the team see the UAF Developers and PIK Developers pages.

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, NNX16AQ40G) and by NSF grants PLR-1603799 and PLR-1644277.

home.txt · Last modified: 2017/02/21 20:48 by Ed Bueler
© 2016 by PISM | webmaster