EAGER funding is to be used to open, to the wider academic community in the US and abroad, the source code for a maturing numerical ice-sheet modeling tool. The JPL Ice Sheet System Model (ISSM) is intended as a numerical modeling tool for the representation of the earth's ice sheets, and to be capable of large-scale satellite and other data assimilation. ISSM has high spatial resolution capable of resolving both continent wide (Antarctica) and local (down to ~100's meters) ice flow dynamical features, along with full resolution of Stokes equation ice flow projections. Opening up the source code of the model is a logical step towards its coupling with other earth systems modeling efforts, such as global circulation atmospheric and ocean models intended to include a full range of cryosphere ocean and atmosphere processes.

A specific focus goal of the EAGER proposal, is the development and testing of a new solver to study the three-dimensional simulation of the evolution of the Pine Island Glacier grounding lines. Housing of this effort at UC Irvine will involve UCI undergraduate and graduate student training and use, along with participation of scientists and students from other academic institutions taking part in planned ISSM workshops.

As recognized in the most recent reports from Intergovernmental Panel on Climate Change (IPCC AR-4), current scientific uncertainty as to the future mass changes in the Antarctic and Greenland ice sheets, and possible accelerations in ice sheet flow into a warming ocean remains a major source in uncertainty in projections for global and local sea-level rise over the coming century. Uncertainty of sea-level rise, on a notably rapid time scale of decades to centuries, is a matter of some societal and economic relevance.

Project Report

The Ice Sheet System Model (ISSM) code has been developed over the years as a joint effort between JPL and UC Irvine, leveraging previous Caltech's Jet Propulsion Laboratory investments in the arena of parallel computing and finite-element modeling for thermo-mechanical modeling for satellite systems components. Adapting these computational tools has been a logical progression to improving projections of ice flow dynamics and ice sheet mass balance in a warming world. NASA has been encouraging migration of the ISSM from JPL proprietary status to a more open community framework for its continued development. UC Irvine was a logical place to house this migration effort because of the close ties between the PI, Rignot, and the JPL ISSM team. Under this effort, ISSM became an open source software. Three open workshops were organized over the years to train young researchers, postdocs and students how to employ and contribute to ISSM, worldwide. These workshops helped establish and support community use of the ISSM model. Under this effort, a number of technical and scientific goals for model development and applications were proposed and achieved. Technical goals: The project examine a large variety of code available to simplify and make ice sheet numerical solutions more affordable yet without major impact on the quality of the results. Recommendations were made to the modeling community at large on the best available solvers, which will help other users improve their model efficiency and the quality of their results. A paper was published in the open literature to describe ISSM and its technical capabilities. Science objectives: Several peer-reviewed papers were published to illustrate the capabilities of ISSM and its science applications. These publications include an assessment of the impact of the geothermal flux on simulations of Antarctic ice flow, a sensitivity analysis of ice flow in Antarctica using sophisticated statistical techniques to determine which observations were most critical to adequately constrain the ISSM solutions, several results describing community wide efforts to evaluate evolution scenarios of the ice sheets in the coming centuries in response to climate change and their impact on sea level rise, inversions of the coefficient of friction of ice on its bed across the entire continent of Antarctica revealed the pattern of fast sliding for the first time and showing that ice streams are tighly connected to the interior of the ice sheet, hence that changes taking place at the coast affected very large sectors of Antarctica. Finally, the project demonstrated the combined use of ISSM with a global ocean model part of the MITgcm, hence opening the possibility to run coupled ice-ocean models and significantly improve simulations of ice sheet flow by numerical models. The intellectual merit of this work is that it will benefit the research community interested in employing state-of-the-art ice sheet numerical models to project their evolution in a warming world. The coupling of the ISSM model and MITgcm is one of the most fundamental blocks enabling realistic simulations of ice sheet evolution forced by oceanic and atmospheric changes. The broader impact of this work is that it addresses sea level rise from melting ice sheets in a warming climate, a problem of global, societal and economical importance. At present, ice sheet numerical models are not sufficiently well developed and evaluated to enable realistic projections of ice flow dynamics, which results in some of the largest uncertainty in sea level rise in the coming century and beyond. This work also help young researchers involved in this project to gain experience in conducting basic research in a highly dynamic and interdisciplinary field.

National Science Foundation (NSF)
Division of Polar Programs (PLR)
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Peter J. Milne
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University of California Irvine
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