Principal Investigator (PI): Ian Joughin, University of Washington

Numerous recent studies have revealed rapid change in ice discharge from, as many of the ice sheet's outlet glaciers have accelerated dramatically over the last decade. These observations are significant in that they show Greenland's mass balance can fluctuate rapidly and unpredictably. Despite the large magnitudes of these changes, we do not yet understand the underlying processes controlling fast flow well enough to determine their long-term impact on sea level.

As a consequence, outlet glacier dynamics were a "wild card" in the sea-level projections included in the Fourth Assessment Report (AR4) by the Intergovernmental Panel on Climate Change, and will remain so in the upcoming Fifth Assessment Report (AR5). Improving such predictions and gaining a firm understanding of the dynamics that drive mass balance requires annual to sub-annual observations of outlet glacier variability (velocity and ice front position) to avoid aliasing of this rapidly varying signal. The technology for measuring velocity in Greenland is mature and, under the ongoing Greenland Ice Mapping Project (GIMP-1), we are regularly measuring the velocity of the Greenland Ice Sheet, establishing a record from 2000 to 2012.

Here we propose to continue this effort so that we continue to measure Greenland ice flow velocity until 2017, a period when Greenland should continue to evolve rapidly with the current warming. In addition to providing products of utmost priority to the community currently trying to assess ice sheet stability, this project will provide important baseline data for future generations. In particular, GIMP-2 will provide an important precursor data set to NASA's Deformation, Ecosystem Structure and Dynamics of Ice (DESDynI) L-band synthetic aperture radar (SAR) mission scheduled to launch near the end of the decade. In addition, GIMP-2 velocity measurements will provide a strong complement to the thinning measurements made by NASA's Ice, Cloud, and land Elevation Satellite (ICESAT-2) and IceBridge missions.

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