Browsing by Author "Madsen, F. B."

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    Accelerating changes in ice mass within Greenland, and the ice sheet's sensitivity to atmospheric forcing
    Bevis, M.; Harig, C.; Khan, S. A.; Brown, A.; Simons, F. J.; Willis, Michael J.; Fettweis, X.; Van Den Broeke, M. R.; Madsen, F. B.; Kendrick, E.; Caccamise, D. J.; Van Dam, T.; Knudsen, P.; Nylen, T. (Proceedings of the National Academy of Sciences, 2019-01-22)
    From early 2003 to mid-2013, the total mass of ice in Greenland declined at a progressively increasing rate. In mid-2013, an abrupt reversal occurred, and very little net ice loss occurred in the next 12-18 months. Gravity Recovery and Climate Experiment (GRACE) and global positioning system (GPS) observations reveal that the spatial patterns of the sustained acceleration and the abrupt deceleration in mass loss are similar. The strongest accelerations tracked the phase of the North Atlantic Oscillation (NAO). The negative phase of the NAO enhances summertime warming and insolation while reducing snowfall, especially in west Greenland, driving surface mass balance (SMB) more negative, as illustrated using the regional climate model MAR. The spatial pattern of accelerating mass changes reflects the geography of NAO-driven shifts in atmospheric forcing and the ice sheet's sensitivity to that forcing. We infer that southwest Greenland will become a major future contributor to sea level rise.
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    Bedrock displacements in Greenland manifest ice mass variations, climate cycles and climate change
    Bevis, M.; Wahr, J.; Khan, S. A.; Madsen, F. B.; Brown, A.; Willis, Michael J.; Kendrick, E.; Knudsen, P.; Box, J. E.; Van Dam, T.; Caccamise, D. J.; Johns, B.; Nylen, T.; Abbott, R.; White, S.; Miner, J.; Forsberg, R.; Zhou, H.; Wang, J.; Wilson, T.; Bromwich, D.; Francis, O. (Proceedings of the National Academy of Sciences, 2012-07-11)
    The Greenland GPS Network (GNET) uses the Global Positioning System (GPS) to measure the displacement of bedrock exposed near the margins of the Greenland ice sheet. The entire network is uplifting in response to past and present-day changes in ice mass. Crustal displacement is largely accounted for by an annual oscillation superimposed on a sustained trend. The oscillation is driven by earth's elastic response to seasonal variations in ice mass and air mass (i.e., atmospheric pressure). Observed vertical velocities are higher and often much higher than predicted rates of postglacial rebound (PGR), implying that uplift is usually dominated by the solid earth's instantaneous elastic response to contemporary losses in ice mass rather than PGR. Superimposed on longer-term trends, an anomalous 'pulse' of uplift accumulated at many GNET stations during an approximate six-month period in 2010. This anomalous uplift is spatially correlated with the 2010 melting day anomaly.