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B.3 - Cryosphere
(Convener: Isabella Velicogna)
A new global mascon solution tuned for high-latitude ice studies
(Luthcke, Sabaka, Rowlands, McCarthy, Loomis)
Improved estimates of Antarctica seasonal and inter-annual ice mass varibility from GRACE
(Pangaluru, Velicogna, Swenson)
Ice sheet mass balance, error sources and impact on sea level
(Velicogna)
Recent Changes in the Earth's Oblateness Driven by Greenland and Antarctic Ice Mass Loss
(Nerem and Wahr)
Session: B.3 - Cryosphere
Title: A new global mascon solution tuned for high-latitude ice studies
First Author: Scott Luthcke
Presenter: Scott Luthcke
Co-Authors: T. Sabaka, D. Rowlands, J. McCarthy, B. Loomis
Abstract: A new global mascon solution has been developed with 1-arc-degree spatial and 10-day temporal sampling. The global mascons are estimated from the reduction of nearly 8 years of GRACE K-band range-rate data. Temporal and anisotropic spatial constraints have been applied for land, ocean and ice regions. The solution construction and tuning is focused towards the Greenland and Antarctic ice sheets (GIS and AIS) as well as the Gulf of Alaska mountain glaciers (GoA). Details of the solution development will be discussed, including the mascon parameter definitions, constraints, and the tuning of the constraint damping factor. Results will be presented, exploring the spatial and temporal variability of the ice sheets and GoA regions. A detailed error analysis will be discussed, including solution dependence on iteration, damping factor, forward modeling, and multi-technique comparisons. We also investigate the fundamental resolution of the solution and the spatial correlation of ice sheet inter-annual change. Finally, we discuss future improvements, including specific constraint application for the rest of the major land ice regions and improvements in solution regularization.
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Session: B.3 - Cryosphere
Title: Improved estimates of Antarctica seasonal and inter-annual ice mass varibility from GRACE
First Author: Kishore Pangaluru
Presenter: Kishore Pangaluru
Co-Authors: Isabella Velicogna; Sean Swenson
Abstract: Estimate of seasonal and inter-annual ice mass change in Antarctic from GRACE has been particularly difficult because of the large uncertainties in the estimates of Atmospheric mass correction from ECMWF model output. We compare geopotential heights from CHAMP GPS radio occultation (RO) and ECMWF model output to assess accuracy of the ECMWF estimates of atmospheric mass distribution. Because the CHAMP data are not assimilated into the ECMWF model this should provide an independent way to assess the accuracy of the ECMWF estimates. We analyze about 7 years of data between Jan 2002 to Sep 2008. We examine special and temporal differences between the two datasets, and we interpret those patterns in term of uncertainties in the two estimates of Atmospheric mass change. We compare those differences with GRACE derived mass changes over Antarctica and in light of this comparison we generate improved estimates of Antarctica seasonal and inter-annul ice surface mass balance from GRACE.
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Session: B.3 - Cryosphere
Title: Ice sheet mass balance, error sources and impact on sea level
First Author: Isabella Velicogna
Presenter: Isabella Velicogna
Co-Authors:
Abstract: We present an update on ice sheet mass balance for Greenland and Antarctica from GRACE. We show a comparison of GRACE results with the mass flux method and how they fit with the longer-term trend. We compare the different reconstructions of surface mass balance in Antarctica with GRACE to highlight that ERA-Interim derived products generate the best fit with GRACE time series. We discuss regional scale changes in Greenland and Antarctica. We clearly see the increase of mass loss in the Northwest of Greenland. In Pine island bay the mass loss is ongoing despite a reduction in acceleration of the glacier after 2009. Finally we present preliminary results of relative sea level changes based on present-day mass losses of both ice sheets.
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Session: B.3 - Cryosphere
Title: Recent Changes in the Earth's Oblateness Driven by Greenland and Antarctic Ice Mass Loss
First Author: R. Steven Nerem
Presenter: R. Steven Nerem
Co-Authors: John M. Wahr
Abstract: We use temporal gravity variations from GRACE to investigate changes in a 34-year time series of Earth’s oblateness (J2) observed by satellite laser ranging (SLR). We use 2002-2010 GRACE data to compute the effects of Greenland and Antarctic ice mass variations on J2 (2.0 and 1.7 x 10^-11/year respectively). Their combined effect on the J2 trend during the GRACE mission is 3.7 x 10^-11/year, which agrees well with the GIA-corrected SLR J2 trend over the same time period. The results suggest that at least since 2002, ice loss from Greenland and Antarctica has been the dominant contributor to the current GIA-corrected J2 trend, which apparently began sometime in the 1990s.
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