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Climate Variability & Change

Satellite altimetry has measured global sea level rise with accurate orbits since 1992, and we find that the combined rate due to changes in ocean-water density and mass to be 3.0±0.4 cm/decade (without GIA). Since 2003, the GRACE mission has measured directly the mass loss from the Greenland and Antarctic ice sheets, and the Alaska glaciers, and the GRACE data have been used to estimate the mass increase over the oceans. In order to predict future rates of change and their societal impact, we must understand the sources of error in these measurements. In this investigation we will use GRACE to track the cryospheric sources of mean sea level rise and directly monitor the mass change in the Earth’s oceans. By processing uniformly the entire available GRACE time series with different methodologies (e.g. regional and global mascons vs. spherical harmonics) and different forward models, we will characterize and bound errors in these mass-driven components of the sea level rise budget. Reference frame accuracy and stability directly affect MSL estimates (Beckley et al. 2007). We will quantify errors in the reference frame and their impact on sea level change. The reference frame is constructed using space geodetic observations (SLR, DORIS, GPS, and VLBI). We will implement and test modeling improvements for each of the individual space geodetic techniques, and quantify how they improve reference accuracy and stability. We will also explore alternate strategies for combination of geodetic observations into a single unified frame, emphasizing geodetic stations important to tracking of TOPEX, Jason-1 and Jason-2, and on stations near tide gauges which will improve altimeter calibrations. The temporal variation of the geocenter has been estimated in different ways using forward models and geodetic observations, but these geocenter solutions have not been fully exploited. Using these different geocenter solutions, including those we compute, we will quantify the impact of the geocenter on altimeter data geolocation and MSL rise estimates, as well as on estimates of ocean mass change from GRACE. One of the challenges for prediction of future sea level rise trends, is how the relatively short altimetric record relates to the much longer record of sea level rise on centennial time scales measured through tide gauges and on millennial time scales as measured from sea level rise estimates derived from salt-marsh proxy data. We propose to revisit the reconstruction of 20th century sea level rise accounting for the large scale regional correlations in nearby tide gauges, and better accounting for vertical motion at tide gauge sites using new reference frame products (e.g. ITRF2008) and those from our own multi-technique reference frame reconstructions. Recent evidence has accumulated that variability in basin-scale atmospheric forcing exists on 100-year time scales or longer. This means the largely coastal tide gauges may produce a biased record of global sea level rise on centennial to millenial time scales. We propose to obtain a 500-1000 year record of salt-marsh-derived sea level rise data at Bermuda, from the center of an ocean gyre, to compare directly with existing measurements at the edge of the ocean gyre along the Atlantic coast of North America to better understand these long-period ocean-gyre variations and their impact on records of sea level rise.

PI: Frank Lemoine/NASA Goddard Space Flight Center

NASA/GSFC Mail Code 698 Greenbelt, MD 20771

Phone: 301.614.6109 Fax: 301.614.6522

Email: frank.g.lemoine at nasa.gov

http://science.gsfc.nasa.gov/sed/index.cfm?fuseAction=people.jumpBio&&iPhonebookId;=19437

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Started: Sep 29, 2010

Last Activity: Dec 07, 2010

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