HR: 0800h
AN: C11B-0421    [Abstracts]
TI: Arctic Sea-Ice Freeboard Heights and Estimated Ice Thicknesses from ICESat: Seasonal and Interannual Variations (2003-2007)
AU: * Zwally, H J
EM: zwally@icesat2.gsfc.nasa.gov
AF: Cryospheric Sciences Branch, Code 614.1, NASA Goddard Space Flight Center, Greenbelt, MD 20771, United States
AU: Yi, D
EM: donghui@icesat2.gsfc.nasa.gov
AF: SGT, Inc., Cryospheric Sciences Branch, Code 614.1, NASA Goddard Space Flight Center, Greenbelt, MD 20771, United States
AU: Kwok, R
EM: ron.kwok@jpl.nasa.gov
AF: Jet Propulsion Laboratory California Institute of Gech, 4800 Oak Grove Dr., Pasadena, CA 91109, United States
AB: Sea ice freeboard heights (sea ice plus snow cover) are derived from ICESat's along-track elevation measurements made over 70 m footprints at 172 m spacings with a range precision of 2 cm. For each measurement location, an ocean reference level is selected by constructing distributions of the measured surface elevations within +- 50 km of the location and taking the average elevation of the lowest 1 percent of the elevations, which are assumed to be over open water and/or very thin ice. The method has also provided a new estimate of the ocean geoid, which has been iteratively used as the initial ocean reference level in the analysis. Snow cover estimates from both climatology and derived from ECMWF analysis are used to estimate sea-ice thicknesses from the derived sea-ice freeboards. Probability-density functions (PDF) of ice thicknesses, which are constructed on 50-km scales, show the classic patterns of thin ice, first year, multiyear ice, etc in various regions. ICESat measurements from 2003 to present have been made in the fall (Oct-Nov) and winter (Feb-Mar) and in some springs (May-Jun). The PDF's of the mean thickness in 50 km grids show typical mixtures of areas of new thin ice and areas of residual multiyear ice in fall (1.48 m mean in 2005), growth of thicker ice in winter (1.93 m mean in 2006), and continued growth and loss of thinner ice by spring (2.67 m in 2006). The mean thickness and ice volume in the fall appears to be decreasing, while the mean thickness in the winter has had significant interannual variability. In 2004, a significant decrease of thicker ice occurred in the classic region of thicker ice north of Canada and Greenland, followed by some regrowth in 2005, and then by decreases of the thicker ice in 2006 and 2007. Compared to the typical ice thickness distributions typical of the Arctic Ocean in 1980-1990's, there appears to have been a fundamental loss of much of the thicker 3 to 5 m ice in recent years.
DE: 0750 Sea ice (4540)
DE: 1616 Climate variability (1635, 3305, 3309, 4215, 4513)
DE: 1621 Cryospheric change (0776)
SC: Cryosphere [C]
MN: 2007 Fall Meeting