HR: 1340h
AN: C23A-1141    [Abstracts]
TI: Analysis of Surface-Melt Dynamics on the Greenland Ice Sheet Using MODIS Data Products: 2000-2005
AU: * Hall, D K
EM: dorothy.k.hall@nasa.gov
AF: Cryospheric Sciences Branch, Code 614.1, NASA/Goddard Space Flight Center, Greenbelt, MD 20771 United States
AU: Williams, R S
EM: rswilliams@usgs.gov
AF: U.S. Geological Survey, Woods Hole Science Center, Woods Hole, MA 02543-1598 United States
AU: Casey, K A
EM: kcasey@icecap.gsfc.nasa.gov
AF: Science Systems and Applications, Inc., 10210 Greenbelt Rd., Lanham, MD 20706 United States
AB: The albedo and surface temperature dynamics of the Greenland ice sheet have been analyzed at the approximate time of maximum melting, from 2000 to 2005, using Moderate Resolution Imaging Spectroradiometer (MODIS) images and standard data products. Results show significant interannual differences in albedo, especially in the ablation area on the west coast, contrasted by relative stability in the albedo in the accumulation area. Significant interannual differences in surface temperature in the ablation area are evident. The year 2005 exhibits relatively high surface temperatures and lower albedos (in the ablation area on the west coast of Greenland) as compared to the other years. Preliminary indications are that 2005 was either the warmest or one of the warmest years during the study period. The 16 day average MODIS white sky albedo, and 8 day average land surface temperature (LST) standard data products beginning on day 209 (27 or 28 July) at the approximate time of the maximum melt extent on Greenland were studied for each of the six years. A digital elevation model (DEM) of Greenland was also used. Two west to east transects across the ice sheet show distinct changes in the albedo and LST moving from land to bare ice in the ablation area, while changes are more subtle over the snow covered ice in the accumulation area. For example, in the more southern transect, in 2005 the albedo rose from about 0.03 to 0.70, from land to bare ice then dipped in the slush zone (the bare ice and slush zone roughly correspond to the ablation area) before rising again, to about 0.97 over snow covered ice, where the albedo remained quite stable until it began to decrease on the east coast with a sharp lowering of the elevation and an increase in LST. Also from west to east in the southern transect, LST dropped from about 290.4 K to 272.1 K, from land to bare ice, and continued to drop as the elevation increased, to a low of 265.6 K at 2993.5 m. (LSTs are accurate to about 1 K.) The pattern was similar in the other years, but the LSTs were different. In the southern transect within the ablation area, the average LST was similar in each of five years (the year 2000 is not considered in this area due to persistent clouds in this 8 day product), averaging 271.8 K. Also in the southern transect, 2005 had the lowest average albedo (0.59) in the approximate location of the ablation area, and 2000 had the highest (0.79) in this 16 day product. Low albedos represent more energy absorption and surface melt, leading to higher surface temperatures. In the northern transect (excluding land areas), the LST for 2005 showed the highest average temperature (266.2 K) of the six years, and 2002 showed the lowest (262.1 K). Average albedo values from the northern transect are lowest (0.76) in 2005 and highest in 2000 (0.93). MODIS albedo and surface temperature data products are sensitive indicators of the surface melt conditions of the Greenland ice sheet, revealing differences in ice-sheet surface dynamics during the six year study period. The year 2005 appears to have the greatest extent of bare ice and slush or generally the lowest albedo in the ablation area of western Greenland of the six years studied, and a relatively low surface temperature.
DE: 1827 Glaciology (0736, 0776, 1863)
SC: Cryosphere [C]
MN: Fall Meeting 2005