Extended Abstract (84K)6.5
Top-of-atmosphere Radiation Budget Over Snow and Sea Ice Surfaces Derived from CERES Measurements
Seiji Kato, NASA Langley Research Center, Hampton, VA
Top-of-atmosphere net radiation over snow and sea ice is estimated from Clouds and the Earth's Radiant Energy System (CERES) shortwave and longwave radiance measurements using two-year of data taken from March 2000 to February 2002. Newly developed empirical angular distribution models convert the top-of-atmosphere shortwave and longwave radiance to the irradiance. To reduce the error in the irradiance, angular distribution models depend on scene type. The shortwave model depends on the sea ice or snow fraction, cloud fraction, cloud optical thickness and surface brightness. The longwave model depends on cloud fraction, surface temperature, and surface and cloud top temperature difference. Angular distribution model derived irradiances indicate that the clear-sky albedo over sea ice varies from approximately from 0.55 to 0.6 while allsky albedo varies from approximately 0.6 to 0.63. Outgoing longwave radiation is primarily a function of surface temperature and varies from 180 W m^-2 to 230 W m^-2 for clear-sky and from 180 W m^-2 to 220 W m^-2 for allsky conditions. Net radiation changes from positive to negative (positive when the energy is deposited to the earth system) for both clear-sky and allsky conditions as the solar zenith angle increases. Net radiation is close to zero for both clear-sky and allsky conditions when the solar zenith angle is approximately 68 degrees. The net clouds radiative effect at the top of the atmosphere over sea ice is a cooling effect because of increasing the top-of-atmosphere albedo and a small change in the outgoing longwave radiation by clouds. A similar analysis over permanent snow suggests that clouds also increase the albedo and slightly decreases outgoing longwave radiation. Net cloud radiative effect over permanent snow is a slightly cooling effect.
Session 6, The Polar Atmosphere - Clouds, Radiation, Aerosols
Tuesday, 11 January 2005, 3:30 PM-5:45 PM
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