HR: 11:32h
AN: A52A-06    [Abstracts]
TI: Elevation Dependence of the Direct Aerosol Radiative Forcing on Spring Snowmelt in the Southern Sierra Nevada
AU: * Kim, J
EM: jkim@atmos.ucla.edu
AF: UCLA Dept. Atmospheric Sciences, 405 Hilgard Ave., Los Angeles, CA 90095-1565 United States
AU: Gu, Y
EM: gu@atmos.ucla.edu
AF: UCLA Dept. Atmospheric Sciences, 405 Hilgard Ave., Los Angeles, CA 90095-1565 United States
AU: Liou, K
EM: knliou@atmos.ucla.edu
AF: UCLA Dept. Atmospheric Sciences, 405 Hilgard Ave., Los Angeles, CA 90095-1565 United States
AB: Aerosol radiative forcing plays an important role in determining the energy cycle within the climate system, but its role remains uncertain. The impact of aerosol radiative forcing on spring snowmelt is a particular concern in the western US as changes in the surface insolation can alter the amount and timing of snowmelt that are crucial for projecting warm season water resources. In addition, changes in snowmelt produced by aerosol radiative forcing can significantly affect the energy and hydrological cycles via snow-albedo feedback. We examined the direct aerosol radiative forcing and its impact on snowmelt in the southern Sierra Nevada region during March-May 1998, using a regional climate model that included a state-of-the-art radiation parameterization scheme developed by Fu and Liou (1993) and improved by Gu and Liou (2003) for efficient use in climate models. The southern Sierra-Nevada region is characterized by large elevation change and heavy winter snowfall that are important sources of water supply for California during the dry warm season. Simulation results showed that the magnitude of aerosol radiative forcing on the surface insolation and its impact on snowmelt depended on terrain elevation. For clear sky, the magnitude of the surface insolation change due to the direct aerosol radiative forcing was similar in all elevation ranges. The effect of aerosols on the surface insolation averaged over the 3-month period, however, decreased with increasing terrain elevation as both the frequency and amount of cloud cover increased with increasing terrain elevation. Elevation dependence of the aerosol impacts on snowmelt was related with the low-level air temperature changes associated with terrain elevation changes. The effect of aerosol radiative forcing on snowmelt via the surface-insolation change was largest at elevations higher than 2000 m. We further found that the largest effect of aerosol radiative forcing on snowmelt occurred in a temperature range from -3 to 5 C. Outside this temperature range, lower (higher) temperatures tend to control snowmelt by means of suppressing (enhancing) its growth.
DE: 3354 Precipitation (1854)
DE: 4215 Climate and interannual variability (3309)
DE: 1655 Water cycles (1836)
DE: 1803 Anthropogenic effects
DE: 1630 Impact phenomena
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting