HR: 08:50h
AN: C11C-03 INVITED     [Abstracts]
TI: The Role of Terrestrial Snow Cover in the Climate System
AU: * Vavrus, S J
EM: sjvavrus@wisc.edu
AF: Center for Climatic Research, University of Wisconsin-Madison, 1225 W. Dayton St., Madison, WI 53706 United States
AB: Snow cover is known to exert a strong influence on the overlying atmosphere and underlying soil, but quantifying this impact is difficult. Besides its well-accepted ability to cool locally, snow cover can also force climate remotely in complex ways by inducing changes in the atmospheric circulation. Most research on the impact of snow cover has focused on the regional rather than global scale. By contrast, this study investigates the global impact of terrestrial snow cover in the present climate by comparing a pair of Community Climate System Model (CCSM3) simulations run with prognostic snow cover (control case) and with all snow cover on land eliminated (NOSNOWCOVER). In this experiment all snowfall over land was converted into liquid water-equivalent upon reaching the surface. Compared with the control run, NOSNOWCOVER produces mean-annual surface air temperatures up to 5 K higher over northern North America and Eurasia and 8 to 9 K greater in these regions during winter. The global-mean warming of 0.8 K in NOSNOWCOVER is nearly 1/3 as large as the simulated 2 x CO₂ response. This pronounced surface heating dramatically increases geopotential heights throughout the troposphere: annual increases of up to 50 m occur at the 250 hPa level, along with even larger inflations during winter. Despite the large surface warming, the absence of an insulating snow pack causes soil temperatures in NOSNOWCOVER to fall throughout northern Asia and Canada, including extreme wintertime cooling of more than 20 K in Siberia and a 5 to 10^o equatorward expansion of simulated permafrost. The absence of local melt-water percolation causes significantly drier soils over northern boreal regions and a consequent decrease in cloudiness. The removal of snow cover also drastically affects extreme weather in middle latitudes. Extreme cold-air outbreaks (CAOs), defined relative to the control simulation, essentially disappear in NOSNOWCOVER. The loss of CAOs appears to stem from both the local effect of eliminating the chilling influence of snow cover in mid-latitudes and a remote effect over CAO source regions in the Arctic, where -40^oC air masses are unable to form in NOSNOWCOVER.
DE: 0700 CRYOSPHERE (4540)
DE: 0736 Snow (1827, 1863)
DE: 0798 Modeling
DE: 1800 HYDROLOGY
DE: 1863 Snow and ice (0736, 0738, 0776, 1827)
SC: Cryosphere [C]
MN: Fall Meeting 2005