The role of terrestrial snow cover in the climate system |
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Authors: | Steve Vavrus |
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Institution: | (1) Center for Climatic Research, University of Wisconsin-Madison, 1225 W. Dayton St., Madison, WI 53706, USA |
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Abstract: | Snow cover is known to exert a strong influence on climate, but quantifying its impact is difficult. This study investigates
the global impact of terrestrial snow cover through a pair of GCM simulations run with prognostic snow cover and with all
snow cover on land eliminated (NOSNOWCOVER). In this experiment all snowfall over land was converted into its 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 8–10 K greater during winter. The globally averaged warming of
0.8 K is one-third as large as the model’s response to 2 × CO2 forcing. The pronounced surface heating propagates throughout the troposphere, causing changes in surface and upper-air circulation
patterns. Despite the large atmospheric 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 over 20 K in Siberia and a 70% increase
in permafrost area. The absence of snow melt water also affects extratropical surface hydrology, causing significantly drier
upper-layer soils and dramatic changes in the annual cycle of runoff. Removing snow cover also drastically affects extreme
weather. Extreme cold-air outbreaks (CAOs)—defined relative to the control climatology—essentially disappear in NOSNOWCOVER.
The loss of CAOs appears to stem from both the local effects of eliminating snow cover in mid-latitudes and a remote effect
over source regions in the Arctic, where −40°C air masses are no longer able to form. |
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