8.3
Cause and Effect of Variations in Western Arctic Snow and Sea Ice Cover
Robert S. Stone, Cooperative Institute for Research in Environmental Sciences, University of Colorado,, Boulder, CO; and D. C. Douglas, G. I. Belchansky, S. D. Drobot, and J. M. Harris
Recent decreases in snow and sea ice cover in the high northern latitudes are indicators of climate change. A radiative perturbation know as the "temperature-albedo feedback" is expected as temperatures rise causing snow and ice to melt, surface albedo decreases (solar absorption increases), and warming is accelerated. Previous studies document the advance in the annual date of snow disappearance (melt date) in northern Alaska as represented by the NOAA/CMDL Barrow Observatory (BRW). Correlated anomalies over adjacent ocean regions suggest physical links between the disposition of sea ice and factors that affect the annual cycle of snow cover. To investigate, passive microwave (PMW) data from polar orbiting satellites were used to evaluate the onset and duration of the melt season at sea compared with the BRW snowmelt record. Over a large region northwest of Alaska the onset of melt over ice is correlated with the BRW time series.
Variations in snow and ice distributions of the Western Arctic are partly attributed to changing patterns of atmospheric circulation, especially during spring. This is demonstrated by comparing subsets of "early" and "late" years of melt at BRW in conjunction with analyses of PMW results and corresponding synoptic-scale circulation patterns. For example, the west-east coupling of Low and High pressure centers indicated in Figure 1b favors an early rather than a late snow melt (Figure 1a) because the flow of warm, moist Pacific air into the region is enhanced. Early onset tends to lengthen the melt season, possibly resulting in an overall loss of ice volume. Concern arises as to whether or not the observed trends are manifestations of natural, low-frequency oscillations or are anthropogenically forced.
Figure 1. Average sea ice concentration and maximum Normalized Difference Vegetation Index (NDVI) during 21-31 May for (a) late years (1985, 1986, 1987, 1988) of snowmelt at BRW compared with (b) early years (1990, 1996, 1998) of melt. The geopotential height contours show, schematically, the mean synoptic patterns and associated prevailing winds at 850 hPa averaged for March, April, and May of the respective years. White over land areas is snow cover with deeper green shading indicating advanced growth. Gray over ocean areas represents open water, with progressively lighter shading indicating higher sea ice concentrations. By the end of May, during years of early melt at BRW, snowmelt is also well advanced over eastern Siberia, and low ice concentrations are observed over much of the western Arctic Ocean. The west-east coupling of Low (L) and High (H) pressure centers favors an early onset of melt due to enhanced flow of warm Pacific air into the western Arctic region. An overall decline of sea ice volume may result if such a pattern persists in a succession of years.
Session 8, The Cryosphere - Sea Ice Extent
Wednesday, 12 January 2005, 1:30 PM-2:30 PM
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