CGRG Bibliography of Canadian Geomorphology
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Author : Fastook, J.L.
Date : 2003.
Title : New developments in umism: mass balance and temperatures.
Publication : Joint Annual Meeting of the Canadian Quaternary Association and the Canadian Geomorphology Research Group. Halifax, Nova Scotia, June 8-12, 2003.
Issue :
Page(s) :
Abstract
We report on various components of the University of Maine Ice Sheet Model (UMISM), with particular emphasis on a new way of producing mass balance patterns for paleo-climates. The new scheme blends the old simple climatology, whereby mass balance at a point depended only on its distance from the pole and its elevation. In the new scheme we begin with climatological data from the NCEP2 gridded reanalysis. A climate reanalysis begins with observations of weather, which are distributed non-uniformly over the globe, and then uses these observations to guide a GCM, which then produces regular gridded output (sort of a physics-based interpolation scheme). We use two components of the NCEP2 data: the monthly mean surface temperatures, and the monthly precipitation totals. Precipitation is partitioned into either snow or rain based on the monthly mean temperature, offset by whatever "climate knob" we are using (GRIP core proxy temperatures for instance). The year's sum of snow represents the accumulation portion of the mass balance. We also count positive degree days (PDD) based on the monthly mean temperatures. From this we obtain the ablation portion of the mass balance. The net accumulation/ablation rate for the year is the sum of these two. Since we want the climate (temperature and mass balance) to respond to the changing height of the ice sheet surface, we also include a vertical lapse rate that lowers the temperature with increasing elevation. The NCEP2 data set provides an adequate representation of the climate for ice sheet initiation, since the general circulation patterns are probably not too different from the present. As the ice sheets form and grow, however, there is considerable re-organization of the circulation patterns. To accommodate this we have provided ice sheet configuration results for a reasonable Laurentide, Scandinavian, Greenland, and Antarctic Ice Sheets to a GCM modeler and results in the same form that we used from the NCEP2 data. This results-based climate we call the Ice Age Climate and the data-based NCEP2 the Interglacial Climate. Currently we shift between the two climates by a linear interpolation based on the sea level (a direct representation of the ice sheet volume, and hence a measure of how fully "re-organized" the circulation is).
Bibliography of Canadian Geomorphology