DETERMINATION OF DEGREE-DAY FACTORS AND MASS BALANCE SIMULATION ON RABOTS GLACIÄR, SWEDISH LAPLAND

Measurements of snow and ice ablation were taken at 29 sites on the surface of Rabots Glaciär during the 1981-82, 1982-83, and 1983-84 hydrologic years. Measurement intervals ranged from 8 to 31 days during the melt season. Temperature data recorded at the Tarfala Research Station were used to calculate the number of positive degree days (PDDs) during each interval. Regression analysis revealed a strong correlation between ablation and the number of PDDs, an empirical relationship commonly expressed as a degree-day factor (DDF).

Regression of ice ablation on PDDs yielded a DDF of 6.8 mm w.e. d^-1 C^-1 (r²=0.81, n=56, p < 0.0001). The DDF for snow was similarly determined to be 4.7 mm w.e. d^-1 C^-1 (r²=0.61, n=99, p <0.0001). The lower DDF for snow is assumed to be largely due to the snow's higher albedo. The variance in ice and snow ablation not accounted for by that in temperature most probably results from: (1) differences in surface aspect of the measurement localities which affect the magnitude and duration of exposure to incoming solar radiation; (2) non-uniform albedo over snow or ice surfaces; and (3) differences in ice and, especially, snow densities. The values for DDFs obtained on Rabots Glaciär are consistent with those suggested for nearby Storglaciären (6.3 and 4.4 mm w.e. d^-1 C^-1 for ice and snow respectively), as well as those determined for other glaciers throughout the world.

A simple degree-day model using these DDFs has been created to simulate mass balance variations on Rabots Glaciär. Preliminary results indicate that with appropriate tuning of model parameters, a reliable synthetic record of mass balance variation can be constructed.