ABSTRACT. A simple flux model using twice-daily measurements of wind, humidity, and temperature from standard upper-air levels in a distant radiosonde estimated winter balance of South Cascade Glacier over 1959-98 with error 0.24 m w.e. Correlation between net and winter balance is strong; the model estimates net balance with error 0.53 m w.e. Over the past 40 years, average net balance of South Cascade Glacier has been strongly negative (-0.46 m w.e.), and it has been shrinking steadily. In comparison, 200 km WSW at Blue Glacier, the average balance has been less negative (-0.13 m w.e.); that glacier has undergone little change over the 40 years. Balance histories of the two glaciers are positively correlated (r =+0.54), and South Cascade has been more out of balance than Blue, presumably because it is still adjusting to climate change since the Little Ice Age. Recent warming and drying has made the net balance of both glaciers strongly negative since 1976 (-0.84 m w.e. at South Cascade, -0.56 m w.e. at Blue). If South Cascade Glacier were in balance with the 1986-1998 climate, it would be about 1/4 of its present area.

ABSTRACT. A simple model uses once-daily upper-air conditions from the NCEP-NCAR Reanalysis database to estimate summer balance of South Cascade Glacier each year over 1959-99. The rms error, 0.30 m water equivalent, (r² = 0.71) is comparable to measurement error. The model relates summer balance linearly to temperature T > 0 C at 2000 m and to snow flux at 1650 m, the altitudes in recent years of the equilibrium line and terminus. The snow flux is the product of the humidity and westerly wind component at 850 hPa when temperature T < +2 C at 1650 m. Temperatures are interpolated linearly between the 850 and 700-hPa levels. Both the positive 2000-m temperature and the snow flux are summed April 26 to October 4. When the summer estimates are combined with those from a winter balance model using the same database, the rms error in estimating net balance is 0.40 m (r² = 0.81). The indicated sensitivities of balance to warming of 1 C are -0.51 m for summer, and -0.24 m for winter. On the assumption that the total -0.75 m/C sensitivity exists at all altitudes, a warming of only 0.7C would be sufficient to overcome the 1986-98 average net balance +0.5 m at the top of the glacier.

ABSTRACT. A simple model using once-daily upper air values in the NCEP-NCAR Reanalysis database estimates seasonal mass balance at two glaciers in southern Alaska, one in western Canada, and one in Washington substantially better than any of several seasonally-averaged, large-scale climate indices commonly used. Whereas sea level pressure and sea surface temperature in the Pacific exert a strong influence on the climate in the region, temperature and moisture flux at 850-hPa have a more direct effect on mass balance processes -- accumulation and ablation -- because their temporal variability better matches that of those processes. The 40-year record of 850-hPa temperature shows 1976-77 winter warming and 1988-89 summer warming throughout the region; mass balance records reflect the summer warming at all four glaciers but winter warming only at the southern two. The only pronounced long-term change in the moisture regime is a decrease of precipitation in the south and an increase in the north. Interannual variations in the location of the moisture flux, however, apparently account for the strong negative correlation between the Alaska glaciers and the other two.