Controls on Advective Snowmelt in a Maritime Alpine Basin

Abstract

The surface energy budget of a snowpack in an alpine basin near the Main Divide of New Zealand's South Island was calculated from meteorological observations during a spring melt period. The sensible and latent heat exchanges account for 82% of the energy used for melting snow, net radiation accounts for 16% and the sensible heat of rain for 2%. Regression analysis shows that indices of airmass characteristics and regional circulation explain most of the variances in the observed temperature and wind at the site, which are the major controls on turbulent exchange. Local advection of heat is important during periods of strong insolation. Local thermally-generated winds enhance turbulent exchange over the snowpack during calm, anticyclonic periods. The airmass and regional circulation indices account for 75% of the variance in the daily totals of sensible plus latent heat flux. These results support the utility of large-scale indices for forecasting snowmelt during flood-producing rain-on-snow events.