AN ENERGY-BALANCE MODEL OF LAKE-ICE EVOLUTION

A physically based mathematical model of the coupled lake, lake ice, s now and atmosphere system is developed for studying terrestrial-atmosp heric interactions in high-elevation and high-latitude regions. The ab ility to model lake-ice freeze-up, break-up, total ice thickness and i ce type offers the potential to describe the effects of climate change in these regions. Model output is validated against lake-ice observat ions made during the winter of 1992-93 in Glacier National Park, Monta na, U.S.A. The model is driven with observed daily atmospheric forcing of precipitation, wind speed and air temperature. In addition to simu lating complete energy-balance components over the annual cycle, model output includes ice freeze-up and break-up dates, and tile end-of-sea son clear ice, snow-ice and total ice depths for two nearby lakes in G lacier National Park, each in a different topographic setting. Modeled ice features are found to agree closely with the lake-ice observation s. Model simulations illustrate the key role that the wind component o f the local climatic regime plays on the growth and decay of lake ice. The wind speed affects both the surface temperature and the accumulat ion of snow on the lake-ice surface. Higher snow accumulations on the lake ice depress the ice surface below the water line, causing the sno w to become saturated and leading to the formation of snow-ice deposit s. In regions having higher wind speeds, significantly less snow accum ulates on the lake-ice surface, thus limiting snow-ice formation. The ice produced hy these two different mechanisms has distinctly differen t optical and radiative properties, and affects the monitoring of froz en lakes using remote-sensing techniques.