SNOW-ALBEDO FEEDBACK AND THE SPRING TRANSITION IN A REGIONAL CLIMATE SYSTEM MODEL - INFLUENCE OF LAND-SURFACE MODEL

Using the Arctic regional climate system model (ARCSYM), we investigat e the spring seasonal transition and mechanisms controlling snowmelt o ver a domain covering the northern half of Alaska. Annual simulations for 1992 comparing the Biosphere-Atmosphere Transfer Scheme (BATS) and the land surface model scheme (LSM) show that the BATS experiment ent ers the spring transition with respect to the large-scale atmospheric regime approximately one month earlier than observed climate and the L SM experiment transitions a month later than observed, even though the air temperature in the LSM experiment is generally warmer than in the BATS experiment. A more detailed examination reveals that each simula tion commences and completes the snowmelt period at about the same tim e but that the LSM snowmelt is more rapid than in the BATS experiment. Controlling the snowmelt is the initial snowpack depth and the surfac e energy budget, both of which involve a complex series of feedbacks b etween shortwave and longwave radiation, cloud, surface turbulent flux es, and vegetation. The snowmelt over tundra regions dominates the mor e rapid snowmelt seen in the LSM simulation. It is determined that the most crucial differences between the BATS and the LSM schemes are the partitioning of net ground heat flux between patches of snow and bare ground and the formulation of snow albedo.