CHARACTERISTICS OF ENERGY AND WATER BUDGETS OVER WET SEDGE AND TUSSOCK TUNDRA ECOSYSTEMS AT NORTH-SLOPE IN ALASKA

Energy budgets were measured at Arctic tundra ecosystems in Alaska, US A. Measurements were carried out over coastal tundra at Prudhoe Bay in 1994, and at wet sedge, moist and dry tussock tundra around Happy Val ley in 1995. Sensible heat flux, H, and latent heat flux, lE, were det ermined by an eddy correlation technique. Over the Arctic coastal tund ra, the energy partition changed remarkably as a result of air mass co nditions. Under cold and humid wild (onshore) from the Arctic Ocean, t he temperature gradient over the tundra ecosystem increased, which res ulted in a high level of H. Under warm and dry air mass on clear days from the inland tundra (offshore), air and soil temperatures and the w ater vapour deficit increased, which resulted in an increase in lE. Th e same effect or air mass condition on energy partition was observed a t the tundra ecosystem in Happy Valley located 135 km inland from the Arctic coast. The energy budget at wet sedge tundra was characterized as the heat storage within the water layer on a daily basis, which was partitioned mainly to lE in daytime and lE and H at night. Latent hea t flux, lE, was largest at wet sedge tundra and lowest at dry tussock tundra. The Bowen ratio decreased with air temperature over wet sedge and dry tussock tundra ecosystems. The aerodynamic resistance r(a), an d canopy resistance, r(c), over the wet sedge tundra at Happy Valley h ad different levels over four major wind directions. These levels decr eased with increase in wind speed. r(a) was slightly higher than over other vegetation, which seemed to be owing to a relatively lower wind speed, while the canopy resistance r(c) was lower than over other vege tation. Global warming will affect the energy partition of the Arctic tundra ecosystem, and the warming and drying climate will increase the lE of tundra, especially in flooded areas. Expanding dry tundra incre ases H rather than lE, which enhances the warming of the tundra ecosys tem. (C) 1998 John Wiley & Sons, Ltd.