RADIATION AND ENERGY BUDGETS OF ALPINE TUNDRA ENVIRONMENTS OF NORTH-AMERICA

Recent physical climatology research from North American alpine tundra environments is summarized and directions for further research sugges ted. Despite a rather limited database, the essential themes in the ph ysical climatology of alpine tundra are understood. With numerous perm utations of slope angle, azimuth and surface types in the alpine zone, generalizations of alpine tundra radiation and energy balances are ha rd to define. Several aspects of the alpine tundra radiation budget ar e very similar to nonalpine ones, such as the controls exerted on net radiation by atmospheric and surface conditions, and the strong relati on between global solar radiation and net radiation. The larger inputs of solar radiation experienced at high altitudes are typically offset by the moderating effects of orographic clouds. Turbulent energy flux partitioning is dependent upon both the effects of macroscale weather and microscale variations in surface soil moisture. Evaporation regim es tend to be moisture-limiting in the dry tundra and energy-limiting in wetter alpine/ subalpine meadows, but there are also significant se ason-to-season variations. Theory suggests that the surface heterogene ity common to the alpine zone must at times stimulate vigourous horizo ntal heat advection at a wide range of spatial scales, but the true si gnificance of this process remains almost entirely undocumented. Sugge sted future research directions include analyses of the spatial variat ions of albedo, the role of sloping surfaces, and the relative importa nce of atmospheric and surface controls on the energy balance.