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 suggested. Despite a rather limited database, the essential themes in the physical climatology of alpine tundra are understood. With numerous permutations of slope angle, azimuth and surface types in the alpine zone, generalizations of alpine tundra radiation and energy balances are hard to define. Several aspects of the alpine tundra radiation budget are very similar to nonalpine ones, such as the controls exerted on net radiation by atmospheric and surface conditions, and the strong relation 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 regimes tend to be moisture-limiting in the dry tundra and energy-limiting in wetter alpine/ subalpine meadows, but there are also significant season-to-season variations. Theory suggests that the surface heterogeneity common to the alpine zone must at times stimulate vigourous horizontal heat advection at a wide range of spatial scales, but the true significance of this process remains almost entirely undocumented. Suggested future research directions include analyses of the spatial variations of albedo, the role of sloping surfaces, and the relative importance of atmospheric and surface controls on the energy balance.