PNNL

Abstract

Cloud characteristics at two sites on the North Slope of Alaska separated by ~100 km have been examined for the warmer months of 2001–2003 using data collected from microwave radiometers, ceilometers, rotating shadowband radiometers, and pyranometers. Clouds at the inland site, Atqasuk, were found to have approximately 26% greater optical depths than those at the coastal site, Barrow, and the ratio of measured irradiance to clear sky irradiance was nearly 20% smaller at Atqasuk under cloudy conditions. We hypothesize that these differences are largely attributable to enhanced upward fluxes of heat and water vapor over the wet tundra as clouds move inland from Barrow. Further support for this hypothesis is found from the behavior of the liquid water paths for low clouds, which tend to be higher at Atqasuk than at Barrow for onshore winds but not for offshore ones, and from differences in sensible heat fluxes, which are small but significant over the tundra but are nearly zero at an offshore island located just to the northeast of Barrow.