Longwave constraints on the timing of Arctic sea ice melt

Analysis of warm-season surface, sub-surface, and atmospheric data obtained during the Surface Heat Budget of the Arctic Ocean (SHEBA) program indicates that the timing of melt on the ice-covered Beaufort Sea is influenced primarily by the longwave characteristics of the overlying atmosphere. As successively warmer and moister spring season airrmasses arrive at the SHEBA site, longwave emission - from clouds located at or near the peak of the surface temperature inversion, and from near-surface clouds, as well - is the primary determinant of the rate of increase of temperature at the snow - sea ice interface. Cloud longwave emission, dictated by cloud opacity and vertical structure, is shown to be associated with distinct synoptic atmospheric conditions. While the diurnal cycle of surface temperature is apparent during spring, insolation plays a secondary role to synoptic atmospheric conditions in warming until after the snow - sea ice interface reaches the melting temperature. Relevant satellite observations from the International Satellite Cloud and Climatology Project (ISCCP) will also be shown.