Characteristics and Radiative Effects of Diamond Dust over the Western Arctic Ocean Region

Abstract

Atmospheric observations from active remote sensors and surface observers, obtained in the western Arctic Ocean between November 1997 and May 1998, were analyzed to determine the physical characteristics and to assess the surface radiative contribution of diamond dust. The observations showed that diamond dust contributed only a negligible radiative effect to the sea ice surface. Surface radiative fluxes and radiative forcing values during diamond dust events were similar in magnitude when compared to observed clear-sky periods. Combined information from lidar, radar, and surface observers showed that diamond dust occurred ?13% of the time between November and mid-May over the Arctic Ocean and was not observed between mid-May and October. Diamond dust vertical depths, derived from lidar measurements, varied between 100 and 1000 m but were most often observed to be about 250 m. Lidar and radar measurements were analyzed to assess if precipitation from boundary layer clouds was present during times when surface observers reported diamond dust. This analysis revealed that surface observers had incorrectly coded diamond dust events ?45% of the time. The miscoded events occurred almost exclusively under conditions with limited or no illumination (December?March). In 95% of the miscoded reports, lidar measurements revealed the presence of thin liquid water clouds precipitating ice crystals down to the surface.