Characterization of arctic leads and melt ponds from airborne observations.

摘要

Aircraft observations over the Beaufort and eastern Chukchi Seas during 1998 and over the Beaufort Sea in 1994 are analyzed to characterize springtime arctic leads and summertime and autumn arctic melt ponds and open water. The description of leads includes distributions for lead width and orientation, as well as estimates of lead fraction, and is derived from airborne passive microwave retrievals. Lead fraction near SHEBA declined from 8.6% on May 11 to 3.9% on May 18, as a result of ice pack convergence, observed by RGPS. A lead width distribution during May favors smaller (<100 m wide) leads, with the number of leads decreasing exponentially with increasing lead width. Mean lead orientation is northwesterly and is related to prevailing wind conditions. Summertime melt pond and open water characterization is inferred from airborne observations from a downward-looking color video camera. Pond areal coverage near the SHEBA camp is found to increase from 24.6% on July 8, 1998 to 34.1% by July 24, then decrease to 26.3% by July 26. Open water fraction was 5--6% for most of July, but increased to 9% between July 24 and 26. The influence of open water and ponds on the summertime surface albedo is assessed from analysis of upward and downward-looking broadband hemispheric radiometers and is compared to an ice model parameterization. The summertime arctic surface albedo within the ice pack varied from 0.3 to 0.55. For most areas within the pack, the melt pond fraction had the greatest influence on albedo, since their areal coverage was higher than open water. Despite the anomalous thin ice cover in the Beaufort and Chukchi Seas encountered during SHEBA, the characterization of leads, melt ponds and open water are comparable to previous observations during periods of more typical conditions.