PNNL

Abstract

Different cloud types are generated over Antarctica as a result of various synoptic conditions. The cloud characteristics affect their impact on the surface energy budget. In this study, the dominating synoptic regimes over Antarctica (centered on the Ross Ice Shelf) are classi?ed using self-organizing map analysis, applied over long-term ERA-Interim 700-hPa geopotential height data. The corresponding cloud properties over McMurdo Station (measured as part of the AWARE campaign) are described and discussed with respect to the synoptic settings and sea-ice extent conditions. Cloud radiative forcing calculations are performed as well, and a particular focus is given to the net longwave “radiatively cloudy/opaque” (RO) regime. These results are compared with measurements performed at the West Antarctic Ice Sheet (WAIS) Divide to examine their variability and applicability to other Antarctic locations. It is found that the McMurdo cloud properties are strongly affected by the regional ?ow patterns and mesoscale cyclonic activity, which often moderates the larger-scale synoptic regime in?uence. In contrast, the WAIS clouds are more susceptible to the varying synoptic settings. It is suggested that the positive trend in the (frequent) cyclonic activity near the Antarctic coastal regions makes ice clouds an increasingly prominent contributor for the RO cases, especially during freezeup and maximum sea-ice conditions.