Low-level atmospheric jets and inversions over the western Weddell Sea

For four months in the fall and early winter of 1992, as Ice Station Weddell (ISW) drifted northward through the ice-covered western Weddell Sea, ice station personnel profiled the atmospheric boundary layer (ABL) with radiosondes. These showed that the ABL was virtually always stably stratified during this season: 96% of the soundings found a near-surface inversion layer. Forty-four percent of these inversions were surface-based. Eighty percent of the soundings that yielded unambiguous wind profiles showed an atmospheric jet with speeds as high as 14 m s(-1) in a core below an altitude of 425 m. This paper documents the features of these inversions and low-level jets. Because the inversion statistics, in particular, are like those reported in and around the Arctic Ocean, similar local processes seem to control the ABL over sea ice regions in both hemispheres. A simple two-layer model, in which an elevated layer becomes frictionally decoupled from the surface, does well in explaining the ISW jet statistics. This model also implies a new geostrophic drag parameterization for sea-ice regions that depends on the magnitude of the geostrophic wind, the 10-m drag coefficient C-DN10, and the ABL height, but not explicitly on any stratification parameter.