Inside Katabatic Winds Over the Terra Nova Bay Polynya: 1. Atmospheric Jet and Surface Conditions

Abstract

The atmospheric and surface conditions during a late autumnal strong katabatic wind event were quantified using ship and rawinsonde measurements over the Terra Nova Bay coastal polynya. Wind speeds decreased from 35 to 18 ms−1, while the wind direction decreased 18° over the distance from the Nansen Ice Shelf edge out 99 km eastward toward the Ross Sea. Maximum velocity winds (jet cores) at 173, 238, 179 and 144 m elevation were associated with atmospheric boundary layers capped by temperature inversions with bases at 294, 325, 226 and 196 m elevation. The tops of the inversion layers (near 700 m at all locations) also marked the top of the katabatic wind layer. Boundary layer air temperature and specific humidity increased from −31 to −21°C and 0.1 to 0.6 gkg−1, respectively, in response to the warm polynya surface. The air at 15 ± 8 m elevation was saturated with respect to ice, causing supersaturation and snow growth where the air parcels become cooler in the upper atmospheric boundary layer. The surface was characterized by three zones, a fluid zone (open ocean, frazil, shuga and pancake floes), an accumulation zone (fused, rafted and compressed pancake floes) and a young floe zone (large floes). The surface temperature varied from freezing (−1.7°C) in the fluid zone to near air temperature (−20°C) in the floe zone with the largest horizontal surface temperature gradient occurring in the transition between the fluid zone and the accumulation zone, and at the edges of leads in the floe zone.