Abstract
Two aircraft missions to sample the boundary layer dynamics associated with the intense katabatic wind regime at Terra Nova Bay, Antarctica were flown on successive days in early November 1987. Light winds averaging 5 m s−1 were monitored at the 170 m flight level over the interior of the ice sheet. Dramatic acceleration of the airflow and abrupt 5°–7°C cooling were encountered on both days near the head of Reeves Glacier just upslope from where the terrain steepens considerably. These results suggest that much of the airflow convergence which sustains the coastal katabatic winds is forced by localized topographic channeling into Reeves Glacier, and that the descending airstream is negatively buoyant. The horizontally propagating katabatic winds were followed for 250 km directly offshore and for 200 km southward parallel to the Victoria Land coast the airstream momentum gradually decreased along both flight paths.
In conjunction with the descent of negatively buoyant air down Reeves Glacier and horizontal flow acres Nansen Ice Sheet, thermal infrared satellite images showed a warm katabatic signature along the trajectory. This paradox is explained by vigorous vertical mixing within the katabatic layer which makes the temperature of the emitting snow surface beneath the katabatic jet much warmer than that for adjacent light-wind areas. Thermal images often suggest that katabatic winds propagate for hundreds of kilometers beyond the slope break; this interpretation is strongly supported by the offshore aircraft data.
Primitive-equation model simulations for the aircraft flight level reproduced the light Dearly frictionless contour-parallel winds wen in the interior. The model also reproduced the abrupt airflow acceleration near the head of Reeves Glacier. Maximum speeds within the steeply-sloping glacier valley are underestimated, however, and it appears that a much finer rid spacing than 32 km is required to accurately simulate katabatic drainage through the complex coastal mountains.