Structure and dynamics of the summertime atmospheric boundary layer over the Antarctic plateau: 1. Measurements and model validation

Abstract

Profile mast, tethersonde and radiosonde measurements are used to describe the structure and dynamics of the summertime atmospheric boundary layer over the slightly sloping snow surface at Kohnen base (75°00'S, 0°04'E, 2892 m above sea level), located on the interior plateau of East Antarctica. During a 4-day clear-sky period at the end of summer, we found a shallow but dynamic boundary layer. Net radiation contributed between -40 and +35 W m-2 to the surface energy balance and was negative on average; the sensible and latent heat fluxes contributed less than 10 W m-2 and 1 W m-2, respectively; the subsurface heat flux mostly counteracted the radiative flux. Owing to nighttime radiative cooling at the surface an increasingly deep stable layer formed with a temperature deficit of over 12 K. Within this layer we observed a katabatically driven low-level jet which increased in altitude from 20 to 70 m during the night and persisted up to noon. By that time a shallow mixed layer was deepening and warming underneath the stable layer. The mixed layer obtained a maximum depth of 70 m halfway through the afternoon. During the experiment the ABL was near saturation. The observations were used to validate a one-dimensional atmospheric boundary layer model.