Structure and dynamics of the summertime atmospheric boundary layer over the Antarctic plateau: 2. Heat, moisture, and momentum budgets

Abstract

This paper presents the summertime budgets of heat, moisture and momentum in the atmospheric boundary layer at Kohnen base (75 000S, 0 040E, 2892 m above sea level), located in the interior of East Antarctica. For this purpose we performed a model simulation for clear-sky conditions and constant large-scale forcing, using a high-resolution one-dimensional atmospheric model which has been validated by observations (see van As et al., 2006). Turbulent exchange is the dominant component in the heat budget, heating the daytime well-mixed layer by a maximum of 1.0 K h 1. Radiative heating and cooling are important, and are largest near the surface and just above and below the large temperature and humidity gradients of the nighttime stable layer. Vertical heat advection, which is introduced by the wind speed component along the slope, is the smallest heat-budget component in the atmospheric boundary layer, but becomes significant above it. The same is valid for vertical advection in the moisture budget, which is again dominated by turbulent exchange in the atmospheric boundary layer. The model generates solid precipitation (diamond dust) in the nighttime stable boundary layer. In the stable layer the temperature deficit with respect to the free atmosphere can be larger than 10 K, forcing a relatively large katabatic acceleration (up to 2.7ms 1 h 1). Katabatic forcing is chiefly opposed by turbulent momentum transfer (friction). The katabatic forcing decreases with height but is nonzero above the atmospheric boundary layer. In the nighttime stable layer we find a jet which is chiefly forced by katabatics, and in the residual layer above it we find alternating wind maxima and minima as a result of an inertial oscillation.