Daily cycle of the surface energy balance in Antarctica and the influence of clouds

Abstract

We present the summertime daily cycle of the Antarctic surface energy balance (SEB) and its sensitivity to cloud cover. We use data of automatic weather stations (AWS) located in four major Antarctic climate zones: the coastal ice shelf, the coastal and interior katabatic wind zone and the interior plateau. Absorbed short wave radiation drives the daily cycle of the SEB, in spite of the high surface albedo (0.84–0.88). The dominant heat sink is the cooling by long wave radiation, but this flux is distributed more evenly throughout the day so that a pronounced daily cycle in net all-wave radiation remains with all-sky night-time heat losses of 20–30 W m−2 and noontime heat gains of 30–40 W m−2. During the night, heat is re-supplied to the snow surface by the sensible heat flux, especially in the katabatic wind zone, and the sub-surface heat flux. Daytime radiative energy excess is removed from the surface by sublimation (except at the high plateau) and sub-surface heat transport. Daytime convection occurs at all sites around solar noon but is generally weak. Spatial differences in the SEB are largely controlled by differences in cloud cover. Clouds are associated with higher surface temperatures and near-surface wind speeds. This especially limits nocturnal cooling, so that the strongest daytime convection is found during overcast conditions on the interior plateau.