Properties and temporal variability of summertime temperature inversions over Dronning Maud Land, Antarctica

The occurrence, properties and temporal variations of temperature inversions over Dronning Maud Land, Antarctica, were examined on the basis of tethersonde and 10 m tower measurements during the austral summer 2010-2011. Temperature inversions occurred in 96% of the observed tethersonde profiles, and a surface-based inversion in 58% of the profiles. Although the sun did not set during the study period, the amplitude of solar radiation was large enough to generate a diurnal cycle in near-surface temperatures, temperature gradients and inversion properties. However, daytime heating was not strong enough to destroy the entire inversion layer and therefore a long-living inversion layer often persisted, the lowest part of which strengthened during the nights. The surface-based inversions were strongly curved, with large negative values of the scaled curvature parameter. The majority of temperature change with height took place within the lowest approximate to 5-25 m (so-called strong inversion layer), and in the thicker part of the inversion above the temperature gradient was close to zero. The temporal evolution of near-surface temperature at fixed levels was notably affected by temporal changes of the depth of the strong inversion layer. A case-study, focusing on a typical nocturnal evolution of a surface-based inversion, demonstrated a deepening of the inversion layer during the night, presumably caused by radiative cooling at the top of the layer. Closer to the surface, where the temperature inversion was strongest, the warmer overlying layers caused a long-wave warming that probably compensated the large near-surface cooling due to sensible heat divergence. The factors most strongly favouring strong inversions with low base temperatures were the time of the day (early morning), a small cloud fraction, weak winds, and an air-mass of continental origin.