Stable boundary layer regimes at Dome C, Antarctica

Multi-year continuous observations along a 45m tower at Dome C on the high Antarctic Plateau demonstrate the existence of two physical regimes in the stable boundary layer. The first regime is characterized by strong winds, a moderate temperature inversion and strong and continuous turbulence responsible for net temperature, wind speed and wind direction coupling between the surface and each measurement levels in the boundary layer. The temperature inversion and the amplitude of turbulence are in this case strongly dependent on the wind speed. The second regime takes place in low wind conditions and is associated to a very weak turbulence activity as well as large temperature inversions, occasionally reaching 30 K between 10m and the ground. The wind speed and the temperature inversion become significantly less correlated and the amplitudes of the observed thermal inversion suggest that diffusive processes like infrared radiation loss are the dominant actors of the heat transfer. The transition between the two regimes is abrupt and is clearly identifiable by a wind speed threshold, paralleling the concept of the 'minimum wind speed for sustainable turbulence'. An analysis of the curvature of the vertical temperature profile in each regime is then performed revealing two typical profile types: the 'S' shape and the 'exponential' shape. The sharpness of the regimes transition and the extremes of temperature inversions in the very stable regime lead to new challenges for both the conceptual model of the stable boundary layers and for the numerical modeling of stratified flows.