  The atmospheric properties above three sites (Dome C, Dome A and the South
Pole) on the Internal Antarctic Plateau are investigated for astronomical
applications using the monthly median of the analyses from ECMWF (the European
Centre for Medium-Range Weather Forecasts). Radiosoundings extended on a yearly
time scale at the South Pole and Dome C are used to quantify the reliability of
the ECMWF analyses in the free atmosphere as well as in the boundary and
surface layers, and to characterize the median wind speed in the first 100 m
above the two sites. Thermodynamic instability properties in the free
atmosphere above the three sites are quantified with monthly median values of
the Richardson number. We find that the probability to trigger thermodynamic
instabilities above 100 m is smaller on the Internal Antarctic Plateau than on
mid-latitude sites. In spite of the generally more stable atmospheric
conditions of the Antarctic sites compared to mid-latitude sites, Dome C shows
worse thermodynamic instability conditions than those predicted above the South
Pole and Dome A above 100 m. A rank of the Antarctic sites done with respect to
the strength of the wind speed in the free atmosphere (ECMWF analyses) as well
as the wind shear in the surface layer (radiosoundings) is presented.
