Comparison of the atmospheric properties above Dome A, Dome C, and the South Pole

摘要

The atmospheric properties above three sites on the Internal AntarcticPlateau are investigated for astronomical applications calculating the monthlymedian of the analysis-data from ECMWF (European Centre for Medium-RangeWeather Forecasts) for an entire year (2005) thus covering all seasons.Radiosoundings extended on a yearly time scale from Dome C and the South Poleare used to verify the reliability of the analyses in the free atmosphere andto study the wind speed in the first 100 m as the analysis-data are notoptimized for this altitude-range. The wind speed in the free atmosphere isobtained from the ECMWF analyses from all three sites. It appears that thestrength of the wind speed in the upper atmosphere in winter is correlated tothe distance of the site from the centre of the polar high. The Richardsonnumber is employed to investigate the stability of the free atmosphere and,consequently, the probability to trigger thermodynamic instabilities above thethree sites. We find that, in a large majority of the cases, the freeatmosphere over the Internal Antarctic Plateau is more stable than atmid-latitude sites. Given these data we can obtain a ranking of the three siteswith respect to wind speed, in the free atmosphere as well as in the surfacelayer, and with respect to the stability of the atmosphere, using theRichardson number.