CONCORDIASTRO

Balloon experiments

The PTU (Pressure, Temperature, hUmidity) balloon consists of commercial meteorological radiosondes (RS80 and RS90 from Vaisala, Finland) fixed to an helium balloon. A GPS system is contained in the sonds to track its position. Wind speed and direction are computed from these positions. Data are transmitted by VHF. Balloons can get up to an altitude of 25-30 km at a medium speed of 3 to 5 m/s. They were launched approximately once a day (twice a day in 2003-2004). Wind speed, temperature and humidity profiles are recorded. Wind data have been processed for the 4 summer campaigns (2000-2001, 2001-2002, 2002-2003 an 2003-3004). 197 ballons have been launched. Flight statistics are summarized in the daily and monthly histograms below.

Movie on ballon launching (mpg, 40 sec) Another movie, Dec 2003 (mpg, 1mn)

Dome C profiles

Figure on the right shows typical wind speed, wind direction, temperature and humidity profiles at dome C in summer. Altitude is measured from the ground (3268 m). Temperature plot shows a tropopause at height 5km (altitude 8km, pressure 330mb).   These curves show the exceptionnal wind conditions at dome C in summer, with a wind speed lower than 10 m/s whatever the altitude. We can also see the absence of the high altitude strong winds in summer.

Typical profile

Temperatures in the first 30 km above the snow surfaces ranges typically between -25°C and -50°C. Minimum temperature is 5km above ground, that defines the tropopause level. Figure below present the mean temperature profile observed at different moments of the day. First 200m temperature profiles (right curves) shows the classical inversion layer at night, with strong gradient in the first 50m. In the afternoon the snow surface is heated by the sun and the temperature gradient is negative. Two equilibriums are reached near 10 and 18 o’clock, where DIMM measurements have shown very low turbulence on stellar images.

Wind statistics have been computed at different altitudes from balloon data. Altitudes of interest are: ground, tropopause (alt. 8km, 330mb), 200mb and 50mb standart pressure levels (about 11km and 20km). Ground data were collected from the AWS meteo station of Dome C (summer data only). Ground Tropopause 200 mb 50 mb Nb of data 7114 145 123 75 Mean wind speed (m/s) 3.6 12.2 7.4 6.6 Median wind speed (m/s) 3.5 10.7 5.9 4 Standart deviation of speed (m/s) 2.7 7.2 5.3 6.1 Maximum wind speed (m/s) 10.5 41 25.7 34.4 Mean wind direction (m/s) 179° 188° 212° 193° The wind speed profile shows maximum at the tropopause level. Red curve is the mean wind speed, green ones are the standart deviations. Wind direction polar diagram shows the direction from where the wind comes. Ground wind is mainly from South (180°) and turns to South-West after the tropopause.

Wind speed at particular levels

Tropopause wind (pressure 330 mb - altitude 8 km)


Wind at 200 mb  (altitude 11 km)


Wind at 50 mb  (altitude 20 km)



Dome C vs other locations

Curves on the right are a comparison of average wind profiles obtained at Dome C in three summer campaigns (2000-01, 2001-02, 2002-03) with other astronomical sites : Cerro Paranal (Chile, hosting the VLT), Cerro Pachon (Chile) and Canaries Island. Wind speed is in m/s. Curves for Paranal, Pachon and Canaries were obtained by the group of J. Vernin, Nice University. Each plot has three curves which are the maximum, average and minimum wind speed at a given altitude. Dome C curves exhibit a calm atmosphere with no speed gradients. However the first balloons lauched in the 2003-04 campaign (mid-november) have shown high altitude wind of 40m/s (despite the very good seeing observed at the same period).