High resolution VHF radar measurements of tropopause structure and variability at Davis, Antarctica (69° S, 78° E)

Abstract

Abstract. Two years of VHF radar echo power observations are used to examine the structure and variability of the tropopause at Davis, Antarctica. Co-located radiosonde and ozonesonde launches provide data with which to calculate the thermal (lapse-rate) and chemical tropopauses at Davis. The dynamically-controlled radar tropopause can be used as a definition of the Antarctic tropopause throughout the year under all meteorological conditions. During the extended summer period of December–April (DJFMA) inclusive, radar tropopauses are (0.2 ± 0.4) km lower than co-located radiosonde thermal tropopauses and during the extended winter period of June–October (JJASO) inclusive, the radar tropopauses are (0.8 ± 1.0) km lower. The radar and ozone tropopauses both show a decrease in altitude under increasingly strong cyclonic conditions. During strong JJASO cyclonic conditions, there are large (several km) differences between radiosonde lapse-rate tropopause altitudes and radar tropopause altitudes. However, the radar tropopause altitude closely corresponds to the altitude of the 2 PVU surface (where 1 PVU = 106 m2 s−1 K kg−1) for both cyclonic and anticyclonic conditions. The monthly mean occurrence frequency of tropopause folds is investigated using the radar tropopause and is about 1 per month during DJFMA and about 3 per month during JJASO. The power spectrum of the Davis radar tropopause altitude indicates its influence by the passage of inertio-gravity waves. The higher power spectral density during JJASO also indicates an increase in gravity wave activity during this time.