The exchange across the tropical tropopause in overshooting convective cores

Abstract

Coordinated measurements of Indian MST radar and radiosonde during the passage of overshooting convective cores in SAFAR pilot campaign (May–November 2008) are utilized to quantify the mass flux across the tropopause and strength of the turbulence in up- and down-draft cores. The distribution of retrieved mass flux is found to be wide, ranging from −0.6 (downward flux) to 0.8 kg m−2 s−1 (upward flux). The net mass flux, is, however, from the troposphere to stratosphere, in spite of the existence of significant amount of downward flux. For the first time, the turbulence strength in the vicinity of the tropopause in convective cores is quantified. Large spectral widths with magnitudes >4 m s−1 are observed during convection. However, such large spectral widths are rare and are observed only for 1.6% of total observations. The average spectral width (and also the variation or standard deviation) in draft cores is found to be ~4.5 times larger than that in fair-weather. The turbulence strength in updraft cores is much higher than that of in downdraft cores. The mean (median) spectral width in updraft cores is larger by ~0.8 m s−1 (a factor of ~2) than that of in downdraft cores. The turbulence strength does not show any systematic variation with the intensity of convection in both up- and down-draft cores. The distributions and mean values of mass flux and turbulence strength obtained in the present study will be useful to quantify the STE due to direct intrusion of mass by overshooting convection and the exchange of constituents (in particular water vapor) due to turbulence in a better way.