Abstract
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.
Highlights
There is a renewed interest on the exchange between the troposphere and stratosphere (STE) in recent years because of the intriguing processes occurring in this region, such as ozone depletion in extratropics, dehydration of air in tropics, etc
Earlier studies used a variety of methods to quantify the mass flux across the tropopause and found that the flux due to diabatic circulation is from the troposphere to stratosphere in tropics (Rosenlof, 1995; Sherwood, 2000)
It is widely accepted that the exchange between the troposphere and stratosphere in tropics occurs primarily through two mechanisms; a fast transport by convection and a slow transport by stratospheric diabatic circulation
Summary
There is a renewed interest on the exchange between the troposphere and stratosphere (STE) in recent years because of the intriguing processes occurring in this region, such as ozone depletion in extratropics, dehydration of air in tropics, etc. Earlier studies used a variety of methods to quantify the mass flux across the tropopause and found that the flux due to diabatic circulation is from the troposphere to stratosphere in tropics (Rosenlof, 1995; Sherwood, 2000). These studies have shown that tropical diabatic mean lift and mass fluxes are about half as strong in northern summer as in northern winter. Quantification of exchange by these processes is difficult, because of their variability in space, time and the magnitude In tropics, these processes include deep penetrative convection (Jain et al, 2001; Kumar, 2006) and enhanced turbulence mixing induced by wave breaking (Fujiwara et al, 2003) and shear instabilities
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