Dynamics of Heavy Rain Spells over India during 2005

Abstract

High-impact mesoscale weather events, occurring in different parts of India in all seasons, lead to major weather and climate related disasters. In view of this, an attempt has been made in the present study to understand the dynamics of atmospheric circulation over the Indian region (50˚E-100˚E and EQ-30˚N) during super active monsoon period 21st-30th June and 22nd-31st July 2005 using NCEP/NCAR reanalyzed daily winds (u and v), temperature (T) from surface to 200 hPa to compute the divergence (D), vorticity , vertical velocity ,static stability and heat source (QH). (p) profiles clearly indicate the unstable zone between 850 to 650 hPa. The necessary condition of barotropic instability and condition of baroclinic instability are also satisfied in the layer 850- 650 hPa for all the active monsoon days. Further, zonal (u) and meridional (v) winds, are examined in the zonal (x-p) and meridional (y-p) planes. It is noticed that there exist low level cyclonic circulations in the boundary layer over major portion of the country and abnormal increase in the meridional wind in the lower and middle troposphere. Significant increase in the cyclonic vorticity upto 300 hPa and the upward motion throughout in the troposphere with maximum value around 700 to 500 hPa and positive heat source explain the possibility of highly convective and unstable mid-tropospheric zone. The study indicates that there are few mesoscale systems embedded in the synoptic scale system that are already present in the large-scale monsoon circulation.