Mean vertical motions and their time-height variations in the lower troposphere obtained from a UHF wind profiler at Pune, a tropical Indian station

Abstract

A 404 MHz wind profiler (UHF radar) system has been in continuous operation since June 2003 at Pune (18°32′N, 73°51′E), a tropical Indian station. The system enables measurement of all three components (zonal, meridional and vertical) of the wind field with height coverage from 1.05 km to about 10 km and a height resolution of 300 in. Daily mean profile data of vertical velocity in the lower troposphere obtained during the 3-year period, June 2003 to May 2006, has been used in this study to investigate the long-term mean clear-air vertical velocity, its variability, and seasonal/intraseasonal variations. Mean vertical velocities varied between -5.30 cm s -1 and +1.30 cm s -1, and mean vertical motions are predominantly downward at altitudes above 3 km. Significant seasonal variation in vertical velocity has been observed. During southwest monsoon months (June- September) a vertical two-cell structure in vertical velocity has been noticed with upward motions below 4 km and downward motion above. In the premonsoon months (March-May) vertical motions are predominantly downward throughout the lower troposphere. Variability is larger during the monsoon and premonsoon seasons and is smaller during postmonsoon (October-November) and winter (December-February) seasons. Vertical velocities at altitudes below 3 km reveal significant semiannual and annual oscillations. Mean diurnal variations during SW monsoon period show interesting features. The observed variability in vertical velocities, especially in layers close to the surface, is explained to be due to the highly variable weather conditions on local as well as synoptic scale at this tropical station. Copyright 2008 by the American Geophysical Union.