Mean Vertical Velocities Measured by Indian MST Radar and Comparison with Indirectly Computed Values

• Published in: Journal of applied meteorology (1988) 2003-04, Vol.42 (4), p.541-552
• Main Authors: Jagannadha Rao, VVM, Narayana Rao, D, Venkat Ratnam, M, Mohan, K, Vijaya Bhaskar Rao, S
• Format: Article
• Language: English
• ISSN: 0894-8763
• DOI: 10.1175/1520-0450(2003)042(0541:MVVMBI)2.0.CO;2

Mean vertical velocities and their variations observed with Indian mesosphere-stratosphere-troposphere (MST) radar located at Gadanki (13.5 degree N, 79.2 degree E), a tropical station in India, are presented. In this study, a comparison has been made between Indian MST radar-measured vertical velocities and those computed by radiosonde data using kinematic and adiabatic methods. From this study, it is observed that the signs of vertical motion estimated by the kinematic method agree well with MST-radar values, although the magnitudes differ, except in a small region where radar vertical velocity changes in sign from negative to positive in the lower troposphere during monsoon months. This upward motion in this season is attributed to horizontal convergence due to change in wind direction that is not observed in radiosonde data when averaged, because of poor height resolution of the radiosonde (500 m or more varying with height) as compared with the radar range resolution (150 m). Profiles of vertical velocities computed using the kinematic method tend to approach the shape of radar vertical velocity profiles as the separation of the radiosonde network decreases. The vertical velocities computed using the adiabatic method are found to be small and are attributed to a small tilt in isentropic surfaces caused by small latitudinal temperature gradients commonly observed in the Tropics; they also may be partly due to neglect of diabatic heating. The bias between radar and radiosonde vertical velocities tends to decrease when the time used for averaging of MST radar data is approximately 6 h (before and after 3-h average).