Coordinated MST radar and lidar observations for the study of mesospheric structures over a tropical station

摘要

VHF radar observations at a frequency of 53 MHz at Gadanki (13.5°N, 79.2°E), India, during the period from September 1995 to August 1999 are used to study the tropical mesospheric structures. MST radar echoes have shown an enhancement in echo power of about 6-8 dB above the average noise level. These echoes are intermittent in time and can be observed at an altitude between 70 and 76 km. The seasonal variation of these echoes shows the maximum percentage occurrence during summer, closely followed by equinoxes and minimum during winter. This seasonal variation is also accompanied by shifting of height to lower heights during winter. Coordinated MST radar and Nd:YAG lidar observations were conducted to study the mesospheric structures during March 1998-June 1999. In the lidar temperature profiles, inversion of about 20-30 K is observed at the heights of the MST radar-enhanced echoes. Enhanced radar reflectivity is observed on both the preceding and succeeding days of lidar observations of strong temperature inversions. Percentage occurrence of MST radar echoes and temperature inversions show one-to-one correspondence for most of the cases. The effect of temperature inversion on the radar reflectivity is also studied. The presence of temperature inversion and enhanced radar reflectivity are discussed in the light of gravity-wave breaking processes at that height region.