Middle atmospheric thermal structure over sub-tropical and tropical Indian locations using Rayleigh lidar

摘要

Earth's middle atmospheric thermal structure is unique, and having imprints of various physical and chemical processes taking place in the Earth's atmosphere. Nd-YAG laser based Rayleigh lidars are operational at Mt. Abu (24.5°N, 72.7°E) and at Gadanki (13.5°N, 79.2°E) to study the middle atmospheric temperature structure in the altitude region of 30-75 km. Temperature profiles are derived using Rayleigh lidar measured neutral density profiles. Nightly mean temperature profiles, during 1997-2001, are utilized to obtain average temperature profile for each month over Mt. Abu. Lidar observed temperatures are compared with the temperatures observed by Halogen Occultation Experiment (HALOE), on-board Upper Atmospheric Research Satellite (UARS), the CIRA-86 and MSISE-90. Observed temperature profiles are in qualitative agreement with CIRA-86 and MSISE-90 model below 50 km, and the agreement is better during winter months. Quantitatively there are significant differences noted, up to 10 K, above 50 km. The temperature profiles are also compared with the equatorial model for the Indian region, based on rocket and balloon measurements. Significant day to day variability is found, which is as high as +10 K at ～70 km. The mean values of the stratopause height and temperature are found to be 48 km and 271 K, respectively. Seasonal variation shows equinoctial and summer maxima below 55 km, whereas above 70 km winter maximum with equinoctial minima are present. Comparative study of thermal structure with Gadanki, a tropical station, revealed significant differences in the thermal structure over tropical and sub-tropical locations.