Lidar Measurement of Winter Time Cirrus Clouds at a Tropical Coastal Station Trivandrum, India

摘要

The cirrus clouds which are global in nature have been identified as one of the important constituents if the atmosphere. They play a dual role in the earth radiation budget increasing the Earth's albedo while simultaneously decreasing the emission of Infrared radiation to space. Tropical cirrus clouds come in a variety of forms ranging from optically thick anvil cirrus closely associated with deep convection to optically thin cirrus layers frequently observed near the tropopause. For better understanding of the formation, subsistence and dissipation of cirrus clouds extended studies are necessary. From earlier investigations it is realized that the climatology of cirrus clouds is distinctly different at the low latitude coastal station at the west coast of India. Some of the important characteristics of the cirrus clouds like time history of formation and dissipation, geometrical and optical properties during the winter time have been investigated using the ground based Mutiwavelength Lidar system designed and developed in house at the Space Physics Laboratory, Vikram Sarabhai Space Centre, Trivandrum, India. The lidar provides a vertical resolution of 3.75m by making use of the modified receiver electronics of the MWL system. The high resolution measurements have facilitated the study of the fine internal structure, optical depth extinction coefficient and other parameters of importance of cirrus clouds. The present paper describes lidar system and the results obtained over a period of one year covering all the seasons and the peculiar characteristics of the cirrus during winter time at this coastal station.