Climatology Of Thin Cirrus Clouds at Gadanki (13.5°N, 79.2°E) Using Ground Based Lidar And Satellite Based Measurements
Keywords: Remote sensing, Atmosphere, Lidar, Cirrus clouds, Optical depth, Depolarization ratio, Lidar ratio
Abstract. High altitude cirrus clouds play a significant role in the radiative balance of Earth atmosphere system. Information on cirrus occurrences and their optical properties is essential for climate modeling studies. The influence of high altitude thin cirrus clouds on the climate is important due to their optical and thermodynamic properties. In order to quantify their effect on atmosphere, the vertical structure and optical properties of these thin cirrus clouds are to be characterized. The Lidar technique has become a unique tool for detecting and characterizing cirrus clouds for their optical properties. Ground based LIDAR system offers an excellent way to obtain characteristic values on the cirrus formations, although the microphysical and optical properties of thin cirrus clouds can also obtained on global scale by the observations from Earth-orbiting Satellites .The ground-based lidar observations could provide more intensive measurements on continuous basis, compared to satellite observations. Utilising observations from both, the statistical characteristics, physical and optical properties of thin cirrus clouds can be retrieved more precisely. The present study is based on the ground based lidar measurements using the pulsed monostatic LIDAR system at the National Atmospheric Research Laboratory [NARL], Gadanki (13.5° N, 79.2° E), Andhra Pradesh, India. The data obtained in the altitude range of 8−20 km are used for this study. Cirrus observations made using CALIPSO and MODIS satellites are compared with the ground based lidar data for systematic statistical study of cirrus climatology. Optically thin cirrus clouds (τ < 0.3) observed during 2009 are selected and their microphysical and geometrical properties are studied. The microphysical properties such as optical depth, lidar ratio and depolarisation ratio for cirrus clouds were obtained. It is observed that the variability in optical depth depends on the composition and thickness of the clouds. The relationships between various quantities were also processed. The study shows that the thin cirrus generally was present in higher altitudes and the optical properties show correlation with the height and the temperature.