Abstract
The present study describes variation of peak linear depolarization ratio (LDR) with wind around the cloud altitude using simultaneous observation of winds and cirrus cloud for the first time using Indian MST radar and polarization lidar co-located over a low latitude station Gadanki (13.7°N and 79.2°E). Three different cases of passage of the cirrus at different altitudes are noticed, one during a North-East monsoon day and other two during South-West monsoon days. The zonal wind below the cloud height has shown similar variation with LDR during 02 November 2006 and the meridional wind within the cloud height during 25 July 2007 and 08 June 2006 has shown opposite variation with LDR. Even though there is a significant increase in zonal wind due to the existence of tropical easterly jet (TEJ) above cloud height during 25 July 2007 and 08 June 2006, also, the vertical wind is found to be continuously varying during 25 July 2007 and it is upward dominant in the initial stage and is mostly downward in the later stage of observation on 08 June 2006, there is a slight descent in cloud altitude only during 25 July 2007. Thus, the wind above the cloud height alone may not affect the ascent/descent of the cloud top altitude. The potential temperature gradient is high within the cloud heights when the cirrus present near the cold point tropopause indicates the maximum air-mass mixing near the tropopause.
Highlights
Cirrus clouds have long fascinated the scientists because of their variable microphysical and optical properties
Wind variations around the cirrus clouds were monitored by using MST radar and Mie lidar co-located over Gadanki (13.5 ̊N, 79.18 ̊E) using three different cases, one during postmonsoon season and the other two during Indian summer monsoon
It is clear from the values of cloud optical depth (COD) for the cirrus observed at different altitudes in Cases-(a), -(b) and -(c) that the cirrus clouds are found to be visible in all cases except for the cirrus noticed near the tropoapuse region during Case-(c), which is sub-visual [6]
Summary
Cirrus clouds have long fascinated the scientists because of their variable microphysical and optical properties They are thin wispy clouds blown in high winds and intermittently associated with strong turbulence in the region of upper troposphere and lower stratosphere [1]. These clouds will significantly affect the Earth’s climate through infrared absorption and solar albedo effect [2]. In situ measurements and ground based experiments showed that nearly, 20% - 30% of Earth’s atmosphere is covered with cirrus clouds They are globally distributed and composed predominantly of ice particles Their frequency of occurrence is so high over tropics causing a significant warming to the equilibrium climate through the interaction processes between cloud and radiation [4]
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