Satellite estimated water vapour in relation to Asian monsoon Circulation
Keywords:Tropospheric water vapour, Satellite observation, Southwest monsoon, TOVS
Water vapour plays a crucial role in various exchange and transport processes in the atmosphere and its knowledge in the tropics is extremely important for input to various global circulation models. The vast oceans of earth's surface provide a large source of moisture and continuously modify the thermodynamics of the atmosphere through latent heat flux and condensational heating. In the tropics, especially in the Indian ocean the water vapour is highly heterogeneousin nature, and is one of the parameters which is responsible for cloud formation, associated with tropical systems like monsoon flows, depression, cyclones etc. The present paper reviews the various information’s available from deferent geostationary and polar orbiting satellites about water vapour affecting the southwest monsoon region around the Indian Ocean and Indian subcontinent.
The temperature and moisture data from TIROS operational vertical sounder (TOVS) and INSAT-2E water vapour channel are examined to study water vapour distribution. Their usefulness in characterizing the Asian south-west (SW) monsoon circulation is focused. The Western Indian ocean showed an increase in mid-tropospheric moisture (700-500hPa) over about 8 to 10 days prior to the onset over Kerala coast. NOAA/TOVS layer tmperature and humidity is used to extrapolate the humidity profile at standard pressure levels. It is also used to compute latent and sensible heat flux. Total integrated water vapour from SSM/I is also used for estimating latent heat fluxes and for the diagnostics of NWP models. Recently, INSAT-2E water vapour channel was used to monitor the monsoon circiulation features. The new WV channel brought out clearly the feeding of various air masses, especially water vapour associated with monsoon onset and monsoon lows.
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