Large-Scale Precipitation and Outgoing Longwave Radiation from INSAT-1B during the 1986 Southwest Monsoon Season

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Abstract
Areally averaged precipitation and broadband outgoing longwave radiation (OLR) have been estimated from infrared window channel observations from INSAT-1B, the Indian geostationary satellite, for the period June–September 1986. The estimation techniques used were identical with those contained in previously published work using GOES (for precipitation) and NOAA (for OLR) satellite data. The fields of estimated monthly mean precipitation and OLR are quite similar, with regions of low flux corresponding to arm of heavy precipitation. Two bands of heavy rainfall were found, one near the equator, possibly associated with the Intertropical Convergence Zone, and another extending northwestward from Indonesia through the Bay of Bengal and over India. This latter feature exhibited a pronounced southeastward retreat during the course of the season. The rainfall estimates are reasonably consistent in both distribution and magnitude over India with climatological mean fields derived from rain gauge measurements. The OLR is similar in distribution but is about 5–10 W m−1 lm in magnitude over land than that derived from observations from NOAA polar-orbiting satellites. Comparisons between weekly estimated rainfall and station rainfall observations show that the quantitative relationships between cloudiness and rainfall found in previous work are confirmed over most of India. An area along the west coast where orographic rainfall is important exhibits much higher correlations when a cloud top temperature of 265 or 270 K is used as the upper threshold for precipitation instead of 235 K.

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