Some flow features of the Indian summer monsoon deduced from Nimbus-II radiation data

Abstract

Radiation data obtained from Nimbus-II MRIR (10–11μ) and HRIR (3.5–4.1μ) radiometer for 14–19 June 1966, over the Indian Ocean are used to study some features of the monsoon circulation during the six-day period. Low values of radiation which are associated with cloudiness show two distinct features from 15–17 June: (i) a very extensive band of approximately 1000 km in width at the equator between 50°–60° E extending towards both hemispheres, and (ii) a synoptic-scale cell covering the equatorial region approx. between 70°–90° E and 0°–10° S. The two cloud systems are separated from each other by a wide region of high radiation indicating clear conditions. Sub-synoptic scale features could be detected in the radiation field (which in turn are related to the cloud field). Northern and Western sections of the Arabian Sea were relatively cloud-free.

An attempt is made to relate the cloud fields with computed vertical motion fields. Areas of upward motion seem to coincide well with centers of low radiation (clouds) and those of subsidence with regions of high radiation. Horizontal flow features related to the computed vertical motion fields are discussed in the paper.