3 YEARS OF RAINFALL OVER THE INDIAN-OCEAN

Monthly rain falling on the Indian Ocean is mapped for the period 1979 through 1981 by means of observations of the Nimbus-7 Scanning Multic hannel Microwave Radiometer. Both stationary and mobile parts were fou nd in the pattern of rain. The stationary part consisted of three zona l and two meridional bands. Only one, the band along and south of the equator, maintained a strong presence through all seasons. A north equ atorial counterpart to this south equatorial band also was persistent, but weak. The mobile part of the pattern took the form of a wave. The locus of this wave was an eastward-tilted figure eight, which straddl ed the equator. The wave moved clockwise along the north loop of the f igure eight, counter-clockwise along the south loop. The crest of the wave crossed the equator from south to north in May or June and crosse d the equator from north to south between August and October. Along it s path the equatorial bands were alternately amplified and damped, and the transient bands were activated and suppressed. The effect of the bands and wave was to produce a strong ''monsoon'' (annual cycle, summ er peak) signature in rain falling over both the northeastern and sout hwestern reaches of the Indian Ocean.