Intraseasonal periodicities in Indian rainfall

Abstract

A 40-50 day spectral peak corresponding to the Madden-Julian Oscillation is found over most of the portion of India south of 23°N. The phase of the oscillation is such that the precipitation maximum appears first over the relatively dry southeastern portion of the peninsula. Ten to 12 days later the precipitation peaks simultaneously all along the coast west of the Western Ghats and along a line running across India between 20° and 25°N. The precipitation maximum then spreads slowly northward and loses significance. In addition to the 40-50 day oscillation, significant spectral peaks and coherent structures in precipitation are found whose characteristics correspond to those of monsoon lows. These are associated with a peak in the precipitation spectrum between about 5 and 7 days, which is strongest on the Bay of Bengal coast near 21°N. Evidence for a spectral peak near 15 days is sparse, being limited to a few regions in the north of India where the 40-50 day oscillation does not dominate the low-frequency variance. -from Authors