Wavelet transform technique to study the behavior of the 10–20-day and 25–50-day modes during indian summer monsoon onset

Abstract

Wavelet transform (WT) has been employed to study the behavior of the 10–20-day and 25–50-day modes during Indian monsoon onset. Daily time-series of the zonal and meridional components of surface wind over off the Somali coast and onset dates over south Kerala during 23 years (1954–1976) have been used. In 63% of cases the results of this analysis indicate a link between summer monsoon onset and the 10–20-day and 25–50-day bands expressed by the simultaneously occurrence of fluctuations in these two bands. This suggests the presence of undulatory behavior within the Somali jet whose periods are situated in the 10–20-day and 25–50-day bands during summer monsoon onset.