On the intraseasonal variations of the Asiastic Summer monsoon

Abstract

Intraseasonal fluctuations of the Asiatic summer monsoon are investigated using Outgoing Longwave Radiation (OLR) covering eight northern hemisphere summers (1 may to 30 September 1975-83, except 1978). The intraseasonal variance is large in the equatorial Indian Ocean and the northwest pacific. OLR fluctuations in the equatorial Indian ocean over India and the northwest Pacific show spectral peaks on time with the interannual variation. Over India below normal summer rainfall years are associated with 30-60 oscillation, near normal summer rainfall years are associated with 30-60 day and 10-20 day oscillations and above normal rainfall years are associated with oscillations less than 10 days.

Empirical Orthogonal Function (EOF) analysis has been carried out for the whole Asiatic summer monsoon domain. The first four EOF coefficients explain 15% of the total variance. EOF analysis confirms existence of oscillations at least on three time scales, viz., 30-60 day,10-20 day, and less than 10 days over the Asian summer monsoon region.