Role of Ocean in the Variability of Indian Summer Monsoon Rainfall - The Earth's Hydrological Cycle - page 245

Fig. 15 a The 850 hPa wind
flow showing the LLJ and a
monsoon depression vortex
cantered over north BoB b The
decreasing trend of the mean
850 hPa zonal wind (LLJ) of
June to September flowing
through peninsular India

(a)

(b)

5 Rapid Warming of the Indian Ocean

In the global warming scenario, Joseph and Sabin ( 2008b ) reported a rapid increase in the
SST of the equatorial Indian Ocean during the monsoon season from 1950 which resulted
in an increase in the convection over the area—Fig. 14 a, b. This increased equatorial
convection resulted in the weakening of the monsoon Hadley circulation and the conse-
quent weakening of the LLJ and the Tropical Easterly Jetstream. The weakening of the LLJ
flowing through peninsular India (Fig. 15 ) could be the possible cause for the observed
decreasing trend in the frequency of monsoon depressions that form north of the LLJ in the
BoB. As may be seen from Fig. 16 , the SST of June to September averaged over an area
bounded by latitudes 5Sto5 N and longitudes 60Eto90 E showed only a small
increasing trend during the period 1891-1960 and the number of monsoon depressions