Role of Ocean in the Variability of Indian Summer Monsoon Rainfall - The Earth's Hydrological Cycle - page 236

( a)

( b)

Fig. 2 850 hPa wind as mean of 1979-2010. a January and February and b July and August

shown by observational studies (Joseph et al. 1994 , 2006 ) and modelling studies (Ju and
Slingo 1995 ; Soman and Slingo 1997 ; Annamalai et al. 2005 ). The correlation coefficient
between the date of monsoon onset over Kerala and the SST (Fig. 5 ) shows that when SST
anomaly is positive south of the equator and negative north of it, monsoon onset is delayed.
This correlation pattern has persistence of several months prior to the monsoon onset.

3 Active-Break Cycle of Monsoon

Monsoon has an active-break (AB) cycle of period varying between 30 and 60 days. This
is the most important intra-seasonal variability of the monsoon. There is a large volume of
observational and modelling studies that demonstrate the air-sea interactions associated
with the monsoon active-break cycle, an excellent review of which may be found in
Goswami ( 2005 ). During active monsoon spells, there is an east-west band of raining
convective clouds passing through India in the latitude belt 10N-20N from longitude
70E extending beyond 120E and the associated LLJ is located just south of this cloud
band from central Arabian sea through peninsular India and the BoB to the west Pacific
ocean. LLJ serves as a conduit for the transportation of the large quantity of moisture
needed for the monsoon rainfall of Asia and for providing the dynamics for the monsoon