1. Epochal changes in Arabian Sea Mini Warm Pool
ABSTRACT
Arabian Sea Mini warm Pool (ASMWP) is the anomalous pool of warm surface water in
the South Eastern Arabian Sea (SEAS) prior to the onset of south-west monsoon. The monsoon
onset vortex usually forms over this warm water making this phenomenon very important for
monsoon research. It is found that the warm pool forms almost all the years but the formation of
well-established warm pool is closely associated with El Nino formation in the Pacific. The
warming patterns in the El-Nino developing years and El-Nino decaying years are different.
Thus it is very important to understand the mechanism associated with formation of ASMWP.
The availability of monthly HadISST data and NCEP-NCAR reanalysis surface wind
fields from March to Aug over 40 ᴼE-80 ᴼE, 10 ᴼS-20 ᴼN for period of 1948 to 2006 are explored
to understand the epochal changes in the ASMWP.
The averaged HadISST of March-May during 1948-2008 shows expansion in region of
ASMWP extending southwestward. In El-Nino years Epoch 1 (1948 to 1976) displayed weak
warming during March-May due to strengthening of mean wind. However June to August
experienced warming due to reduced upwelling along the Somalia coast driven mainly by
weaker mean winds. The weak mean winds are caused by the anomalous winds opposing the
mean winds. Epoch 2 (1978 to 2006) is warmer during March-May of the years following El-
Nino years (especially in May). The lead lag correlation between ASMWP and Nino3.4 index
further strengthen our findings.