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Link between convection and meridional gradient of sea surface temperature in the Bay of Bengal

DRS at CSIR-National Institute of Oceanography

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Title Link between convection and meridional gradient of sea surface temperature in the Bay of Bengal
 
Creator Shankar, D.
Shetye, S.R.
Joseph, P.V.
 
Subject Southwest monsoon
Indian summer monsoon
Sea surface temperature gradient
ITCZ
Summer Monsoon Current
Southwest Monsoon Current
Tropical Convergence Zone
Indian Ocean
 
Description We use daily satellite estimates of sea surface temperature (SST) and rainfall during 1998-2005 to show that onset of convection over the central Bay of Bengal (88-92E, 14-18N) during the core summer monsoon (mid-May to September) is linked to the meridional gradient of SST in the bay. The SST gradient was computed between two boxes in the northern (88-92E, 18-22N) and southern (82-88E, 4-8N) bay; the latter is the area of the cold tongue in the bay linked to the Summer Monsoon Current. Convection over central bay followed the SST difference between the northern and southern bay (Delta T) exceeding 0.75 degC in 28 cases. There was no instance of Delta T exceeding this threshold without a burst in convection. There were, however, five instances of convection occurring without this SST gradient. Long rainfall events (events lasting more than a week) were associated with an SST event (Delta T >= 0.75 degC); rainfall events tended to be short when not associated with an SST event. The SST gradient was important for the onset of convection, but not for its persistence: convection often persisted for several days even after the SST gradient weakened. The lag between Delta T exceeding 0.75 degC and the onset of convection was 0-18 days, but the lag histogram peaked at one week. In 75% of the 28 cases, convection occurred within a week of Delta T exceeding the threshold of 0.75 degC. The northern bay SST, T_N, contributed more to Delta T, but it was a weaker criterion for convection than the SST gradient. A sensitivity analysis showed that the corresponding threshold for T_N was 29 degC. We hypothesise that the excess heating (~ 1 degC above the threshold for deep convection) required in the northern bay to trigger convection is because this excess in SST is what is required to establish the critical SST gradient.
Department of Ocean Development, New Delhi.
 
Date 2007-05-14T07:04:52Z
2007-05-14T07:04:52Z
2007
 
Type Journal Article
 
Identifier Journal of Earth System Science, vol.116(5); 385-406
http://drs.nio.org/drs/handle/2264/607
 
Language en
 
Rights Indian Academy of Sciences, Bangalore
 
Format 810380 bytes
application/pdf
 
Publisher Indian Academy of Sciences