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

Shankar, D. ; Shetye, S. R. ; Joseph, P. V. (2007) Link between convection and meridional gradient of sea surface temperature in the Bay of Bengal Journal of Earth System Science, 116 (5). pp. 385-406. ISSN 0253-4126

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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 (88-92°E, 14-18°N) 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 (88-92°E, 18-22°N) and southern (82-88°E, 4-8°N) 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 (ΔT) exceeding 0.75°C in 28 cases. There was no instance of ΔT 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 (ΔT≥0.75°C); 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 ΔT exceeding 0.75°C 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 ΔT exceeding the threshold of 0.75°C. The northern bay SST, TN, contributed more to ΔT, but it was a weaker criterion for convection than the SST gradient. A sensitivity analysis showed that the corresponding threshold for TN was 29°C. We hypothesise that the excess heating (∼1°C 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.

Item Type:Article
Source:Copyright of this article belongs to Indian Academy of Sciences.
Keywords:Southwest Monsoon; Indian Summer Monsoon; Sea Surface Temperature Gradient; Itcz; Summer Monsoon Current; Southwest Monsoon Current; Tropical Convergence Zone; Indian Ocean
ID Code:54081
Deposited On:11 Aug 2011 12:03
Last Modified:18 May 2016 06:56

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