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Factors controlling January-April rainfall over southern India and Sri Lanka

Vialard, J and Terray, P and Duvel, JP and Nanjundiah, RS and Shenoi, SSC and Shankar, D (2011) Factors controlling January-April rainfall over southern India and Sri Lanka. Climate Dynamics, 37 (3). pp. 493-507.

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Most of the annual rainfall over India occurs during the Southwest (June-September) and Northeast (October-December) monsoon periods. In March 2008, however, Southern peninsular India and Sri Lanka received the largest rainfall anomaly on record since 1979, with amplitude comparable to summer-monsoon interannual anomalies. This anomalous rainfall appeared to be modulated at intraseasonal timescale by the Madden Julian Oscillation, and was synchronous with a decaying La Niña event in the Pacific Ocean. Was this a coincidence or indicative of a teleconnection pattern? In this paper, we explore factors controlling rainfall over southern India and Sri Lanka between January and April, i. e. outside of the southwest and northeast monsoons. This period accounts for 20 of annual precipitation over Sri Lanka and 10 over the southern Indian states of Kerala and Tamil Nadu. Interannual variability is strong (about 40 of the January-April climatology). Intraseasonal rainfall anomalies over southern India and Sri Lanka are significantly associated with equatorial eastward propagation, characteristic of the Madden Julian Oscillation. At the interannual timescale, we find a clear connection with El Niño-Southern Oscillation (ENSO); with El Niños being associated with decreased rainfall (correlation of -0. 46 significant at the 98 level). There is also a significant link with local SST anomalies over the Indian Ocean, and in particular with the inter-hemispheric sea surface temperature (SST) gradient over the Indian Ocean (with colder SST south of the equator being conducive to more rainfall, correlation of 0. 55 significant at the 99 level). La Niñas/cold SSTs south of the equator tend to have a larger impact than El Niños. We discuss two possible mechanisms that could explain these statistical relationships: (1) subsidence over southern India remotely forced by Pacific SST anomalies; (2) impact of ENSO-forced regional Indian Ocean SST anomalies on convection. However, the length of the observational record does not allow distinguishing between these two mechanisms in a statistically significant manner.

Item Type: Article
Additional Information: An edited version of this paper was published by Springer. This paper is for R & D purpose and Copyright [2011] Springer.
Uncontrolled Keywords: Rainfall interannual variability over India El Niño/Southern Oscillation;Madden-Julian;Oscillation; Teleconnections
Subjects: Oceanography > oceanography
Depositing User: INCOIS Library
Date Deposited: 08 Dec 2013 06:20
Last Modified: 08 Dec 2013 06:20

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