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

Abstract

The factors controlling rainfall over southern India and Sri Lanka between January and April, i.e. outside of the southwest and northeast monsoons are explored. 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, a clear connection is noticed with El Nino-Southern Oscillation (ENSO); with El Ninos 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 Ninas/cold SSTs south of the equator tend to have a larger impact than El Ninos.