Impact of ENSO and the Indian Ocean Dipole on the north-east monsoon rainfall of Tamil Nadu State in India

Tamil Nadu State in south-eastern India receives most of its rainfall from October through December, a phenomenon known as north-east monsoon rainfall (NEMR). Tamil Nadu's south-west monsoon rainfall (SWMR), received between June and September, correlates positively with the Southern Oscillation Index (SOI), whereas NEMR correlates negatively. We undertook Study to investigate the relationship between global teleconnection indicators, namely the El Nino-Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD), and precipitation over Tamil Nadu during NEMR. The results showed that NEMR had significant positive correlation with Nino-3 sea-surface temperatures (SST) in July. The statistical relationships between the IOD and NEMR were much weaker than those between ENSO and NEMR. To understand the relationship and/or local dynamic structure, composites of the Circulation field for the extreme El Nino/La Nina years were compared with the mean state for July, September and November. Composite Circulation analysis clearly showed that in extreme El Nino years, the Bay of Bengal exhibited a positive sea-level pressure (SLP) anomaly, and the Arabian Sea exhibited a negative SLP anomaly, which resulted in strong north-easterly winds, bringing Moisture and precipitation to the Southern part of India in November. The reverse was also true: A strong negative anomaly was observed in the Bay of Bengal during La Nina years, which resulted in a weak NE monsoon. However, local circulation anomalies (Bay of Bengal through Arabian Sea) did not continue from July to November. Copyright (C) 2009 John Wiley & Sons, Ltd.