Impact Of Enso And The Indian Ocean Dipole On The North-east Monsoon Rainfall Of Tamil Nadustate In India

摘要

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 a 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.