Influence of Pacific Decadal Oscillation on the relationship between ENSO and tropical cyclone activity in the Bay of Bengal during October–December

The relationship between ENSO and tropical cyclones (TCs) activity in the Bay of Bengal (BoB) during October–December under cold (1950–1974) and warm (1975–2006) phase of Pacific Decadal Oscillation (PDO) is investigated. A statistically significant difference in the formation of total number of TCs and intense TCs (Category-1 and above) between El Niño and La Niña years is observed when the PDO was in warm phase. Our analysis shows that, there is a tendency to form more number of TCs during La Niña years (2.62 TCs per season) than during El Niño years (1.6 TCs per season) under warm phase of PDO. Moreover, the difference is quite high for intense TCs cases, such as, relatively more number of intense TCs forms in the BoB during La Niña years (1.4 TCs per season) compared to El Niño years (0.10 TCs per season) under warm phase of PDO. However, the difference in the formation of total number of TCs and intense TCs between La Niña and El Niño years is not significant under cold phase of PDO. Significant enhancement in low level cyclonic vorticity and mid-troposphere humidity during La Niña years compared to El Niño years when the PDO was in warm phase, rather than the PDO was in cold phase leads to this difference. Our analysis further shows that how the ENSO related teleconnection to the Indian Ocean region differ under warm and cold phase of PDO.