Tropical cyclone activity over Bay of Bengal in relation to El Nino-Southern Oscillation

The present paper investigates the impact of El Nino-Southern Oscillation (ENSO) on the Bay of Bengal tropical cyclone (TC) activity and associated alterations in environmental conditions during post-monsoon (October-December) season for a period of 44 years (1972-2015). The analysis reveals that the post-monsoon season TCs frequency, accumulated cyclone energy (ACE) and power dissipation index (PDI) values are negatively correlated with the Nino 3.4 sea surface temperature (SST) anomalies (significant at the 95% confidence level). La Nina years are characterized by more frequent and intense cyclonic events compared with El Nino years. The mean ACE and PDI values are approximately two times higher in La Nina than El Nino years. The mean number of TC days per year is also higher in La Nina (7.64 days) than El Nino (3.68 days) years (significant at 95% confidence level). In addition, a significant shift in genesis locations, tracks and landfalling locations of TCs has been observed under different ENSO phases. The mean genesis location of TCs have shifted eastward with tendency of more recurving tracks in La Nina than El Nino years. The presence of strong convective activity, reduced vertical wind shear, high SST (>= 28 degrees C), enhanced mid-tropospheric relative humidity and low-level cyclonic circulation aids the TCs formation and strengthening during La Nina and vice-versa in El Nino conditions.