Active and inactive tropical cyclone years over the Bay of Bengal: 1972-2015

The present study examines the tropical cyclones (TCs) activity over the Bay of Bengal (BoB) during post-monsoon season (October-December) for the period 1972-2015 (44 years period). The study has explored the active and inactive TC years on the basis of mean +/- 1 standard deviation, respectively. A total of nine active (when TCs frequency is >= 4 in a year) and 18 inactive (when TCs frequency is <= 1 in a year) TC years have been identified during the 44 years period. The mean frequency of TCs during the active TC years (4.22 TCs/year) is approximately five times higher than the inactive TC years (0.78 TCs/year). These active and inactive TC years have shown association to some extent with El Nino-Southern Oscillation and Indian Ocean Dipole events. Various environmental factors influencing the occurrence of TCs have been investigated, by analyzing the composites of nine active and 18 inactive TC years. Further, the existence of more precipitable water, strong convective activities, less sea level pressure, reduced vertical wind shear, upper-level easterly winds and high low-level cyclonic vorticity have provided favourable conditions for the TCs genesis during the active TC years.