Influence of Indian Summer Monsoon on the Post-Monsoon Cyclones

The North Indian Ocean (NIO) has two Tropical cyclone (TC) seasons, i.e., pre-monsoon and post-monsoon. We find that the Indian summer monsoon (ISM) has an influence on the frequency of cyclones in the post-monsoon in the NIO. Flood years show a higher frequency of TCs, and drought years show a lesser frequency of TCs than normal years. By the examination of Grey-Sikka parameters for cyclogenesis, we show that during the drought years, the mid-tropospheric humidity, low-level vorticity, and Tropical Cyclone Heat Potential are lower than in normal years and the vertical shear is higher over most of the NIO. These factors lead to the reduced cyclonic frequency in the Bay of Bengal during drought years and more frequent cyclones in flood years, though the relation is more ambiguous in the Arabian Sea. This study builds an unexplored relation between ISM and TCs in the NIO and would help in improving TC seasonal prediction.