Environmental controls on the track and intensity of tropical cyclones in the Bay of Bengal

Tropical cyclones (TCs) in the Bay of Bengal (BoB) cause substantial damage to lives and property. This thesis aims to further our understanding of the BoB TC activity in the present and the future and the large-scale environmental conditions influencing the genesis and intensification of BoB TCs. Although used by the Indian Meteorological Department (IMD) for operational fore casting, the Genesis Potential Parameter (GPP) is found not to be a good predictor of the development of low pressure systems into TCs during their early stage. Addition ally, GPP is unable to predict further TC intensification once they reach cyclonic storm strength (∼ 18 ms−1). However, the mid-tropospheric instability, scaled mid-tropospheric humidity and vertical wind shear components of the GPP can explain the intensification of a low-pressure system in the BoB. Six of the high-resolution HighResMIP (High Resolution Model Intercomparison Project) Global Climate Models (GCMs, atmosphere-only and coupled), mostly capture the bi modal seasonal cycle of the BoB TCs, with lower TC frequency during pre-monsoon sea son (April-May) than post-monsoon (October-November]). The largest model bias in the environmental variables influencing the genesis occurs for the windshear term in the Gen esis Potential Index (GPI) in all models during the post-monsoon season. The positive windshear term (inverse of actual windshear) bias suggests an increase in the model TC frequency compared to the observations in the post-monsoon season. Ocean-atmosphere coupling causes a reduction in the SST and TC frequency in almost all coupled models compared to their atmosphere-only counterparts. Future projections of BoB TCs in five HighResMIP models show a decrease in TC frequency even though there is an increase in the SST in the future for most models. Comparing the pre-monsoon and post-monsoon seasons, there is relatively more moisten ing in post-monsoon and a relatively smaller reduction in TC frequency in the future for most models.