Impact of sea surface temperature on the secondary circulation of tropical storm mora

Tropical Cyclones (TC) are warm core regions that are composed of primary circulation (PC) and secondary circulation (SC). PC dominates the overall intensity of TCs and SC is considered as a second order superimposed perturbation on it. Studies have shown that SC helps define the vertical structure of PCs inside the radius of maximum winds. Therefore, the present study analyzes the changes in Sea Surface Temperature (SST) and corresponding build-up of heat and moisture over the Atmospheric Boundary Layer (ABL) of TC Mora. Mora emerged as a Severe Cyclonic Storm (SCS) during May 2017 over the Bay of Bengal (BoB) region. The analysis is carried out by performing different sensitivity experiments using a cloud resolving model. Four experiments with varying SST inputs have been performed to comprehend the variations in storm induced convection and overturning of secondary circulation inside the storm system. The inputs have been taken from realtime reanalysis Hybrid Coordinate Ocean Model (HyCOM), National Centres for Environmental Information (NCEI) and the Climatological input available for the model. Classical Sawyer-Eliassen equation is used to discuss the pattern and strength of secondary circulation. The findings demonstrate the dominance of inertial stability at low levels and static stability at higher levels which has helped in the maintenance of overturning circulation inside the storm. It has been found that the intensity of overturning circulation is reinforcing the updrafts and spread of cloud cover up to the radius of maximum winds. The study further focuses on inflow-outflow characteristics and phase changes in cloud hydrometeors during the intensification of Mora. It has been seen that SST needs to be managed carefully in modeling-based studies as they determine the vertical structure of the atmosphere. The work can help analyze energy balances during the genesis and intensification of storms for further applications. The analysis is expected to be helpful for storm prediction studies and understanding the complex processes inside the storm system.