Soil moisture–precipitation feedbacks in pre‐ and post‐monsoon landfalling tropical cyclones in Bay of Bengal

Abstract

The Bay of Bengal (BoB) experiences an average of three to four tropical cyclones (TCs) annually. The high population density of surrounding countries often leads to disastrous consequences when a TC makes landfall. As a result, it is critical to understand the evolution and intensity of rainfall associated with a TC that originates in the BoB. In this study, we examine the impact of initial soil moisture (SM) conditions on the TC track, TC recycled precipitation, and other TC variables using the Weather Research and Forecasting (WRF) model upgraded with Eulerian water‐tagging capabilities. We simulated pre‐monsoon TCs Amphan, Titli, Viyaru and post‐monsoon cyclones Phailin, Titli and Helen originating in the BoB. We conducted sensitivity experiments with dry and wet initial SM conditions to determine the impact of initial SM changes on TCs. We also generated four control simulations for each TC by changing the initial time to assess the effect of internal model variability. Our results indicate that initial SM conditions impact TC more than the internal model variability. We find that changes in the initial SM affect the latent heat flux, which influences the temperature and the synoptic wind pattern over the entire domain, resulting in changes in the TC properties. We find the feedback of SM to TC precipitation (quantified as recycled precipitation) is stronger as the TC approaches the landfall. The post‐landfall recycling ratio for pre‐monsoon TCs is approximately 5%–10%, but is around 20%–30% for post‐monsoon TCs. We observe that the Viyaru, Titli and Helen TC tracks are more sensitive to the initial SM conditions compared to the other three TCs. In addition to SM, we find that factors such as proximity to land, and TC intensity also have a role in determining the quantity of recycled precipitation for a TC.