Study of upper ocean parameters during passage of tropical cyclones over Indian seas

ABSTRACT

The primary energy supply for tropical cyclones is the upward latent heat fluxes that are directly related to Sea Surface Temperatures (SST). The strong winds induce a negative SST anomaly in the tropical cyclone wake. This is usually referred to as the ‘cold wake’. Many studies have suggested that the cold wake results in a significant reduction of upward latent heat fluxes that supply energy to the tropical cyclone, and hence provides a negative feedback on its intensity. The cold-wake feedback on the intensity of tropical cyclones is a strong motivation to understand the oceanic response to tropical cyclones. A recent study of re-examining the mechanisms controlling the cold wake has shown the importance of vertical Ekman pumping. Under the core of tropical cyclones (typically over a disk of 100 km radius), vertical pumping is responsible for a cooling of the entire water column, while surface heat fluxes and vertical mixing both contribute to the surface cooling during the cyclone passage. Farther away from the cyclone core, vertical mixing generally overwhelms the effect of vertical pumping, and also the effect of heat fluxes in the case of strong tropical cyclones. The study examines the Ekman pumping during the passage of few cyclonic storms in the Arabian Sea (AS) and Bay of Bengal (BOB) during last decade using different datasets such as Satellite (QuikScat) and reanalysis (ERA-Interim) data and calls up the value for satellite deliverables. Surface currents and subsurface temperature structure is examined further and for different Ekman pumping velocity (EPV), variable subsurface response is illustrated. The changes in ocean surface temperature, sea level and heat content obtained from the remote sensing data products, in the wake of cyclone are also reported and thus the usefulness of satellite products to study the coupled tropical system is demonstrated.

Acknowledgments

Authors are thankful to the anonymous reviewers for their constructive comments which helped to improve the quality of the paper. They wish to thank the Director, IITM for providing the facilities. Wind data from QuikScat and ERA-Interim, SST data from Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) and currents, temperature and SSHA data from CMEMS, also best track data from IMD e-atlas, is gratefully acknowledged. Authors are thankful to K. Rama Krishna, G. Srinivas, & P. Prakash Rao for scientific discussions. Thanks are also due to COLA for the GrADS software used to do the illustrations.

Disclosure statement

No potential conflict of interest was reported by the authors.