Upper Ocean Thermal Features during Tropical Cyclones over Bay of Bengal

Abstract

The upper ocean is dramatically affected during tropical cyclones (TCs). Cyclones interact not only with the surface but also with the deeper oceans, the depth depending upon the strength of the wind mixing. Hence, it is necessary to consider the thermal structure of the upper ocean for cyclone studies. Rapid intensification of cyclone Nargis in the Bay of Bengal from category-1 to category-4 within 24 hours was attributed to the presence of a pre-existing warm SSHA evidenced by the insitu (Argo data) and altimeter observations. The warmer layers of 26°C extended up to 100 m beneath the surface such as Isothermal layer depth (ILD) and barrier layer thickness (BLT) and Upper Ocean Heat Content (UOHC) during the cyclone progression were computed. The rate of intensification and final intensity of cyclones are sensitive to the initial spatial distribution of the mixed layer. The most apparent effect of TC passage is noted by the marked SST cooling, and the response of the ocean mixed layer temperature typically 1 to 6°C towards the right of the storm track. In the present work, the response of Upper Ocean to the tropical cyclones over Bay of Bengal based on the satellite Altimetry, ARGO, RAMA buoys and QUICKSCAT forced (MOM-GODAS) data. The present studies suggest the use of sea surface height anomalies (SSHA) data derivable from satellite altimeters are more useful instead of sea surface temperatures in the atmospheric models, particularly, in the cyclone and coupled models.