Interaction of Anticyclonic Eddies and Cyclones in the Bay of Bengal

The objective of this work is to find the interaction between mesoscale anticyclonic eddies (ACEs) and the tropical cyclones in the Bay of Bengal (BOB), a cyclone prone region in the North Indian Ocean. There are several reasons in formation and development of tropical cyclones but we mainly concentrate on sea surface height (SSH) and eddies effect. The spatial, temporal and statistical variability of the ACEs in the BOB from 1993 to 2010 has been revealed by the automated eddy detection and tracking algorithm. We consider potential mesoscale eddies with radius more than 50 km and lifespan not less than 30 days in this study. Two anticyclonic eddy-productive zones are detected in the BOB: the western BOB and the central BOB. Autumn and spring are the favorable seasons for the occurrence of ACEs. Each year tropical cyclones are generally formed in central BOB and are generating mostly in autumn and in spring which are the highest eddy intensity (EI) seasons for ACEs in the BOB. The EI of ACEs has increased sharply in the El Niño Southern Oscillation (ENSO) years 1998-2000 and 2006-2008 by 20% and 40% respectively. Five of the six devastating cyclones in the BOB generated during these high EI years from 1996 to 2009. We further analyze the trajectory of three cyclones (Nargis, Mala of category 4 and Sidr of category 5) developed during the years 2006-2008. The dynamic topographic conditions during the cyclones are calculated as the difference of SSH before the formation of cyclones and prior to the attenuation of cyclonic energy. The corresponding cyclones are superimposed on the SSH information. In all three cases it is clear that cyclones formed over the warm core eddies (ACEs) and have been guided by the warm eddies in the BOB. So the position, variability of ACEs and their high intensities during ENSO years play a significant role in the development and intensification of cyclones in the BOB.