Variation of tropospheric energy and its fluxes during severe cyclone affecting Bangladesh coast in the last decade

Abstract

The present slndy have been made with a view to find out the changes of various atmospheric energy components and their fluxes during "cyclone period" as compared to thm of .'before occurrence.' and '.after landfall" for seven cyclones that occurred in the Bay of Bengal in the !<1stdecade. Three of them Were pre-monsoon cyclone and lour "f them were post-monsoon cyclone. It was found that sensible heat decreased with the increase of height. For most of the cyclones sensible hem was large during the "cyclone period" compared !o that of other phases, On the other hand, potential energy increased with the inerea,e of heigh! and for most of the cyclones it was large in magnitude during "cyclone period", It wa~ observed that latent heat for most of the cyclones increased to initiate the cyclone. Latent heat was also increased at "after landfall" and wus maximum at the middle troposphere (500-250 mb). At the lower level, almost no variation was observed for latent beat a! different phases of the cyclone. Kinetic energy was nearly zero from lower !o middle troposphere und was increased Irom middle to upper tropm;phere for all three phases. It wus large at 300-150 mb level. For most of the cyclones kinetic energy wus maximum a! the initiation of"eycIone period" und ut "ufter landfall". It was fOl.llldthilt zonal flux ,vas \vcstward{casterly) up to about 700 mh level. Beyond this lcvcl it wa, eastward('Wes!erly). For most ofthc cyclones the magnitude of zonal flux was found largc just before starting "cyclone period" and was maximum at 250-150 mb levcl. .'Bcfore occurrence.' and during "cyclonc period'" meridional flux varied between northward and somhVv"llTd, However, ul "aIler bndral1" for most of thc cyclones it ""as southward, Its magnimde was large during "qclone period.', From the energy budget it was found that sensible heat, potential energy, kinetic energy as well as total energy were large for pre-monsoon cyclones as compared (0 postmon, oon cyclones, It was also found that 70nul und meridional fluxes wcrc high in magnitude for prc-monsoon cyclones thun thal oJ"posl-lnollsoon cycloncs,