Energetics of super cyclone ‘GONU’ and very severe cyclonic storm ‘SIDR’

Abstract

This paper discusses the energetics aspects of two tropical cyclones formed over the north Indian Ocean during 2007, viz., the Super Cyclonic Storm (GONU) and the Very Severe Cyclonic Storm (SIDR). From the analysis of various energetics terms such as the Eddy Available Potential Energy (AE), Zonal Available Potential Energy (AZ), Zonal Kinetic Energy (KZ), Eddy Kinetic Energy (KE) and their generation and inter-conversions i.e., G(AE), G(AZ), C(AE, KE), C(AZ, KZ), C(KZ, KE) and C(AZ, AE) have been computed on day to day basis during the periods of their intensifications over the domain 5° N to 25° N, 55° E to 75° E in respect of ‘GONU’ and 5° N to 25° N, 77° E to 97° E for ‘SIDR’. Besides the above, the area averaged value of s (Sigma), the vertically averaged Moist Static Energy (MSE), has also been computed on each day. Day-to-day evolution of these parameters is mapped and described. Some of the distinguishing features in the energetic of these two intense vortices which formed in entirely different climatological settings have been brought out. It is noticed that in the case of ‘GONU’, though both barotropic and baroclinic energy conversions have taken place during the life cycle, the intensification phase is characterized by an enhancement in AE, KE and vertically integrated Moist Static Energy. Enhancement in AE can be attributed to the generation of AE, which may again be attributed to the asymmetric latent heat of condensation associated with the asymmetric rainfall in the cyclone field. Enhancement in KE may be attributed to the enhancement in both barotropic and baroclinic conversion into KE. Though most of these observations made for ‘GONU’ are found to be attributable to ‘SIDR’ as well, the intensification of ‘SIDR’ appears to have more similarity to that of a typical growing mid-latitude baroclinic wave. In this case, the enhancement in AE, could also be attributed to positive C(AZ,AE), which is mainly due to interaction with mid-latitude baroclinic westerly wave. The energetics analysis also indicates that GONU had helped in the enhancement of seasonal mean meridional circulation where as the SIDR had inhibited the enhancement of seasonal mean meridional circulation.