Genesis potential parameter using satellite derived daily tropical cyclone heat potential for North Indian ocean

Abstract

ABSTRACT Tropical Cyclone Heat Potential (TCHP) is the heat content relative to 26°C isotherm, which is important in the development of cyclone. Cyclonic events last for few weeks and become intensified within few days or in some cases few hours. To study such low pressure systems, daily TCHP is required which is created in our study using Two Layer Gravity Model (TLGM) using monthly climatologies of temperature and salinity profiles, daily Sea Surface Height Anomaly (SSHA) and daily Sea Surface Temperature (SST). This satellite-based data of SSHA and SST are used to create daily TCHP fields which are validated using collocated ARGO in-situ data. ARGO derived TCHP and TLGM TCHP showed correlation coefficient , which indicates that TLGM can be used for near real time TCHP calculation for cyclone studies. Analysis done on 92 non-developing and 93 developing systems shows that, on the day of formation of depression, average TCHP is 89.3 kJ cm for developing systems while average TCHP is 78.3 kJ cm for non-developing systems in North Indian Ocean (NIO). Minimum TCHP was found to be 27.2 kJ cm and 28.6 kJ cm for developing and non developing systems out of 93 and 92 cases, respectively. Further, Genesis Potential Parameter (GPP) using low-level relative vorticity, middle troposphere relative humidity, middle troposphere temperature instability and vertical wind shear is created based on past similar studies, but with six hourly as well as daily resolution (1993 to 2017) and 0.125° 0.125° spatial resolution. Using daily TCHP, another index called Genesis Potential Index (GPI) is created and then both the GPP and GPI are analysed for 93 developing and 92 non-developing systems in north Indian ocean from the year 1993 to 2017. Our study shows that both are good predictors for the lead periods of less than 2 days, while for the lead periods of more than 2 days, the distinction becomes difficult between developing and non-developing systems. Abbreviations: TLGM - Two Layer Gravity Model; TCHP - Tropical Cyclone Heat Potential; - Depth of 26°C isotherm; - Depth of 20°C isotherm; NIO - North Indian Ocean; AS - Arabian Sea; India Meteorological Department - IMD; BOB - Bay of Bengal