Quantification of the ocean surface and subsurface parameters for Cyclogenesis and intensification in the North Indian Ocean

Tropical cyclones (TCs) are intensifying over the years leading to destruction and disasters, particularly in the heavily inhabited coasts of the tropical regions. Cyclogenesis is dependent on various ocean and atmospheric conditions. However, most of the statistical and numerical prediction models used in cyclone related studies rely primarily on atmospheric parameters with sea surface temperature (SST) being one of the only oceanic parameters used. Past studies have found that the dynamics and thermodynamics of the ocean subsurface has a strong role in the genesis and intensity changes of TCs. In the present work, we analyzed pre-storm (upto 5 days prior to cyclogenesis) oceanic surface and subsurface conditions to evaluate the magnitude of influence of these parameters on genesis and intensifications of TCs. For this, SST from Tropical Rainfall Measuring Mission’s (TRMM) Microwave Imager (TMI), TropFlux heat fluxes (sensible and latent), Sea Level Anomaly (SLA) from Archiving, Validation and Interpretation of Satellite Oceanographic (AVISO) data centre, Tropical Cyclone Heat Potential (TCHP) from National Remote Sensing Centre, Indian Space Research Organization and cyclone best track data archived from Indian Meteorological Department were utilized.. From the analysis carried out for 55 cyclones spanning the years 2001-2015 in the Northern Indian Ocean (NIO), it was observed that genesis of most of the cyclones occurred in the pre-existing SST range of 29 °C to 31 °C, TCHP range of ~60 to 100 KJ/cm² and SLA range of ~0.0 to 0.15 m Similarly, intensification of the cyclones was observed in SST range 28 °C to 30 °C or TCHP range 40 to 100 KJ/cm², or SLA range of 0.0 to 0.15 m in the NIO. Out of the total 55 cyclones analysed, ~87% form and ~91% cyclone intensify when SLA lies between 0.0 to 0.15 m. Further, SST and TCHP values were observed to reduce from its 5^th day values before genesis to the day of genesis. The corresponding sensible and latent heat fluxes are observed to increase during this period, which provide a favourable condition for TC genesis and intensification.

Key Word: Tropical Cyclones, Sea Surface Temperature, Sea Level Anomaly, Heat Fluxes, North Indian Ocean