Genesis and Intensification of Tropical Cyclone of North Indian Ocean Using Numerical Model

Abstract

Tropical cyclones (TCs) represent one of the most prevalent and devastating forms of natural disasters. Despite their significant impact, accurately predicting tropical cyclones (TCs) remains a challenging endeavour due to the complexities involved. Over the past fifty years, numerous theories have been proposed to elucidate the genesis and intensification of TCs. However, no single theory has been able to explain the genesis and intensification of TC fully. Consequently, there remains a division among scientists regarding a comprehensive understanding of TC formation. The current study conducted in the North Indian Ocean (NIO) aims to provide new insights into the various stages involved in the genesis and intensification of TCs from low-pressure systems (LPS). This study employed data from the NCEP FNL reanalysis of 1x1 degree resolution as input for the Weather Research and Forecasting (ARW) model of version 4. We utilized the domain configuration of child and parent domain through one-way nesting. A combination of Kain-Fritsch (new Eta) scheme for cumulus parameterization and the WRF Single-Moment 6 class (WSM6) graupel scheme for microphysics was incorporated in model run. The findings indicate that upper wind circulations and the geographical positioning of LPS are critical to the genesis and intensification of TCs. An upper cyclonic circulation located to the left or northwest of the centre, along with an anticyclonic circulation or poleward winds to the right or northeast, significantly increases the likelihood of TC formation. Furthermore, the dominance of upper-level westerlies over LPS creates favourable conditions for the genesis of TCs. Easterly winds tend to hinder both genesis and intensification in the NIO. Additionally, proximity to coastal regions can adversely affect TC genesis. Vertical wind shear (VWS) values between 3 and 10 m/s are crucial for the transformation of LPS into TCs. Sustained declines in central pressure and mid-level Geopotential Height (GPH) foster an environment conducive to both the TC genesis and intensification. Sea Surface Temperatures (SST) exceeding 26°C and a radial gradient in SST enhance the likelihood of TC genesis. The warming of the inner core of LPS is favourable for both the genesis and 8 heightened intensity of TCs. Minimum potential vorticity (PV) of 1 at the upper level is critical for TC genesis, with a sustained increase in upper PV over time supporting further intensification. The Convective Available Potential Energy (CAPE) was lowest at the centre of the LPS, with CAPE values ranging from 2000 to 4000 J/kg within the LPS, which are conducive to tropical cyclone genesis.. A maximum CAPE value of 5000 J/kg during the genesis stage indicates potential for high-intensity TCs. Elevated relative humidity at mid-level altitudes and a symmetric cloud band pattern around the centre of the LPS significantly promote the genesis of TCs and enhance the potential for high-intensity TCs. The boundary layer air is substantially influenced by heat flux from the underlying warm sea surface. Continuous enhancement of upward vertical heat flux accelerates the genesis and intensification of TCs. Despite differences in data resolution, scale, and domain configuration, the model results and analyses derived from the European Centre for Medium-Range Weather Forecasts (ECMWF) concerning TC genesis and intensification substantially corroborate each other. Thus, the outcomes of this study are deemed reliable. The insights acquired from this research are invaluable in enhancing accurate predictions of TC genesis and intensification in the NIO. This study will serve as a guiding tool for governmental departments in Bangladesh and India, assisting in the protection of human life and the mitigation of damage to property, infrastructure, environment, and biodiversity resulting from TCs. Various government agencies will have sufficient time to be well-equipped to execute timely responses and implement appropriate disaster management measures.