Study on the Structure of Weak Intensity Tropical Cyclones over Bay of Bengal Using WRF Model.

Abstract

Comprehensive sensitivity analysis on Cumulus parameterization schemes of Weather Research and Forecasting model (WRF version 3.80) has been carried out for the effects on structure of weak intensity Tropical Cyclones Rashmi, Viyaru, Nilam and Khaimuk those formed in the Bay of Bengal and crossed Bangladesh, Bangladesh, Sri Lanka and Indian coast during 21 UTC of 26 October to 0300 UTC of 27 October 2008, around 0800 UTC of 16 May 2013, 0900 to 1200 UTC of 31October 2012 and during 2200 to 2300 UTC of 15 November 2008 respectively. The initial and boundary conditions of tropical cyclone (TC) are drawn from the global operational analysis and forecast products of National Center for Environmental Prediction (NCEP-GFS) available for the public at 1°×1o resolution. The model was run by using WSM6-class graupel microphysics (MP) schemes with different cumulus (Kain- Fritsch, Betts-Miller-Janjic, Grell- Fritsch, Grell-3, Grell-Denenyi and Old Kain- Fritsch) parameterization (CP). Different cumulus schemes have been used to study the effects on system intensification and structure of TC. The model domain consists of 3-27oN and 75-98oE and has 9 km horizontal resolution with 32 vertical sigma levels. The model is run for 96 hours using initial conditions at 0000 UTC of 24 October 2008 for TC Rashmi, 0000 UTC of 13 May 2013 for TC Viyaru, 0000 UTC of 28 October 2012 for TC Nilam and 0000 UTC of 13 November 2008 for TC khaimuk. Single domain (3-27oN & 75-98oE) is considered to examine the effect on structure of weak intensity TC. In this research the Minimum sea level pressure (MSLP), Maximum wind speed (MWS), Vorticity, Temperature anomaly, Relative humidity, Relative humidity at 2m and Water vapor mixing ratio have been analyzed to observe the impact on these parameters of weak intensity TC. Using different CP options, variation of MSLP is around -20 to 10 hPa compared to observed value for all cyclones except Viyaru. Temperature anomaly from 3-12 0C is obtained. Around 100 km cyclone eye is also observed. It may be concluded that the different CP options have their own impact on the structure of weak intensity cyclonic Rashmi, Viyaru, Nilam and Khaimuk with more or less value with the available observed value.