The impact of realistic representation of sea surface temperature (SST) on the numerical simulation of track and intensity of tropical cyclones formed over the north Indian Ocean is studied using the Weather Research and Forecast (WRF) model. We have selected two intense tropical cyclones formed over the Bay of Bengal for studying the SST impact. Two different sets of SSTs were used in this study: one from TRMM Microwave Imager (TMI) satellite and other is the weekly averaged Reynold's SST analysis from National Center for Environmental Prediction (NCEP). WRF simulations were conducted using the Reynold's and TMI SST as model boundary condition for the two cyclone cases selected. The TMI SST which has a better temporal and spatial resolution showed sharper gradient when compared to the Reynold's SST. The use of TMI SST improved the WRF cyclone intensity prediction when compared to that using Reynold's SST for both the cases studied. The improvements in intensity were mainly due to the improved prediction of surface latent and sensible heat fluxes. The use of TMI SST in place of Reynold's SST improved cyclone track prediction for Orissa super cyclone but slightly degraded track prediction for cyclone Mala. The present modeling study supports the well established notion that the horizontal SST gradient is one of the major driving forces for the intensification and movement of tropical cyclones over the Indian Ocean.

In this study, the simulation of an extreme weather event like heavy rainfall over Mumbai (India) on July 26, 2005 has been attempted with different horizontal resolutions using the Advanced Research Weather Research Forecast model version 2.0.1 developed at the National Center for Atmospheric Research (NCAR), USA. The study uses the Betts-Miller-Janjic (BMJ) and the Grell-Devenyi ensemble (GDE) cumulus parameterization schemes in single and nested domain configurations. The model performance was evaluated by examining the different predicted parameters like upper and lower level circulations, moisture, temperature, and rainfall. The large-scale circulation features, moisture, and temperature were compared with the National Centers for Environmental Prediction analyses. The rainfall prediction was assessed quantitatively by comparing rainfall from the Tropical Rainfall Measuring Mission products and the observed station values reported in the Indian Daily Weather Reports from India Meteorological Department (IMD). The quantitative validation of the simulated rainfall was done by calculating the categorical skill scores like frequency bias, threat scores (TS), and equitable threat scores (ETS). It is found that in all simulations, both in single and nested domains, the GDE scheme has outperformed the BMJ scheme for the simulation of rainfall for this specific event.

In the present study we have carried out few experiments to see the impact of sea surface temperature (SST) field obtained from TRMM Microwave Imager on the simulation of tropical cyclone MALA, formed over the Bay of Bengal on 24th April 2006 and made landfall on 29 April 0600 UTC at Arakan coast in Myanmar (17.7 N, 94.5 E). We have used NCEP global analysis data for this study. In this global analysis the Reynolds SST field is used as ocean boundary condition, which is having coarser resolution. Some experiments were carried out in past where people found that the wind stress fields in the ECMWF model improved dramatically after implementation of improved SST boundary condition. Also, satellite microwave measurement of SST by the TMI and Advance Microwave Scanning Radiometer (AMSR-E) have revealed that SST in regions of strong SST fronts associated with ocean currents exert a strong influence on the marine atmospheric boundary layer, resulting in a remarkably high positive correlation between surface winds and SST on scales smaller than few thousand kilometers. Here we have replaced coarser resolution SST in the control runs with high-resolution microwave based SST, obtained from TMI. Results are sowing that, the use TMI SST as ocean boundary condition has positive impact on the simulation of tropical cyclone.

Tropical cyclone stochastic eventset is a critical component in any cyclone risk assessment model. In this study, a novel methodology is proposed for the development of basin wide tropical cyclone stochastic eventset. The proposed methodology utilizes the reanalysis data to represent the environmental conditions of cyclones, which in turn governs the cyclone behaviour and variability