Convective activity is one of the major processes in the atmosphere influencing the local and large-scale weather in the tropics. The heavy rainfall events over the west coast of India are frequent mostly due to the organized meso-convective system associated with monsoonal flow. An attempt is made to numerically simulate heavy rainfall events occurred during monsoon period along the west coast of India using Weather Research and Forecasting (WRF) mesoscale modeling system. This study investigates the assimilation of Indian observations through WRF-Var and its impact to simulate the extreme heavy rainfall events which occurred due to the presence of the mid-tropospheric circulation (MTC) over the region during southwest monsoon period. The WRF-Var data assimilation system using the different Indian observations viz. conventional (SYNOP, BUOY, SHIP, AWS, RS/RW, AMDAR, AIREP, PILOT etc) and non-conventional (Satellite) observations collected from India Meteorological Department (IMD).

Two numerical experiments are carried out using WRF (version 2.1) mesoscale modeling system with a single domain (horizontal resolution 30km) to study the specified event. The first experiment, namely the control simulation (CNTRL), the low-resolution global analyses are used as initial and boundary conditions of the model. It is noticed that the model is not able to comprehensively capture the prominent features associated with organized convective processes. A second experiment, called as 3DV-ANA is carried out after the model initial condition is improved with insertion of the additional observations through WRF-Var data assimilation scheme. The model is allowed to integrate freely for 48 hours in both the experiments. After a successful inclusion of additional observation data through WRF-Var data assimilation technique, the resulting reanalysis is able to produce the structure of convective organization as well as prominent synoptic features associated with MTC. The location, intensity and movement of the MTC are well represented with 3DV-ANA simulations. The results also indicate that the improved initial condition of the mesoscale model through WRF-Var is enhanced the location and amount of rainfall. However, all of the model simulations underestimate the maximum value of the observed rainfall as observed. Furthermore, to improve the model simulation by inserting additional high-resolution Doppler Weather Radar data and high quality dense network surface and upper-air observation data.

Key words: mesoscale; convection; WRF-Var; MTC; heavy rainfall