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Sea-breeze Convergence and Convection over Chennai, India

Vinod Kumar, A. Chandrasekar, R. Suresh


Sea-breeze circulations as well as associated convergence over Chennai (13.0oN / 80.18oE), India are being investigated in this study numerically. The Doppler weather radar (DWR) indicates a clear case of sea- breeze convergence and associated convection over Chennai on 28 June 2003. First the RAMS model is utilized in the horizontal homogeneous mode to simulate the sea-breeze circulation, resultant convection and associated precipitation. Subsequently, the MM5 model is used to simulate the same sea-breeze event by utilizing the limited area model (LAM) analysis of India Meteorological Department (IMD) and employing a system of two nested domains and use of four-dimensional data assimilation (FDDA). The results of both the RAMS and MM5 simulations are compared with DWR and rainfall observations from IMD. The results indicate that the sea-breeze front is well simulated by the RAMS model despite using it in the horizontal homogeneous mode. Although the arrival of the sea-breeze front as simulated by the RAMS model is late, the changeover to south easterlies at low levels is well simulated. The MM5 simulation shows a slight early arrival of the sea-breeze front as compared to the DWR observations. The MM5 results show that the PBL height, water vapor mixing ratio as well as vertical velocity over Chennai are well simulated. The 24-hr accumulated precipitation from the MM5 model shows intense maximum rainfall centered over Chennai while the RAMS model fails to simulate the same. The better rainfall simulation of the MM5 model is due to higher horizontal resolution, utilization of three-dimensional analysis and use of FDDA.

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