Evaluation of convective parameterization schemes in simulation of tropical cyclones by Climate Forecast System model: Version 2

Recently, a high resolution atmospheric general circulation model, i.e., Global Forecast System has been operationalized for 10 days weather forecast over Indian region. However, for extreme weather systems such as cyclones, different physical processes and their interactions with atmosphere and ocean play an important role in cyclone intensity, track, etc. Keeping this in view, Coupled Forecast System model version 2 has been used to evaluate the simulation for three severe cyclones (Phailin, Viyaru and Lehar) of 2013. In the present study, along with already existing mass-flux cumulus parameterization, i.e., Simplified Arakawa-Schubert (SAS) and revised SAS (RSAS) parameterization schemes, an additional convective adjustment scheme, i.e., Betts-Miller-Janjic (BMJ) is implemented and its performance is evaluated for the Indian Ocean cyclones. The experiments are conducted with three cumulus schemes at three different resolutions (T126, T382, and T574). Both SAS and RSAS overestimate convective rain, whereas BMJ scheme produces convective rain comparable with the observation due to the fact that BMJ produces deeper convection and does not trigger the convection too often. BMJ sustains the instability and deep convection longer thereby impacting the cyclone intensity and heavy rainfall associated with it. It is also noted that BMJ is efficient in producing rain than the SAS and RSAS. From the analyses of OLR and rain rate, BMJ is found to simulate a much realistic relation of cloud and precipitation. The paper argues that compared to available SAS and RSAS, BMJ scheme realistically produces heavy precipitation associated with the tropical cyclone over Indian region in a coupled model.