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Abstract. A significant source of uncertainty in Numerical Weather Prediction (NWP) models arises from the parameterization of sub-grid scale convection, whose inherent nature of complexity is amplified while applied to tropical regions where weather systems are controlled by many intricate factors. However, as the model resolution becomes finer, it is possible to switch off the convection parameterization, although it is still unclear at what resolution this can be achieved. Ambiguity arises due to the inter-linking of various parameterization schemes within a model, and efficiency of one scheme depends on the output of another. In order to explore these issues, an intense convective episode with very heavy precipitation over the coastal Arabian Sea associated with the passage of OCKHI, one of the very severe cyclonic storms, is chosen as a case study. A set of distinct numerical simulations are carried out using Consortium for Small-scale Modelling (COSMO) to assess the direct and indirect impacts of dynamical downscaling on the treatment of convection. Results obtained from the present investigation indicate dynamical downscaling together with switching off the convection parameterization could simulate the magnitudes of CAPE, one of the proxies for characterizing the occurrence of tropical convection, more realistically. But the downscaling did not improve the rainfall prediction, which were seen to deteriorate in the absence of convection parameterization.

Accurate and reliable representation of convective processes is one of the major sources of uncertainty in numerical weather prediction (NWP) models, especially for those operating in the grey zone resolutions. The performance of NWP models become more sensitive to their grid resolutions, when they are used for simulation of severe weather events, such as a cyclonic storm. In this paper, we present a detailed assessment of an intense convective episode with heavy precipitation associated with the passage of a very severe cyclonic storm "OCKHI" using the Consortium for Small-scale Modelling (COSMO). A set of distinct numerical simulations are carried out using COSMO to address the impact of grid resolution and the treatment of explicit and implicit convection. Results obtained from the present investigation indicate that explicit treatment of convection in the COSMO model led to improved prediction of the cyclonic event in terms of sea level pressure, maximum sustained surface wind speeds and the accumulated rainfall, but reduction of the spatial grid resolution from 7 to 3 km did not show appreciable differences in the forecast fields. Conclusively, the current study recommends switching off the convection parameterization scheme at a grid resolution of 7 km for improved predictability of tropical cyclones.