An assessment of a very severe cyclonic storm in the Arabian sea using the COSMO model
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An assessment of a very severe cyclonic storm in the Arabian sea using the COSMO model Roshny S.1,2 · D. Bala Subrahamanyam1 · Anurose T. J.3 · Radhika Ramachandran1 Received: 20 June 2020 / Accepted: 7 October 2020 © Springer Nature Switzerland AG 2020
Abstract 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. Keywords COSMO · Tropical cyclone · Convection · Precipitation · OCKHI · Parameterization of convection
1 Introduction Advances in numerical weather prediction (NWP) models is directly linked with the dramatic increase in processing powers of supercomputers which has enabled numerical simulations of the atmosphere at very fine grid spacing in a range as small as 1–10 km [1]. At such resolutions, the physical processes such as turbulence, convective transport and clouds can be partially resolved, which are otherwise represented through parameterization
schemes at coarser resolutions [2]. Presently, there is still no agreement in mainstream researchers on whether a convection parameterization is obligatory at “gray-zone” resolutions as the small grid boxes in the NWP models are still inadequate to represent the complete spectrum of convective motions [3–6]. Moreover, convection involves complex interactions with cloud formation which influence the atmospheric circulation through diabatic and radiative effects. Methods for simulating convective precipitation have been a major focus during the evolution of
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s42452-020-03645-7) contains supplementary material, which is available to authorized users. * D. Bala Subrahamanyam, [email protected]; Roshny S., [email protected]; Anurose T. J., [email protected]; Radhika Ramachandran, 601sree@gmail.
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