Impact of a very severe cyclonic storm ‘OCKHI’ on the vertical structure of marine atmospheric boundary layer over the Arabian Sea

Abstract

Although considerable progress has been made in improving the early predictability of the tropical cyclones, our knowledge of the vertical structure of the marine atmospheric boundary layer (MABL) over a cyclone-affected ocean remains limited. Here, we investigate the impact of a very severe cyclonic storm ‘OCKHI’ on the MABL parameters over the Arabian Sea by using a regional numerical weather prediction model, namely Consortium for Small-scale Modelling (COSMO). Time-series meteograms of the surface-layer and upper-air meteorological parameters are examined for six distinct locations on the trajectory of OCKHI. Equivalent day analysis on the surface-layer turbulent fluxes over these locations reveals a substantial rise in the magnitude of sensible and latent heat fluxes during the passage of the storm. Surface-layer parameters within the MABL exhibit large diurnal variability during the passage of the storm compared with the normal days. Profiles of thermodynamic parameters indicate a significant dip in the mixed layer heights near the eye of the storm due to the formation of deep convective precipitating clouds. A decline in the mixed layer height during the propagation of the storm was a persistent feature. The present study also provides a conserved variable analysis of the equivalent potential temperature (𝜃e) and specific humidity (q) for a diagnostic investigation on the MABL processes and the movement of an air parcel.