Assessment of the role of sea surface fluxes on eastern Mediterranean explosive cyclogenesis with the aid of the limited-area model COSMO.GR

Abstract

Explosive cyclogenesis, being characterised by complex non adiabatic dynamics at low levels, is difficult to be predicted by operational models, especially in closed maritime regions such as the Mediterranean Sea. The objective of this study is to examine the sensitivity of the limited-area atmospheric model COSMO.GR, which runs operationally at the Hellenic National Meteorological Service (HNMS) as a forecast tool, in effectively simulating the deepening rate and to further explore the role of sea surface heat fluxes for two cases of explosive cyclogenesis in the eastern Mediterranean. Model runs were performed for six different values of the sea roughness model parameter, being proven, among others, to significantly affect the evolution of sea surface heat fluxes. The simulation justified the crucial role of sea surface heat fluxes in explosive cyclogenesis in the eastern Mediterranean by influencing the cyclone deepening rates and the respective minimum values of mean seal level pressure. The smaller values of the sea roughness parameter as compared to the default model value (equal to 20), leads to significant enhancement of the simulated sea surface heat fluxes and in turn produces higher deepening rates during the explosive deepening period. For both cases, the evaluation of the simulated mean sea level pressure values against observations demonstrated that values 10 and 1 better simulated the evolution of the mean sea level pressure along the cyclonic tracks. The results of this study act as a motivation to test the role of specific parameters in operational models associated with diabatic processes towards the improvement of local forecasts, mainly during severe phenomena.