Assessing the impact of sea surface temperatures on a simulated medicane using ensemble simulations

Abstract

The sensitivity of the October 1996 Medicane in the western Mediterranean basin to sea surface temperatures (SSTs) is investigated with a regional climate model via ensemble sensitivity simulations. For 11 SST states, ranging from −4 K below to +6 K above the observed SST field (in 1 K steps), 24-member ensembles of the medicane are simulated. By using a modified phase space diagram and a simple compositing method, it is shown that the SST state has a minor influence on the tracks of the cyclones but a strong influence on their intensities. Increased SSTs lead to greater probabilities of tropical transitions, to stronger lower- and upper-level warm cores and to lower pressure minima. The tropical transition occurs sooner and lasts longer, which enables a greater number of transitioning cyclones to survive landfall over Sardinia and re-intensify in the Tyrrhenian Sea. The results demonstrate that SSTs influence the intensity of fluxes from the sea, which leads to greater convective activity before the storms reach their maturity. These results suggest that the processes at steady state for medicanes are very similar to tropical cyclones.