Diagnosis of a high-impact secondary cyclone during HyMeX-SOP1 IOP18

Abstract

Multiple high-impact weather events occurred during HyMeX-SOP1, which was intensively monitored by a large number of ordinary and extraordinary observations. The availability of special observations offers an unprecedented opportunity to explore these events in depth and assess the capabilities of current numerical weather prediction tools. In this case, a small-scale secondary cyclone formed within a prominent cyclone that intensified in the north-western part of the western Mediterranean during IOP18 on October 31, 2012. The small secondary system formed near Catalonia, where heavy rain was observed, and then moved to the northern part of the island of Minorca, producing very strong winds. Finally, the secondary cyclone moved northeast while merging with the main cyclone and evolving as a cyclonic perturbation towards the Gulf of Genoa, bringing heavy precipitation to some Italian regions.This work aims at providing a detailed diagnosis of the genesis and evolution of the secondary cyclone, using high-resolution numerical tools. Furthermore, with the main objective of identifying the main physical mechanisms involved in the genesis and evolution of the small-scale secondary cyclone, sensitivity experiments were performed taking into account three main factors: latent heat release, upper-level dynamical forcing and topographical effects. Results show that in terms of individual cyclogenetic contributions, the upper level PV anomaly contribution dominated the initial phase and the diabatic heating from condensation contributed to the further deepening during the later stages of the secondary cyclone. The initial dynamical effect from the upper-levels forcing was amplified by the local topographic features, becoming a key synergistic factor for the formation of the damaging secondary cyclonic system.