The role of Corsica in initiating nocturnal offshore convection

This is the authors' abstract. We don't add key points for this paper.

In the region of Corsica located in the western Mediterranean Sea, the mean daily lightning activity as an indicator for deep convection in late summer and autumn shows a distinct maximum in mid‐afternoon and a secondary maximum at night. During the night, most of the lightning activity is located offshore and near the island's coastline. Currently there are no observational data which could be used to explain this nocturnal offshore convection, but understanding its formation mechanism is important for accurately forecasting the regional weather. In this article, we explore two possible mechanisms initiating nocturnal offshore convection: (i) convergence with subsequent lifting due to the interaction between drainage winds and the synoptic flow over the sea and (ii) dynamically induced lee‐side convergence due to the island barrier effect. To this end, we perform numerical simulations with the Consortium for Small‐scale Modeling (COSMO) model at a convection‐permitting horizontal grid spacing of 2.8 km for two cases with different synoptic conditions and low‐level wind directions. The simulation results show that the island's drainage flow can either favour or hinder the development of deep convection. Furthermore, convective initiation is very sensitive to terrain elevation and model initialisation time and small changes of these parameters can determine whether deep convection can be successfully simulated.