Numerical simulation of waterspouts observed in the Tyrrhenian Sea

This paper describes the numerical simulation of waterspouts observed on 30 September, 2003 off the coast of Corsica just after sunrise. Based on the hypothesis that proper conditions for shear-line tornadoes would occur as a result of land breeze interactions, a numerical simulation of the system was performed using the Univeristy of Wisconsin Nonhydrosatic Modeling System. Grid nesting was used to achieve 1 km resolution to capture the land breeze front and 200 m resolution to simulate a field of congestus observed to be associated with the funnels. Further grid nesting down to grid scales of 2 m were used to focus in on simulated condensation funnels to study their dynamics. The effects of sea spray and the sorting effects of centrifugal force were used to study the impact of liquid hydrometeors on the funnel dynamics. The flow structure within the simulated condensation funnel showed an interesting relationship between regions of condensation and vertical motion within the funnel. The results also suggest important considerations regarding vorticity dissipation and numerical measures necessary to successfully represent these features.