Numerical Simulation of Lee Cyclogenesis in the Gulf of Genoa

A numerical model framed in isentropic coordinates is applied to the problem of predicting lee cyclogenesis south of the Alps. Since “Genoa cyclones” during their initial stage are mesoscale phenomena, while mid-tropospheric flow configurations conducive to Genoa cyclogenesis are not, a grid nesting approach is followed in the model to capture both large-scale and mesoscale aspects of the problem. The two grids differ in mesh aim by a factor of 4 and interact in a two-way mode. The model is dry and uses a highly simplified surface drag formulation. Twenty-four hour predictions carried out on three occasions of observed cyclogenesis show that the model is capable of simulating cyclonic development approximately in the correct location. However, by slightly underpredicting the development of a high-pressure ridge over the eastern Atlantic the model in two of the three cases fails to build up the lee cyclone to the observed strength.