Cyclogenesis in the lee of the Alps: a review of theories.

Although the phenomenon has been known, and investigated, as early as the nineteenth century, the interest in understanding Alpine lee cyclogenesis (often called Genoa cyclogenesis) has grown since the middle twentieth century, when it was realized that the largest fraction of cyclones affecting the central-eastern Mediterranean and later Eastern Europe originated in the area south of the Alps, more often in the Gulf of Genoa. Forecasting this type of cyclogenesis remained a challenging task until at least the mid- late 1980s, even after the development of the earlier NWP models, which failed in predicting this phenomenon, lacking the ability to adequately represent the orographic forcing. Monitoring and understanding of cyclogenesis in the lee of the Alps was the main objective of field projects, the most important being GARP-ALPEX in 1982. The following years were full of ideas and theories about this phenomenon, which is representative of orographic cyclogenesis in other regions of the world. The main steps in understanding the complex phenomenon of lee cyclogenesis, with particular reference to the Alps, are outlined here, focusing on theoretical explanations.