NUMERICAL EXPERIMENTS ON OROGRAPHIC CYCLOGENESIS - RELATIONSHIP BETWEEN THE DEVELOPMENT OF THE LEE CYCLONE AND THE BASIC FLOW CHARACTERISTICS

dealized numerical experiments are performed using a channel version of the HIBU (Mesinger-Janji?) primitive equation model to reproduce cyclogenesis in the lee of a mountain chain resembling the Alps. Cyclones of differing intensity and behavior are reproduced and are discussed in relation to the characteristics of the large-scale developing baroclinic wave (i.e., amplitude, phase speed and vertical shear); concepts of absolute and convective instability are re-examined in this context. An experiment in which the mountain is removed after the initial growth of the cyclone clarifies the role of the mountain in the instability process.