Orographically Induced Cyclogenesis: Analysis of Numerical Experiments

Abstract

Cyclogenesis induced by an isolated mountain chain in a baroclinic flow is simulated in a channel version of the HIBU (Mesinger-Janji?) primitive equation model. The main features characteristic of cyclogenesis in the Ice of the Alps am reproduced when the mountain interacts with a finite-amplitude baroclinic wave. The distribution of derived quantities like vertical velocity and potential vorticity compare well with those analyzed in case studies. The intercomparison of the evolution of the various fields and the analysis of energetics in experiments with and without mountains highlights the nature of the physical processes involved. A small-scale baroclinic process is responsible for an amplification of the initial disturbance produced by the mountain when the cold front, associated with the large-scale wave, moves over it. This process, though enhancing the local energy conversion, reduces the efficiency of the baroclinic conversion over the whole domain.