Vorticity Budgets for Alpine Cyclogenesis with and Without the Forcing of Terrain

摘要

Three cases of Alpine cyclogenesis are examined. All had similar initiating conditions with northwesterly flow, an upstream short wave, and jet streak. Using the ALPEX 2-b data set, objective analyses were performed and vorticity budget computations made. In each case, vorticity tendencies in a quasi-Lagrangian volume moving with the surface disturbance, are dominated by vorticity advection aloft and convergence of Earth vorticity at low levels. A second series of budgets produced from fields derived in a no mountain environment and then subtracted from the mountain budgets, indicate that the major effect of mountains is to increase differential vorticity advection and low level vorticity convergence up to 625 hPa. However, mountains reduce vorticity in these same layers.