Effects of Terrain Height and Blocking Initialization on Numerical Simulation of Alpine Lee Cyclogenesis

摘要

Numerical experiments were performed to test the evolution of lee cyclones with various terrain representations, and to test forecast sensitivity to initial wind fields. Using the data set collected during the operational phase of the ALPEX field experiment, a mesoscale model was initialized with data from two markedly different cases, 12 hr prior to formation of a cyclone in the Mediterranean. The terrain used ranged from flat, sea level terrain, to orography that conserved the maximum barrier height of the Alps (similar to envelope terrain currently used at the ECMWF). Results show that even in the 12 hr period preceding cyclogenesis the mountain plays a crucial role in the evolution of the cyclone. Sharp variation in position and strength is evident depending on the terrain employed. Comparisons of terrain versus no-terrain cases show perturbations that compare well with those proposed by theory.