The Modified Envelope Orography and the Air Flow over and around Mountains

By use of the two-layer adiabatic globe spectral model and the zonally averaged climatic data of winter season as initial values, 10-day integrations are carried out based on three kinds of model topography (i.e., (1) the averaged to-pography; (2) the envelope topography; (3) the modified envelope topography). The results show that the orography of the Northern Hemisphere plays an important role in the simulation of large-scale weather patterns in winter sea-son. The simulation based on the envelope topography developed by Wallace et al. has some improvements in the Rocky Mountains area. But this scheme causes very serious horizontal expansion around the Tibetan Plateau (hereafter referred to as the TP). A modified envelope topography scheme has been worked out that increases the slope of the TP by decreasing; the horizontal expansion while keeping the maximum altitude. The results show some improve-ments of the scheme around the TP. By analysis of the mechanical effects of the large-scale orography on the currents, the different forcings of the air flow over and around the TP sad the Rocky Mountain (the RM) are investi-gated.