Application of Edge Wave Theory to Terrain-Bounded Cold Surges: A Numerical Study

摘要

A theory based upon topographically trapped edge waves is developed to explain the phenomenology of shallow cold surges adjacent to major topographic features of the earth's surface. It is proposed that a trapped response, composed of baroclinic Kelvin modes, shelf modes and couples motions, is a dominant mechanism within the surge regime. Three case studies concerning events near the Himalayas, Rockies and the Great Dividing Range were examined using the NCAR/PSU mesoscale model. The control experiments, with full terrain and physical parameterizations, implied the existence of a shallow multiscale structure, as well as other characteristics expected of edge waves, in the regions affected by the surges. Sensitivity studies strongly pointed to the topography as the key dynamic forcing agent for the three cases. The results generally support the edge wave hypothesis proposed, with slight modifications. Further, they indicated the importance of terrain and PBL specification for satisfactory simulation of cold surges.