The Influence Of The Rocky Mountains And North American Continental Area On The North American Monsoon Regio

In this study,a series of sensitivity experiments were designed using the Community Atmosphere Model version 5.1 to explore the influence of the Rocky Mountains and the North American continental area on the formation of the North American monsoon(NAM),The main conclusions are as follows:(1)The extent of the NAM region is sensitive to the elevation of the Rocky Mountains.As the mountains rise,the NAM increases.In winter,the mechanical effects of mountain ranges was dominant.With the elevation of mountain ranges,the circulation pattern of "east trough and west ridge" in North America was strengthened.At the same time,the west wind climbing enhanced the subsidence movement on the east side of the mountain.Conducive to the emergence of dry winter climate.In summer,the thermal effect of mountains becomes dominant.Mountains act as a heat source to enhance the upper Mexican high,and the cyclonic circulation develops in the lower level,leading to large-scale upward movement and the increase of summer precipitation.Form obvious "winter dry summer wet" monsoon characteristics.The experiment of extending the area of the Rocky Mountains to the east found that the NAM was not sensitive to the increase of the area of the mountains,and the height of the mountains played a more important role than the area of the mountains in the NAM.(2)The extent of the NAM region is sensitive to the increase of continental area.As the continent expanded westward,the NAM expanded over central and southern North America.Summer precipitation centers are located in southern North America.With the increase of continental area,the surface sensible heat flux was enhanced,and the zonal sea-land thermal contrast was increased.The southerly wind anomaly appeared in the lower layer and the northerly wind anomaly in the upper layer.The vertical shear of the meridional wind increased,which corresponded to the development of upward movement.The release of latent heat from condensation has a positive feedback effect on this mechanism,which enhances the monsoon circulation.