Influence Of The Latitude Of North American Continent And Mountains On North American Monsoon

This study examines the role of the southward shift of the North American continent and the Rocky Mountains in determining North American monsoon(NAM)regions using the Community Atmosphere Model version 5.1.The main conclusions are as follows:(1)Results show that the meridional position of the North American continent plays a fundamental role in the NAM.When the North American continent is moved southward to a certain latitude,large areas of NAM appear,as strong and long-lasting surface sensible heating occurs from spring to summer,together with enhanced zonal land-sea thermal contrast.Thus,the low-level southerly wind and wind convergence are strengthened,resulting in a strong ascending motion.On the other hand,the enhanced southerly wind and northward equatorial airflow act to transport more moisture from the low-latitude oceans to the North American continent.As a result,the NAM circulation is strengthened,which is further maintained and developed via the “thermal adaptation” feedback.(2)Results show that the Rocky Mountains plays a role in the NAM.When the Rocky Mountains is uplifted to a certain height,large areas of NAM appear,as the mechanical effects of the mountain range form a "dipole" deviation circulation near the mountain in winter.So,the ridge is strengthened and eastward,making the trough deeper.North America are located in this northerly current.Also,the enhanced sinking movement and weakened water vapor transport are beneficial to the dry climate in winter.In summer,on the east side of the Mountains,the Mexico high is strengthened,the negative vortex anomaly enhancing the eastern sinking movement and the Atlantic high.So,the southerly wind is strengthened.Also,a cyclonic deviation circulation around the plateau is formed with the airflow converge and rise.These are beneficial to the summer precipitation,which makes the NAM stronger.