Influence of Tibetan Plateau on the North American summer monsoon precipitation

Abstract

It has been well known that the uplift of the Tibetan Plateau (TP) can significantly enhance the Asian monsoon. Here, by comparing the sensitivity experiments with and without the TP, we find that the TP uplift can also increase the precipitation of the North American Summer Monsoon (NASM), with atmosphere teleconnection accounting for 6% and oceanic dynamical process accounting for another 6%. Physically, the TP uplift generates a stationary Rossby wave train traveling from the Asian continent to the North Atlantic region, resulting in an high-pressure anomaly over the tropical-subtropical North Atlantic. This high pressure system enhances the low-level easterly winds, forcing an enhanced upward motion over the North American monsoon (NAM) region and then an increase in summer precipitation there. In addition, the TP uplift enhances the Atlantic meridional overturning circulation, which reduces the meridional temperature gradient and leads to a northward shift of Hadley Cell over eastern Pacific-Atlantic section. The latter shifts the convection center northward to 10°N and further increases the NASM precipitation. The enhanced NASM precipitation can also be understood by the northward shift of Intertropical Convergence Zone. Our study implies that the changes of NAM climate can be affected by not only local process but also remote forcing, including those from Asian highland region.