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 vs without the TP, we find that TP uplift can also increase the precipitation of North American Summer Monsoon (NASM), with atmosphere teleconnection accounting for 6% and oceanic dynamical process accounting for another 6%. Physically, TP uplift generates a stationary Rossby wave train traveling from Asian continent to the North Atlantic region, resulting in an anomalous high-pressure over tropical-subtropical North Atlantic. The anomalous subtropical high enhances the low level southerly winds, forcing an anomalous upward motion over North American monsoon (NAM) region and then an increased summer precipitation there. In addition, 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 the Asian highland.

Why a large‐scale monsoon does not exist in North America: Orographic effects

“…The CAM 5.1 is the atmospheric component of the Community Earth System Model version 1 (CESM1.0), developed by the National Center for Atmospheric Research (NCAR). It can simulate the atmospheric circulation in stand‐alone mode (e.g., Chen et al, 2022) or via coupling with land, ocean and sea‐ice model components (e.g., Wen et al, 2021). Detail on this model can be found in Neale et al (2010).…”

“…Detail on this model can be found in Neale et al (2010). Previous studies reported that the NAM is well reproduced when using fine resolutions (e.g., 0.25 grid spacing) based on different models (Pascale et al, 2016(Pascale et al, , 2017Varuolo-Clarke et al, 2019), but some studies validated the good performance of the CESM with coarse resolution in simulating the atmospheric circulation and mean state of monsoon precipitation over North America (Bhattacharya et al, 2017;Wen et al, 2021). Given that we need to conduct a large number of sensitivity experiments, we set the resolution of CAM5.1 to be 1.9 × 2.5 horizontally with 30 vertical levels to minimize computing consumption.…”

“…Importantly, the existence of large terrain alters land surface characteristics, thus amplifying the land‐sea thermal contrast that further affects the monsoon (Chen & Bordoni, 2014; Dirmeyer, 1998; Manabe & Terpstra, 1974). For example, the Tibetan Plateau (TP) uplift significantly affected the development and maintenance of the Asian monsoon circulation (Acosta & Huber, 2020; An et al, 2001; Boos & Kuang, 2010, 2013; Harrison et al, 1992; Molnar et al, 2010; Wu & Zhang, 1998; Wu et al, 2007) and even the North American summer monsoon (Wen et al, 2021).…”