The role of the North American continent in strengthening the Asian monsoon

Most studies on the formation of the modern Asian monsoon focus on mechanisms arising on the Afro-Eurasian continent. While few compare the effects of other remote continents. Using a fully coupled general circulation model, this study decomposes the relative contribution of each continent on the formation, distribution and intensity of the Asian monsoon. Here we show that the existence of the North American continent is critical for the formation and intensity of the Asian summer monsoon. The mechanism involves North America acting as an additional heating center, resulting in the strengthening and extension of oceanic advection towards the Asian monsoon region. This is achieved by the Rodwell-Hoskins mechanism that strengthens the North Pacific subtropical high and through a wide-spread Northern Hemispheric heating that shifts poleward the subsidence center of Hadley circulation. This teleconnection is not dependent on the Tibetan Plateau and its impact on East Asian summer precipitation is found to be smaller but comparable to the Tibetan Plateau. The individual role of the other non-Afro-Eurasian continents was found to be less important. Previous work has shown that the Asian monsoon has global impact, including changing the climate of North America. This study firstly shows the "reversed" teleconnection that North America can have a very significant impact on the Asian monsoon. Although these experiments are idealized and based on contemporary land-sea geometry, they also highlight the role of North America in the geologic evolution of the Asian monsoon, and imply the impacts of the anthropogenic climate change of North America to the Asian monsoon in the recent history and future.