The direct and ocean-mediated influence of Asian orography on tropical precipitation and cyclones

Prior global climate model (GCM) experiments have shown that the Tibetan Plateau and related orography play a significant role in enhancing the Indian Monsoon, particularly during its onset, and the East Asian monsoon. However, these experiments have been largely performed with atmosphere-only, lower-resolution GCMs that neglect the influence of atmosphere-ocean coupling, and do not resolve tropical cyclones (TCs). Here we explore the influence of Asian orography on tropical circulations in a Geophysical Fluid Dynamics Laboratory GCM at two different atmosphere/land resolutions (approximate to 50 and 200km), and with or without atmosphere-ocean coupling. Atmosphere-ocean coupling is found to play a significant role in the precipitation response due to the Asian orography, enhancing the precipitation increase over the Western North Pacific (hereafter WNP), and drying the Arabian Sea. In these same regions, the higher resolution model, which resolves TCs up to category 3, suggests that Asian orography has a significant influence on TCs, increasing TC frequency in the WNP, and decreasing it in the Arabian Sea. However, in contrast to precipitation, this TC response does not appear to be strongly affected by the atmosphere-ocean coupling. Connections between the direct atmospheric circulation response to Asian orography, ocean circulation changes, and these various effects on precipitation and tropical cyclones are analyzed and discussed.