The 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 (hereafter TP) 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 lower-resolution, atmosphere-only GCMs that neglect the influence of atmosphere-ocean coupling, and do not resolve tropical cyclones. Here we explore the influence of the TP on tropical circulations in a GFDL GCM at two different atmosphere/land resolutions (50 km and 2 degrees), and with or without atmosphere-ocean coupling via relaxing the sea-surface temperatures (SSTs) to a monthly climatology. Atmosphere-ocean coupling is found to play a significant role in the precipitation response due to the TP, enhancing the precipitation increase over the northwest Pacific, and drying the Arabian Sea. In these same regions, the higher resolution model, which resolves TCs up to category 3, suggests that the TP has a significant influence on TCs, increasing TC frequency in the northwest Pacific, 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 the TP, ocean circulation changes, and these various effects on precipitation and tropical cyclones are analyzed and discussed.