Competing Topographic Mechanisms

<p>The Indo-Asian Monsoon (IAM) circulation is an exemplar for how tectonic processes interact with regional climate systems. However, topography-atmosphere interaction is complex, challenging to model, and understanding the IAM at a specific period in Earth’s history involves the consideration of multiple topographically induced circulations. To better capture such processes, we simulate the global climate using high-resolution (~25 km) simulations with alternative Asian topographic boundary conditions. Here, we determine the individual importance of the Himalayas, Tibetan, and Iranian Plateaus. Instead of the previously proposed heating or insulating mechanisms, we find that the primary role of topography is to redirect and lift the onshore monsoon air to produce orographic precipitation. We show that onshore flows exist regardless of topography and are governed by sea surface temperature gradients. Thus, neither topography nor localized enthalpy air drives onshore monsoon flow. Our findings have implications for tropical monsoon theories and the paleoclimatology of Asia.</p>