UC San Diego

Abstract: A hierarchy of idealized monsoons with increased degrees of complexity is built using an intermediate model with simplified physics and idealized land–sea geometry. This monsoon hierarchy helps formulate a basic understanding about the distribution of the surface equivalent potential temperatureθe, which proves to provide a general guide on the monsoon rainfall. The zonally uniform monsoon in the simplest aquaplanet simulations is explained by a linearized model of the meridional distribution ofθe, which is driven by the seasonally varying solar insolation and damped by both the monsoon overturning circulation and the local negative feedback. The heat capacities of the surface and the atmosphere give rise to an intrinsic time scale that causes the monsoon migration to lag behind the sun and reduces the monsoon extent and intensity. Monsoons with a zonally confined continent can be understood based on the zonally uniform monsoon by considering the ocean influence on the land through the westerly jet advection, which reduces the monsoon extent and induces zonal asymmetry. Monsoon responses to more realistic factors such as land geometry, albedo, and ocean heat flux are consistently predicted by their impacts on the surfaceθedistribution. The soil moisture effect, however, does not fully fit into the surfaceθeargument and provides additional control on monsoon rainfall by inducing regional circulation and rainfall patterns.