Ocean-atmosphere-land feedbacks in an idealized monsoon

An intermediate complexity atmospheric model, coupled to a simple land surface model and a mixed layer ocean is used to investigate the processes involved in an idealized monsoon occuring on a single rectangular continent. Idealized ocean heat transports are specified as an annual average "Q-flux". These fixed transports can have a substantial impact on the land monsoon when land hydrology feedbacks are active. If ocean transports are set to zero, subtropical subsidence tends to produce deserts over land that substantially reduce the poleward movement of summer monsoon rains. When ocean transports are not zero, tropical oceans are slightly disfavored as regions for producing convection, allowing the land monsoon to be initiated. The monsoon circulation then produces moisture transport from the ocean regions that allows substantial progression into the subtropics over the eastern portion of the continent. The western portion of the continent remains dry. This east-west asymmetry is due to dynamical effects: Rossby wave induced subsidence occurs to the west of the heating region, which we term the Rodwell-Hoskins mechanism. The heat source and land surface each induce feedbacks with this mechanism, enhancing the asymmetry of the monsoon response. These feedback mechanisms appear sufficiently complex that understanding them in this simple system may be helpful to understanding the basic mechanisms and interannual variability of more realistic monsoon systems.