Asian monsoon rainfall impacts one third of the global population and
predicting its variability and future change is of clear importance.
However, the dynamics of even the climatological monsoon are not fully
understood. Three independent subsystems are traditionally considered:
the East Asian, South Asian, and Western North Pacific monsoons. Here we
use idealized model simulations with east-west thermal contrast to
explore the complex observed onset behavior of these subsystems. Our
results suggest that the summertime ‘stationary wave’ monsoon
circulation is not simply a passive response to insolation, but instead
expands northwestwards and then eastwards via advective and evaporative
feedbacks. In particular, our simulations indicate that onset over the
Western North Pacific results from eastward extension of the summertime
continental low via atmospheric feedbacks. We propose that the regional
monsoons’ responses to forcings may be understood by considering how
these feedbacks are influenced by the background state.