Orbital time-scale circulation controls of the Australian summer monsoon: a possible role for mid-latitude Southern Hemisphere forcing?

Discussions of the Quaternary paleoclimatology of the northwestern Australian summer monsoon have emphasized inter-hemispheric forcing of the northern Australian summer monsoon by the East Asian winter monsoon. Here we draw on the results of general circulation model experiments to examine Southern Hemisphere circulation characteristics that controlled the Australian summer monsoon in response to Milankovitch insolation forcing. The experiments suggest that during tilt- and precession-driven Southern Hemisphere low-latitude insolation highs, the monsoon regime has the potential to be forced by inflow from the mid-latitudes of the Southern Hemisphere. To lend credence to the general circulation model results, we employ a simple force balance model to demonstrate the dynamics controlling Southern Hemisphere inflow into the monsoon region of northwestern Australia, and draw attention to work that suggests this mechanism may explain recent precipitation trends in the region. Our findings caution against drawing correlations of stratigraphic events in the East Asian – Australian monsoon records, without first having a full appreciation of the dynamics that controlled paleoclimate states.

► We consider northwest Australian summer monsoon forcing over Quaternary time scales. ► Evaluate hemisphere/inter-hemisphere links. ► Undertake AOGCM and analytical modeling. ► Show a prominent role for Southern Hemisphere mid-latitude forcing of the monsoon.