An extratropical influence on Australian monsoon bursts

The Australian monsoon is characterised by bursts of rainfall lasting for several days, interspersed with break periods. The rapid transition from break period to burst is characterised by a cyclonic increase in the circulation over the monsoon region. By utilising the relationship between the circulation tendency and the convergence of absolute vorticity flux, we investigate the dynamical influences on Australian monsoon bursts. It is found that changes to the vorticity flux through the southern boundary are the the most important influence on the timing of bursts. The physical mechanism responsible for the southern boundary fluxes is a mid-latitude front or trough. Approximately one third of all bursts do not have a strong southerly influence. These are found be more closely related to the phase of the Madden-Julian Oscillation.