Impacts of the Madden-Julian Oscillation on Australian Rainfall and Circulation
Matthew C. Wheeler, Harry H. Hendon, Sam Cleland, Holger Meinke, and Alexis Donald
2008: J. Climate, In press.
Abstract
Impacts of the Madden-Julian oscillation (MJO) on Australian rainfall and circulation are examined
during all four seasons. We examine circulation anomalies and a number of different rainfall metrics, each
composited contemporaneously for eight MJO phases derived from the Real-time Multivariate MJO index.
Multiple rainfall metrics are examined to allow for greater relevance of the information for
applications. The greatest rainfall impact of the MJO occurs in northern Australia in (austral)
summer, although in every season rainfall impacts of various magnitude are found in most locations,
associated with corresponding circulation anomalies. In northern Australia in all seasons except
winter, the rainfall impact is explained by the direct influence of the MJOs tropical convective
anomalies, while in winter a weaker and more localized signal in northern Australia appears to
result from the modulation of the Trades as they impinge upon the eastern coasts, especially in
the northeast. In extratropical Australia, on the other hand, the occurrence of enhanced/suppressed
rainfall appears to result from induced upward/downward motion within remotely-forced extratropical
lows/highs, and from anomalous low-level northerly/southerly winds that transport moisture from
the Tropics. Induction of extratropical rainfall anomalies by remotely forced lows and highs
appears to operate mostly in winter, whereas anomalous meridional moisture transport appears
to operate mainly in summer, autumn, and to some extent in spring.
MJO impact in DJF on rainfall and 850hPa winds
MJO impact in JJA on rainfall and 850hPa winds
