Impacts of the Madden–Julian Oscillation on Australian Rainfall and Circulation

Abstract

Impacts of the Madden-Julian oscillation (MJO) on Australian rainfall and circulation are examined during all four seasons. The authors 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 MJO's tropical convective anomalies, while in winter a weaker and more localized signal in northern Australia appears to result from the modulation of the trade winds 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 the summer, autumn, and to some extent in the spring.

The variability of tropical ice cloud properties as a function of the large-scale context from ground-based radar-lidar observations over Darwin, Australia

“…Jones, 2000;Pohl et al, 2007). It has in particular been shown that it had a large impact on Northern Australian rainfall and circulation (Wheeler et al, 2009), which is the region of interest of our study. As a result it could be expected that the ice cloud production over the Darwin ARM site by deep convection be also modulated by these large-scale characteristics.…”

“…Finally, largest occurrences of ice clouds are found during phase 5 (15 % peak) and phase 6 (20 % peak). Going back to the study of Wheeler et al (2009) about the modulation of weekly rainfall probabilities by the MJO phase, they show that conditional probabilities of receiving accumulated rainfall in the climatological upper tercile shifts from being less than 20 % in phases 1, 2, and 8 to greater than 60 % in phases 5 and 6 over the Darwin area during austral summer. This variability of rainfall probability therefore appears to be fully consistent with enhanced occurrences of tropical ice clouds in phases 5 and 6, and reduced occurrences for phases 1, 2, and 8.…”

The autumn break for cropping in southeast Australia: trends, synoptic influences and impacts on wheat yield

“…The MJO can be classified into eight phases based on the leading patterns of variability of the zonal wind in the near-equatorial latitudes (Wheeler and Hendon, 2004). Wheeler et al (2008) have demonstrated that extratropical rainfall signals are detectable in two of these phases of the MJO in autumn. However, systematic interactions between the mid-latitude systems and the MJO have yet to be established.…”

Evaluation of rainfall drivers and teleconnections in an ACCESS AMIP run

“…These driving processes include tropical processes such as El Niño Southern Oscillation (ENSO) in the Pacific Ocean (Allan 1988;Nicholls et al 1997;Wang and Hendon 2007;Watterson 2010), the Indian Ocean Dipole (IOD) (Ashok et al 2003a) and Madden Julian Oscillation (MJO) (Wheeler and Hendon 2004;Wheeler et al 2009). The focus on extratropical sources of variability has been on the Southern Annular Mode (SAM) Meneghini et al 2007), variations in storm tracks (Simmonds and Keay 2000;Frederiksen and Frederiksen 2007), the subtropical ridge (Pittock 1975;Timbal 2009), and atmospheric blocking (Pook and Gibson 1999).…”