Modulations of local rainfall in northeast Australia associated with the Madden–Julian oscillation during austral summer

Abstract

This study investigates the role of the interaction between the Madden–Julian oscillation (MJO) and local-scale forcings in regulating precipitation and its diurnal variation during the austral summer over coastal areas in northeast (NE) Australia using radar data. The variation of rainfall is influenced by both large-scale and local-scale forcings. During the enhanced convection phases of the MJO, widespread increased rainfall signals are generated by large-scale forcings associated with the MJO, but the environmental factors controlling the type and amount of precipitation during each phase are different. By contrast, the locally enhanced rainfall during suppressed convection phases of the MJO likely results from the interaction of mesoscale land–sea breezes, strong large-scale background winds and topography. Different responses of mean and heavy precipitation to the MJO occur in some MJO phases. The impact of the MJO on diurnal rainfall characteristics is spatially inhomogeneous and likely regulated by local forcings. Although stratiform rainfall is more common, convective rainfall predominantly contributes to the total precipitation over coastal regions of NE Australia. The MJO's influence on convective rainfall is generally stronger and more statistically significant than its impact on stratiform rainfall. The widespread increased rainfall probability during the enhanced convection phases is likely due to increases in both stratiform and convective rainfall. In contrast, the locally enhanced precipitation signal during some suppressed convection phases mainly results from an increase in convective rainfall.