Theoretical and Applied Climatology

, Volume 132, Issue 1–2, pp 313–326 | Cite as

Variability in rainfall over tropical Australia during summer and relationships with the Bilybara High

  • C. J. C. Reason
Original Paper


Variability in summer rainfall over tropical Australia, defined here as that part of the continent north of 25° S, and its linkages with regional circulation are examined. In particular, relationships with the mid-level anticyclone (termed the Bilybara High) that exists over the northwestern Australia/Timor Sea region between August and April are considered. This High forms to the southwest of the upper-level anticyclone via a balance between the upper-level divergence over the region of tropical precipitation maximum and planetary vorticity advection and moves south and strengthens during the spring and summer. It is shown that variations in the strength and position of the Bilybara High are related to anomalies in precipitation and temperature over large parts of tropical Australia as well as some areas in the south and southeast of the landmass. Some of the interannual variations in the High are related to ENSO, but there are also a number of neutral years with large anomalies in the High and hence in rainfall. On decadal time scales, a strong relationship exists between the leading mode of tropical Australian rainfall and the Bilybara High. On both interannual and decadal scales, the relationships between the High and the regional rainfall involve changes in the monsoonal northwesterlies blowing towards northern Australia, and further south, in the easterly trade winds over the region.



NOAA ( and the KNMI ( are thanked for providing the freely accessible online data and plotting tools used in this study.


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Copyright information

© Springer-Verlag Wien 2017

Authors and Affiliations

  1. 1.Department of OceanographyUniversity of Cape TownCape TownSouth Africa

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