Changes and Projections in Australian Winter Rainfall and Circulation: Anthropogenic Forcing and Internal Variability

By Carsten Segerlund Frederiksen, Jorgen Segerlund Frederiksen, Janice Maria Sisson and Stacey Lee Osbrough.

Published by The International Journal of Climate Change: Impacts and Responses

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Article: Electronic $US5.00

Large and continuing reductions in southern Australian winter rainfall are shown to be associated with major shifts in the Southern Hemisphere circulation since the mid-1970s. In particular, these changes have been linked to a reduction in winter storm formation with the growth rate of the leading storm track modes affecting southern Australia being more than 30% lower during the last three decades compared to the period between 1949 and 1968. These effects have become more pronounced with time. In this paper, we focus on the changes in southern Australian winter rainfall and relate them to circulation changes that are directly associated with storm formation. We employ a useful diagnostic of storm development which is the vertical shear in the atmospheric winds, commonly known as baroclinic instability, and is encapsulated in the Phillips (1954) criterion. The relationship between changes in the Phillips criterion and changes in rainfall during the twentieth century is discussed. We also consider projected changes and trends in rainfall and baroclinic instability in SRES scenarios using results from CMIP3 models. We elucidate the roles of anthropogenic forcing and internal variability. Our results show that the impact of further increases in anthropogenic CO₂ concentrations can lead to further large reductions in baroclinic instability, with model trends during the 21st century similar to those simulated during the second half of the 20th century. Associated reductions in modelled southern Australian rainfall can be as much as twice those seen at the end of the 20th century.

Keywords: Australian Rainfall, Atmospheric Circulation, Climate Change, Climate Projections, Storm Formation, Anthropogenic Forcing, Internal Variability

International Journal of Climate Change: Impacts and Responses, Volume 2, Issue 3, pp.143-162. Article: Print (Spiral Bound). Article: Electronic (PDF File; 5.480MB).

Dr. Carsten Segerlund Frederiksen

Senior Principal Research Scientist, Centre for Australian Weather and Climate Research, Bureau of Meteorology Australia, Melbourne, Victoria, Australia

I am a Senior Principal Research Scientist at the Australian Bureau of Meteorology and Team Leader of the Climate Processes team within the Centre for Australian Weather and Climate Research. My research interests cover climate change and attribution studies and causes, climate variability and predictability, and seasonal prediction.

Dr. Jorgen Segerlund Frederiksen

Chief Research Scientist, Centre for Australian Weather and Climate Research, Climate Adaptation Flagship and Centre for Australian Weather and Climate Research, CSIRO Marine and Atmospheric Research, Melbourne, Victoria, Australia

I am a Chief Research Scientist at CSIRO Marine and Atmospheric Research and Fellow of the Australian Academy of Science. My research interests cover dynamical theories of atmospheric processes, weather prediction, turbulence, climate change and attribution, and seasonal prediction.

Janice Maria Sisson

Senior Information Technology Officer, Centre for Australian Weather and Atmospheric Research, Bureau of Meteorology, Melbourne, Victoria, Australia

I am a Senior Information Technology (IT) Officer with the Bureau of Meteorology, supplying scientific and IT support, including diagnostic analysis, to projects on climate variability and change with reference to the atmospheric circulation and Australian climate, as well as supporting projects on dynamical and statistical seasonal prediction.

Stacey Lee Osbrough

Support Scientist, Centre for Australian Weather and Atmospheric Research, CSIRO Marine and Atmospheric Research, Melbourne, Victoria, Australia

I am a support scientist at CSIRO Marine and Atmospheric Research. My work involves investigating ensemble prediction methods for seasonal prediction and managing large data sets created by IPCC climate models for climate change studies.

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