Climate Dynamics

, Volume 39, Issue 1–2, pp 445–459 | Cite as

The simulation of cutoff lows in a regional climate model: reliability and future trends

  • Michael R. Grose
  • Michael J. Pook
  • Peter C. McIntosh
  • James S. Risbey
  • Nathaniel L. Bindoff
Article

Abstract

Cutoff lows are an important source of rainfall in the mid-latitudes that climate models need to simulate accurately to give confidence in climate projections for rainfall. Coarse-scale general circulation models used for climate studies show some notable biases and deficiencies in the simulation of cutoff lows in the Australian region and important aspects of the broader circulation such as atmospheric blocking and the split jet structure observed over Australia. The regional climate model conformal cubic atmospheric model or CCAM gives an improvement in some aspects of the simulation of cutoffs in the Australian region, including a reduction in the underestimate of the frequency of cutoff days by more than 15 % compared to a typical GCM. This improvement is due at least in part to substantially higher resolution. However, biases in the simulation of the broader circulation, blocking and the split jet structure are still present. In particular, a northward bias in the central latitude of cutoff lows creates a substantial underestimate of the associated rainfall over Tasmania in April to October. Also, the regional climate model produces a significant north–south distortion of the vertical profile of cutoff lows, with the largest distortion occurring in the cooler months that was not apparent in GCM simulations. The remaining biases and presence of new biases demonstrates that increased horizontal resolution is not the only requirement in the reliable simulation of cutoff lows in climate models. Notwithstanding the biases in their simulation, the regional climate model projections show some responses to climate warming that are noteworthy. The projections indicate a marked closing of the split jet in winter. This change is associated with changes to atmospheric blocking in the Tasman Sea, which decreases in June to November (by up to 7.9 m s−1), and increases in December to May. The projections also show a reduction in the number of annual cutoff days by 67 % over the century, together with an increase in their intensity, and these changes are strongest in spring and summer.

Keywords

Cutoff low Atmospheric blocking Split jet Climate models Climate change Regional climate models 

Notes

Acknowledgments

The authors would like to acknowledge James Bennett for proofreading and editing, J. J. Katzfey, J. L. McGregor (CAWCR) and Stuart Corney (ACE CRC) for providing the CCAM simulations. Ian Barnes-Keoghan, Neil Adams and W. F. Budd for advice and assistance. This work was supported by the Australian Government’s Cooperative Research Centre Programme through the Antarctic Climate and Ecosystems Cooperative Research Centre (ACE CRC). Climate Futures for Tasmania is possible with support through funding and research of a consortium of state and national partners.

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Copyright information

© Springer-Verlag 2012

Authors and Affiliations

  • Michael R. Grose
    • 1
  • Michael J. Pook
    • 2
  • Peter C. McIntosh
    • 2
  • James S. Risbey
    • 2
  • Nathaniel L. Bindoff
    • 1
    • 2
    • 3
  1. 1.Antarctic Climate and Ecosystems Cooperative Research Centre (ACE CRC)University of TasmaniaHobartAustralia
  2. 2.Centre for Australian Weather and Climate Research (CAWCR)CSIRO Marine and Atmospheric ResearchHobartAustralia
  3. 3.Institute of Marine and Antarctic Studies (IMAS)University of TasmaniaHobartAustralia

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