GMD Geoscientific Model Development GMD 1991-9603 Copernicus GmbH Göttingen, Germany 10.5194/gmd-4-483-2011 The CSIRO Mk3L climate system model version 1.0 – Part 1: Description and evaluation Phipps S. J. 1 2 3 4 Rotstayn L. D. 5 Gordon H. B. 5 Roberts J. L. 2 3 6 Hirst A. C. 5 Budd W. F. 1 2 3 Institute of Antarctic and Southern Ocean Studies, University of Tasmania, Australia Antarctic Climate & Ecosystems CRC, Hobart, Tasmania, Australia Tasmanian Partnership for Advanced Computing, Hobart, Tasmania, Australia Climate Change Research Centre, University of New South Wales, Australia Centre for Australian Weather and Climate Research, A partnership between CSIRO and the Bureau of Meteorology, Aspendale, Victoria, Australia Australian Antarctic Division, Kingston, Tasmania, Australia 17 06 2011 4 2 483 509 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.geosci-model-dev.net/4/483/2011/gmd-4-483-2011.html The full text article is available as a PDF file from http://www.geosci-model-dev.net/4/483/2011/gmd-4-483-2011.pdf

The CSIRO Mk3L climate system model is a coupled general circulation model, designed primarily for millennial-scale climate simulations and palaeoclimate research. Mk3L includes components which describe the atmosphere, ocean, sea ice and land surface, and combines computational efficiency with a stable and realistic control climatology. This paper describes the model physics and software, analyses the control climatology, and evaluates the ability of the model to simulate the modern climate. <br><br> Mk3L incorporates a spectral atmospheric general circulation model, a <i>z</i>-coordinate ocean general circulation model, a dynamic-thermodynamic sea ice model and a land surface scheme with static vegetation. The source code is highly portable, and has no dependence upon proprietary software. The model distribution is freely available to the research community. A 1000-yr climate simulation can be completed in around one-and-a-half months on a typical desktop computer, with greater throughput being possible on high-performance computing facilities. <br><br> Mk3L produces realistic simulations of the larger-scale features of the modern climate, although with some biases on the regional scale. The model also produces reasonable representations of the leading modes of internal climate variability in both the tropics and extratropics. The control state of the model exhibits a high degree of stability, with only a weak cooling trend on millennial timescales. Ongoing development work aims to improve the model climatology and transform Mk3L into a comprehensive earth system model.

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