ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-11-6575-2011 Simulated enhancement of ENSO-related rainfall variability due to Australian dust Rotstayn L. D. 1 Collier M. A. 1 Mitchell R. M. 2 Qin Y. 2 Campbell S. K. 2 Dravitzki S. M. 1 Centre for Australian Weather and Climate Research, CSIRO Marine and Atmospheric Research, Aspendale, Vic, Australia Centre for Australian Weather and Climate Research, CSIRO Marine and Atmospheric Research, Canberra, ACT, Australia 12 07 2011 11 13 6575 6592 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.atmos-chem-phys.net/11/6575/2011/acp-11-6575-2011.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/11/6575/2011/acp-11-6575-2011.pdf

Australian dust emissions are highly episodic, and this may increase the importance of Australian dust as a climate feedback agent. We compare two 160-year coupled atmosphere-ocean simulations of modern-day climate using the CSIRO Mark 3.6 global climate model (GCM). The first run (DUST) includes an interactive treatment of mineral dust and its direct radiative effects. The second run (NODUST) is otherwise identical, but has the Australian dust source set to zero. We focus on the austral spring season, when the correlation between rainfall and the El Niño Southern Oscillation (ENSO) is strongest over Australia. The ENSO-rainfall relationship over eastern Australia is stronger in the DUST run: dry (El Niño) years tend to be drier, and wet (La Niña) years wetter. The amplification of ENSO-related rainfall variability over eastern Australia represents an improvement relative to observations. The effect is driven by ENSO-related anomalies in radiative forcing by Australian dust over the south-west Pacific Ocean; these anomalies increase (decrease) surface evaporation in La Niña (El Niño) years. Some of this moisture is advected towards eastern Australia, where increased (decreased) moisture convergence in La Niña (El Niño) years increases the amplitude of ENSO-related rainfall variability. The modulation of surface evaporation by dust over the south-west Pacific occurs via surface radiative forcing and dust-induced stabilisation of the boundary layer. The results suggest that (1) a realistic treatment of Australian dust may be necessary for accurate simulation of the ENSO-rainfall relationship over Australia, and (2) radiative feedbacks involving dust may be important for understanding natural rainfall variability over Australia.

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