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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 112, D09202, doi:10.1029/2006JD007712, 2007

Have Australian rainfall and cloudiness increased due to the remote effects of Asian anthropogenic aerosols?

Leon D. Rotstayn

Marine and Atmospheric Research, CSIRO, Aspendale, Victoria, Australia


Wenju Cai

Marine and Atmospheric Research, CSIRO, Aspendale, Victoria, Australia


Martin R. Dix

Marine and Atmospheric Research, CSIRO, Aspendale, Victoria, Australia


Graham D. Farquhar

CRC for Greenhouse Accounting, Research School of Biological Sciences, Australian National University, Canberra, ACT, Australia


Yan Feng

Department of Atmospheric, Oceanic, and Space Sciences, University of Michigan, Ann Arbor, Michigan, USA


Paul Ginoux

Geophysical Fluid Dynamics Laboratory, NOAA, Princeton, New Jersey, USA


Michael Herzog

Department of Atmospheric, Oceanic, and Space Sciences, University of Michigan, Ann Arbor, Michigan, USA


Akinori Ito

Department of Atmospheric, Oceanic, and Space Sciences, University of Michigan, Ann Arbor, Michigan, USA


Joyce E. Penner

Department of Atmospheric, Oceanic, and Space Sciences, University of Michigan, Ann Arbor, Michigan, USA


Michael L. Roderick

CRC for Greenhouse Accounting, Research School of Biological Sciences, Australian National University, Canberra, ACT, Australia


Minghuai Wang

Department of Atmospheric, Oceanic, and Space Sciences, University of Michigan, Ann Arbor, Michigan, USA


Abstract

There is ample evidence that anthropogenic aerosols have important effects on climate in the Northern Hemisphere but little such evidence in the Southern Hemisphere. Observations of Australian rainfall and cloudiness since 1950 show increases over much of the continent. We show that including anthropogenic aerosol changes in 20th century simulations of a global climate model gives increasing rainfall and cloudiness over Australia during 1951–1996, whereas omitting this forcing gives decreasing rainfall and cloudiness. The pattern of increasing rainfall when aerosols are included is strongest over northwestern Australia, in agreement with the observed trends. The strong impact of aerosols is primarily due to the massive Asian aerosol haze, as confirmed by a sensitivity test in which only Asian anthropogenic aerosols are included. The Asian haze alters the meridional temperature and pressure gradients over the tropical Indian Ocean, thereby increasing the tendency of monsoonal winds to flow toward Australia. Anthropogenic aerosols also make the simulated pattern of surface-temperature change in the tropical Pacific more like La Niña, since they induce a cooling of the surface waters in the extratropical North Pacific, which are then transported to the tropical eastern Pacific via the deep ocean. Transient climate model simulations forced only by increased greenhouse gases have generally not reproduced the observed rainfall increase over northwestern and central Australia. Our results suggest that a possible reason for this failure was the omission of forcing by Asian aerosols. Further research is essential to more accurately quantify the role of Asian aerosols in forcing Australian climate change.

Received 29 June 2006; accepted 1 December 2006; published 2 May 2007.

Keywords: Asian aerosols; rainfall trends; Australia.

Index Terms: 3311 Atmospheric Processes: Clouds and aerosols; 1610 Global Change: Atmosphere (0315, 0325); 1626 Global Change: Global climate models (3337, 4928); 1637 Global Change: Regional climate change.

Subscriber Access to Full Article (Nonsubscribers may purchase for $9.00, Includes print PDF, file size: 16746174 bytes)

Citation: Rotstayn, L. D., et al. (2007), Have Australian rainfall and cloudiness increased due to the remote effects of Asian anthropogenic aerosols?, J. Geophys. Res., 112, D09202, doi:10.1029/2006JD007712.