ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-7-5229-2007 Observed poleward expansion of the Hadley circulation since 1979 Hu Y. 1 Fu Q. 2 Dept. of Atmospheric Sciences, Peking University, Beijing, China Dept. of Atmospheric Sciences, University of Washington, Seattle, USA 10 10 2007 7 19 5229 5236 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/7/5229/2007/acp-7-5229-2007.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/7/5229/2007/acp-7-5229-2007.pdf

Using three meteorological reanalyses and three outgoing long-wave radiation (OLR) datasets, we show that the Hadley circulation has a significant expansion of about 2 to 4.5 degrees of latitude since 1979. The three reanalyses all indicate that the poleward expansion of the Hadley circulation in each hemisphere occurs during its summer and fall seasons. Results from the OLR datasets do not have such seasonality. The expansion of the Hadley circulation implies a poleward expansion of the band of subtropical subsidence, leading to enhanced mid-latitude tropospheric warming and poleward shifts of the subtropical dry zone. This would contribute to an increased frequency of midlatitude droughts in both hemispheres.

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