ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-10-2643-2010 On the seasonal dependence of tropical lower-stratospheric temperature trends Fu Q. 1 2 Solomon S. 3 Lin P. 1 Department of Atmospheric Sciences, University of Washington, Seattle, WA, USA College of Atmospheric Sciences, Lanzhou University, Lanzhou 730000, China Chemical Science Division, Earth System Research Laboratory, NOAA, Boulder, CO, USA 18 03 2010 10 6 2643 2653 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/10/2643/2010/acp-10-2643-2010.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/10/2643/2010/acp-10-2643-2010.pdf

This study examines the seasonality of tropical lower-stratospheric temperature trends using the Microwave Sounding Unit lower-stratospheric channel (<i>T</i><sub>4</sub>) for 1980–2008. We present evidence that this seasonality is largely a response to changes in the Brewer-Dobson circulation (BDC) driven by extratropical wave forcing. We show how the tropical <i>T</i><sub>4</sub> trend can be used as an indicator of changes in the BDC, and find that the BDC is strengthening for 1980–2008 in June–November related to the Southern Hemisphere (SH) and in December–February to the Northern Hemisphere (NH). In marked contrast, we find that the BDC is weakening in March–May, apparently because of a weakening of its northern cell. The novel observational evidence on the seasonal dependence of the BDC trends presented in this study has important implications for the understanding of climate change in the stratosphere as well as testing climate model simulations.

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