ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-11-5045-2011 Middle atmosphere response to the solar cycle in irradiance and ionizing particle precipitation Semeniuk K. 1 Fomichev V. I. 1 McConnell J. C. 1 Fu C. 2 Melo S. M. L. 2 Usoskin I. G. 3 Department of Earth and Space Science and Engineering, York University, Toronto, Ontario, Canada Canadian Space Agency, St.-Hubert, Quebec, Canada Sodankylä Geophysical Laboratory, University of Oulu, Oulu, Finland 31 05 2011 11 10 5045 5077 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/11/5045/2011/acp-11-5045-2011.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/11/5045/2011/acp-11-5045-2011.pdf

The impact of NO<sub>x</sub> and HO<sub>x</sub> production by three types of energetic particle precipitation (EPP), auroral zone medium and high energy electrons, solar proton events and galactic cosmic rays on the middle atmosphere is examined using a chemistry climate model. This process study uses ensemble simulations forced by transient EPP derived from observations with one-year repeating sea surface temperatures and fixed chemical boundary conditions for cases with and without solar cycle in irradiance. Our model results show a wintertime polar stratosphere ozone reduction of between 3 and 10 % in agreement with previous studies. EPP is found to modulate the radiative solar cycle effect in the middle atmosphere in a significant way, bringing temperature and ozone variations closer to observed patterns. The Southern Hemisphere polar vortex undergoes an intensification from solar minimum to solar maximum instead of a weakening. This changes the solar cycle variation of the Brewer-Dobson circulation, with a weakening during solar maxima compared to solar minima. In response, the tropical tropopause temperature manifests a statistically significant solar cycle variation resulting in about 4 % more water vapour transported into the lower tropical stratosphere during solar maxima compared to solar minima. This has implications for surface temperature variation due to the associated change in radiative forcing.

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