ACP Atmospheric Chemistry and Physics ACP Atmos. Chem. Phys. 1680-7324 Copernicus Publications Göttingen, Germany 10.5194/acp-12-4159-2012 Impact of January 2005 solar proton events on chlorine species Damiani A. 1 Funke B. 2 Marsh D. R. 3 López-Puertas M. 2 Santee M. L. 4 Froidevaux L. 4 Wang S. 4 Jackman C. H. 5 von Clarmann T. 6 Gardini A. 2 Cordero R. R. 1 Storini M. 7 Physics Department, University of Santiago de Chile, Santiago, Chile Instituto de Astrof\'isica de Andaluc\'ia, CSIC, Granada, Spain National Center for Atmospheric Research, Boulder, Colorado, USA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA NASA Goddard Space Flight Center, Greenbelt, Maryland, USA Karlsruhe Institute of Technology, Institute for Meteorology and Climate Research, Karlsruhe, Germany Institute of Interplanetary Space Physics, INAF, Rome, Italy 10 05 2012 12 9 4159 4179 Copyright: © 2012 A. Damiani et al. 2012 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://acp.copernicus.org/articles/12/4159/2012/acp-12-4159-2012.html The full text article is available as a PDF file from https://acp.copernicus.org/articles/12/4159/2012/acp-12-4159-2012.pdf

Sudden changes in stratospheric chlorine species in the polar northern atmosphere, caused by the Solar Proton Events (SPEs) of 17 and 20 January 2005, have been investigated and compared with version 4 of the Whole Atmosphere Community Climate Model (WACCM4). We used Aura Microwave Limb Sounder (MLS) measurements to monitor the variability of ClO, HCl, HOCl and Michelson Interferometer for Passive Atmospheric Sounder (MIPAS) on ENVISAT to retrieve ClONO<sub>2</sub>. SPE-induced chlorine activation has been identified. HCl decrease occurred at nearly all the investigated altitudes (i.e., 10–0.5 hPa) with the strongest decrease (of about 0.25 ppbv) on 21 January. HOCl was found to be the main active chlorine species under nighttime conditions (with increases of more than 0.2 ppbv) whereas both HOCl and ClO enhancements (about 0.1 ppbv) have been observed at the polar night terminator. Further, small ClO decreases (of less than 0.1 ppbv) and ClONO<sub>2</sub> enhancements (about 0.2 ppbv) have been observed at higher latitudes (i.e., at nighttime) roughly above 2 hPa. <br><br> While WACCM4 reproduces most of the SPE-induced variability in the chlorine species fairly well, in some particular regions discrepancies between the modeled and measured temporal evolution of the abundances of chlorine species were found. HOCl changes are modelled very well with respect to both magnitude and geographic distribution. ClO decreases are reproduced at high latitudes, whereas ClO enhancements in the terminator region are underestimated and attributed to background variations. WACCM4 also reproduces the HCl depletion in the mesosphere but it does not show the observed decrease below about 2 hPa. Finally, WACCM4 simulations indicate that the observed ClONO<sub>2</sub> increase is dominated by background variability, although SPE-induced production might contribute by 0.1 ppbv.

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