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Published February 5, 2013 | Published + Supplemental Material
Journal Article Open

Midlatitude atmospheric OH response to the most recent 11-y solar cycle


The hydroxyl radical (OH) plays an important role in middle atmospheric photochemistry, particularly in ozone (O_3) chemistry. Because it is mainly produced through photolysis and has a short chemical lifetime, OH is expected to show rapid responses to solar forcing [e.g., the 11-y solar cycle (SC)], resulting in variabilities in related middle atmospheric O_3 chemistry. Here, we present an effort to investigate such OH variability using long-term observations (from space and the surface) and model simulations. Ground-based measurements and data from the Microwave Limb Sounder on the National Aeronautics and Space Administration's Aura satellite suggest an ∼7–10% decrease in OH column abundance from solar maximum to solar minimum that is highly correlated with changes in total solar irradiance, solar Mg-II index, and Lyman-α index during SC 23. However, model simulations using a commonly accepted solar UV variability parameterization give much smaller OH variability (∼3%). Although this discrepancy could result partially from the limitations in our current understanding of middle atmospheric chemistry, recently published solar spectral irradiance data from the Solar Radiation and Climate Experiment suggest a solar UV variability that is much larger than previously believed. With a solar forcing derived from the Solar Radiation and Climate Experiment data, modeled OH variability (∼6–7%) agrees much better with observations. Model simulations reveal the detailed chemical mechanisms, suggesting that such OH variability and the corresponding catalytic chemistry may dominate the O_3 SC signal in the upper stratosphere. Continuing measurements through SC 24 are required to understand this OH variability and its impacts on O_3 further.

Additional Information

© 2013 National Academy of Sciences. Edited by Steven C. Wofsy, Harvard University, Cambridge, MA, and approved December 19, 2012 (received for review November 1, 2011). Published online before print January 22, 2013. We thank the NASA Aura Science Team and the Upper Atmosphere Research and Tropospheric Chemistry programs for their support. We thank R. C. Willson for providing the ACRIM TSI composite (www.acrim.com) and the Laboratory for Atmospheric and Space Physics Interactive Solar Irradiance Datacenter for composites of Lyman-α and Mg-II indices (http://lasp.colorado.edu/lisird/). We also acknowledge receipt of a TSI dataset from the PMOD (www.pmodwrc.ch/) and receipt of unpublished data from the Variability of Solar Irradiance and Gravity Oscillations on board the Solar and Heliospheric Observatory. Some FTUVS OH data from early years were collected by R. P. Cageao. We thank H. M. Pickett, the principal investigator (retired) for the MLS OH measurements and a NASA Aura Science Team project. We also thank R.-L. Shia and S. Newman for help with the models and error analysis and insightful discussions. Work at the Jet Propulsion Laboratory, California Institute of Technology, was done under contract to NASA. Support from an Australian Research Council Linkage International grant is gratefully acknowledged. Author contributions: S.W., K.-F.L., S.P.S., Y.L.Y., and F.P.M. designed research; S.W., K.-F.L., and T.J.P. performed research; M.-C.L., J.W.H., and M.S. contributed new reagents/analytic tools; S.W., T.J.P., N.J.L., M.L.S., J.W.H., and M.S. analyzed data; and S.W. and K.-F.L. wrote the paper.

Attached Files

Published - PNAS-2013-Wang-2023-8.pdf

Supplemental Material - pnas.201117790SI.pdf

Supplemental Material - sd01.txt


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