Atmospheric OH Response to the 11-Year Solar Cycle ― Could the gap between model
and observations be filled by SORCE data?
Shuhui Wang[Shuhui.Wang@jpl.nasa.gov], Thomas J. Pongetti, and Stanley P. Sander, Jet
Propulsion Laboratory, California Institute of Technology, Pasadena, California; King-Fai
Li and Yuk L. Yung, Division of Geological and Planetary Sciences, California Institute of
Technology, Pasadena, California; and Mao-Chang Liang, Research Center for
Environmental Changes, Academia Sinica, TaiPei, Taiwan
Middle atmospheric OH is a key species in the ozone-destroying HOx reaction cycle
(involving OH, HO2, and H). It is mainly produced through photolysis of ozone and water
vapor in UV. The solar UV variation during the 11-year solar cycle is thus expected to affect
the natural variability in OH and related ozone chemistry. However, such studies had been
limited in the past due to the lack of long-term systematic observations. Here we present the
first effort to investigate such variability using long-term observations from space
(AURA/MLS) and the surface (FTUVS).
Both ground-based OH column record and MLS data suggest a ~10% decrease from solar
maximum to solar minimum. The observed OH variability is highly correlated with changes
in the total solar irradiance (TSI), the solar Mg II index, and Lyman-α during solar cycle 23.
However, chemical transport model simulations using a commonly accepted solar UV
variability parameterization give much smaller OH column variability (~3%). This
discrepancy implies either much-larger-than-expected solar UV variability or a mystery in
middle atmospheric hydrogen chemistry. The recent solar spectral irradiance (SSI)
measurements from SORCE show significantly larger solar UV variability than previously
believed. Model simulations using these new SSI data as solar forcing produce OH
variability that is much closer to observations (~7%). Such OH variability needs to be
further understood in order to accurately assess related impacts on ozone chemistry and
better identify ozone layer changes due to anthropogenic activities.