Solar Cycle Induced Variability in Middle Atmospheric HOx
−−− Abundances and Partitioning
Shuhui Wang, Luis Millan, Stanley P. Sander, Nathaniel J. Livesey, Michelle L. Santee
Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
King-Fai Li
Jack Eddy Fellow, University Corporation of Atmospheric Sciences, Boulder, CO
University of Washington, Seattle, WA
Yuk L. Yung
Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA
Solar UV irradiance variability during the 11-year solar cycle has been shown to have
strong impacts on Earth’s atmospheric composition and climate. The odd hydrogen
species HOx (primarily OH and HO2), which plays a key role in controlling middle
atmospheric ozone, are expected to show distinct variability following the solar cycle.
Wang et al. [2013] investigated the solar cycle signal in total OH abundances from longterm ground-based observation and 5.5 year Aura/Microwave Limb Sounder (MLS) OH
data and compared with model calculations, suggesting that the HOx solar cycle
variability may dominate the ozone solar cycle variability above 40. In the present study,
we expand the investigation to both HO2 and OH, as well as the partitioning between
them, which is important in the catalytic HOx cycle. With the newly developed MLS
offline HO2 product that has significantly improved data quality, vertical and diurnal
coverage, we examine in detail the vertical and latitudinal distribution of the solar cycle
signals in HO2 (~10 year data) and compare it with OH. Model simulations using the
Caltech/JPL 1-D photochemical model are used to understand the detailed mechanisms
controlling the variability in HOx abundances and partitioning. The results of using
different solar spectral irradiance (SSI) variabilities in models and the comparison with
observations will be discussed.
In addition, while the continuous MLS OH data record is only 5.5 year, the MLS THz
sub-system was turned back on for a 30-day OH measurement in every August since
2011. Using the most recent version of MLS retrieval software (v4.1x, to be released),
some first OH data for selected months will be presented, suggesting reliable quality of
the “THz restart” observations and making it promising to combine such OH data with
earlier OH data to build a longer-term record.