Vertical Profile of the Solar Cycle Induced Variability in Atmospheric OH and the Implications on Ozone

Solar irradiance variability during the 11-year solar cycle has been shown to have strong impacts on Earth's atmospheric composition and climate. Wang et al. [PNAS, 2012, under review] extracted the solar cycle signal in atmospheric hydroxyl radical (OH) from ground-based and satellite observations, which shows excellent correlation with the variability in solar parameters such as total soar irradiance (TSI) and Lyman-alpha. The observed 7-10% variability in total OH abundance in mid-latitude is larger than model simulations (~3% and ~6-7% for model runs using solar spectral forcing from reconstruction by Naval Research Laboratory (NRL) model and measurements by Solar Radiation and Climate Experiment (SORCE), respectively). In the present study, we examine in detail the vertical profile of the solar cycle signal in OH and its major source species based on simulations (using the Whole Atmospheric Community Model (WACCM) and the Caltech/JPL 1-D photochemical model) and global observations from Aura Microwave Limb Sounder (MLS). The general shape of the observed OH vertical profile response to solar cycle is close to model simulations using solar forcing from SORCE measurements, showing a primary peak response in the mesosphere and a small secondary peak response in the upper stratosphere. The latitudinal dependence of this variability will also be presented. The corresponding impacts on ozone and hence the climate will be discussed.