Hydroxyl in the middle atmosphere: relationship to ozone, water vapor, and solar radiation changes

An understanding of hydroxyl (OH) photochemistry is critical for many aspects of radiative, chemical, and transport studies of the middle atmosphere, including climate change effects and ozone recovery. The chemical sources and sinks of OH can be quantified using measurements from the Aura Microwave Limb Sounder (MLS) and from the Solar Radiation and Climate Experiment (SORCE). Daytime production of OH is expected to depend primarily on source gases water vapor (H2O) and ozone (O3), both measured by MLS, and on the ozone photodissociation rate which is primarily a function of solar radiative intensity, ozone overburden, and solar zenith angle. We test the key mechanisms presumed to be responsible for HOx production and loss in the stratosphere and mesosphere, separating the impact of variations in source gases from diurnal effects in order to fully isolate the diurnal dependence of OH on solar zenith angle.