Validation of Aura Microwave Limb Sounder OH and HO2 measurements

The Microwave Limb Sounder (MLS) instrument on the Aura satellite obtains global measurements of both OH and HO2 radicals. This paper describes the precision and systematic errors of the MLS version v2.2 of the retrieval software. Estimated systematic errors are less than 8% for OH over 32-0.003 hPa and HO2 over 6.8-0.21 hPa. Comparison of measurements from MLS OH and HO2 profiles and three balloon-based instruments show good agreement among themselves and with a photochemical model using standard chemistry (i.e., recommended rate constants). Similarly, good agreement is seen between column OH found by integrating satellite profiles and ground-based measurements of column OH. The agreement between measured and modeled OH and HO2 is improved following perturbations to the rate constants O+OH and OH+HO2 that are within the recommended uncertainties. Measurements of OH obtained a decade ago by the Middle Atmosphere High-Resolution Spectrograph Investigation (MAHRSI) are smaller than MLS measurements by 20% at 70 km, are similar to MLS data near 50 km, and are 50% larger than MLS observations near 42 km. The MLS and MAHRSI measurements of OH overlap at the limit of their respective 2-sigma uncertainties. Most importantly, we find the shape of the OH profile measured by MLS is simulated well using standard chemistry.