Abstract
Abstract. This study introduces stratospheric and mesospheric hydroperoxyl radical (HO2) estimates from the Aura Microwave Limb Sounder (MLS) using an offline retrieval (i.e. run separately from the standard MLS algorithm). This new data set provides two daily zonal averages, one during daytime from 10 to 0.0032 hPa (using day-minus-night differences between 10 and 1 hPa to ameliorate systematic biases) and one during nighttime from 1 to 0.0032 hPa. The vertical resolution of this new data set varies from about 4 km at 10 hPa to around 14 km at 0.0032 hPa. A description of the methodology and an error analysis are presented. Comparisons against the Whole Atmosphere Community Climate Model (WACCM), the Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES) and the Far Infrared Spectrometer (FIRS-2) measurements, as well as photochemical simulations, demonstrate the robustness of the retrieval and indicate that the retrieval is sensitive enough to detect mesospheric HO2 layers during both day and night. This new data set is the first long-term HO2 stratospheric and mesospheric satellite record and it provides needed constraints to help resolve the O3 deficit problem and the "HOx dilemma".
Highlights
Since 1985, when for the first time the famous O3 hole was reported (Farman et al, 1985), the stratospheric O3 layer has received massive scientific attention
When comparing against the global climate or the photochemical model simulations, their high vertical resolution has been reduced to the Microwave Limb Sounder (MLS) one using a least square fit as described by Livesey et al (2011, Sect. 1.9)
The MLS HO2 profile corresponds to day-minus-night differences averaged over a 20◦ latitude bin centred at 30◦ N averaged over 10 days centred on the day of the balloon flight
Summary
Since 1985, when for the first time the famous O3 hole was reported (Farman et al, 1985), the stratospheric O3 layer has received massive scientific attention. We introduce a new data set of global observations of stratospheric and mesospheric HO2 from the MLS instrument This new offline (i.e. run separately from the standard MLS algorithm) retrieval extends the HO2 vertical range well into the mesosphere (up to 0.003 hPa or ∼ 90 km), which, in addition to the standard MLS H2O, OH and O3, potentially allows the MLS data set to study the HOx–O3 chemical system to provide insights for the long-standing O3 deficit problem. To date, this data set provides 10 years of data and, in the near future, it will be publicly available for download in a daily-based hierarchical data format (HDF).
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