Odin stratospheric proxy NO_y measurements and climatology

Abstract. Five years of OSIRIS (Optical Spectrograph and InfraRed Imager System) NO₂ and SMR (Sub-millimetre and Millimetre Radiometer) HNO₃ observations from the Odin satellite, combined with data from a photochemical box model, have been used to construct a stratospheric proxy NO_y data set including the gases: NO, NO₂, HNO₃, 2×N₂O₅ and ClONO₂. This Odin NO_y climatology is based on all daytime measurements and contains monthly mean and standard deviation, expressed as mixing ratio or number density, as function of latitude or equivalent latitude (5° bins) on 17 vertical layers (altitude, pressure or potential temperature) between 14 and 46 km. Comparisons with coincident NO_y profiles from the Atmospheric Chemistry Experiment-Fourier Transform Spectrometer (ACE-FTS) instrument were used to evaluate several methods to combine Odin observations with model data. This comparison indicates that the most appropriate merging technique uses OSIRIS measurements of NO₂, scaled with model NO/NO₂ ratios, to estimate NO. The sum of 2×N₂O₅ and ClONO₂ is estimated from uncertainty-based weighted averages of scaled observations of SMR HNO₃ and OSIRIS NO₂. Comparisons with ACE-FTS suggest the precision (random error) and accuracy (systematic error) of Odin NO_y profiles are about 15% and 20%, respectively. Further comparisons between Odin and the Canadian Middle Atmosphere Model (CMAM) show agreement to within 20% and 2 ppb throughout most of the stratosphere except in the polar vortices. The combination of good temporal and spatial coverage, a relatively long data record, and good accuracy and precision make this a valuable NO_y product for various atmospheric studies and model assessments.