Abstract
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 NOy data set including the gases: NO, NO2, HNO3, 2×N2O5 and ClONO2. This Odin NOy 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 NOy 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 NOy 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 NOy product for various atmospheric studies and model assessments.
Highlights
Reactive nitrogen species, known collectively as NOy, play an important role in stratospheric ozone chemistry and are intimately linked to hydrogen, chlorine, and bromine compounds
The standard deviation of the mean difference is within 15% (1σ ) if ignoring bins with very few coincidences and altitude below 22 km in A-M-J-J-A, see Fig. 7. These results indicate that the precision and accuracy of the Odin NOy proxy data is 15% and 20% respectively, if Atmospheric Chemistry Experiment (ACE) is assumed to be unbiased with zero noise and no real atmospheric differences exist between the co-located Odin and ACE measurements
The extremely low concentrations in September and October south of 60◦ S below 22 km corresponds to the region where Polar Stratospheric Cloud (PSC) are most frequently found
Summary
Known collectively as NOy (where NOy is the sum of NO, NO2, NO3, HNO3, 2×N2O5, ClONO2, BrONO2 and HO2NO2), play an important role in stratospheric ozone chemistry and are intimately linked to hydrogen, chlorine, and bromine compounds. A much smaller, and more sporadic source, is downward transport from the mesosphere of NO created by the precipitation of energetic particles in the polar regions (Randall et al, 2005; Funke et al, 2005a; Randall et al, 2007; Seppalaet al., 2007). This source represents about 2% of total stratospheric NOy (Vitt et al, 2000). The loss of stratospheric NOy occurs via transport into the troposphere, and through the reaction sequence
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