L. Froidevaux, et al.
Validation of Aura Microwave Limb Sounder HCl measurements
Journal of Geophysical Research: Atmospheres, 113(15), D15S25, 2008; doi: 10.1029/2007JD009025
HCl Middle atmosphere atmospheric composition hydrogen chloride Aura MLS data validation


[1] The Earth Observing System (EOS) Microwave Limb Sounder (MLS) aboard the Aura satellite has provided daily global HCl profiles since August 2004. We provide a characterization of the resolution, random and systematic uncertainties, and known issues for the version 2.2 MLS HCl data. The MLS sampling allows for comparisons with many (∼1500 to more than 3000) closely matched profiles from the Halogen Occultation Experiment (HALOE) and Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS). These data sets provide HCl latitudinal distributions that are, overall, very similar to those from (coincident) MLS profiles, although there are some discrepancies in the upper stratosphere between the MLS and HALOE gradients. As found in previous work, MLS and ACE HCl profiles agree very well (within ∼5%, on average), but the MLS HCl abundances are generally larger (by 10–20%) than HALOE HCl. The bias versus HALOE is unlikely to arise mostly from MLS, as a similar systematic bias (of order 15%) is not observed between average MLS and balloon-borne measurements of HCl, obtained over Fort Sumner, New Mexico, in 2004 and 2005. At the largest pressure (147 hPa) for MLS HCl, a high bias (∼0.2 ppbv) is apparent in analyses of low to midlatitude data versus in situ aircraft chemical ionization mass spectrometry (CIMS) HCl measurements from the Aura Validation Experiment (AVE) campaigns in 2004, 2005, and 2006; this bias is also observed in comparisons of MLS and aircraft HCl/O3 correlations. Good agreement between MLS and CIMS HCl is obtained at 100 to 68 hPa. The recommended pressure range for MLS HCl is from 100 to 0.15 hPa.


  author = "L. Froidevaux and Y. B. Jiang and A. Lambert and N. J. Livesey and W. G. Read and J. W. Waters and R. A. Fuller and T. P. Marcy and P. J. Popp and R. S. Gao and D. W. Fahey and K. W. Jucks and R. A. Stachnik and G. C. Toon and L. E. Christensen and C. R. Webster and P. F. Bernath and C. D. Boone and K. A. Walker and H. C. Pumphrey and R. S. Harwood and G. L. Manney and M. J. Schwartz and W. H. Daffer and B. J. Drouin and R. E. Cofield and D. T. Cuddy and R. F. Jarnot and B. W. Knosp and V. S. Perun and W. V. Snyder and P. C. Stek and R. P. Thurstans and P. A. Wagner",
  title = "Validation of Aura Microwave Limb Sounder HCl measurements",
  year = 2008,
  journal = "Journal of Geophysical Research: Atmospheres",
  volume = 113,
  number = 15,
  pages = "D15S25",
  month = "May",
  keywords = "HCl, Middle atmosphere, atmospheric composition, hydrogen chloride, Aura MLS data validation",
  doi = "10.1029/2007JD009025",
  url = ""
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