Articles | Volume 8, issue 1
Earth Syst. Sci. Data, 8, 61–78, 2016
Earth Syst. Sci. Data, 8, 61–78, 2016

Review article 11 Feb 2016

Review article | 11 Feb 2016

The SPARC Data Initiative: comparisons of CFC-11, CFC-12, HF and SF6 climatologies from international satellite limb sounders

S. Tegtmeier1, M. I. Hegglin2, J. Anderson3, B. Funke4, J. Gille5,6, A. Jones7,a, L. Smith6, T. von Clarmann8, and K. A. Walker7 S. Tegtmeier et al.
  • 1GEOMAR Helmholtz Centre for Ocean Research Kiel, Ocean Circulation and Climate Dynamics, Kiel, Germany
  • 2University of Reading, Department of Meteorology, Reading, UK
  • 3Hampton University, Atmospheric and Planetary Sciences, Hampton, Virginia, USA
  • 4Instituto de Astrofísica de Andalucía, CSIC, Solar system Department, Granada, Spain
  • 5University of Colorado, Atmospheric and Oceanic Sciences, Boulder, Colorado, USA
  • 6National Center for Atmospheric Research, Atmospheric Chemistry Observations and Modeling, Boulder, Colorado, USA
  • 7University of Toronto, Department of Physics, Toronto, Ontario, Canada
  • 8Karlsruhe Institute of Technology, Institute for Meteorology and Climate Research, Karlsruhe, Germany
  • anow at: Chalmers University, Earth and Space Sciences, Göteborg, Sweden

Abstract. A quality assessment of the CFC-11 (CCl3F), CFC-12 (CCl2F2), HF, and SF6 products from limb-viewing satellite instruments is provided by means of a detailed intercomparison. The climatologies in the form of monthly zonal mean time series are obtained from HALOE, MIPAS, ACE-FTS, and HIRDLS within the time period 1991–2010. The intercomparisons focus on the mean biases of the monthly and annual zonal mean fields and aim to identify their vertical, latitudinal and temporal structure. The CFC evaluations (based on MIPAS, ACE-FTS and HIRDLS) reveal that the uncertainty in our knowledge of the atmospheric CFC-11 and CFC-12 mean state, as given by satellite data sets, is smallest in the tropics and mid-latitudes at altitudes below 50 and 20 hPa, respectively, with a 1σ multi-instrument spread of up to ±5 %. For HF, the situation is reversed. The two available data sets (HALOE and ACE-FTS) agree well above 100 hPa, with a spread in this region of ±5 to ±10 %, while at altitudes below 100 hPa the HF annual mean state is less well known, with a spread ±30 % and larger. The atmospheric SF6 annual mean states derived from two satellite data sets (MIPAS and ACE-FTS) show only very small differences with a spread of less than ±5 % and often below ±2.5 %. While the overall agreement among the climatological data sets is very good for large parts of the upper troposphere and lower stratosphere (CFCs, SF6) or middle stratosphere (HF), individual discrepancies have been identified. Pronounced deviations between the instrument climatologies exist for particular atmospheric regions which differ from gas to gas. Notable features are differently shaped isopleths in the subtropics, deviations in the vertical gradients in the lower stratosphere and in the meridional gradients in the upper troposphere, and inconsistencies in the seasonal cycle. Additionally, long-term drifts between the instruments have been identified for the CFC-11 and CFC-12 time series. The evaluations as a whole provide guidance on what data sets are the most reliable for applications such as studies of atmospheric transport and variability, model–measurement comparisons and detection of long-term trends. The data sets will be publicly available from the SPARC Data Centre and through PANGAEA (doi:10.1594/PANGAEA.849223).

Short summary
The first comprehensive intercomparison of CFC-11, CFC-12, HF, and SF6 satellite data was performed as part of the SPARC Data Initiative following a new "top-down" concept of satellite measurement validation and thus providing a global picture of the data characteristics. The comparisons will provide basic information on quality and consistency of the various data sets and will serve as a guide for their use in empirical studies of climate and variability, and in model-measurement comparisons.