Articles | Volume 8, issue 6
Atmos. Chem. Phys., 8, 1483–1499, 2008

Special issue: Validation results for the Atmospheric Chemistry Experiment...

Atmos. Chem. Phys., 8, 1483–1499, 2008

  13 Mar 2008

13 Mar 2008

Validation of ACE-FTS satellite data in the upper troposphere/lower stratosphere (UTLS) using non-coincident measurements

M. I. Hegglin1, C. D. Boone2, G. L. Manney3,4, T. G. Shepherd1, K. A. Walker1,2, P. F. Bernath2,5, W. H. Daffer6, P. Hoor7, and C. Schiller8 M. I. Hegglin et al.
  • 1Department of Physics, University of Toronto, Toronto, Canada
  • 2Department of Chemistry, University of Waterloo, Waterloo, Canada
  • 3Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA
  • 4New Mexico Institute of Mining and Technology, Socorro, New Mexico, USA
  • 5Department of Chemistry, University of York, York, UK
  • 6Columbus Technologies Inc., Pasadena, California, USA
  • 7Max Planck Institute for Chemistry, Air Chemistry, Mainz, Germany
  • 8Institute for Chemistry and Dynamics of the Geosphere 1: Stratosphere, Research Centre Jülich GmbH, Jülich, Germany

Abstract. CO, O3, and H2O data in the upper troposphere/lower stratosphere (UTLS) measured by the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) on Canada's SCISAT-1 satellite are validated using aircraft and ozonesonde measurements. In the UTLS, validation of chemical trace gas measurements is a challenging task due to small-scale variability in the tracer fields, strong gradients of the tracers across the tropopause, and scarcity of measurements suitable for validation purposes. Validation based on coincidences therefore suffers from geophysical noise. Two alternative methods for the validation of satellite data are introduced, which avoid the usual need for coincident measurements: tracer-tracer correlations, and vertical tracer profiles relative to tropopause height. Both are increasingly being used for model validation as they strongly suppress geophysical variability and thereby provide an "instantaneous climatology". This allows comparison of measurements between non-coincident data sets which yields information about the precision and a statistically meaningful error-assessment of the ACE-FTS satellite data in the UTLS. By defining a trade-off factor, we show that the measurement errors can be reduced by including more measurements obtained over a wider longitude range into the comparison, despite the increased geophysical variability. Applying the methods then yields the following upper bounds to the relative differences in the mean found between the ACE-FTS and SPURT aircraft measurements in the upper troposphere (UT) and lower stratosphere (LS), respectively: for CO ±9% and ±12%, for H2O ±30% and ±18%, and for O3 ±25% and ±19%. The relative differences for O3 can be narrowed down by using a larger dataset obtained from ozonesondes, yielding a high bias in the ACE-FTS measurements of 18% in the UT and relative differences of ±8% for measurements in the LS. When taking into account the smearing effect of the vertically limited spacing between measurements of the ACE-FTS instrument, the relative differences decrease by 5–15% around the tropopause, suggesting a vertical resolution of the ACE-FTS in the UTLS of around 1 km. The ACE-FTS hence offers unprecedented precision and vertical resolution for a satellite instrument, which will allow a new global perspective on UTLS tracer distributions.

Final-revised paper