Atmospheric Chemistry and Physics www.atmos-chem-phys.net 1680-7316 1680-7324 8 6 2008 10.5194/acp-8-1483-2008 http://www.atmos-chem-phys.net/8/1483/2008/ http://www.atmos-chem-phys.net/8/1483/2008/acp-8-1483-2008.html http://www.atmos-chem-phys.net/8/1483/2008/acp-8-1483-2008.pdf 1483 1499 2008-03-13 Validation of ACE-FTS satellite data in the upper troposphere/lower stratosphere (UTLS) using non-coincident measurements M. I. Hegglin michaela@atmosp.physics.utoronto.ca C. D. Boone G. L. Manney T. G. Shepherd K. A. Walker P. F. Bernath W. H. Daffer P. Hoor C. Schiller Department of Physics, University of Toronto, Toronto, Canada Department of Chemistry, University of Waterloo, Waterloo, Canada Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA New Mexico Institute of Mining and Technology, Socorro, New Mexico, USA Department of Chemistry, University of York, York, UK Columbus Technologies Inc., Pasadena, California, USA Max Planck Institute for Chemistry, Air Chemistry, Mainz, Germany Institute for Chemistry and Dynamics of the Geosphere 1: Stratosphere, Research Centre Jülich GmbH, Jülich, Germany 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. 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