Trajectory matching of ozonesondes and MOZAIC measurements in the UTLS - Part 1: Method description and application at Payerne, Switzerland.

With the aim of improving ozonesonde observations in the upper troposphere/lower stratosphere (UTLS), we use three-dimensional forward and backward trajectories, driven by ERA-Interim wind fields to match and compare ozonesonde measurements at Payerne (Switzerland) with observations from the MOZAIC aircraft program from 1994- 2009. The uncertainties associated with the sonde-MOZAIC match technique were assessed using "self-matches", i.e. matches of instruments of the same type, such as MOZAIC- MOZAIC. Despite strong vertical gradients of ozone at the tropopause, which render the match approach difficult, the method provides excellent results, showing mean differences between different MOZAIC aircraft of ±2% (typically with a few hours between the up- and downstream match points). Matches between MOZAIC aircraft and Payerne ozonesondes show an agreement of ±5% for sondes equipped with electrochemical concentration cells (ECC) and between <5% (not scaled to total ozone) and <10% (scaled) for the Brewer-Mast (BM) sondes after 1998. Prior to 1998, BM sondes show an offset of around 20% (scaled). No break can be identified through the change from the BM to ECC sonde types in September 2002. A comparison of BM sondes with ozone measurements from the NOXAR B747 project for the period 1995-1996 show a smaller offset of around 15% (scaled), which may indicate a small drift in the MOZAIC calibration. [ABSTRACT FROM AUTHOR]