ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-4-903-2004 Influence of stratospheric airmasses on tropospheric vertical O<sub>3</sub> columns based on GOME (Global Ozone Monitoring Experiment) measurements and backtrajectory calculation over the Pacific Ladstätter-Weißenmayer A. 1 Meyer-Arnek J. 1 Schlemm A. 1 Burrows J. P. 1 Institute of Environmental Physics, University of Bremen, P.O. Box 330440, D-28334 Bremen, Germany 21 06 2004 4 4 903 909 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/4/903/2004/acp-4-903-2004.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/4/903/2004/acp-4-903-2004.pdf

Satellite based GOME (Global Ozone Measuring experiment) data are used to characterize the amount of tropospheric ozone over the tropical Pacific. Tropospheric ozone was determined from GOME data using the Tropospheric Excess Method (TEM). In the tropical Pacific a significant seasonal variation is detected. Tropospheric excess ozone is enhanced during the biomass burning season from September to November due to outflow from the continents. In September 1999 GOME data reveal an episode of increased excess ozone columns over Tahiti (18.0&deg; S; 149.0&deg; W) (Eastern Pacific) compared to Am.&nbsp;Samoa (14.23&deg; S; 170.56&deg; W) and Fiji (18.13&deg; S; 178.40&deg; E), both situated in the Western Pacific. Backtrajectory calculations show that none of the airmasses arriving over the three locations experienced anthropogenic pollution (e.&nbsp;g.&nbsp;biomass burning). Consequently other sources of ozone have to be considered. One possible process leading to an increase of tropospheric ozone is stratosphere-troposphere-exchange. An analysis of the potential vorticity along trajectories arriving above each of the locations reveals that airmasses at Tahiti are subject to enhanced stratospheric influence, compared to Am.&nbsp;Samoa and Fiji. As a result this study shows clear incidents of transport of airmasses from the stratosphere into the troposphere.