Influence of stratospheric airmasses on tropospheric vertical Osub3/sub columns based on GOME (Global Ozone Monitoring Experiment) measurements and backtrajectory calculation over the Pacific

摘要

Satellite based GOME (Global Ozone Measuring experiment) data are used tocharacterize the amount of tropospheric ozone over the tropical Pacific.Tropospheric ozone was determined from GOME data using the TroposphericExcess Method (TEM). In the tropical Pacific a significant seasonalvariation is detected. Tropospheric excess ozone is enhanced during thebiomass burning season from September to November due to outflow from thecontinents. In September 1999 GOME data reveal an episode of increasedexcess ozone columns over Tahiti (18.0° S; 149.0° W)(Eastern Pacific) comparedto Am. Samoa (14.23° S; 170.56° W) and Fiji(18.13° S; 178.40° E), both situatedin the Western Pacific. Backtrajectory calculations show that none of theairmasses arriving over the three locations experienced anthropogenicpollution (e. g. biomass burning). Consequently other sources of ozone haveto be considered. One possible process leading to an increase of troposphericozone is stratosphere-troposphere-exchange. An analysis of the potentialvorticity along trajectories arriving above each of the locations revealsthat airmasses at Tahiti are subject to enhanced stratospheric influence,compared to Am. Samoa and Fiji. As a result this study shows clearincidents of transport of airmasses from the stratosphere into thetroposphere.