| Summary: | Several recently published studies indicate that many uncertainties still exist concerning the stratosphere-troposphere exchange of ozone which mainly occurs during mid-latitude tropopause folding as well as during cut-off low events. We performed a series of ozone sonde ascents in Athens, Greece (37.9° N, 23.8° E), during the winter 1991–1992 in the framework of both the European Arctic Stratospheric Ozone Experiment (EASOE) and the Tropospheric Ozone Research (TOR) programme. In this paper we examine the cases of four ascents. Two ascents were made when a cut-off low system was installed over our region, others when the station was situated at the flank of the polar vortex. In both cases strong indications of cross-tropopause flow were observed, with a remarkable minimum in ozone partial pressure near 15 km. © 1994, Taylor & Francis Group, LLC. All rights reserved.
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