Sampling of an STT event over the Eastern Mediterranean region by lidar and electrochemical sonde

A Papayannis,D Balis,C Zerefos,S Eckhardt,E Galani,A Stohl,V Amiridis,P Zanis,H Wernli

doi:10.5194/angeo-23-2039-2005

Abstract

Abstract. A two-wavelength ultraviolet (289–316nm) ozone Differential Absorption Lidar (DIAL) system is used to perform ozone measurements in the free troposphere in the Eastern Mediterranean (Northern Greece). The ozone DIAL profiles obtained during a Stratosphere-to-Troposphere Transport (STT) event are compared to that acquired by an electrochemical ozonesonde, in the altitude range between 2 and 10 km. The measurement accuracy of these two instruments is also discussed. The mean difference between the ozone profiles obtained by the two techniques is of the order of 1.11 ppbv (1.86%), while the corresponding standard deviation is 4.69 ppbv (8.16%). A case study of an STT event which occurred on 29 November 2000 is presented and analyzed, using ozone lidar, satellite and meteorological data, as well as air mass back-trajectory analysis. During this STT event ozone mixing ratios of 55–65 ppbv were observed between 5 and 7 km height above sea level (a.s.l.). Stratospheric air was mixed with tropospheric air masses, leading to potential vorticity (PV) losses due to diabatic processes. The ozone DIAL system can be used for following STT events and small-scale mixing phenomena in the free troposphere, and for providing sequences of vertical ozone profiles in the free troposphere. Keywords. Atmospheric composition and structure (Evolution of the atmosphere; Instruments and techniques) – Meteorology and atmospheric dynamics (Middle atmosphere dynamics; Turbulence)

Highlights

Ozone plays a significant role in the gas-phase chemistry of the troposphere as an important oxidant and as a major precursor of the hydroxyl (OH) radicals, which in turn act as removal agents, through oxidation, for a large number of trace gases in the troposphere
The purpose of this paper is to present a case of sampling of an Stratosphere-toTroposphere Transport (STT) event and the corresponding mixing of stratospheric with tropospheric air over the Eastern Mediterranean region, by using the ozone Differential Absorption Lidar (DIAL) system of the Aristotle University of Thessaloniki (AUTH) in the frame of the STACCATO project (Stohl et al, 2003)
Middle) ending at similar heights with potential vorticity (PV) values less than 1 PVu (Fig. 8, bottom), imposing the hypothesis of mixing between stratospheric and tropospheric air masses before arriving at the level where the ozone maximum is observed above the observation site

Summary

Introduction

The most common occurrences of STT events in the extratropics are associated with tropopause folds (Danielsen, 1968; Davies and Schuepbach, 1994; Kentarchos et al, 2000; Kowol-Santen and Ancellet, 2000; Bertin et al, 2001; James et al, 2003). Ozone vertical profile measurements in the free troposphere and the lower stratosphere using the differential absorption lidar (DIAL) technique have been performed during the last twenty years, mostly in the Northern Hemisphere, either from ground-based or airborne platforms (Pelon and Megie, 1982; Browell et al, 1987; Papayannis, 1989; Ancellet et al, 1991; Kempfer et al, 1994; Eisele et al, 1999; Guirlet et al, 2000; Galani et al, 2003; Zanis et al, 2003; Ancellet and Ravetta, 2005). The purpose of this paper is to present a case of sampling of an STT event and the corresponding mixing of stratospheric with tropospheric air over the Eastern Mediterranean region, by using the ozone DIAL system of the Aristotle University of Thessaloniki (AUTH) in the frame of the STACCATO project (Stohl et al, 2003).

The UV DIAL system

ECC-sonde

Case study of 29 November 2000

Findings

Discussion and concluding remarks