High-Resolution Lidar Measurements of Stratosphere–Troposphere Exchange

The tropospheric ozone lidar at the Fraunhofer-Institut für Atmosphärische Umweltforschung has been upgraded for measurements in an extended range with high accuracy (mostly 5%), high vertical resolution (50–500 m within the troposphere), and under automatic control. The operating range is now from 0.15 to about 16 km, the upper limit varying by ±2 km depending on the average ozone density in the troposphere. Routine measurements were resumed in January 1996. The current research efforts are concentrated mainly on an optimum observational coverage of tropopause folds and on evaluating more details of stratosphere–troposphere exchange. Ozone tongues associated with tropopause folds may be as narrow as 300 m. Their detection and correct analysis greatly benefits from the improved instrumental performance of the lidar. From the data acquired during the first 23 months of this project it is concluded that roughly 98% of the stratospheric air intrusions reach the Zugspitze summit station (2962 m above sea level). Many of the examples of stratospheric intrusions show pronounced secondary ozone maxima in the upper troposphere starting a few hours to one day after the subsidence of a tropopause fold and have been tracked with the lidar under automatic control for up to four consecutive days. More work is needed to understand and to analyze the contribution of these ozone structures to the overall downward flux during such an episode.