The impact of free convection on late morning ozone decreases on an Alpine foreland mountain summit
1Biogeochemistry Department, Max Planck Institute for Chemistry, Mainz, Germany
2Department of Micrometeorology, University of Bayreuth, Bayreuth, Germany
3German Meteorological Service, Observatory Hohenpeißenberg, Hohenpeißenberg, Germany
4Department of Physics, University of Zimbabwe, Harare, Zimbabwe
Abstract. Exceptional patterns in the diurnal course of ozone mixing ratio at a mountain top site (998 m a.s.l.) were observed during a field experiment (September 2005). They manifested themselves as strong and sudden decreases of ozone mixing ratio with a subsequent return to previous levels. The evaluation of corresponding long-term time series (2000–2005) revealed that such events occur mainly during summer, and affect the mountain top site on about 18% of the summer days. Combining (a) surface layer measurements at mountain summit and at the foot of the mountain, (b) in-situ (tethered balloon) and remote sensing (SODAR-RASS) measurements within the atmospheric boundary layer, the origin of these events of sudden ozone decrease could be attributed to free convection. The free convection was triggered by a rather frequently occurring wind speed minimum around the location of the mountain.