The impact of free convection on late morning ozone decreases on an Alpine foreland mountain summit J.-C. Mayer1, K. Staudt2, S. Gilge3, F. X. Meixner1,4, and T. Foken2 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.
Citation: Mayer, J.-C., Staudt, K., Gilge, S., Meixner, F. X., and Foken, T.: The impact of free convection on late morning ozone decreases on an Alpine foreland mountain summit, Atmos. Chem. Phys., 8, 5941-5956, doi:10.5194/acp-8-5941-2008, 2008.