A composite study on the structure and formation of ozone miniholes and minihighs over central Europe

[ 1] Two different mechanisms have been proposed to be important for the formation of extreme total ozone events in mid-latitudes, so-called miniholes: ( A) far-range meridional transport of air masses from regions with different climatological ozone mixing ratios, and ( B) ( local) adiabatic vertical displacement of isentropes. Here, the relative importance of these two mechanisms is studied using two different ozone profile reconstruction techniques for all miniholes and minihighs ( events with anomalously high ozone) during the time period 1980-1989 over Switzerland. Composites for the two types of events of their vertical potential vorticity ( PV) reveal a vertical dipole structure of PV anomalies in the lower and middle stratosphere. They, in agreement with the profile reconstructions, highlight the importance of fast far-range transport ( mechanism A). Dynamically consistent with this PV structure is a relatively weak vertical displacement of isentropes between the PV dipole, that provides an additional but less important contribution ( mechanism B).