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2. Methodology

Ten of the thirteen ozone soundings of Marambio during APE-GAIA show some layering. Trajectories were calculated isentropically by means of a global trajectory model by G. Redaelli and R. Dragani at the University of l«Aquila. In the tables potential vorticities (PV) of the filaments at the sounding and after seven days backward advection are compared with the each other and to the PV values of the core of the vortex edge of the corresponding isentrophic surface (theta). PV unit used here is PVU (=10**-6*K*m**2*kg**-1s**-1).

PV of the vortex edge on each surface was determined to be the mean PV value at the location of maximum gradient along 14 longitudes around the globe between the latitudes of -40.0¡ and -82.5¡ . The mean value was calculated separately for each seven days period.

Winds from ECMWF were retrieved and PV was calculated and drawn together with position of the air parcel on the specific thetas in a 2.5¡ x 2.5¡ grid. Thus the trajectories were compared also to the position and the overall development of the vortex. The trajectories of the ozone filaments and Geophysica were compared in order to find a best possible match and a possibility to use in situ trace gas measurements in the filament analysis. One match, that of 23.09.1999 sounding on 413 K, was found.

In the study the basic assumption is that the filaments of low ozone originate from the chemically perturbed region inside the vortex where as the high ozone filaments originate outside the vortex or from outer side of the edge region. This difference in origin should in turn be seen in differences of PV and tracers. If not, the cause of the filamentation is else than horizontal mixing of air through the vortex edge. In the Southern Hemisphere the PV values inside the vortex are typically very low compared to the PV values in surf zone. Between the two largely isolated air masses there is a transition zone where PV changes rapidly. Thus, low values of PV indicate origin inside the vortex.