The NAO-index is employed to separate the dynamically contribution from the observed mid-latitudal ozone trends to have a clearer view on the anthropogenic ozone destruction.

Nice Poster!  presented at the AGU,  San Francisco, Dec 1999 can be downloaded:  ftp://bach.ethz.ch/pub_read/andrea/posterAW.ps.gz  (0.3 MB, gunzipped 7.6 MB).

What is NAO ?

The North Atlantic Oscillation (NAO) is a  dominant mode of multi-annual variability in the atmosphere,
most pronounced in winter, over Europe and the North Atlantic region. The same pattern occurs in many meteorological variables such as surface winds, temperatures and precipitation. It is characterized with the NAO-index, which is defined as the pressure difference between Ponta Delgada (Azores) and Stykkisholmur (Iceland). NAO variability is found also in oceanic parameters and in the troposphere-stratosphere system.
 

NAO still puzzles the scientists:
Where does it come from? How will it change in future?  Is the current change already  a greenhouse effect?
Useful links are collected at Christof Appenzeller's page  and David B Stephenson's page.
The NAO- index can be found at the Climate Research Unit.

What is AO ?

The Arctic Oscillation (AO)  also describes atmospheric variability, but in contrary to the NAO, for the
Northern Hemisphere and not only the North Atlantic/European region.

The AO is explained at David Thompson's page.

What have  NAO and AO to do with ozone ?

The tropopause pressure varies in concert with NAO/ AO with a distinct geographical pattern,
causing  reversible transport of ozone. The ozone profile is influenced mostly in the lower stratosphere.
 

We have already one paper about this in press:

Appenzeller, C. and Weiss, A. K. and Staehelin, J.
North Atlantic Oscillation modulates total ozone winter trends.
Geophysical Research Letters, in press, 2000.

See  chapters 2, 6, 7, 8 of my PhD thesis (available after April 2000) for further information.