Basics: Proxies |APSC| and |VPSC|

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 |APSC| specifies the area at a certain height, which is below a

 typical temperature threshold below which the chlorine-catalyzed polar

 ozone depletion takes place.  |VPSC| is the corresponding volume in a

 given height range (here: 14-22 km).  Here the average value of this

 size between mid December and the end of March is considered.  Since

 usually in cold arctic winters there is a stable polar vortex, it has

 been found empirically that this quantity can provide good

 approximations for ozone depletion [#]_.  High values of [VPSC] mean

 high ozone losses.

 .. |APSC| replace:: A\ :sub:`PSC`\ 

 .. |VPSC| replace:: V\ :sub:`PSC`\ 

 .. |H2O| replace:: H\ :sub:`2`\ O

 .. [#] see e.g. Rex, M. et al., Geophys. Res. Lett., 31, doi:10.1029/2003GL018844, 2004