Stratospheric observations in the Southern Hemisphere show that the Antarctic ozone hole exhibited unprecedented features in 2002. During the second half of September 2002, the size of the Antarctic ozone hole was around half of that observed in September of the last few years. Apart from its smaller size, the Antarctic ozone hole broke up into two holes on 24–25 September 2002.
These unusual events concerning both the size and break-up of the Antarctic ozone hole in September 2002 have been examined by Varotsos . Both events have been attributed to the occurrence of a major, sudden stratospheric warming (SSW) in Antarctica, an event that appeared for the first time in that region. In particular, concerning the smaller size of the ozone hole, it was suggested that the major SSW did not allow the heterogeneous chemical reactions, which are substantially active at very low temperatures, to lead to a considerable chemical ozone loss. The early break-up was attributed to the 2-month early polar vortex splitting in two. It began 2 days earlier, with the unusual early building of a quasi-stationary anti-cyclone, and an opposite, secondary anti-cyclone later on, due to the major SSW.