STRATOSPHERIC OZONE TRENDS AS DETERMINED BY REGIME ANALYSIS: THE SOUTHERN HEMISPHERE

Abstract

Recent studies in the Northern Hemisphere have shown that the total ozone field can be classified by meteorological regimes, whose boundaries are the tropospheric upper-level jets. A similar approach has been followed to classify the Southern Hemisphere. Total ozone data from the TOMS instruments have been used to locate the upper-level jets and therefore, the regimes' boundaries. Here however, I use vertically integrated potential vorticity from the reanalysis data from NCEP/NCAR and ECMWF to estimate the first guess in an iterative procedure that calculates the ozone regime boundary values. The classification of the total ozone field using these boundary values was validated using daily rawinsonde temperature profiles, SAGE II ozone profiles, and TOMS total ozone data. Rawinsondes showed that, on any given day, the tropopause heights within a regime were relatively constant despite the large latitudinal extent of the regime itself. Data from SAGE II also showed that the classification produces distinct ozone profiles for each regime, which is consistent with the fact that total ozone is nearly constant within each regime, as shown by TOMS data.

The temporal behavior of total ozone within each regime between 1979 and 2004 was analyzed for the 25º-60ºS latitude band. Total ozone trend analysis showed that statistically significant decadal trends within each regime were smaller than the overall trend in this band with no classification. In addition, the areas of the meteorological regimes within the 25º-60ºS latitude band also showed statistically significant trends. During the period of study, the area of the tropical regime has increased at the expense of the areas of the midlatitude and polar regimes. Both processes, changes in total ozone within each regime as well as changes in their contribution to the 25º-60ºS band, are responsible for the overall trend in that region. The analysis also showed that the QBO and the solar flux have an important influence on the temporal behavior of both the total ozone within each regime and their corresponding areas. The results indicate, as is the case of the Northern Hemisphere, that the total ozone regime boundaries have migrated poleward between 1979 and 2004.