Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 6 4 2006 10.5194/acpd-6-6183-2006 http://www.atmos-chem-phys-discuss.net/6/6183/2006/ http://www.atmos-chem-phys-discuss.net/6/6183/2006/acpd-6-6183-2006.html http://www.atmos-chem-phys-discuss.net/6/6183/2006/acpd-6-6183-2006.pdf 6183 6209 2006-07-11 The total ozone field separated into meteorological regimes. Part II: Northern Hemisphere mid-latitude total ozone trends R. D. Hudson M. F. Andrade M. B. Follette A. D. Frolov Department of Atmospheric and Oceanic Science, University of Maryland, College Park, MD 20742-2425, USA Atmospheric Physics Laboratory, Campus Universitario Cota-Cota, Calle 27, Universidad Mayor de San Andres, La Paz, Bolivia STG, Inc., 11710 Plaza America Drive, Reston, Virginia, USA Previous studies have presented clear evidence that the Northern Hemisphere total ozone field can be separated into distinct regimes (tropical, midlatitude, polar, and arctic) the boundaries of which are associated with the subtropical and polar upper troposphere fronts,and in the winter, the polar vortex. This paper presents a study of total ozone variability within these regimes, from 1979–2003, using data from the TOMS instruments. The change in ozone within each regime for the period January 1979–May 1991, a period of rapid total ozone change, was studied in detail. Previous studies had observed a zonal linear trend of –3.15% per decade for the latitude band 25°–60° N. When the ozone field is separated by regime, smaller linear trends (–2.5%, –2.2%, and –1.9% per decade for the polar, midlatitude, and tropical regimes, respectively) are observed. The trend in the zonal total ozone is larger because the relative areas of the regimes also changed over this time period. The relative area of the polar regime decreased by about 15%; the tropical regime increased by about 10% over this period. The changes in the relative areas can be associated with a change of the mean latitude of the sub-tropical and polar fronts within the latitude interval 25° to 60° N. Over the period from January 1979-May 1991, both fronts moved northward by 1.1±0.2 degrees per decade. Over the entire period of the study the subtropical front moved northward at a rate of 1.1±0.1 degree per decade, while the polar front moved by only 0.5±0.1 degrees per decade.