Long-term variations in total ozone derived from Dobson and satellite data

Total ozone growth rates are calculated using flexible ‘tendency curves’ that can follow ozone variations on all timescales greater than that of the quasi-biennial oscillation. This method improves on traditional trend analysis using straight line fits because it follows ozone variations more closely, providing visual information about the timing and global distribution of ozone variations. Results are compared from long-running Dobson sites and from two homogenized satellite data sets, one constructed at NASA/Goddard Space Flight Center and the other developed at New Zealand's National Institute of Water and Atmospheric Research. Although the most negative ozone trends in the Southern Hemisphere appear to be linked to polar vortex chemistry, those in the Northern Hemisphere have occurred between 35°N and 40°N and may be related to dynamical trends and/or chemistry on episodically occurring volcanic aerosols. A quasi-decadal cycle in total ozone was present since the mid-1920s and hence is independent of halogen chemistry. Its cause remains unknown. Including the deseasonalized and detrended local temperature in the ozone trend model decreases the standard error of the ozone trend over most of the globe.