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We have extended the satellite-based ozone anomaly time series to thepresent (December 2012) by merging SAGE II (Stratospheric Aerosol and Gas ExperimentII) with OSIRIS (Optical Spectrograph and Infrared Imager System)and correcting for the small bias (~0.5%) between them,determined using their temporal overlap of 4 years. Analysis of the mergeddata set (1984–2012) shows a statistically significant negative trend at allaltitudes in the 18–25 km range, including a trend of (−4.6 ± 2.6)% decade<sup>−1</sup>at 19.5 km where the relative standard error is a minimum. We arealso able to replicate previously reported decadal trends in the tropicallower-stratospheric ozone anomaly based on SAGE II observations.Uncertainties are smaller on the merged trend than the SAGE II trend at allaltitudes. Underlying strong fluctuations in ozone anomaly due to El Niño–Southern Oscillation (ENSO), the altitude-dependent quasi-biennialoscillation, and tropopause pressure need to be taken into account to reducetrend uncertainties and, in the case of ENSO, to accurately determine thelinear trend just above the tropopause. We also compare the observed ozonetrend with a calculated trend that uses information on tropical upwellingand its temporal trend from model simulations, tropopause pressure trendinformation derived from reanalysis data, and vertical profiles from SAGE IIand OSIRIS to determine the vertical gradient of ozone and its trend. Weshow that the observed trend agrees with the calculated trend and that themagnitude of the calculated trend is dominated by increased tropicalupwelling, with minor but increasing contribution from the vertical ozonegradient trend as the tropical tropopause is approached. Improvements aresuggested for future regression modelling efforts which could reduce trenduncertainties and biases in trend magnitudes, thereby allowing accuratetrend detection to extend below 18 km

Trend and variability in ozone in the tropical lower stratosphere over 2.5 solar cycles observed by SAGE II and OSIRIS