Quantifying variability in the lowermost stratosphere (LMS) is important because of feedbacks among changing temperature, dynamics and species like ozone. We used reprocessed Southern Hemisphere Additional Ozonesondes data from 1998-2018 in a Multiple Linear Regression (MLR) model to analyze variability and trends in free tropospheric (FT) and LMS ozoneacross five well-distributed tropical regions. The MLR also computed trends in a proxy for convection as determined from laminae in each ozonesonde-radiosonde pair. Only the equatorial Americas exhibits statistically significant annual trends in FT or LMS ozone. At the other sites, ozonetrends occur in isolated layers during months when convection has changed, February-April or July-November. Our results imply that large FT ozone increases reported for populated tropical areas may be caused by growing pollution overlying smaller changes caused by perturbed dynamics. They also provide regional data for evaluating LMS ozonetrends based on zonal averages of often sparse satellite measurements

A rare disturbance of the stratospheric Antarctic polar vortex in September 2019 led to a significantly higher than usual polar total ozone column. We use assimilation of ozone, HCl, and NO data from the Microwave Limb Sounder with the Global Earth Observing System Constituent Data Assimilation System driven by reanalysis meteorology to study the evolution of the 2019 Antarctic polar ozone. We find that the maximum 2019 ozone hole area was near 10 million km, and as little as 20% of that in 2018 in mid-September. However, the magnitude of vortex-averaged chemical ozone depletion was not significantly different between the two years despite earlier chlorine deactivation in 2019. The assimilation results show that most of the differences between 2018 and 2019 Antarctic ozone resulted from two factors: (1) the geometry of the 2019 vortex, with ozone-rich middle-stratospheric air masses overlying the lower portion of the vortex and leading to a significant reduction of the total column; (2) significantly reduced vortex volume. The anomalously small ozone hole of 2019 was comparable in size to the record breaking 2002 case and the mechanisms responsible were similar in the two cases. While the 2019 sudden stratospheric warming is classified as minor, its impact on ozone was very significant.