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This study investigates the origin of a zonal asymmetry in stratospheric ozone trends at northern high latitudes, identified in satellite limb observations over the past two decades. We use a merged data set consisting of ozone profiles retrieved at the University of Bremen from SCIAMACHY and OMPS‐LP measurements to derive ozone trends. We also use TOMCAT chemical transport model (CTM) simulations, forced by ERA5 reanalyses, to investigate the factors that drive the asymmetry observed in the long‐term changes. By studying seasonally and longitudinally resolved observation‐based ozone trends, we find, especially during spring, a well‐pronounced asymmetry at polar latitudes with values up to +6 % per decade over Greenland and −5 % per decade over western Russia. The control CTM simulation agrees well with these observed trends, whereas sensitivity simulations indicate that chemical mechanisms involved in the production and removal of ozone, or their changes, are unlikely to explain the observed behavior. The decomposition of TOMCAT ozone time series and ERA5 geopotential height into the first two wavenumber components shows a clear correlation between the two variables in the middle stratosphere and demonstrates a weakening and a shift in the wavenumber‐1 planetary wave activity over the past two decades. Finally, the analysis of the polar vortex position and strength points to a decadal oscillation with a reversal pattern at the beginning of the century. The same is found in the ozone trend asymmetry. This further stresses the link between changes in the polar vortex position and the identified ozone trend pattern. Monitoring long‐term ozone changes in the stratosphere is important and aims to assess the ozone layer's evolution in response to the Montreal Protocol and climate change. In this study, we investigate the origin of a zonal asymmetry in stratospheric ozone trends over the past two decades, which was identified at northern polar latitudes by analyzing satellite observations. To this aim, we use a merged data set consisting of ozone profiles retrieved at the University of Bremen from SCIAMACHY and OMPS‐LP measurements to derive ozone trends. We also use TOMCAT chemical transport model (CTM) simulations to investigate the factors that determine the asymmetry observed in long‐term ozone changes. The asymmetry is largest in springtime, and the CTM simulation agrees well with the observation‐based trends. Sensitivity simulations indicate that chemical mechanisms involved in the production and destruction of ozone are unlikely to explain the observed pattern. In contrast, changes in atmospheric dynamics are found to be relevant. Our analysis of the polar vortex position and strength shows a cyclical pattern that reverses its phase near the year 2000. We observe this same pattern in the ozone trend asymmetry. A longitudinal asymmetry in stratospheric ozone trends at northern high latitudes is found in satellite observations in the past two decadesThe asymmetry is particularly large in springtime and the TOMCAT chemistry transport model well reproduces the patternChanges in polar wave activity and in the position and strength of the polar vortex are found to be relevant to explain this pattern A longitudinal asymmetry in stratospheric ozone trends at northern high latitudes is found in satellite observations in the past two decades The asymmetry is particularly large in springtime and the TOMCAT chemistry transport model well reproduces the pattern Changes in polar wave activity and in the position and strength of the polar vortex are found to be relevant to explain this pattern

On 15 January 2022, the submarine Hunga Tonga volcanic eruption lofted materials high into the upper stratosphere, reaching a record‐breaking altitude of ∼58 km, unprecedented in the satellite observations era. Within two weeks, the bulk of the injected material circulated the globe between 20–30 km altitude, as observed by satellite instruments. We estimate that the stratospheric aerosol optical depth (sAOD) is the largest since the Pinatubo eruption and is at least twice as great as the sAOD after the 2015 Calbubo eruption despite the similar SO2injection from that eruption. We use space‐based observations to monitor the Hunga‐Tonga volcanic plume evolution and transport at different altitudes as it circulates the globe. While the main aerosol layer remains trapped in the tropical pipe, small parts have already made it to both the northern and southern hemisphere poles by April, which is almost certain to influence this year's ozone hole. The Hunga Tonga‐Hunga Ha'apai eruption on 15 January 2022 injected volcanic materials up to 58 km altitude, which is unprecedented in the satellite era. Using measurements from the Ozone Monitoring and Profiler Suite (OMPS LP) on NASA's S‐NPP satellite, we track the volcanic plume in the upper and middle stratosphere. OMPS LP detects the cloud at altitudes up to 50 km and measured the aerosol layer above 36 km for two and half months. It also confirms that the amount of aerosol in the stratosphere is the highest since the Pinatubo eruption in 1991. We also estimate that because of the large amount of water injected from this eruption, the aerosol extinction in the stratosphere is double what would be expected from the 0.4 Tg of SO2injected from this eruption, caused by the rapid SO2to sulfate conversion and faster particle growth, as suggested by previous studies. By April, parts of the volcanic cloud have already reached the Southern Hemisphere and Northern Hemisphere polar regions. Ozone Monitoring and Profiler Suite measured the Hunga Tonga aerosol layer in the upper stratosphere at altitudes up to 50 km, and tracked it above 36 km for 2.5 monthsThis eruption resulted in the highest stratospheric aerosol optical depth since Pinatubo in 1991Within weeks, parts of the volcanic cloud reached the Southern Hemisphere pole, and by April, it also reached the Northern Hemisphere pole Ozone Monitoring and Profiler Suite measured the Hunga Tonga aerosol layer in the upper stratosphere at altitudes up to 50 km, and tracked it above 36 km for 2.5 months This eruption resulted in the highest stratospheric aerosol optical depth since Pinatubo in 1991 Within weeks, parts of the volcanic cloud reached the Southern Hemisphere pole, and by April, it also reached the Northern Hemisphere pole