Oksana Ivaniha

Accurate representation of large‐scale stratospheric transport in chemistry–climate models is essential for understanding and interpreting observed atmospheric variability and for making reliable projections. The subtropical transport barriers (STBs) separate the tropical stratosphere, influenced by slow upwelling, from the midlatitudes, where rapid mixing occurs. Long‐lived tracer contours reflect the combined effects of advection and mixing, making them valuable for identifying these barriers. This study compares a set of tracer‐based and dynamical diagnostics of the STBs in the CESM1‐WACCM chemistry‐climate model with various observational data sets. Tracer‐based barriers in the model show excellent agreement with observations between approximately 50‐5 hPa in seasonal climatology, variability associated with the Quasi‐Biennial Oscillation (QBO), and trends. The STBs exhibit a QBO‐driven displacement due to secondary meridional circulation in the winter hemisphere and due to the enhanced isentropic mixing associated with waves crossing the equator in the summer hemisphere. Tracer‐based barriers reveal a statistically significant southward shift of the tropical pipe from 2005 to 2012 consistent with prior findings. We show that this southward shift is a non‐linear effect of the QBO and disappears over longer periods. Dynamical estimates of the STBs show overall good agreement between model and reanalysis in terms of the climatology but are unreliable in the summer hemisphere. Moreover, they fail to capture the QBO‐related variability and trends observed in the tracer‐based boundaries. This discrepancy highlights that dynamical metrics isolate specific instantaneous transport processes, whereas tracer‐based metrics capture their cumulative impact, displaying a lagged and damped seasonality compared to the dynamical estimates.

The representation of stratospheric transport in Chemistry-Climate Models (CCMs) is key for accurately reproducing and projecting the evolution of the ozone layer and other radiatively relevant trace gases. We evaluate stratospheric transport in CCMs that have participated in three model intercomparison initiatives (CCMVal-2, CCMI-1, and CCMI-2022) over the last ∼ 15 years using modern satellite datasets and reanalyses. Key long-standing model biases persist across generations, with some worsening in recent simulations. Transport remains overly fast in the models, with a global mean age of air young bias of ∼ 1 year for the CCMI-2022 median. It is argued that this bias could be associated with too fast tropical upwelling in the lower stratosphere and possibly to excessive vertical diffusion, with mixing biases being more uncertain. In the springtime southern polar stratosphere, the final warming is delayed (∼ 3 weeks), downwelling is underestimated (∼ 25 %), and the depth of the ozone minimum is overestimated (∼ 10 DU) on average in the most recent models. The tropopause is too high in all generations, and the tropical cold point tropopause is too warm in the latest generation (∼ 1–2 K). Long-term trends in transport over 1980–1999 are consistent across model generations and highlight the crucial role of ozone depletion in contributing to accelerate the Brewer-Dobson circulation and delaying the southern polar vortex breakdown.

The representation of stratospheric transport in Chemistry-Climate Models (CCMs) is key for accurately reproducing and projecting the evolution of the ozone layer and other radiatively relevant trace gases. We evaluate stratospheric transport in CCMs that have participated in three model intercomparison initiatives (CCMVal-2, CCMI-1, and CCMI-2022) over the last ~15 years using modern satellite datasets and reanalyses. Key long-standing model biases persist across generations, with some worsening in recent simulations. Transport remains overly fast in the models, with a global mean age of air young bias of ~1 year for the CCMI-2022 median. It is argued that this bias could be associated with too fast tropical upwelling in the lower stratosphere, insufficient horizontal mixing and/or excessive vertical diffusion. In the springtime southern polar stratosphere, the final warming is delayed (~3 weeks), downwelling is underestimated (~25 %), and the depth of the ozone minimum is overestimated (~10 DU) on average in the most recent models. The tropopause is too high in all generations, and the tropical cold point tropopause is too warm in the latest generation (~1–2 K). Long-term trends in transport and over 1980–1999 are consistent across model generations and highlight the crucial role of ozone depletion in contributing to accelerate the Brewer-Dobson circulation and delaying the southern polar vortex breakdown.

The representation of stratospheric transport in Chemistry-Climate Models (CCMs) is key for accurately reproducing and projecting the evolution of the ozone layer and other radiatively relevant trace gases. We evaluate stratospheric transport in CCMs that have participated in three model intercomparison initiatives (CCMVal-2, CCMI-1, and CCMI-2022) over the last ~15 years using modern satellite datasets and reanalyses. Key long-standing model biases persist across generations, with some worsening in recent simulations. Transport remains overly fast in the models, with a global mean age of air young bias of ~1 year for the CCMI-2022 median. It is argued that this bias could be associated with too fast tropical upwelling in the lower stratosphere, insufficient horizontal mixing and/or excessive vertical diffusion. In the springtime southern polar stratosphere, the final warming is delayed (~3 weeks), downwelling is underestimated (~25 %), and the depth of the ozone minimum is overestimated (~10 DU) on average in the most recent models. The tropopause is too high in all generations, and the tropical cold point tropopause is too warm in the latest generation (~1–2 K). Long-term trends in transport and over 1980–1999 are consistent across model generations and highlight the crucial role of ozone depletion in contributing to accelerate the Brewer-Dobson circulation and delaying the southern polar vortex breakdown.

Accurate representation of the large-scale stratospheric transport in chemistry-climate models is crucial for interpreting observed variability in chemical species, such as ozone, and making reliable projections regarding future changes. Subtropical transport barriers separate the tropical stratosphere, influenced by slow upwelling, from the surf zones, where rapid mixing occurs due to wave breaking. Long-lived tracer contours reflect the combined effects of advection and mixing and can be used to identify the location of the subtropical transport barriers. This study comprehensively compares tracer- and dynamics-based diagnostics of the subtropical transport barriers in the CESM-WACCM4 chemistry-climate model and various observational datasets. The model tracer-based estimates show excellent agreement with observations regarding seasonal climatology and variability linked to the Quasi-Biennial Oscillation (QBO). The chemical boundaries shift due to the secondary meridional circulation induced by the QBO in the winter hemisphere and due to the enhanced isentropic mixing associated with waves crossing the equator in the summer hemisphere. Consistent with previous studies, the observational tracer metrics feature a southward shift of the tropical pipe over 2005–2012. The model, which nudges the QBO to observations, captures qualitatively the shift over this period. Dynamical metrics represent individual transport processes and thus fail to capture the variability and trends in the tracer-based boundaries.

Sudden stratospheric warming (SSW), a well-known phenomenon in the polar atmosphere, changes the distribution of various atmospheric parameters due to the enhanced activity of planetary waves. These processes produce zonal asymmetry in total ozone content (TOC) with a wave-1 pattern. However, regional characteristic properties of the Antarctic TOC anomalies that occur during the SSW life cycle have not been studied in detail. We aim to analyze the connection of zonally asymmetric variations of TOC with SSW events. The analysis is based on a time series of ten research stations in the Antarctic region and gridded fields from MSR-2 TOC data. Here, we compare the evolution of TOC and wave amplitudes in three Southern Hemisphere SSW events. The TOC time series over ten stations in the Antarctic region and superposed epoch analysis for ±60-day time lags relative to the SSW central date were used. A regional division according to the geographic location of the stations and TOC climatology was introduced. According to the TOC asymmetry pattern, a division between Eastern and Western Hemisphere stations is used. We observe zonally asymmetric ozone responses in the two hemispheres during the SSW life cycle, including distinct precursor properties before the SSW onset. This research clarifies the different SSW properties in local ozone observations under the zonally asymmetric TOC field. The previously unknown regional manifestations of Antarctic TOC anomalies in the early stage of the SSW are discussed. The role of wave-1 and the zonally asymmetric Brewer-Dobson circulation in the Eastern–Western Hemisphere difference in the Antarctic TOC variability is also discussed. We also characterize total ozone levels in the years immediately preceding and following the three most significant SSW events. We examine the influence of planetary wave activity and large-scale climate modes on the level of interannual ozone variability and its regional patterns. There is evidence that Antarctic total ozone in the years adjacent to these SSW events is reduced, which may serve as a precursor signal of these events and an indicator of their longer-lasting influence. We discuss the implications and importance of these ozone perturbations for the regional Antarctic climate.

Sudden stratosphere warming (SSW) is a distinctive phenomenon characteristic of the winter stratospheric circulation. SSW is linked to the activity of planetary waves. Planetary waves are one of the most prominent waves in the stratosphere, and their evolution, propagation, and anomalies are critical scientific issues in atmospheric dynamics. This study primarily investigates the persistent trend changes in planetary waves and SSW-related climate indices within the stratosphere. Analyzing these trends to enhance the prediction of stratospheric atmospheric evolution. We conducted a zonal harmonic analysis using the potential height fields from ERA5, MERRA-2, and MLS satellite data to determine the amplitudes of planetary waves with wave numbers 1 to 3, analyzing a time period covers 40 winter-spring seasons in the Northern Hemisphere. Climatology for the last four decades allows us to reliably determine the average indicators that characterize zonal waves 1 – 3 during 4 months (December – March) in the stratosphere and lower mesosphere. We are looking for signs and possibilities of the SSW prediction by analyzing the trends of anomalous changes in planetary wave activity. We also discuss the trend changes in climate indices associated with stratospheric atmospheric dynamics, mainly focusing on El Nino Southern Oscillation, Arctic Oscillation, Equivalent Effective Stratospheric Chlorine, Quasi-Biennial Oscillation and NH Coupled Mode Index, over the 40 winter and spring season in the Northern Hemisphere from 1980 to 2023. We investigate the possible connections between these indices and SSW events to identify potential precursors associated with SSW. We try to find appropriate parameters that can trigger SSW. Therefore, the analysis of planetary wave parameters and climate indices can provide insights into SSW events' frequency and dynamic characteristics.

Transport in the stratosphere is characterized by upwelling in the tropics and downwelling in the extratropics, and these regions are separated by the so-called turnaround latitudes. In the winter hemisphere, a region of intense wave breaking (the ‘surf zone’) separates the tropics from the polar vortex. In the summer hemisphere, easterly winds do not allow for penetration of planetary waves into the middle and upper stratosphere.Observational evidence of this global transport circulation comes from the shape of long-lived tracer contours. While the overturning circulation tends to steepen latitudinal gradients of tracers, large-scale stirring by wave breaking leads to quasi-horizontal mixing and thus flattens the gradients. The observed shape of tracer contours results from the combined effects of the two transport processes, and is therefore not trivially related to the turnaround latitudes or mixing diagnostics.In this study we compare several tracer-based and dynamical-based diagnostics of the tropical width computed both from a CESM1-WACCM model simulation and from satellite observations and reanalysis data. We find notable differences between the dynamical and tracer metrics particularly in the seasonality, with good correspondence only in the equinox seasons. We also examine the interannual variability and long-term trends.

We use Multi-Sensor Reanalysis and ground-based total ozone content (TOC) data to study total ozone variations in Antarctica near the dates of sudden stratospheric warmings (SSW). Three events were analyzed, including the warmings in 1988, 2002 (major warming), and 2019. All of them occurred in September, during the period of ozone hole development. Total ozone over stations with different latitudes and longitudes was considered to understand the properties of its variations in different parts of the stratospheric polar vortex and over the surrounding area. The 1979–2022 TOC climatology was obtained from the Multi-Sensor Reanalysis data. The multi-year mean shows a main total ozone minimum in September–October with values lower than 200 Dobson Units (DU) in the Atlantic longitudinal sector (Rothera, Faraday/Vernadsky). The annual TOC maximum of 280–300 DU occurs at the Antarctic stations, mainly in December. The exception is Dumont-d’Urville, located in the zonal maximum region and characterized by higher ozone levels of about 340 DU, which are reached in October–November. Composite analysis is carried out to study the interrelation between SSW events and total ozone variations. We considered a time range covering 60 days before and 60 days after an SSW. Of course, three events do not allow proper statistical material, but some tendencies can be traced. Preliminarily, there is a TOC increase by ~100 DU at Amundsen-Scott (located at the South Pole) near the SSW date. The corresponding increase in the Atlantic longitudinal sector (Rothera, Faraday/Vernadsky, and even mid-latitude Ushuaia station) occurred several days later. It is noticed that after several weeks, TOC values in the Atlantic sector become lower than climatological ones, which a partial recovery of the polar vortex can cause. In the opposite Australian longitudinal sector, TOC values are maintained over the climatological level by tens of DU at least 30–40 days before the SSW. Consequently, the SSW events seem to be prepared by stratospheric processes connected with the intensification of the TOC zonal maximum.This work was partly supported by the projects of the Australian Antarctic Division and by the International Center of Future Science, Jilin University, under Grant No G2023129024.