Fires in southeastern Australia produced at least 18 pyrocumulonimbus (pyroCb) between 29 December 2019 and 4 January 2020. The largest plumes from this event exhibited several previously undocumented phenomena in the stratosphere. These include (i) the generation of potential vorticity and anticyclonic circulations from absorptive aerosol heating, (ii) the formation of a vertical temperature anomaly dipole, (iii) the rapid ascent from the lowermost stratosphere (15–16 km) to altitudes above 31 km in less than 2 months, (iv) an unprecedented abundance of H2O and CO in the stratosphere, and (v) the displacement of background O3 and N2O from rapid ascent of air from the troposphere and lower stratosphere. Each of these phenomena is traced back to a 5‐day‐old stratospheric plume composed of a massive amount of aerosol and biomass burning gases from a pyroCb outbreak. Until now, there has been no documented evidence that pyroCb plumes can affect stratospheric winds.

Abstract. A 7-year (1992-1998) seasonal climatology of effective horizontal diffusivity is presented for the stratosphere (350-1900 K). As in previous studies, the diagnosis is based on the equivalent length of a test tracer advected on isentropic surfaces, in this case using the van Leer flux-limiting scheme driven by the United Kingdom Meteorological Office assimilated winds. Although the magnitude of equivalent length is resolution dependent, its structure is shown to be reasonably robust for quantifying the inhomogeneous mixing in the stratosphere. The van Leer calculation agrees well with a more expensive spectral transform calculation at a comparable resolution, suggesting that the diagnostic is not sensitive to the advection scheme or subgrid representation of the models. A first attempt is also made at estimating the implicit numerical diffusion of the van Leer scheme, which is necessary to convert equivalent length to effective diffusivity. Compared with the spectral calculations with a constant diffusion coefficient, the van Leer results show notably greater diffusivity within the winter polar vortices despite the comparable equivalent lengths, suggesting that the scheme may be overdiffusing in the vicinities of mobile tracer extrema. The climatology of equivalent length is then presented, and the seasonal evolution is discussed in detail for the lower, middle, and upper stratosphere. The major mixing barriers (winter and summer polar vortices and tropical eddy transport barrier) are easily identified, as well as the strong mixing regions (surf zones). Generally, equivalent length tends to be small in regions of strong zonal wind and large in regions of weak wind. Large values of equivalent length are observed in the summer lower stratosphere and in the middle stratosphere during the breakup of the polar vortices. Interhemispheric asymmetry is observed both after the winter polar vortex breakup, where in the middle stratosphere the Southern Hemisphere shows much larger equivalent lengths, and in the summer tropical region, where larger equivalent lengths are observed in the Northern Hemisphere, likely related to the monsoon circulation. A monthly averaged equivalent length climatology is presented, and implications for two-dimensional stmtospheric chemistry-transport modeling are discussed.

Unusually large planetary wave activity in the 2002 Antarctic winter stratosphere weakened and warmed the polar vortex. Three minor warmings during August and early September preceded a late‐September major warming when the middle stratospheric zonal winds reversed to easterly and the polar temperature increased by an additional 25 K. Polar Ozone and Aerosol Measurement (POAM III) ozone data at high southern latitudes show unusually large variability in 2002 compared to previous POAM III years (1998–2001). Analyses of air parcel transport indicate this variability is caused by large‐scale isentropic transport. Diagnostics of transport and mixing show that during the major warming the lower stratospheric vortex remained intact, while the middle stratospheric vortex split into two pieces; one piece rapidly mixed with extravortex air, while the other returned to the pole as a much weaker and smaller vortex.

An unusually strong and prolonged stratospheric sudden warming (SSW) in January 2006 was the first major SSW for which globally distributed long-lived trace gas data are available covering the upper troposphere through the lower mesosphere. We use Aura Microwave Limb Sounder (MLS), Atmospheric Chemistry Experiment-Fourier Transform Spectrometer (ACE-FTS) data, the SLIMCAT Chemistry Transport Model (CTM), and assimilated meteorological analyses to provide a comprehensive picture of transport during this event. The upper tropospheric ridge that triggered the SSW was associated with an elevated tropopause and layering in trace gas profiles in conjunction with stratospheric and tropospheric intrusions. Anomalous poleward transport (with corresponding quasi-isentropic troposphereto-stratosphere exchange at the lowest levels studied) in the region over the ridge extended well into the lower stratosphere. In the middle and upper stratosphere, the breakdown of the polar vortex transport barrier was seen in a signature of rapid, widespread mixing in trace gases, including CO, H 2 O, CH 4 and N 2 O. The vortex broke down slightly later and more slowly in the lower than in the middle stratosphere. In the middle and lower stratosphere, small remnants with trace gas values characteristic of the pre-SSW vortex lingered through the weak and slow recovery of the vortex. The upper stratospheric vortex quickly reformed, and, as enhanced diabatic descent set in, CO descended into this strong vortex, echoing the fall vortex development. Trace gas evolution in the SLIMCAT CTM agrees well with that in the satellite trace gas data from the upper troposphere through the middle stratosphere. In the upper stratosphere and lower mesosphere, the SLIMCAT simulation does not capture the strong descent of mesospheric CO and H 2 O values into the reformed vortex; this poor CTM performance in the upper stratosphere and lower mesosphere results primarily from biases in the diabatic descent in assimilated analyses.

The 2002 southern hemisphere winter was marked by unusually large wave activity, culminating with an unprecedented major warming in late September. This led to an ∼250 DU increase in column ozone near the pole as measured by the Polar Ozone and Aerosol Measurement (POAM) III instrument. POAM measurements of unusually high ozone mixing ratio throughout most of the stratosphere resulted primarily from air from outside the polar vortex being transported to the POAM measurement latitude. In the altitude region where chemical ozone loss from chlorine catalyzed chemistry occurs (below 600 K potential temperature) the 2002 ozone loss was similar to previous years up to the time of the major warming. The ozone loss diminished after this time (about 1 week earlier than usual), resulting in up to 20% less chemical ozone loss within the vortex than in previous winters. This corresponds to partial column ozone values below 600 K inside the polar vortex that were ∼25 DU larger in 2002 than in previous years.