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Abstract The inorganic chlorine (Cl_y) and odd nitrogen (NO_y) chemical families influence stratospheric O₃. In January 2020 Australian wildfires injected record‐breaking amounts of smoke into the southern stratosphere. Within 1–2 months ground‐based and satellite observations showed Cl_yand NO_ywere repartitioned. By May, lower stratospheric HCl columns declined by ∼30% and ClONO₂columns increased by 40%–50%. The Cl_yperturbations began and ended near the equinoxes, increased poleward, and peaked at the winter solstice. NO₂decreased from February to April, consistent with sulfate aerosol reactions, but returned to typical values by June ‐ months before the Cl_yrecovery. Transport tracers show that dynamics not chemistry explains most of the observed O₃decrease after April, with no significant transport earlier. Simulations assuming wildfire smoke behaves identically to sulfate aerosols couldn't reproduce observed Cl_ychanges, suggesting they have different composition and chemistry. This undermines our ability to predict ozone in a changing climate. 

Noetzli, J., Christiansen, H.H, Guglielmin, M., Hrbáček, F., Hu, G., Isaksen, K., Magnin, F., Pogliotti, P., Smith, S. L., Zhao, L. and Streletskiy, D. A. 2024. Permafrost temperature and active layer thickness. In: State of the Climate in 2023. Bulletin of the American Meteorological Society, 105 (8), S43–S44, https://doi.org/10.1175/BAMS-D-24-0116.1 

Abstract A remarkable, large‐amplitude, mountain wave (MW) breaking event was observed on the night of 21 June 2014 by ground‐based optical instruments operated on the New Zealand South Island during the Deep Propagating Gravity Wave Experiment (DEEPWAVE). Concurrent measurements of the MW structures, amplitudes, and background environment were made using an Advanced Mesospheric Temperature Mapper, a Rayleigh Lidar, an All‐Sky Imager, and a Fabry‐Perot Interferometer. The MW event was observed primarily in the OH airglow emission layer at an altitude of ~82 km, over an ~2‐hr interval (~10:30–12:30 UT), during strong eastward winds at the OH altitude and above, which weakened with time. The MWs displayed dominant horizontal wavelengths ranging from ~40 to 70 km and temperature perturbation amplitudes as large as ~35 K. The waves were characterized by an unusual, “saw‐tooth” pattern in the larger‐scale temperature field exhibiting narrow cold phases separating much broader warm phases with increasing temperatures toward the east, indicative of strong overturning and instability development. Estimates of the momentum fluxes during this event revealed a distinct periodicity (~25 min) with three well‐defined peaks ranging from ~600 to 800 m²/s², among the largest ever inferred at these altitudes. These results suggest that MW forcing at small horizontal scales (<100 km) can play large roles in the momentum budget of the mesopause region when forcing and propagation conditions allow them to reach mesospheric altitudes with large amplitudes. A detailed analysis of the instability dynamics accompanying this breaking MW event is presented in a companion paper, Fritts et al. (2019,https://doi.org/10.1029/2019jd030899).