Following the Hunga Tonga–Hunga Ha’apai (HTHH) eruption in January 2022, stratospheric ozone depletion was observed in the Southern Hemisphere mid-latitudes and Antarctica during the 2022 austral wintertime and springtime. This eruption injected sulfur dioxide and unprecedented amounts of water vapor into the stratosphere. This work examines and quantifies the chemistry contribution of the volcanic materials to the ozone depletion using chemistry-climate model simulations with nudged meteorology. Simulated 2022 ozone and nitrogen oxides (NOx) anomalies show a good agreement with satellite observations. We find that chemistry only contributes up to 6% and 20% ozone destruction at mid-latitudes wintertime and Antarctic springtime respectively. The majority of the ozone depletion is attributed to the internal variability and dynamical changes forced by the eruption. Both the simulation and observations show a significant NOx reduction associated with the HTHH aerosol plume, indicating the enhanced dinitrogen pentoxide hydrolysis on sulfate aerosol.

Stratospheric transit time distributions (age-of-air spectra) are estimated using satellite water vapor (H2O) measurements from the Microwave Limb Sounder over 2004-2021 assuming stationary transport. Latitude-altitude dependent spectra are derived from correlations of interannual H2O anomalies with respect to the tropical tropopause source region, fitted with an inverse Gaussian distribution function. The reconstructions accurately capture interannual H2O variability in the ‘tropical pipe’ and global lower stratosphere, regions of relatively fast transport (~1-2 years) in the Brewer-Dobson circulation. The calculations provide novel observational estimates of the corresponding ‘short transit-time’ part of the age spectrum in these regions, including the mode. However, the H2O results do not constrain the longer transit-time ‘tail’ of the age spectra, and the mean age of air and spectral widths are systematically underestimated compared to other data. We compare observational results with parallel calculations applied to the WACCM chemistry-climate model and the CLaMS chemistry-transport model, and additionally evaluate the method in CLaMS by comparing with spectra from idealized pulse tracers. Because the age spectra accurately capture H2O interannual variations originating from the tropical tropopause, they can be used to identify ‘other’ sources of variability in the lower stratosphere, and we use these calculations to quantify H2O anomalies in the Southern Hemisphere linked to the Australian New Years fires in early 2020 and the Hunga volcanic eruption in 2022.

The Hunga Tonga Hunga-Ha’apai (HTHH) volcanic eruption on 15 January 2022 injected water vapor and SO2 into the stratosphere. Several months after the eruption, significantly stronger westerlies, and a weaker Brewer-Dobson circulation developed in the stratosphere of the Southern Hemisphere and were accompanied by unprecedented temperature anomalies in the stratosphere and mesosphere. In August 2022 the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) satellite instrument observed record-breaking temperature anomalies in the stratosphere and mesosphere that alternate signs with altitude. Ensemble simulations carried out with the Whole Atmosphere Community Climate Model (WACCM6) indicate that the strengthening of the stratospheric westerlies explains the mesospheric temperature changes. The stronger westerlies cause stronger westward gravity wave drag in the mesosphere, accelerating the mesospheric mean meridional circulation. The stronger mesospheric circulation, in turn, plays a dominant role in driving the changes in mesospheric temperatures. This study highlights the impact of large volcanic eruptions on middle atmospheric dynamics and provides insight into their long-term effects in the mesosphere. On the other hand, we could not discern a clear mechanism for the observed changes in stratospheric circulation. In fact, an examination of the WACCM ensemble reveals that not every member reproduces the large changes observed by SABER. We conclude that there is a stochastic component to the stratospheric response to the HTHH eruption.

The Hunga Tonga-Hunga Ha’apai (HTHH) volcanic eruption in January 2022 injected extreme amounts of water vapor (H2O) and a moderate amount of the aerosol precursor (SO2) into the Southern Hemisphere (SH) stratosphere. The H2O and aerosol perturbations have persisted and resulted in large-scale SH stratospheric cooling, equatorward shift of the Antarctic polar vortex, and slowing of the Brewer-Dobson circulation associated with a substantial ozone reduction in the SH winter midlatitudes. Chemistry-climate model simulations forced by realistic HTHH inputs of H2O and SO2 reproduce the observed stratospheric cooling and circulation effects, demonstrating the observed behavior is due to the volcanic influences. Furthermore, the combination of aerosol transport to polar latitudes and a cold polar vortex enhances springtime Antarctic ozone loss, consistent with observed polar ozone behavior in 2022.

A new constellation of radio occultation satellites called COSMIC-2 (Constellation Observing System for Meteorology, Ionosphere and Climate-2) is providing unprecedented dense measurements of the tropical atmosphere, with on average more than 4,000 high quality observations per day over 40o N-S. We use these data to evaluate large- and small-scale thermal variability in the tropical lower stratosphere during October 2019 – April 2020. Space-time spectral analysis of gridded COSMIC-2 data reveals a rich spectrum of traveling planetary-scale waves, including Kelvin waves, mixed Rossby-gravity waves and inertia gravity waves, in addition to propagating diurnal tides. These coherent modes show enhanced amplitudes from the tropical tropopause through the lower stratosphere (~17-25 km). Characteristics of small-scale temperature variances, calculated as deviations from the gridded fields, reveal systematic spatial patterns including time average maxima over Africa and South America overlying persistent deep convection. Small-scale variances also exhibit transient maxima in the equatorial lower stratosphere tied to large-scale Kelvin waves. The new COSMIC-2 observations provide novel details on the rich spectrum of large- and small-scale waves near and above the tropical tropopause.

The eruption of the Hunga Tonga – Hunga Ha’apai (HTHH) volcano on January 15, 2022 injected large amounts of water vapor directly into the stratosphere. While normal background levels of stratospheric water vapor are not detectable in radio occultation (RO) measurements, effects of the HTHH eruption are clearly observed as anomalous refractivity profiles from COSMIC-2, suggesting the possibility of detecting the HTHH water vapor signal. To separate temperature vs. water vapor effects on refractivity, we use co-located temperature observations from the Microwave Limb Sounder (MLS) to constrain a simplified water vapor retrieval. Our results show enhancements of water vapor up to ~1500-2300 ppmv in the stratosphere (~29-33 km) in the days following the HTHH eruption, with propagating patterns that follow the dispersing volcanic plume. The stratospheric water vapor profiles derived from RO are in reasonable agreement with limited radiosonde observations over Australia.

The Asian monsoon anticyclone (AMA) exhibits a trimodal distribution of sub-vortices and the western Pacific is one of the preferred locations. Amplification of the western Pacific anticyclone (WPA) is often linked with eastward eddy shedding from the AMA, although the processes are not well understood. This study investigates the dynamics driving eastward eddy shedding associated with the emergence of the WPA in the upper troposphere and lower stratosphere on synoptic scales. Using reanalysis data during 1979 to 2019, our composite analysis reveals that amplified WPA events are closely related to the upstream Silk Road (SR) wave-train pattern over mid-latitude Eurasia as identified in previous studies. The quasi-stationary eastward propagating eddies result from baroclinic excitation along the westerly jet, as identified by coherent eddy heat fluxes and relaxation of the low-level temperature gradient. The upper-level westerly jet is important in determining the longitudinal phase-locking of wave trains, which are anchored and amplify near the jet exit. Occasionally enhanced convection near the Philippines also triggers anticyclonic eddies that propagate upward and northeastward via the Pacific-Japan (PJ) pattern, forming the WPA in the upper troposphere. Correlation analysis suggests that the SR and PJ mechanisms are not physically correlated.

Since June 2017, the Stratospheric Aerosol and Gas Experiment III instrument on the International Space Station (SAGE III/ISS) has been providing vertical profiles of upper tropospheric to stratospheric water vapor (WV) retrieved from solar occultation transmission measurements. The goal of this paper is to evaluate the publicly released SAGE III/ISS beta version 5.1 WV retrieval through intercomparison with independent satellite- and balloon-based measurements, and to present recommendations for SAGE III/ISS data quality screening criteria. Overall, we find that SAGE III/ISS provides high quality water vapor measurements. Low quality profiles are predominately due to retrieval instabilities in the upper stratosphere that cause step-like changes in the profile, and aerosol/cloud-related interferences (below ~20 km). Above 35 km, the retrieved uncertainty and noise in the data rapidly grow with increasing altitude due to relatively low extinction signal from water vapor. Below the tropopause, retrieved uncertainty increases with decreasing altitude due to enhanced molecular scattering and aerosol extinction. After screening low-quality data using the procedures described herein, SAGE III/ISS WV is shown to be in good agreement with independent satellite and balloon-based measurements. From 20 – 40 km, SAGE III/ISS WV v5.1 data exhibit a bias of 0.0 to -0.5 ppmv (~10 %) relative to the independent data, depending on the instrument and altitude. Despite its status as a beta version, the level of SAGE III/ISS WV agreement with independent data is similar to previous SAGE instruments, and therefore the data are suitable for scientific studies of stratospheric water vapor.