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This study attempts to quantify the radiative impact over Réunion Island (21° S, 55° E) in the southern tropical Indian Ocean of the aerosols and water vapor (WV) injected into the stratosphere by the eruption of the Hunga underwater volcano in the South Pacific on 15 January 2022. Ground-based lidar and satellite passive instruments are used to parameterize a state-of-the-art radiative transfer (RT) model for the first 13 months after the volcano eruption. The descending rate of the aerosol volcanic plume is - 8 m d−1. At this rate, aerosols are expected to be present in the stratosphere until the first half of 2025. The overall aerosol and water vapor impact on the Earth's radiation budget for the whole period is negative (cooling, - 0.82 ± 0.35 W m−2) and dominated by the aerosol impact (∼ 95 %; the remaining ∼ 5 % is due to the water vapor). At the Earth's surface, aerosols are the main drivers and produce a negative (cooling, - 1.04 ± 0.36 W m−2) radiative impact. Water vapor has hardly any radiative effect at the surface. Between the short-term (months 2 to 4 after the eruption, February–April 2022) and mid-term (months 5 to 14 after the eruption, May 2022–February 2023) periods, the aerosol and water vapor radiative effect at the surface and top of atmosphere (TOA) reduces by 22 % and 25 %, respectively. During the mid-term period, heating / cooling (H / C) rate profiles show a clear vertical difference locally in the stratosphere between the aerosol warming impact (18 to 26 km) and the water vapor cooling (22 to 30 km). The resulting aerosol and water vapor heating / cooling rate profile follows an S-shaped curve with peaks slightly larger for the moist layer (- 0.09 K d−1) than for the sulfate layer (+ 0.06 K d−1). [ABSTRACT FROM AUTHOR]

The behavior of ozone gas (O 3) in the atmosphere varies according to the region of the globe. Its formation occurs mainly in the tropical stratosphere through the photodissociation of molecular oxygen with the aid of the incidence of ultraviolet solar radiation. Still, the highest concentrations of O 3 content are found in high-latitude regions (poles) due to the Brewer–Dobson circulation, a large-scale circulation that takes place from the tropics to the pole in the winter hemisphere. This work presents a multi-instrumental analysis at two Brazilian sites, a subtropical one (Santa Maria – 29.72° S, 53.41° W) and an equatorial one (Natal – 5.4° S, 35.4° W), to investigate ozone distributions in terms of vertical profiles (2002–2020) and total abundance in terms of total columns of ozone (1979–2020). The study is based on the use of ground-based and satellite observations. Ozone profiles over Natal, from the ground up to the mesosphere, are obtained by radiosonde experiments (0–30 km) in the framework of the SHADOZ program and by satellite measurements from the SABER instrument (15–60 km). This enabled the construction of a continuous time series for ozone, including monthly values and climatological trends. There is a good agreement between the two measurements in the common observation layer, mainly for altitudes above 20 km. Below 20 km, SABER ozone profiles showed high variability and overestimated ozone mixing ratios by over 50 %. Dynamic and photochemical effects can interfere with O 3 formation and distribution along higher latitudes through the Brewer–Dobson circulation. The measurements of the total ozone columns used are in good agreement with each other (TOMS/OMI × Dobson for Natal and TOMS/OMI × Brewer for Santa Maria) in time and space, in line with previous studies for these latitudes. Wavelet analysis was used over 42 years. The investigation revealed a significant annual cycle in both data series for both sites. The study highlighted that the quasi-biennial oscillation (QBO) plays a significant role in the variability of stratospheric ozone at the two study sites – Natal and Santa Maria. The QBO's contribution was found to be stronger at the Equator (Natal) than at the subtropics (Santa Maria). Additionally, the study showed that the 11-year solar cycle also has a significant impact on ozone variability at both locations. Given the study latitudes, the ozone variations observed at the two sites showed different patterns and amounts. Only a limited number of studies have been conducted on stratospheric ozone in South America, particularly in the region between the Equator and the subtropics. The primary aim of this work is to investigate the behavior of stratospheric ozone at various altitudes and latitudes using ground-based and satellite measurements in terms of vertical profiles and total columns of ozone. [ABSTRACT FROM AUTHOR]

During the 2020 austral summer, the pristine atmosphere of the southwest Indian Ocean (SWIO) basin experienced significant perturbations. This study examines the variability of aerosols and carbon monoxide (CO) over this remote oceanic region and investigates the underlying processes in the upper troposphere–lower stratosphere (UT-LS). Aerosol profiles in January and February 2020 revealed a multi-layer structure in the tropical UT-LS. Numerical models – the FLEXible PARTicle dispersion model (FLEXPART) and the Modèle Isentropique de transport Mésoéchelle de l'Ozone Stratosphérique par Advection (MIMOSA) – indicated that the lower-stratospheric aerosol content was influenced by the intense and persistent stratospheric aerosol layer generated during the 2019–2020 extreme Australian bushfire events. A portion of this layer was transported eastward by prevailing easterly winds, leading to increased aerosol extinction profiles over Réunion on 27 and 28 January. Analysis of advected potential vorticity revealed isentropic transport of air masses containing Australian biomass burning aerosols from extratropical latitudes to Réunion at the 400 K isentropic level on 28 January. Interestingly, we found that biomass burning (BB) activity in eastern Africa, though weak during this season, significantly influenced (contributed up to 90 % of) the vertical distribution of CO and aerosols in the upper troposphere over the SWIO basin. Ground-based observations at Réunion confirmed the simultaneous presence of African and Australian aerosol layers. This study provides the first evidence of African BB emissions impacting the CO and aerosol distribution in the upper troposphere over the SWIO basin during the convective season. [ABSTRACT FROM AUTHOR]

On 15 January 2022, the Hunga Tonga-Hunga Ha'apai (HTHH) volcano (20.5° S, 175.4° E) erupted, releasing significant amounts of aerosols, sulfur dioxide (SO2), and water vapor (H2O) into the stratosphere. Due to the general stratospheric circulation of the southern hemisphere, this volcanic plume traveled westward and impacted the Indian Ocean and Reunion (21.1° S, 55.5° E) a few days after the eruption. This study aims to show how the currently available ozone observations highlight the stratospheric dynamics during the first week following the eruption. The Ozone Mapping and Profiler Suite Limb Profiler (OMPS-LP) aerosol extinction profiles were used to investigate the vertical and latitudinal extension of the volcanic plume over the Indian Ocean. The volcanic aerosol plume was also observed with an aerosol lidar and a sunphotometer located at Reunion. The impact of this plume on stratospheric ozone was then investigated using MLS (Microwave Limb Spectrometer), OMI (Ozone Monitoring Instrument), MERRA-2 (Modern-Era Retrospective analysis for Research and Applications, version 2) and M2-SCREAM (MERRA-2 Stratospheric Composition Reanalysis of Aura MLS) ozone profiles and total ozone. The results show that the volcanic plume traveled over Reunion at altitudes ranging from 26.8 to 29.7 km and spanned more than 20 degrees of latitude over the Indian Ocean. Ozone analyses reveal an ozone mini-hole structure, with the Total Column Ozone (TCO) anomaly of -15 DU from MERRA-2 covering an area of 12.06×105 km2 on 17 January and 4.94 × 105 km2 on 22 January. The ozone profiles from MLS show that a maximum stratospheric column ozone anomaly of -14.66 DU (-6.38 %) was found within the aerosol plume on 20 January. [ABSTRACT FROM AUTHOR]

The pristine atmosphere of the southwest Indian Ocean (SWIO) basin underwent significant perturbations during the 2020 austral summer. This study documents the complex variability of aerosols and carbon monoxide (CO) over this remote oceanic region and identifies the processes governing it in the upper troposphere – lower stratosphere (UT-LS). Aerosol profiles exhibit a multi-layer structure in the tropical UT-LS in January and February 2020. The numerical models (FLEXPART and MIMOSA) showed that the modulation of the aerosol content in the lower stratosphere is due to the intense and persistent stratospheric aerosol smoke layer generated during the 2019–20 extreme Australian bushfire events. One part of this stratospheric aerosol smoke layer was advected zonally by the prevailing easterly winds and its passage over Reunion was recorded by increased aerosol extinction profiles on 27th and 28th January. The analysis of the advected potential vorticity highlights an isentropic transport of air masses containing Australian biomass burning aerosol from extra-tropical latitudes to Reunion at the 400 K isentropic level, on 28th January. Interestingly, our results show that the biomass burning activity in eastern Africa, weak during this season, contributed to modulate (up to 90 %) the vertical distribution of CO and aerosols in the upper troposphere over the SWIO basin. The simultaneous presence of African and Australian aerosols smoke layers has been recorded by ground-based observations at Reunion. This study highlights for the first time the influence of the African emissions from biomass burning to the CO and aerosols distribution in the upper troposphere over the SWIO basin during the convective season. The results show that besides PyroCb -driven injection of biomass burning products to the stratosphere, an alternative pathway may exist during the regular deep-convection season in the tropics. [ABSTRACT FROM AUTHOR]