This study examines the biomass burning vertical distribution and aerosol loading in relation to the El Niño Southern Oscillation (ENSO) during a 26-year period, using an innovative machine learning method. The use of machine learning in the present work is twofold: i) to build a long aerosol optical depth (AOD) hybrid-dataset (1998-2024) by combining sunphotometer observations in Skukuza with statistical model predictions and ii) to identify the most relevant variables among those observed during the measurement campaigns. The analysis of the aerosol variability reveals that the three most significant variables are ENSO, the Fire Radiation Power (FRP) and the Black Carbon (BC). This corroborates the fact that biomass burning activity plays a key role in the variability of AOD in Skukuza. We highlighted that one significant factor that supports the influence of El Niño on the variability of the aerosols produced by biomass burning activity is the intensity of the La Niña episode that precedes it. In contrast, the impact of a La Niña episode on the variability of biomass burning aerosols is independent of the strength of the El Niño episode that precedes it. Our findings are consistent with work published during the SAFARI 92 and 2000 campaigns. We conclude that the machine learning method employed in this work enhanced the statistical model's understanding of how ENSO affects AOD variability when compared to previous studies using similar observations

Wildfires have emerged as one of the most severe natural hazards of the21st century, with increasing frequency and intensity due to climate change.These events not only devastate ecosystems and human health locally butalso inject vast amounts of smoke into the atmosphere, where plumes canpersist and travel intercontinentally. This study investigates the long-rangetransport of smoke from the 2019–2020 Australian bushfires to South Amer-ica, particularly Brazil. Using a multi-sensor approach—including OMPSsatellite data, LIDAR observations, radiosondes, AERONET measurements,and HYSPLIT back trajectories—we detected and characterized the arrival ofthe smoke plume over São Paulo during January 2020. Observations suggestthat aerosols were injected into the stratosphere and transported intercon-tinentally, reaching altitudes between 15 and 18 km, consistent with pre-vious evidence of persistent stratospheric smoke plumes reported by Bègueet al. (2024). The findings demonstrate the critical importance of integratedmonitoring systems for understanding extreme atmospheric events and theirhemispheric impacts.

Abstract. Biomass burning (BB) aerosols emitted over Southern Africa (SAF) and South America (SA) represent a major seasonal perturbation to the usually pristine atmosphere of the South-West Indian Ocean (SWIO) but remain understudied in this remote region. Following a multi-instrumental approach, we characterize BB plumes reaching Reunion Island (21° S, 55° E) during September 2017, combining ground-based measurements (sun-photometer, lidars, Fourier Transform Infrared spectrometer), spaceborne observations, CAMS EAC4 reanalysis, and the Lagrangian transport model FLEXPART. Aerosol optical depth at 550 nm over Reunion reached unusually high values (0.16–0.42) during the second half of September, with organic matter contributing up to 60 %. MODIS imagery revealed two large-scale smoke plumes originating from SAF and SA transported toward the SWIO, and CALIOP profiles showed smoke layers extending from 4 to 9 km of altitude above Madagascar. On September 19th, a single layer was identified over Reunion between 2.8 and 4.7 km with an Ångström exponent (Å₃₅₅/₅₃₂) of 1.32±0.23, consistent with moderately aged BB particles essentially originating from SAF. On September 25th, two vertically decoupled layers were identified: a lower layer (3.3–5 km, Å=1.45±0.12) associated with mixed aged aerosols of SAF and SA origin, and an upper, drier layer (5–9 km, Å=1.60±0.06) of potentially fresher SAF smoke, consistent with rapid convective uplift into the mid-troposphere. This study offers new insights concerning the dynamical processes that govern aerosol variability over Reunion Island and highlights its value as a strategic long-term observational site in the SWIO.

North Africa is the world's largest source of atmospheric mineral dust, with frequent outbreaks that significantly affect regional air quality and global climate. The objective of this study is to characterize the seasonal variability, vertical distribution, and dominant types of aerosols over southern Morocco, and to assess the influence of large-scale circulation on dust activity. A multiinstrument approach is applied, combining ground-based AERONET observations, CALIPSO/ CALIOP LiDAR profiles, and reanalysis data at the Saada site near Marrakech. Aerosol Optical Depth (AOD) and & Aring;ngstro & uml;m Exponent (AE) exhibit pronounced seasonal variability. Summer conditions are dominated by high AOD (0.35 f 0.21) and low AE (0.47 f 0.30), indicating intense coarse-mode desert dust loading, whereas winter is characterized by lower AOD (0.12 f 0.10) and higher AE (0.97 f 0.38), reflecting a greater contribution of fine-mode aerosols. LiDAR observations confirm the year-round dominance of desert dust, with maximum occurrence between 1 and 6 km altitude and a clear intensification during summer. Additional aerosol types, including marine, continental, and polluted dust, display distinct seasonal signatures. A detailed case study of a major dust storm in June 2022, together with a statistical analysis of 56 dust events from 2004 to 2022, shows that 67.9% of events occur in summer and are associated with coarse particle sizes (1.5-2.5 mu m). Dust occurrence is further modulated by the North Atlantic Oscillation, with 65.8% of summer events linked to negative NAO phases. Overall, this study demonstrates that southern Morocco is a persistent dust-dominated region whose aerosol variability is strongly controlled by seasonality and large-scale atmospheric circulation, highlighting its critical role as a major Saharan dust outflow corridor toward the Atlantic and downwind regions. These findings underscore the importance of sustained aerosol monitoring near dust source regions, particularly in southern Morocco, a key outflow corridor for Saharan dust toward the Atlantic, Europe, and the Americas.

We provide trend estimates for total, stratospheric, and tropospheric ozone columns over Reunion (21.1°S, 55.5°E) from 1998 to 2021, using only Système d’Analyze par Observation Zénithale and Southern Hemisphere Additional OZonesonde observations. Trends are derived using Trend‐Run, a multiple linear regression model, and a dynamic linear model (DLM) to identify potential turning points. Overall, total ozone exhibits a positive trend (3.0 1.5 DU/decade), with increases in both stratospheric (1.1 1.6 DU/decade) and tropospheric ozone (2.2 1.0 DU/decade). DLM identifies a turning point in stratospheric ozone in 2008, with a clear decrease in stratospheric ozone before this point and an increase afterward. We also determined changes in the lapse rate tropopause (LRT), the subtropical barrier position, and ERA5 wind and geopotential fields during the same period to investigate possible links between mid‐tropospheric ozone increase and transport‐related perturbations. Although trends in LRT height and temperature are barely significant, they suggest a recent deepening of the troposphere, indicative of climate change. Intensification of the anticyclonic gyre over Southern Africa and a weakening of the Mascarene anticyclone are found. This suggests that, independent of possible changes in ozone precursor emissions over Africa or South America, dynamics are driving increases of ozone and ozone precursors over Reunion from 1998 to 2021. Furthermore, the rate of Reunion's free tropospheric trends exceeds that observed at all other southern hemisphere ozonesonde stations, including those in tropical, subtropical and mid‐latitude regions.

This study attempts to quantify the radiative impact over R & eacute;union Island (21 degrees S, 55 degrees 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 (similar to 95 %; the remaining similar to 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).

On 15 January 2022, the Hunga volcano (20.5 degrees S, 175.4 degrees E) erupted, releasing significant amounts of water vapor (H2O) and a moderate quantity of sulfur dioxide into the stratosphere. The resulting volcanic plume traveled westward with the southern hemispheric stratospheric circulation, reaching the Indian Ocean and R & eacute;union (21.1 degrees S, 55.5 degrees E) within days. This study presents the first analysis of Infrared Atmospheric Sounding Interferometer (IASI) ozone data to investigate the impact of the Hunga eruption, and also incorporates Microwave Limb Sounder (MLS) and Ozone Mapping and Profiler Suite Limb Profiler (OMPS-LP) data, as well as ground-based measurements from R & eacute;union. IASI observations revealed a transient ozone depletion event in the first week following the eruption. OMPS-LP aerosol extinction profiles, sun-photometer measurements, and lidar observations characterized the plume's vertical and latitudinal extent, showing its presence over R & eacute;union at altitudes ranging from 26.8 to 29.7 km and its spread across more than 30 degrees longitude and 20 degrees latitude by 21 January. IASI ozone spatial distributions showed marked decreases in total and stratospheric ozone on that date, with the fifth percentile of the anomaly reaching -18.6 DU for total column ozone and -14.5 DU for stratospheric column ozone. A key finding, as shown by MLS profiles, is that the ozone reduction was confined to two separate layers (-0.7 +/-(1 sigma) 0.6 ppmv in the 14.68-12.12 hPa range, and -0.6 +/-(1 sigma) 0.5 ppmv in the 31.62-21.54 hPa range), each associated with a distinct aerosol cloud with excess H2O. This layered structure of ozone loss offers new insight into the chemical and radiative effects of the Hunga plume on stratospheric ozone.

Most major field campaigns, such as the Southern Africa Fire Atmosphere Research Initiative (SAFARI-92 and SAFARI-2000) and AErosol, RadiatiOn and CLOuds in southern Africa (AEROCLO-sA), have focused on the west coast of southern Africa, leaving the east coast underexplored. To address this, the Biomass Burning Aerosol Campaign (BiBAC) was initiated by the IRP ARSAIO (International Research Project – Atmospheric Research in Southern Africa and Indian Ocean) during the 2022 biomass burning season to study aerosol optical properties over southern Africa and the southwestern Indian Ocean (SWIO). This study analyzes aerosol properties during the intensive observation period (IOP) of BiBAC at Skukuza in Kruger National Park during two events: 18–23 September (Event 1) and 9–17 October (Event 2). Sun-photometer data, consistent with CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization), revealed a predominance of biomass burning aerosols. Transport analyses show southeastward movement of carbon monoxide (CO) and aerosols, reaching up to 6 km during Event 1 and 10 km during Event 2. Synoptic conditions, including frontal systems and baroclinic waves, drove regional and intercontinental pollutant transport, impacting the Mozambique Channel and surrounding areas. A “river of smoke” observed in Event 1 suggests novel synoptic conditions compared to previous studies. This study is the first to highlight two distinct transport mechanisms of aerosol plumes and CO from southern Africa and South America toward the SWIO basin, underscoring the significance of east-coast observations in understanding regional and global atmospheric dynamics.

Understanding optical and radiative properties of aerosols and clouds is critical to reducing uncertainties in climate models. For over 10 years, the Observatory of Atmospheric Physics in Reunion (OPAR; 21.079° S, 55.383° E) has been operating three active lidar instruments, named lidar 1200 (Li1200), stratospheric ozone lidar (LiO3S), and tropospheric ozone lidar (LiO3T), providing time series of vertical profiles from 3 to 45 km of the aerosol extinction and backscatter coefficients at 355 and 532 nm as well as the linear depolarization ratio at 532 nm. This work provides a full technical description of the three systems, the details about the methods chosen for the signal preprocessing and processing, and an uncertainty analysis. About 1737 nighttime averaged profiles were manually screened to provide cloud-free and artifact-free profiles. Data processing consisted of Klett inversion to retrieve aerosol optical products from preprocessed files. The measurement frequency was lower during the wet season and the holiday periods. There is a good correlation between the Li1200 and LiO3S instruments in terms of stratospheric aerosol optical depth (AOD) at 355 nm (0.001–0.107; R=0.92±0.01) and with LiO3T in terms of Ångström exponent 355/532 (0.079–1.288; R=0.90±0.13). The lowest values of the averaged uncertainty in the aerosol backscatter coefficient for the three time series are 64.4 ± 31.6 % for LiO3S, 50.3 ± 29.0 % for Li1200, and 69.1 ± 42.7 % for LiO3T. These relative uncertainties are high for the three instruments because of the very low values of extinction and backscatter coefficients for background aerosols above Maïdo observatory. Uncertainty increases due to the signal-to-noise ratio (SNR) decrease above 25 km for LIO3S and Li1200 and above 20 km for LiO3T. The lidar ratio (LR) is responsible for an uncertainty increase below 18 km (10 km) for LiO3S and Li1200 (LiO3T). LiO3S is the most stable instrument at 355 nm due to fewer technical modifications and fewer misalignments. Li1200 is a valuable addition meant to fill in the gaps in the LiO3S time series at 355 nm or for specific case studies about the middle and low troposphere. Data described in this work are available at https://doi.org/10.26171/rwcm-q370 (Gantois et al., 2024).

This paper presents the observational, remote sensing, and model simulation used to analyze southern Brazil Antarctic ozone hole influence (SBAOHI) events that occurred between 2005 and 2014. To analyze it, we use total ozone column (TOC) data provided by a Brewer spectrophotometer (BS) and the OMI (Ozone Monitoring Instrument). In addition to the AURA/MLS (Microwave Limb Sounder) instrument, satellite ozone profiles were utilized with DYBAL (Dynamical Barrier Localization) code in the MIMOSA (Modélisation Isentrope du Transport Mésoéchelle de l’Ozone Stratosphérique par Advection) model Potential Vorticity (PV) fields. TOC has 7.0 ± 2.9 DU reductions average in 62 events. October has more events (30.7%). Polar tongue events are 19.3% in total, being more frequently observed in October (50% of cases), with medium intensity (58.2%), and in the stratosphere medium levels (55.0%). Already, polar filament events (80.7%) are more frequent in September (32.0%), with medium intensity (42.0%), and stratosphere medium levels (40.7%).

Abstract. This case study presents the evolution of aerosol optical properties during Intensive Observational Period (IOP) of the Biomass Burning Aerosol Campaign (BiBAC) in the Kruger National Park at Skukuza, between 18 and 23 September (Event 1) and 9 and 17 October (Event 2) 2022. The aerosol classification from sun-photometer data is consistent with the CALIOP, showing a predominance of biomass burning aerosols. The transport of CO and aerosols shows a southeastward transport over Southern Africa and toward the SWIO basin. The vertical distribution of aerosols spans vertically from the surface to 6 km (Event 1) and until 10 km (Event 2). The study discusses the synoptic conditions that have favored the significant perturbation of aerosol loading from September to October 2022. During Event 1, the "river of smoke" phenomenon was driven by surface ridge tongues with the westerly wave not being converted into a COL. During Event 2, a surface heat low, mid-tropospheric anti-cyclonic system, and warm air column resulted in stable conditions, which was also influenced by strong subsidence. The study investigates the long-range transport of biomass burning from South America to Southern Africa, with the plume exiting over southern Brazil, likely driven by the Southern American low-level jet (SALLJ), which is driven by climate forcings like El Niño–Southern Oscillation (ENSO) and Madden-Julian Oscillation (MJO). Further research addresses to the contribution of biomass burning plumes from Southern Africa and South America to those observed during both events and determines the atmospheric pattern.

The behavior of ozone gas (O3) 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 O3 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 O3 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.

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.

Ozone plays an important role in the Earth’s atmosphere. It is mainly formed in the tropical stratosphere and is transported by the Brewer–Dobson Circulation to higher latitudes. In the stratosphere, ozone can filter the incoming solar ultraviolet radiation, thus protecting life at the surface. Although tropospheric ozone accounts for only ~10%, it is a powerful GHG and pollutant, harmful to the health of the environment and living beings. Several studies have highlighted biomass burning as a major contributor to the tropospheric ozone budget. Our study focuses on the Natal site (5.40°S, 35.40°W, Brazil), one of the oldest ozone-observing stations in Brazil, which is expected to be influenced by fire plumes in Africa and Brazil. Many studies that examined ozone trends used the total atmospheric columns of ozone, but it is important to assess ozone separately in the troposphere and the stratosphere. In this study, we have used radiosonde ozone profiles and daily TCO measurements to evaluate the variability and changes of both tropospheric and stratospheric ozone separately. The dataset in this study comprises daily total columns of colocalized ozone and weekly ozone profiles collected between 1998 and 2019. The tropospheric columns were estimated by integrating ozone profiles measured by ozone sondes up to the tropopause height. The amount of ozone in the stratosphere was then deduced by subtracting the tropospheric ozone amount from the total amount of ozone measured by the Dobson spectrometer. It was assumed that the amount of ozone in the mesosphere is negligible. This produced three distinct time series of ozone: tropospheric and stratospheric columns as well as total columns. The present study aims to apply a new decomposition method named Empirical Adaptive Wavelet Decomposition (EAWD) that is used to identify the different modes of variability present in the analyzed signal. This is achieved by summing up the most significant Intrinsic Mode Functions (IMF). The Fourier spectrum of the original signal is broken down into spectral bands that frame each IMF obtained by the Empirical Modal Decomposition (EMD). Then, the Empirical Wavelet Transform (EWT) is applied to each interval. Unlike other methods like EMD and multi-linear regression (MLR), the EAWD technique has an advantage in providing better frequency resolution and thus overcoming the phenomenon of mode-mixing, as well as detecting possible breakpoints in the trend mode. The obtained ozone datasets were analyzed using three methods: MLR, EMD, and EAWD. The EAWD algorithm exhibited the advantage of retrieving ~90% to 95% of ozone variability and detecting possible breakpoints in its trend component. Overall, the MRL and EAWD methods showed almost similar trends, a decrease in the stratosphere ozone (−1.3 ± 0.8%) and an increase in the tropospheric ozone (+4.9 ± 1.3%). This study shows the relevance of combining data to separately analyze tropospheric and stratospheric ozone variability and trends. It highlights the advantage of the EAWD algorithm in detecting modes of variability in a geophysical signal without prior knowledge of the underlying forcings.

O trabalho proposto tem como intuito avaliar as condições sinóticas durante o evento de queimadas na região amazônica no mês de agosto de 2019 o qual acabou acarretando no transporte de particulados para a região sudeste, impactando diretamente na cidade de São Paulo no dia 19 transformando o dia em noite. Para a avaliação, foi utilizado os dados de reanálise do ERA5 juntamente aos dados modelo HYSPLIT com objetivo de analisar a trajetória das parcelas de ar durante o evento. A partir das avaliações observou-se a passagem de um sistema frontal o qual teve como função a convergência de umidade e escoamento de ventos sobre a região de São Paulo favorecendo o desenvolvimento de nebulosidade. Além disso, o aumento de particulados ao longo da atmosfera pode ter contribuido como núcleo de condensação, podendo assim favorecer o aumento considerável de nuvens escuras durante o perı́odo da tarde no municı́pio impactando diretamente na radiação refletida dando um aspecto noturno para a cidade.

Abstract. On 15 January 2022, the Hunga volcano (20.5° S, 175.4° E) erupted, releasing significant amounts of aerosols, water vapor (H2O) and a moderate quantity of sulfur dioxide (SO2) 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 describe current observations of an ozone mini-hole in 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 sun-photometer located at Reunion. The impact of this plume on stratospheric ozone was then investigated using the Microwave Limb Spectrometer (MLS) and Infrared Atmospheric Sounding Interferometer (IASI) ozone profiles and total ozone maps. Results show that the volcanic plume was observed over Reunion at altitudes ranging from 26.8 to 29.7 km and spanned more than 20 degrees of latitude on 22 January while over the Indian Ocean. Ozone maps reveal an ozone mini-hole structure, with a maximum Total Column Ozone (TCO) anomaly of -38.97 ± 25.39 DU from IASI on 21 January. The MLS profiles impacted by the Hunga water vapor plume show an average ozone anomaly of -0.43 ppmv with a standard deviation of 0.66 ppmv at the 14.68 hPa pressure level.

Abstract. The austral spring in the Southern Hemisphere presents temporary reductions in ozone content mainly in the Antarctic region known as the Antarctic Ozone Hole (AOH). However, studies show an influence in mid-latitude regions, such as southern Brazil, where days with temporary decreases in the total column ozone (TCO) are identified. The main objective of this work is to investigate this influence of AOH on the southern region of Brazil, using data from the TCO and vertical profiles that will help to identify the preferential height at which these decreases occur in southern Brazil, in addition to analyzing the atmospheric dynamic behavior during these events in the period 42 years of data (1979 to 2020). The methodology used comprises the analysis of average daily data of the total column of ozone through ground-based instruments (Brewer Spectrophotometer), satellite data (TOMS and OMI), and to compare reanalysis data from the ECMWF-ERA5, for the identification of events of influence of the AOH on the southern region of Brazil. The analysis of the vertical content of ozone (O3) data from the TIMED/SABER satellite provides daily data from 15 to 110 km in height and has 19 years of O3 profiles available in the period from 2002 to 2020. From this, 102 events were identified that influenced Santa Maria (29.4º S; 53.7º W), in the south of Brazil, with a temporary decrease in the ozone content in the period, where between 24.1–28 km of altitude the more significant reductions in O3 during events. In the dynamic analysis, the stratospheric fields showed an increase in the absolute potential vorticity, mainly in September and October. The conceptual models in the horizontal and vertical section of the atmosphere explain the action of the stratospheric and tropospheric jet during the occurrence of events of decrease in the O3 content in Santa Maria. It was possible to identify the strong influence on the development of these events through the connection of the stratospheric jet (polar vortex) with the tropospheric jets (polar and subtropical jet) at medium and high levels of the atmosphere.

Fires occur seasonally in Southern Africa, from June to November, increasing tropospheric aerosol loading and triggering harmful consequences for the environment and human health. This study aims to examine 13 years of aerosol optical characteristics and types over Southern Africa and Reunion Island. Using AERONET sun photometers and MODIS observations, we found that a high aerosol optical depth and Angström exponent are associated with two predominant types of aerosols (biomass burning/urban industrial and mixed type) throughout the spring season. According to CALIOP observations, the major aerosol types with occurrence frequencies above 10% are polluted continental/smoke, polluted dust, and elevated smoke, whereas dust, clean continental, and dusty marine have occurrence frequencies below 1%. In comparison to other seasons, the vertical profiles of elevated smoke have different shapes in spring, with a seasonal shift in the peak altitude (from 3–4 km), when fire activity is at its maximum. At these altitudes, the northern regions presented occurrence frequencies of 32% on average, while lower values were found for the southern or farthest regions (<10–20% on average). The Lagrangian HYSPLIT model back-trajectories demonstrated eastward transport, with air masses from South America and the Atlantic Ocean that recirculate around the study sites. The aerosols are mainly derived from active biomass burning areas near the study sites and, to a lesser extent, from remote sources such as South America.

This study attempts to quantify the radiative impact over Reunion Island (21°S, 55°E) in the southern tropical Indian Ocean of the aerosols and water vapor injected in the stratosphere by the eruption on 15 January 2022 in the South Pacific of the Hunga Tonga-Hunga Ha'apai underwater volcano. Ground-based lidar and satellite passive instruments are used to parametrize a state-of-the-art radiative transfer model for the first thirteen months after the volcano eruption. The descending rate of the aerosol volcanic plume is -0.008 km day-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 positive (warming, +0.06 ± 0.45 W m-2) and dominated by the aerosol impact. However, the decreasing rate with time of the aerosol warming effect is larger than that of the water vapor cooling effect, so that, in the long run, the impact on the Earth's radiation budget might reduce to quasi-neutral, or even become slightly negative. At the Earth's surface, aerosols are the main driver and produce a negative (cooling, -0.91 ± 0.61 W m-2) radiative impact with also a decreasing tendency with time. Heating/cooling rate profiles show a clear vertical difference in the stratosphere between the aerosol warming impact (17 to 25 km) and the water vapor cooling one (25 to 40 km).

The exceptionally violent eruption of the Hunga Tonga-Hunga Ha'apai volcano (HTHH) of 15 January 2022, in the South Pacific, was associated with a powerful blast that injected gases, steam and aerosol to unprecedentedly high altitudes. This article details unique observations of the young volcanic plume from ground-based lidars at Reunion (21 degrees S, 55 degrees E). Two lidars, operating at wavelengths of 355 and 532 nm, recorded the plume overhead from 19 January until 28 January providing the vertical structure and the optical properties of the plume. A series of thick stratospheric plumes between 36 and 18 km altitude have been characterized along time, with aerosol optical depth as high as 0.84 at 532 nm and negative Angstrom exponents for the main layers down to -0.8 +/- 0.8. The diversity of plumes properties is explained by the injection heights of the volcanic material as well as stratospheric dynamics and chemistry. Plain Language Summary In January 2022, the Hunga Tonga-Hunga Ha'apai (HTHH) underwater volcano exploded in the southern Pacific (20.5 degrees S, 175.4 degrees W). Eruption metrics of this outbreak is to be compared to historic climate impacting volcanic events of the past century (e.g., Mount Pinatubo). Based on laser remote-sensing observations of the HTHH plume, its early structural and optical properties were assessed during its passage over Reunion (21 degrees S, 55 degrees E). Our results show record-breaking optical characteristics for such high altitudes, deep in the stratosphere between 18 and 36 km. In particular, peak values of aerosol optical thickness which represents the opacity of the atmosphere, were never recorded as high. Moreover, although this property is expected to decrease with increasing wavelength of the light spectrum, the thickest aerosol layers we recorded show a different optical behavior. They are opaquer in the visible spectrum around 532 nm than in the UV at 355 nm. This is likely to be link to the specific size distribution of these volcanic particles, driven by an unusual stratospheric chemistry resulting from the presence of large amount of water vapor. These findings are original and essential observations to question our understanding of such atmospheric processes and to help improve global climate models.