The Hunga Tonga-Hunga Ha'apai (hereafter referred to as Hunga Tonga) volcano (20.57°S, 175.38°W) started an eruptive phase on 20 December 2021, with gas, steam and ash plumes periodically injected at around 12 km altitude. In mid-January larger eruptive events occurred on 13 and 15 January e.g., Yuen et al. (2022), Carr et al. (2022. The sub-aerial eruption on 13 January started at 15:20 UTC, injected plumes into the stratosphere that were observed at altitudes as high as 20 km, with an estimated sulfur dioxide (SO 2 ) burden of 0.05 Tg (Witze, 2022). A larger, submarine, explosive eruption started on 15/01 at 04:02 UTC (Yuen et al., 2022), with an estimated SO 2 burden of 0.4-0.5 Tg (Witze, 2022). The CALIPSO-CALIOP (The Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation) space LiDAR observed an aerosol plume with depolarizing properties at altitude of 38 km, on 15/01 (Sellitto et al., 2022). The plume is composed of sub-mironic sulfate particles, whereas no residual signature of ash is found starting a few hours after the injection with HIMAWARI and CALIOP observations (Legras et al., 2022). Stereoscopic geostationary observations suggest plume top altitudes

Abstract. This study investigates the influence of the 2015 Calbuco eruption (41.2∘ S, 72.4∘ W; Chile) on the total columnar aerosol optical properties over the Southern Hemisphere. The well-known technic of sun photometry was applied for the investigation of the transport and spatio-temporal evolution of the optical properties of the volcanic plume. The CIMEL sun photometer measurements performed at six South American and three African sites were statistically analysed. This study involves the use of the satellite observations and a back-trajectory model. The passage of the Calbuco plume is statistically detectable in the aerosol optical depth (AOD) observations obtained from sun photometer and MODIS observations. This statistical detection confirms that the majority of the plume was transported over the northeastern parts of South America and reached the South African region 1 week after the eruption. The plume impacted the southern parts of South America to a lesser extent. The highest AOD anomalies were observed over the northeastern parts of South America. Over the South African sites, the AOD anomalies induced by the spread of the plume were quite homogeneously distributed between the east and west coasts. The optical characteristics of the plume near the source region were consistent with an ash-bearing plume. Conversely, sites further from the Calbuco volcano were influenced by ash-free plume. The optical properties discussed in this paper will be used as inputs for numerical models for further investigation of the ageing of the Calbuco plume in a forthcoming study.

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The present study investigates the optical properties of aerosols on daily and seasonal scales with the use of the aerosol optical depth (AOD) and Angström exponent (AE) data retrieved from AErosol RObotic NETwork (AERONET) and collected at four stations in Southern Morocco—Saada (31.63° N; 8.16° W), Ouarzazate (30.93° N; 6.91° W), Oukaïmeden (31.21° N; 7.86° W) and Ras-El-Aïn (31.67° N; 7.60° W). An evaluation of the aerosol volumetric size distribution (AVSD) is also obtained for Saada and Ouarzazate. An AOD inter-comparison is performed between AERONET data and satellite sensors (MODerate resolution Imaging Spectroradiometer—MODIS), as well as assimilation products (Modern-Era Retrospective analysis for Research and Applications, version 2 (MERRA-2) and Copernicus Atmosphere Monitoring Service (CAMS)), by the means of a linear regression. Regardless of site location and elevation, the results show the prevalence of the annual cycle of AOD, with a maximum in summer and a minimum in winter. In association with this seasonal variation, the variations in AE and AVSD showed an increase in coarse mode over Ouarzazate and Saada during summer (July to August), underlining that Southern Morocco is prone to the regular transport of desert dust on a seasonal basis. The inter-comparison reveals that the MERRA-2 dataset is slightly more appropriate for the study region, since it shows correlation coefficients (r) ranging from 0.758 to 0.844 and intercepts ranging from 0.021 to 0.070, depending on the study site. The statistical analysis of the back-trajectories simulated by the HYbrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model were consistent with the observations and confirmed the dominance of desert dust aerosols during the summer over the study region. On the other hand, the winter season reveals a predominance of anthropogenic and oceanic aerosols originating from the north and the west of the study site.