A document by Alexis Mariaccia. Click on the document to view its contents.

The 15 January 2022 eruption of the Hunga volcano (Tonga) generated a rich spectrum of waves, some of which achieved global propagation. Among numerous platforms mon- itoring the event, two stratospheric balloons flying over the tropical Pacific provided unique observations of infrasonic wave arrivals, detecting five complete revolutions. Combined with ground measurements from the infrasound network of the International Monitor- ing System, balloon-borne observations may provide additional constraint on the scenario of the eruption, as suggested by the correlation between bursts of acoustic wave emis- sion and peaks of maximum volcanic plume top height. Balloon records also highlight previously unobserved long-range propagation of infrasound modes and their dispersion patterns. A comparison between ground- and balloon-based measurements emphasizes superior signal-to-noise ratios onboard the balloons and further demonstrates their po- tential for infrasound studies.

Recent research has put in evidence the self-lofting capacity of smoke aerosols in the stratosphere and their self-confinement by persistent anticyclones, which prolongs their atmospheric residence time and radiative effects. By contrast, the volcanic aerosols-composed mostly of non-absorptive sulphuric acid droplets-were never reported to be subject of self-lofting nor of dynamical confinement. Here we use high-resolution satellite observations to show that the eruption of Raikoke volcano in June 2019 produced a long-lived stratospheric anticyclone containing 24% of the total erupted mass of sulphur dioxide. The anticyclone persisted for more than 3 months, circumnavigated the globe three times, and ascended diabatically to 27 km altitude through radiative heating of volcanic ash contained by the plume. The mechanism of dynamical confinement has important implications for the planetary-scale transport of volcanic emissions, their stratospheric residence time, and atmospheric radiation balance. It also provides a challenge or “out of sample test” for weather and climate models that should be capable of reproducing similar structures.

The highly-explosive eruption of the Hunga-Tonga Hunga Ha’apai volcano (HTHH), that occurred on 15 Jan. in the South Pacific, was associated with a powerful blast that injected gases, steam and aerosols to unprecedentedly high altitudes. Here we present unique observations of the young volcanic aerosol plumes by ground-based lidars at La Reunion island (21°S, 55°E), located directly downwind of the eruption. Two lidars, operating at 355 nm and 532 nm, sampled the overflying plume every nights from 19 Jan. until 28 Jan. We assess both the vertical structure and the optical properties. A wide plume altitude range from 36 km down to 18 km has been highlighted along time, with heterogeneous aerosol optical depth that reached 0.84 at 532 nm and Angström exponents from-0.8 to 1.2. Such temporal evolution is related to both the injection heights of the volcanic material and the stratospheric dynamic and chemistry.

During the extended activity of Mount Etna volcano in February-April 2021, three distinct paroxysmal events took place from 21 to 26 February, which were associated with a very uncommon transport of the injected upper-tropospheric plumes towards the north. Using a synergy of observations and modelling, we characterised the emissions and three-dimensional dispersion for these three plumes, we monitor their downwind morphological and optical properties, and we estimate their radiative impacts at selected locations. With a satellite-based source inversion, we estimate the emitted sulphur dioxide (SO2) mass at an integrated value of 55 kt and plumes injections at up to 12 km altitudes, which combine to qualify this series as extreme in the eruption strengths spectrum for Mount Etna. We then combine Lagrangian dispersion modelling, initialised with measured temporally-resolved SO2 emission fluxes and altitudes, with satellite observations to track the dispersion of the three individual plumes. The transport towards the north allowed the height-resolved downwind monitoring of the plumes at selected observatories in France, Italy and Israel, using LiDARs and photometric aerosol observations. Volcanic-specific aerosol optical depths in the visible spectral range ranging from about 0.004 to 0.03 and local daily average shortwave radiative forcing ranging from about -0.2 to -1.2 W/m2 (at the top of atmosphere) and from about -0.2 to -3.5 W/m2 (at the surface) are found. Both the aerosol optical depth and the radiative forcing of the plume depends strongly on its morphology (position of the sampled section of the plume) and composition (possible presence of fine ash).

The eruption of the submarine Hunga volcano in January 2022 was associated with a powerful blast that injected volcanic material to altitudes up to 58 km. From a combination of various types of satellite and ground-based observations supported by transport modeling, we show evidence for an unprecedented increase in the global stratospheric water mass by 13% as compared to climatological levels, and a 5-fold increase of stratospheric aerosol load, the highest in the last three decades. Owing to the extreme injection altitude, the volcanic plume has circumnavigated the Earth in only one week and dispersed nearly pole-to-pole in three months. The unique nature and magnitude of the global stratospheric perturbation by the Hunga eruption ranks it among the most remarkable climatic events in the modern observation era, with a range of potential persistent repercussions for stratospheric composition and climate.

The Quasi-Biennial Oscillation (QBO) is a major mode of climate variability with periodically descending westerly and easterly winds in the tropical stratosphere, modulating transport and distributions of key greenhouse gases such as water vapor and ozone. In 2016 and 2020, anomalous QBO easterlies disrupted the QBO’s 28–month period previously observed. Here, we quantify the impact of these QBO disruptions on lower stratospheric circulation, and water vapour and ozone using reanalyses and satellite observations, respectively. Both constituents decrease globally from early spring to late autumn during 2016, while they only weakly decrease during 2020. These dissimilarities result from differences in upwelling and cold-point tropopause temperatures caused by anomalous planetary and gravity wave forcing. Our results highlight the need for a better understanding of the causes of QBO disruptions, their interplay with other modes of climate variability, and their impacts on water vapor and ozone in the face of a changing climate.