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 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.

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.

Following the Hunga Tonga eruption (20.6°S, 175.4°W, mid-January 2022), we present a balloon-borne characterization of the stratospheric aerosol plume one week after its injection (on 23 and 26/01/2022, La Réunion island at 21.1°S, 55.3°E). Satellite observations show that flight #1 took place during the overpass of a denser plume of sulfate aerosols (SA) compared to a more diluted plume during flight #2. Observations show that the sampled plumes (at around 22, 25 and 19 km altitude, respectively) consist exclusively of very small particles (with radius < 1 µm). Particles with radii between 0.5 and 1.0 µm show optically transparent features pointing to predominant SA. Particles with radii below 0.5 µm are partly absorbing, which could point to small sulfate coated ash particles, a feature not identified with space-borne observations. This shows that in situ observations are necessary to fully characterize the microphysical properties of the plumes tracked by space-borne instruments.