We use a combination of spaceborne instruments to study the unprecedented stratospheric plume after the Tonga eruption of 15 January 2022.
The aerosol plume was initially formed of two clouds at 30 ...and 28 km, mostly composed of submicron-sized sulfate particles, without ash, which is washed out within the first day following the eruption.
The large amount of injected water vapour led to a fast conversion of SO2 to sulfate aerosols and induced a descent of the plume to 24–26 km over the first 3 weeks by radiative cooling.
Whereas SO2 returned to background levels by the end of January, volcanic sulfates and water still persisted after 6 months, mainly confined between 35∘ S and 20∘ N until June due to the zonal symmetry of the summer stratospheric circulation at 22–26 km.
Sulfate particles, undergoing hygroscopic growth and coagulation, sediment and gradually separate from the moisture anomaly entrained in the ascending branch Brewer–Dobson circulation.
Sulfate aerosol optical depths derived from the IASI (Infrared Atmospheric Sounding Interferometer) infrared sounder show that during the first 2 months, the aerosol plume was not simply diluted and dispersed passively but rather organized in concentrated patches. Space-borne lidar winds suggest that those structures, generated by shear-induced instabilities, are associated with vorticity anomalies that may have enhanced the duration and impact of the plume.
The Tonga eruption of 15 January 2022 has released a long‐lived stratospheric plume of sulfate aerosols. More than 17 months after, we focus on the high quality data series of SAGE III (Stratospheric ...Aerosol and Gas Experiment) on board the International Space Station (ISS) to determine the mean radius and size distribution of the aerosols and their total mass. The persisting volcanic aerosols—with a mode width of 1.25 and an effective radius of 0.4 μm—differ from the significantly smaller background aerosols and from those measured during recent stratospheric eruptions. The sulfuric acid mass between 50°S and 30°N is estimated to be very stable in spite of considerable redistribution in latitude at a value of 0.66 ± 0.1 Tg, corresponding to an initial sulfur dioxide emission of 0.44 Tg. Such properties are expected to facilitate the persistence of a climate warming due to the volcanic water vapor.
Plain Language Summary
We study the stratospheric aerosol plume produced by the Hunga Tonga–Hunga Ha'apai eruption on 15 January 2022 based on the high quality solar occultation measurements of the instrument SAGE III (Stratospheric Aerosol and Gas Experiment) onboard the International Space Station. These data reveal that the aerosol sizes are about twice as large as after other documented volcanic eruptions and that the total mass of H2SO4 in the liquid droplets of sulfate in the stratosphere has been very stable from March 2022, when it started to be well homogeneized in longitude, to November 2022, when it started to decay. The total mass of 0.66 Tg of H2SO4 is in good agreement with the early estimates of a stratospheric emission of 0.4–0.5 Tg of SO2. The implication is that the aerosol radiative impact will not mask the persisting warming effect of the water vapor injected in the stratosphere by the eruption.
Key Points
The extinction of the stratospheric plume of the 2022 Tonga eruption is well modeled by a unimodal distribution of sulfate particles
The effective radius of the aerosols is large with values close to 0.4 μm, and a mode width of 1.25, from March 2022 to June 2023
We estimate a total H2SO4 mass in stratospheric sulfate aerosols of about 0.66 corresponding to 0.44 Tg of SO2 initially injected
Abstract
The underwater Hunga Tonga-Hunga Ha-apai volcano erupted in the early hours of 15th January 2022, and injected volcanic gases and aerosols to over 50 km altitude. Here we synthesise ...satellite, ground-based, in situ and radiosonde observations of the eruption to investigate the strength of the stratospheric aerosol and water vapour perturbations in the initial weeks after the eruption and we quantify the net radiative impact across the two species using offline radiative transfer modelling. We find that the Hunga Tonga-Hunga Ha-apai eruption produced the largest global perturbation of stratospheric aerosols since the Pinatubo eruption in 1991 and the largest perturbation of stratospheric water vapour observed in the satellite era. Immediately after the eruption, water vapour radiative cooling dominated the local stratospheric heating/cooling rates, while at the top-of-the-atmosphere and surface, volcanic aerosol cooling dominated the radiative forcing. However, after two weeks, due to dispersion/dilution, water vapour heating started to dominate the top-of-the-atmosphere radiative forcing, leading to a net warming of the climate system.
