Stratospheric aerosol formed from the boiling sea induced by the 2022 Hunga Ha’apai volcanic eruption

Abstract. Hot volcaniclastic density currents entering the sea from the Hunga Tonga eruption the 15 January 2022 (HT-22) induced vigorous volcano – sea interaction. Here we study the stratospheric aerosol and water vapor resulting from the eruption using satellite-based instruments: the CALIOP lidar and the Microwave Limb Sounder (MLS). We investigate the stratospheric relative humidity following the record-breaking water vapor injections from the HT-22 eruption, and the particle size of the aerosol. The HT-22 eruption injected its effluents into the deep Brewer-Dobson (BD) branch causing several years of stratospheric perturbation. The long duration, and aerosol concentration among the highest, makes the HT-22 eruption the strongest stratospheric aerosol event since the 1991 Mt. Pinatubo eruption despite a modest SO₂ injection explaining only ~30 % of the AOD from the HT-22 eruption according to our estimates. The stratospheric AOD level was established after 2 weeks, or possibly even earlier, which is a short time compared with the usual 2 – 3 months required to reach the maximum AOD following volcanic eruptions. We discuss the sources of the aerosol from the HT-22 eruption in relation to the low emission of SO₂, its e-folding time and volcanological observations of strong interactions with the sea containing not only water but also high concentrations of dissolved substances.