Radiative impact of the Hunga Tonga-Hunga Ha'apai stratospheric volcanic plume: role of aerosols and water vapor in the southern tropical Indian Ocean

Abstract. 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 of the Hunga Tonga-Hunga Ha'apai underwater volcano in the South Pacific. 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 negative (cooling, -0.54 ± 0.29 W m^-2) and dominated by the aerosol impact (~93 %; the remaining ~7 % are due to WV). At the Earth’s surface, aerosols are the main driver and produce a negative (cooling, -1.19 ± 0.40 W m^-2) radiative impact. Between the short- (month 2 to 4 after the eruption) and mid-term (month 5 to 14 after the eruption) periods, the aerosol and water vapor radiative effect at both the surface and TOA reduces 22 to 25 %. Heating/cooling rate profiles during the mid-term period 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).