Transport of the Hunga Tonga volcanic aerosols inferred from Himawari-8 limb measurements

Abstract

Abstract. The Hunga Tonga-Hunga Ha'apai (Hunga Tonga; 21.545 ºS, 178.393 ºE) volcanic eruption of 15 January 2022 produced copious amounts of aerosols that reached high into the stratosphere, exceeding 30 km and settling into layers a few kilometres deep between 22–28 km. The Advanced Himawari Imager (AHI) on board the geostationary Himawari-8 platform at 140.7 ºE was able to monitor the eruption at 10 minute intervals and 0.25 km2 to 4 km2 spatial resolution within 16 spectral channels ranging from visible to infrared wavelengths and over a latitude/longitude field of view of ~±75º. Here a new use of these data is proposed where the the limb region of of the field of view is exploited to detect aerosol layers extending vertically into the atmosphere. The analyses provide vertical profiles of scattered visible light and are compared to Caliop space lidar measurements. Hunga Tonga aerosols are detected using the ratio of near infrared reflectances at 1.61 µm and 2.25 µm, in the western limb from 22 January and in the eastern limb from 31 January 2022 up until the present time (September 2023). The average zonal velocity is estimated to be ~-25 ms-1 (westwards) and the meridional velocity to be ~0.2 ms-1 (northwards). The latitudinal spread is characterised by a gradual northerly movement of the main layer situated between 22–28 km in the first 60 days, and stagnation or slight southerly spread thereafter. The current methodology does not provide quantitative estimates of the amount or type of aerosol, but based on the spectral properties of water and ice clouds the analysis suggests there is a strong liquid water content in the aerosol layers.