Ash and Ice Aggregation in Satellite Retrieval: The 15 January 2022 Hunga Tonga-Hunga Ha'apai Hydromagmatic Eruption

Explosive volcanic eruptions inject volcanic particles, such as ash and water vapor, into the atmosphere. Ice enriched volcanic clouds can hide the presence of silicate particles, intensifying the fatal risks for aviation. In this scenario, satellite monitoring systems play a key role in volcanic hazard mitigation. Thanks to the full disk perspective over the Pacific Ocean, the GOES-17 geostationary satellite observed the 15 January 2022 Hunga Tonga-Hunga Ha'apai hydromagmatic eruption. The explosive activity produced two volcanic clouds dispersing at different altitudes. In this work, we first focus on the altitude estimates of the two volcanic clouds, by means of volcanic cloud speed and wind components. Next, we study how the fine ash (<64 mu m diameter) total mass in atmosphere varies depending on the assumed fraction of ash and ice in an aggregate. Based on our estimates, the upper volcanic cloud disperses between 27.35 +/- 3.01 and 29.13 +/- 3.20 km altitude; the lower cloud between 14.02 +/- 1.54 and 14.8 +/- 1.63 km altitude. The estimated fine ash total mass doubles if we consider spherical aggregates instead of irregular aggregates, due to a tighter packing of coating particles. The highest estimated fine ash mass for the upper and lower clouds is of 3.81 center dot 10(8) +/- 1.41 center dot 10(8) kg (12:40 UTC) and of 11.61 center dot 10(8) +/- 4.30 center dot 10(8) kg (13:50 UTC), respectively. Estimating the exact amount of erupted fine ash mass, mainly during hydromagmatic eruptions, is challenging and further works should investigate aggregates where the ice fraction is higher than the ash fraction. Plain Language Summary Volcanic eruptions represent one of the most impressive and hazardous natural phenomena on our planet. Violent volcanic eruptions can inject in the atmosphere a huge amount of materials, from gases to ash particles. Finer ash particles remain suspended in the atmosphere for long time, even weeks, and represent a fatal risk for aviation. The work is part of the studies involved in volcanic hazard mitigation by means of satellite observations. Volcanic clouds, formed during eruptions, can be water-enriched. Water particles can mask the presence of ash particles, intensifying the volcanic hazard. We focus our analysis on the 15 January 2022 Hunga Tonga eruption, where we estimate the altitude of the two formed volcanic clouds. We also study how the fine ash (<64 mu m diameter) total mass in atmosphere varies depending on the assumed fraction of ash/ice in an aggregate. Estimating the exact amount of erupted fine ash mass is challenging, mainly in presence of water-enriched volcanic clouds. Further works should investigate aggregates where the ice fraction is higher than the ash fraction.