Evolving Particles in the 2022 Hunga Tonga—Hunga Ha'apai Volcano Eruption Plume

Abstract The Multi‐angle Imaging SpectroRadiometer (MISR) aboard NASA's Terra satellite observed the Hunga Tonga—Hunga Ha'apai (HTHH) 15 January eruption plume on eight occasions between 15 and 23 January 2022. From the MISR multi‐angle, multi‐spectral imagery we retrieve aerosol plume height geometrically, along with plume‐level motion vectors, and derive radiometrically constraints on particle effective size, shape, and light‐absorption properties. Parts of two downwind aerosol layers were observed in different places and times, one concentrated in the upper troposphere (11–18 km ASL), and a mid‐stratosphere layer ∼23–30+ km ASL. After the initial day (1/15), the retrievals identified only spherical, non‐light‐absorbing particles, typical of volcanic sulfate/water particles. The near‐tropopause plume particles show constant, medium‐small (several tenths of a micron) effective size over 4 days. The mid‐stratosphere particles were consistently smaller, but retrieved effective particle size increased between 1/17 and 1/23, though they might have decreased slightly on 1/22. As a vast amount of water was also injected into the stratosphere by this eruption, models predicted relatively rapid sulfate particle growth from the modest amounts of SO 2 gas injected by the eruption to high altitudes along with the water (Zhu et al., 2022, https://doi.org/10.5194/acp‐22‐10267‐2022 ). MISR observations up to 10 days after the eruption are consistent with these model predictions. The possible decrease in stratospheric particle size after initial growth was likely caused by evaporation, as the plume mixed with drier, ambient air. Particles in the lower‐elevation plume observed on 1/15 were larger than all the downwind aerosols and contained significant non‐spherical (likely ash) particles.