Response of Mesospheric Temperature and Water Vapor to Volcanic Activity

Stratospheric sulfate aerosol loading from volcanic eruptions conventionally perturbs planetary radiation budgets, inducing either global-scale cooling or regional thermal anomalies. The January 2022 eruption of Hunga Tonga–Hunga Ha’apai constituted a pronounced departure from this archetype. Here, ERA5 reanalysis products are leveraged to characterise thermodynamic and moisture perturbations at 0.01 hPa (~80 km) throughout the post-eruptive interval. The submarine event delivered approximately 146 Tg of water vapour into the stratosphere, with the plume ascending to 57 km and penetrating the tropical tropopause; a substantial fraction of this anomalous moisture subsequently persisted at mesopause altitudes, forming a reservoir that dissipates only gradually and perturbs upper-atmospheric chemistry across multi-year horizons. Nonlinear interactions between radiative forcing and dynamical feedbacks, both attributable to this exceptional water vapour burden, are elucidated. These observational constraints should advance understanding of upper-atmospheric responses to major volcanic events characterised by substantial water vapour emission.