Before acceptance of this preprint as an ACP Letter, as Executive Editor I requested that the authors clarify that that the approach they have taken to estimating ERFaci is only one of several others. Several other studies have applied multiple constraints simultaneously and reached different conclusions about the tightness of constraint. Reliance on one or a small number of constraints might lead to over-constraint, which I was concerned may be the reason for the overly tight constraint that is presented. In particular, ignoring conflicting constraints can lead to over-constraint. I requested that the author make clear that the tightness of constraint is inconsistent with other approaches in which a larger number of constraining observation types are used. Based on those alternative approaches, a larger uncertainty range remains plausible. Based on the added text drawing comparisons with previous similar and alternative studies, I am happy to accept it as a Letter based on the novelty and advancement in our quantification of aerosol radiative forcing.

The explosive Hunga Tonga eruption in 2022 had several characteristics that are unique in the recent observational record. Its effects on the atmosphere are of great scientific interest and have included rapidly propagating patterns of Lamb and gravity waves and long-lived anomalies in stratospheric water vapour. This modelling study demonstrates how, through a coupled sequence of chemical, radiative and dynamical mechanisms, the additional water vapour in the tropical upper stratosphere is likely to have had a significant effect on the wintertime circulation of the stratosphere and hence the troposphere in Northern Hemisphere mid- and high latitudes. These results on the fascinating Hunga Tonga event have wider relevance to perturbations of the climate system where the initial impact is stratospheric but important secondary effects are felt elsewhere, including at the surface.