Indirect stratospheric moisture increase after a Pinatubo-magnitude eruption can be comparable to direct increase after 2022 Hunga

The 2022 Hunga eruptions injected an observationally unprecedented amount of moisture directly into the stratosphere. However, stratospheric moisture can also be indirectly increased following a volcanic eruption, when heating from volcanic sulfate aerosol raises the tropical cold-point temperatures. In this work, we demonstrate that a 1 K increase in tropical cold-point temperatures can lead to indirect moisture increases in the stratosphere of comparable or even larger magnitude than observed for the direct injections during the Hunga eruptions. We base our reasoning on first-principle thermodynamic arguments combined with climate model and reanalysis output as well as observational data. We argue that following the next large-magnitude explosive eruption in the tropics, the strength of indirect increases in stratospheric moisture should be quantified using current measurement techniques.