| Summary: | The 2022 Hunga eruption caused unprecedented stratospheric hydration. Aura Microwave Limb Sounder (MLS) measurements show that the stratospheric water vapor mass remains essentially unchanged as of early 2024 and that the Hunga hydration occurred atop a robust (possibly accelerating) moistening trend in the stratosphere. Enhanced by the excess Hunga water vapor, dehydration via polar stratospheric cloud (PSC) sedimentation in the 2023 Antarctic vortex exceeded climatological values by ~50%. Simple projections, based solely on Antarctic dehydration, illustrate that the timing of the return to humidity levels that would have been expected absent the Hunga hydration depends on the ongoing stratospheric water vapor trend. For strong moistening, the influx of water entering the stratosphere could offset the enhanced PSC dehydration, resulting in a new, more humid ‘equilibrium’ stratospheric state. With the Hunga hydration compounding an underlying moistening trend, the stratosphere could remain anomalously humid for an extended period.
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