Stratospheric Temperature and Ozone Impacts of the Hunga Tonga‐Hunga Ha'apai Water Vapor Injection

Abstract

The January 2022 eruption of the Hunga Tonga‐Hunga Ha'apai underwater volcano injected a large amount of water vapor into the mid‐stratosphere. This study uses model simulations to investigate the resulting stratospheric impacts out to 2031. Maximum radiatively‐driven model temperature changes occur in the Southern Hemisphere (SH) subtropics in April–May 2022, with warming of ∼1 K in the lower stratosphere and cooling of 3 K in the mid‐stratosphere. The radiative cooling combined with adiabatic cooling driven by the quasi‐biennial oscillation meridional circulation explains the near‐record cold anomaly observed in the SH subtropical mid‐stratosphere. Projected ozone responses maximize in 2023–2024 as the water vapor plume is transported globally throughout the stratosphere and mesosphere. The excess H2O increases the OH radical, causing a negative global ozone response (2%–10%) in the upper stratosphere and mesosphere due to increased odd hydrogen‐ozone loss, and a small positive ozone response (0.5%–1%) in the mid‐stratosphere due to interference of the NOx catalytic loss cycle by the additional OH. In the lower stratosphere, the excess H2O is projected to increase polar stratospheric clouds and springtime halogen‐ozone loss, enhancing the Antarctic ozone hole by 25–30 DU in 2023. Arctic impact is small, with maximum additional ozone loss of 4–5 DU projected in spring 2024. These responses diminish after 2024 to be quite small by 2031, as the excess H2O is removed from the stratosphere with a 2.5‐year e‐folding time. Given the year‐to‐year variability of the stratosphere, the magnitudes of these ozone responses may be below the threshold of detectability in observations.

The evolution of the Hunga hydration in a moistening stratosphere

“…After this date, the hemispheric asymmetry is only 2.5±9.9 Tg (0.2±0.5%). That SWVm remains strongly enhanced into 2024 raises several questions: Will the Hunga water vapor enhancement last 5 to 10 years as hypothesized Fleming et al, 2024;Zhou et al, 2024), or will it linger longer in the stratosphere? Is the fact that high SWVm persists in 2024 merely a consequence of prolonged but transient variability acting on top of the Hunga hydration, or does it reflect increasing background values as the stratosphere is becoming moister?…”

“…r) , where y 0 is the initial anomaly (i.e., ∼150 Tg), r is the decay rate, and t is time in years. So far, model studies have predicted e-folding times of 2.5 (Fleming et al, 2024) or 4 (Zhou et al, 2024) years. Assuming 11.8 Tg dehydration in the first year, MLS data suggest a decay rate of 12.2 years, which results in a removal time for the excess water vapor of more than 50 years (Figure 4e).…”

The Spread of the Hunga Tonga H2O Plume in the Middle Atmosphere Over the First Two Years Since Eruption

“…Yu et al (2023) showed 2022 temperature anomalies from SABER in the stratosphere and mesosphere and concluded, based on WACCM6 calculations, that these could, to some extent be explained by changes in stratospheric winds, possibly driven by changes in H 2 O and SO 2 from the Hunga plume. Fleming et al (2024) have presented some calculations of the effect of this additional H 2 O on O 3 and temperature over the next decade. Nedoluha et al (2023b) (hereafter N23) documented an increase in mesospheric H 2 O in 2022.…”