The Hunga Hunga-Tonga Ha'apai (HT) (20.54°S, 178.3°W) submarine volcano violently erupted on 15 January 2022. The volcanic explosivity index (VEI) was 5, comparable to Krakatau eruption in 1883. Since HT was a submarine volcano, it appears to have lofted a significant amount of water into the stratosphere. Indeed, Microwave Limb Sounder (MLS) measurements show that HT water enhancement was quite high relative to SO 2 (Millán et al., 2022)-hereafter M22. The MLS estimated water injection was up to 146 Tg (M22). The eruption plume was detected up to 57 km on 15 January 2022 (Carr et al., 2022;Proud et al., 2022). The Ozone Mapping and Profile Suite-Limb Profiler (OMPS-LP) detected extinction enhancements above 45 km (Taha et al., 2022).In this paper we will examine at the evolution of the water vapor and aerosol enhancements that followed the HT eruption. M22 noted that the amount of water deposited in the stratosphere by HT was unprecedented in the modern history of volcanic eruption observations. Several MLS water vapor profiles made shortly after the eruption show concentrations exceeding 300 ppmv against a normal stratospheric concentration of ∼4 ppmv. As the eruption evolved, MLS water vapor maps show that above about 2 hPa (∼43 km), the plume quickly spreads and that the water vapor enhancement disperses. A secondary maximum at about 25 hPa (∼26 km) persists (M22). The aerosol field shows similar behavior with rapid dispersal at higher altitudes but persistent high levels of aerosol extinction below ∼25 hPa (∼26 km) (Taha et al., 2022). The aerosol extinction in this layer grows over the 30 days following the eruption presumably due to the conversion of SO 2 to sulfate aerosols (e.g., Zhu et al., 2020).There are several key questions concerning the HT eruption: Why did the unusual water vapor layer form and persist? How is it related to the aerosol layer? Below we show that the water vapor enhancement overlaps the top of the extinction anomaly, but they are distinct, and furthermore the two enhancements vertically separate over

Water vapor interannual variability in the tropical tropopause layer (TTL) is investigated using satellite observations and model simulations. We break down the influences of the Brewer-Dobson circulation (BDC), the quasibiennial oscillation (QBO), and the tropospheric temperature ( T ) on TTL water vapor as a function of latitude and longitude using a two-dimensional multivariate linear regression. This allows us to examine the spatial distribution of the impact of each process on TTL water vapor. In agreement with expectations, we find that the impacts from the BDC and QBO act on TTL water vapor by changing TTL temperature. For T , we find that TTL temperatures alone cannot explain the influence. We hypothesize a moistening role for the evaporation of convective ice from increased deep convection as the troposphere warms. Tests using a chemistryclimate model, the Goddard Earth Observing System Chemistry Climate Model (GEOSCCM), support this hypothesis.

On 15 January 2022, the Hunga Tonga‐Hunga Ha'apai (HT) eruption injected SO2 and water into the middle stratosphere. Shortly after the eruption, the water vapor anomaly moved northward toward and across the equator. This northward movement appears to be due to equatorial Rossby waves forced by the excessive infrared water vapor cooling. Following the early eruption stage, persistent mid‐stratospheric water vapor and aerosol layers were mostly confined to Southern Hemisphere tropics (Eq. to 30°S). However, during the spring of 2022, the westerly phase of the tropical quasi‐biennial oscillation (QBO) descended through the tropics. The HT water vapor and aerosol anomalies were observed to again move across the equator coincident with the shift in the Brewer‐Dobson circulation and the descent of the QBO shear zone.

The Hunga Tonga-Hunga Ha'apai (HTHH) volcanic eruption in January 2022 injected extreme amounts of water vapor (H2O) and a moderate amount of the aerosol precursor (SO2) into the Southern Hemisphere (SH) stratosphere. The H2O and aerosol perturbations have persisted and resulted in large-scale SH stratospheric cooling, equatorward shift of the Antarctic polar vortex, and slowing of the Brewer-Dobson circulation associated with a substantial ozone reduction in the SH winter midlatitudes. Chemistry-climate model simulations forced by realistic HTHH inputs of H2O and SO2 reproduce the observed stratospheric cooling and circulation effects, demonstrating the observed behavior is due to the volcanic influences. Furthermore, the combination of aerosol transport to polar latitudes and a cold polar vortex enhances springtime Antarctic ozone loss, consistent with observed polar ozone behavior in 2022.1

Abstract. We use a forward Lagrangian trajectory model to diagnose mechanisms that produce the water vapor seasonal cycle observed by the Microwave Limb Sounder (MLS) and reproduced by the Goddard Earth Observing System Chemistry-Climate Model (GEOSCCM) in the tropical tropopause layer (TTL). We confirm in both the MLS and GEOSCCM that the seasonal cycle of water vapor entering the stratosphere is primarily determined by the seasonal cycle of TTL temperatures. However, we find that the seasonal cycle of temperature predicts a smaller seasonal cycle of TTL water vapor between 10 and 40∘ N than observed by MLS or simulated by the GEOSCCM. Our analysis of the GEOSCCM shows that including evaporation of convective ice in the trajectory model increases both the simulated maximum value of the 100 hPa 10–40∘ N water vapor seasonal cycle and the seasonal-cycle amplitude. We conclude that the moistening effect from convective ice evaporation in the TTL plays a key role in regulating and maintaining the seasonal cycle of water vapor in the TTL. Most of the convective moistening in the 10–40∘ N range comes from convective ice evaporation occurring at the same latitudes. A small contribution to the moistening comes from convective ice evaporation occurring between 10∘ S and 10∘ N. Within the 10–40∘ N band, the Asian monsoon region is the most important region for convective moistening by ice evaporation during boreal summer and autumn.