Mesospheric Temperature and Circulation Response to the Hunga Tonga‐Hunga‐Ha'apai Volcanic Eruption

Abstract

The Hunga Tonga Hunga‐Ha'apai (HTHH) volcanic eruption on 15 January 2022 injected water vapor and SO2 into the stratosphere. Several months after the eruption, significantly stronger westerlies, and a weaker Brewer‐Dobson circulation developed in the stratosphere of the Southern Hemisphere and were accompanied by unprecedented temperature anomalies in the stratosphere and mesosphere. In August 2022, the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) satellite instrument observed record‐breaking temperature anomalies in the stratosphere and mesosphere that alternate signs with altitude. Ensemble simulations carried out with the Whole Atmosphere Community Climate Model (WACCM6) indicate that the strengthening of the stratospheric westerlies explains the mesospheric temperature changes. The stronger westerlies cause stronger westward gravity wave drag in the mesosphere. Although the enhanced gravity wave drag is partly balanced by a weakening of planetary wave forcing, the net result is an acceleration of the mesospheric mean meridional circulation. The stronger mesospheric circulation, in turn, plays a dominant role in driving the changes in mesospheric temperatures. This study highlights the impact of large volcanic eruptions on middle atmospheric dynamics and provides insight into their long‐term effects in the mesosphere. On the other hand, we could not discern a clear mechanism for the observed changes in stratospheric circulation. In fact, an examination of the WACCM ensemble reveals that not every member reproduces the large changes observed by SABER. We conclude that there is a stochastic component to the stratospheric response to the HTHH eruption.

Stratospheric Climate Anomalies and Ozone Loss Caused by the Hunga Tonga‐Hunga Ha'apai Volcanic Eruption

“…While most of the H 2 O + SO 2 ensemble members show relative cold temperatures and weak wave fluxes, there is considerable stochastic variability among the realizations, and several realizations (6 out of 10) have temperature anomalies comparable to the observed 2022 anomalies. We conclude that internal variability in the ensemble model simulations contributes to the low bias in ensemble average temperature anomalies in Figure 4 compared to the observed pattern in 2022 (Yu et al, 2023). In spite of this difference in magnitude, the similarity in timing and spatial structure of observed and modeled temperature patterns is strongly suggestive of an HTHH attribution for the observed anomalies.…”

“…The vertical structure of the temperature anomalies averaged over 60°S-10°S (Figure 4b) shows cooling covering much of the mid-stratosphere throughout 2022, with largest cold anomalies during SH winter (June-August) extending to ∼45 km. During these months there are anomalous warm temperatures in the lower mesosphere above ∼50 km (Yu et al, 2023, see Section 3.3). Cold anomalies are reduced in 2023.…”

Energy Conservation in the Cooling and Contracting Upper Mesosphere and Lower Thermosphere

“…Trends in ELR power are evaluated from the time series of globally integrated annual power values from 2002 through 2021. The year 2022 is not included in the analysis due to the unprecedented effects on the thermal structure of the upper MLT due to the eruption of Hunga Tonga-Hunga Ha'apai (Yu et al, 2023).…”

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

“…Manney et al (2023) showed that the H 2 O plume did not affect the 2022 Antarctic vortex, and Santee et al (2023) showed that while the sulfate aerosol did result in some heterogeneous processing, it did not lead to appreciable chemical ozone loss. 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.…”

“…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.…”