11:45 AM - 12:00 PM
[AAS07-10] Initial dispersion and conversion of stratospheric SO2 injected by 2022 Hunga Tonga eruption
Keywords:volcanic eruption, Hunga Tonga, SO2, chemistry climate model, satellite observation
Large volcanic eruptions can inject volcanic ash, sulfur dioxide (SO2), and water vapor into the stratosphere. Sulfate aerosols produced by SO2 oxidation and water vapor, in particular, affect not only surface and stratospheric air temperatures, but also atmospheric chemical fields. Water vapor injection will increase the concentration of hydroxyl radicals (OH) and accelerate SO2 oxidation. The eruption of submarine volcano Hunga Tonga (HT) on January 15, 2022, was an unprecedented large-scale submarine volcanic eruption and its various climate effects are being discussed. In this study, we focus on the initial diffusion process of SO2 after the HT eruption, which can largely affect aerosol dispersion and its climate effects, using chemistry climate model simulations and satellite observations. We also discuss the diffusion and oxidation processes of SO2 and related substances.
In this study, the chemistry-climate model CHASER was used to simulate the HT eruption with considering injection of SO2, water vapor, and ash (dust) from the lower to the middle stratosphere. Stratospheric aerosols are represented by the modal approach and dry and wet deposition are also considered. The CHASER simulation results are evaluated with the OMI satellite data. This study focuses on the following three points: 1) enhancement of SO2 oxidation by water vapor injection during HT eruptions (Zhu et al., 2022), 2) SO2 injection altitude, which has not been well determined by observations, 3) effect of radiative heating of volcanic ash on SO2 diffusion. In the experiments for 1) and 2), the meteorological field was nudged toward the NCEP reanalysis data, while the experiment for 3) was conducted without nudging.
Our experiment shows that the residence time for the injected SO2 expressed as the e-folding time significantly decreases in response to the injection of water vapor: ~20 days without water vapor injection, while ~7 days with water vapor injection. The reduced residence time of SO2 (~7 days) is found to be consistent with the OMI observations and is attributed to the enhanced OH formation by the water vapor injection, which accelerates SO2 gas-phase oxidation reaction by a factor of three.
For the injection altitude issue, our experiments show that OMI observations are reproduced well by the model only when all of the volcanic SO2 is injected at altitudes above 20 km. The results of this study suggest that the OMI-observed volcanic SO2 is mainly diffused latitudinally in the northward branch of the BD circulation. Furthermore, this result also suggests that most of the SO2 was likely injected at an altitude of 20-30 km during the HT eruption. This study also conducted an experiment based on the observation of a two-tiered umbrella cloud, but the SO2 simulation results are not consistent with the observation.
In addition, our simulations suggest that the rapid increase in SO2 during the first two days after the eruption was largely attributed to radiative heating by the volcanic ash, indicating the importance of ash radiative heating in the HT eruption. The latitudinal dispersion of SO2 without ash radiative heating was less active than the OMI observations.
Based on this study, it is required to investigate mid- to long-term climate impacts of HT eruption, including effects on radiation and the ozone field.
In this study, the chemistry-climate model CHASER was used to simulate the HT eruption with considering injection of SO2, water vapor, and ash (dust) from the lower to the middle stratosphere. Stratospheric aerosols are represented by the modal approach and dry and wet deposition are also considered. The CHASER simulation results are evaluated with the OMI satellite data. This study focuses on the following three points: 1) enhancement of SO2 oxidation by water vapor injection during HT eruptions (Zhu et al., 2022), 2) SO2 injection altitude, which has not been well determined by observations, 3) effect of radiative heating of volcanic ash on SO2 diffusion. In the experiments for 1) and 2), the meteorological field was nudged toward the NCEP reanalysis data, while the experiment for 3) was conducted without nudging.
Our experiment shows that the residence time for the injected SO2 expressed as the e-folding time significantly decreases in response to the injection of water vapor: ~20 days without water vapor injection, while ~7 days with water vapor injection. The reduced residence time of SO2 (~7 days) is found to be consistent with the OMI observations and is attributed to the enhanced OH formation by the water vapor injection, which accelerates SO2 gas-phase oxidation reaction by a factor of three.
For the injection altitude issue, our experiments show that OMI observations are reproduced well by the model only when all of the volcanic SO2 is injected at altitudes above 20 km. The results of this study suggest that the OMI-observed volcanic SO2 is mainly diffused latitudinally in the northward branch of the BD circulation. Furthermore, this result also suggests that most of the SO2 was likely injected at an altitude of 20-30 km during the HT eruption. This study also conducted an experiment based on the observation of a two-tiered umbrella cloud, but the SO2 simulation results are not consistent with the observation.
In addition, our simulations suggest that the rapid increase in SO2 during the first two days after the eruption was largely attributed to radiative heating by the volcanic ash, indicating the importance of ash radiative heating in the HT eruption. The latitudinal dispersion of SO2 without ash radiative heating was less active than the OMI observations.
Based on this study, it is required to investigate mid- to long-term climate impacts of HT eruption, including effects on radiation and the ozone field.