Transport and Evolution of the Hunga Tonga Volcanic Aerosol Plume in the Stratosphere Simulated With the GEOS-Chem Model

The energetic eruption of the submarine Hunga Tonga-Hunga Ha’apai (HTHH) volcano (20.54°S, 175.38°W) on January 15, 2022 injected a large amount of water vapor (H₂O, ~146 Tg) and a moderate amount of sulfur dioxide (SO₂, ~0.42 Tg) into the Southern Hemisphere stratosphere, exerting strong impacts on stratospheric chemistry, aerosol formation and burden, aerosol optical depth (AOD), and the Earth’s radiative balance. Quantifying these impacts requires understanding of transport of the HTHH volcanic aerosol and H₂O plumes and their temporal evolution in the stratosphere. In this study, we simulate the transport of HTHH volcanic SO₂ and H₂O emissions and examine their impacts on stratospheric aerosol extinction and AOD using the GEOS-Chem global 3-D chemical transport model driven by the MERRA-2 reanalysis (at 2° latitude by 2.5° longitude resolution). Model simulations are conducted for the period of January-August 2022 with: (a) no HTHH emissions; (b) an HTHH SO₂ emission of 0.42 Tg injected at the 19-28 km altitude; or (c) combined HTHH SO₂ (0.42 Tg) and H₂O (146 Tg) emissions injected at the 19-28 km altitude, respectively. Model monthly zonal mean aerosol extinction coefficients are compared with those observed by SAGE-III on ISS. SAGE-III observed the large aerosol extinction enhancements in the lower stratosphere associated with the HTHH volcanic eruption and the plume transport to southern high latitudes. The model simulates the observed vertical and southward transport of the volcanic plume reasonably well, but largely underestimates the magnitude of HTHH volcanic aerosol extinction during the plume evolution. SAGE-III observations indicate significant interhemispheric transport to the Northern Hemisphere, which is underrepresented in the model simulations. Increased sulfate formation due to the addition of HTHH H₂O emission is apparently seen in the model simulation, especially in the couple of months following the eruption. In addition, model aerosol extinctions are evaluated with those from CALIOP/CALIPSO satellite observations as well as balloon measurements conducted during the Brazil Volcano project for the study period. Transport of the HTHH H₂O plume in the model as compared to SAGE-III and MLS observations will also be discussed.