NASA - National Aeronautics and Space Administration

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. Plain Language Summary The Hunga Tonga-Hunga Ha'apai (HT) submarine volcanic eruption on 15 January 2022, produced aerosol and water vapor plumes in the stratosphere. These plumes have persisted in the Southern Hemisphere. Following the eruption, we believe that the strong water vapor cooling forced equatorial Rossby waves whose circulation pushed the eruption plume into the Northern Hemisphere. Then, in April and May 2022, the descending quasi-biennial oscillation (QBO) transported more of the water vapor plume across the equator and widened the latitudinal extent of the aerosol plume. The spring 2022 change in the HT plume distribution shows the importance of forced Rossby waves and the QBO in stratospheric interhemispheric transport.