Plain Language Summary
The Hunga Tonga-Hunga Ha’apai (HT) submarine volcanic eruption on January 15, 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 an equatorial Rossby wave whose circulation pushed the eruption plume into the Northern Hemisphere. Then, in April and May 2022, the descending quasi-biennial oscillation 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.