Were Gravity Waves or Lamb Waves Responsible for the Large-Scale Thermospheric Response to the Tonga Eruption?

The extraordinary eruption of the Tonga volcano on 15 January 2022 lofted material to heights exceeding 50 km, marking the highest observed since the satellite era. This eruption caused significant disturbances spanning from the hydrosphere up to the thermosphere. Our recent investigation discovered the dramatic thermospheric responses at satellite altitudes. This study, however, provides physical insights into two main possible processes, secondary gravity waves (GWs) and Lamb waves, which may explain those observed large-scale thermospheric disturbances. The comparison between the simulations and observations suggests that the MESORAC-HIAMCM secondary GWs are consistent with GRACE-FO measured global-propagation thermospheric density disturbances in timing and amplitude. WACCM-X simulations suggest that the Lamb wave can reach the thermosphere as a sharp, narrow wave packet, and may contribute about 25% to the total disturbances at 510 km.