Primary and Secondary Gravity Waves and Large‐Scale Wind Changes Generated by the Tonga Volcanic Eruption on 15 January 2022: Modeling and Comparison With ICON‐MIGHTI Winds.

We simulate the primary and secondary atmospheric gravity waves (GWs) excited by the upward movement of air generated by the Hunga Tonga‐Hunga Ha'apai (hereafter "Tonga") volcanic eruption on 15 January 2022. The Model for gravity wavE SOurce, Ray trAcing and reConstruction (MESORAC) is used to calculate the primary GWs and the local body forces/heatings generated where they dissipate. We add these forces/heatings to the HIgh Altitude Mechanistic general Circulation Model (HIAMCM) to determine the secondary GWs and large‐scale wind changes that result. We find that a wide range of medium to large‐scale secondary GWs with concentric ring structure are created having horizontal wind amplitudes of u′, v′ ∼ 100–200 m/s, ground‐based periods of τr ∼ 20 min to 7 hr, horizontal phase speeds of cH ∼ 100–600 m/s, and horizontal wavelengths of λH ∼ 400–7,500 km. The fastest secondary GWs with cH ∼ 500–600 m/s are large‐scale GWs with λH ∼ 3,000–7,500 km and τr ∼ 1.5–7 hr. They reach the antipode over Africa ∼9 hr after creation. Large‐scale temporally and spatially varying wind changes of ∼80–120 m/s are created where the secondary GWs dissipate. We analyze the Tonga waves measured by the Michelson Interferometer for Global High‐resolution Thermospheric Imaging (MIGHTI) on the National Aeronautics and Space Administration Ionospheric Connection Explorer (ICON), and find that the observed GWs were medium to large‐scale with cH ∼ 100–600 m/s and λH ∼ 800–7,500 km, in good agreement with the simulated secondary GWs. We also find good agreement between ICON‐MIGHTI and HIAMCM for the timing, amplitudes, locations, and wavelengths of the Tonga waves, provided we increase the GW amplitudes by ∼2 and sample them ∼30 min later than ICON. Plain Language Summary: Atmospheric gravity waves (GWs) are buoyancy driven perturbations in the Earth's atmosphere that can be created by various processes. GW breaking is similar to the breaking of ocean waves when they overturn. A breaking GW imparts momentum to the ambient atmosphere, which can create secondary GWs. We simulated the Tonga eruption on 15 January 2022 using Geostationary Operational Environmental Satellite satellite images, ray tracing, and a GW‐resolving global circulation model. We find that the secondary GWs created by the breaking of the primary GWs from the eruption propagated globally and changed the large‐scale wind patterns in the thermosphere. Furthermore, the phase speeds and wavelengths of these waves simulated by the model agree well with corresponding results from ICON satellite measurements. Thus, this study highlights the importance of a process called "multi‐step vertical coupling", according to which secondary GWs are important drivers in the Earth's thermosphere. Key Points: Modeled secondary gravity waves (GWs) radiate globally from Tonga with cH ∼ 100–600 m/s, λH ∼ 400–7,500 km, and τr ∼ 20 min to 7 hrICON observed northeastward GWs from Tonga with cH ∼ 100–600 m/s and λH ∼ 800–7,500 km, in good agreement with the modelTemporally and spatially variable large‐scale wind changes of ∼80–120 m/s are created by the dissipation of the secondary GWs [ABSTRACT FROM AUTHOR]