Traveling Ionospheric Disturbances Induced by the Secondary Gravity Waves From the Tonga Eruption on 15 January 2022: Modeling With MESORAC‐HIAMCM‐SAMI3 and Comparison With GPS/TEC and Ionosonde Data.

We simulate the gravity waves (GWs) and traveling ionospheric disturbances (TIDs) created by the Hunga Tonga‐Hunga Ha'apai (hereafter "Tonga") volcanic eruption on 15 January 2022 at ∼04:15 UT. We calculate the primary GWs and forces/heatings generated where they dissipate with MESORAC, the secondary GWs with HIAMCM, and the TIDs with SAMI3. We find that medium and large‐scale TIDs (MSTIDs and LSTIDs) are induced by the secondary GWs, with horizontal phase speeds cH ≃ 100–750 m/s, horizontal wavelengths λH ≃ 600–6,000 km, and ground‐based periods τr ≃ 30 min to 3 hr. The LSTID amplitudes over New Zealand are ≃2–3 TECU, but decrease sharply ≃ 5,000 km from Tonga. The LSTID amplitudes are extremely small over Australia and South Africa because body forces create highly asymmetric GW fields and the GWs propagate perpendicular to the magnetic field there. We analyze the TIDs from SAMI3 and find that a 30 min detrend window eliminates the fastest far‐field LSTIDs. We analyze the GPS/TEC via detrending with 2–3 hr windows, and find that the fastest LSTIDs reach the US and South America at ∼8:30–9:00 UT with cH ≃ 680 m/s, λH ≃ 3,400 km, and τr ≃ 83 min, in good agreement with model results. We find good agreement between modeled and observed TIDs over New Zealand, Australia, Hawaii, Japan and Norway. The observed F‐peak height, hmF2, drops by ≃ 110–140 km over the western US with a 2.8 hr periodicity from 8:00 to 13:00 UT. We show that the Lamb waves (LWs) observed by AIRS with λH = 380 km have amplitudes that are ≃ 2.3% that of the primary GWs at z ≃ 110 km. We conclude that the observed TIDs can be fully explained by secondary GWs rather than by "leaked" LWs. Plain Language Summary: Gravity waves (GWs) are created by various processes, such as volcanic eruptions. A breaking GW imparts momentum and energy to the atmosphere, which creates secondary GWs. Traveling ionospheric disturbances (TIDs) are created by GWs through collisions between neutral and ion molecules. We simulate the GWs and TIDs created by the Tonga eruption on 15 January 2022. We find that medium and large‐scale TIDs (MSTIDs and LSTIDs) are induced by the secondary GWs. These TIDs propagate globally, and have speeds of 100–750 m/s and horizontal scales of hundreds to thousands of km. The fastest TIDs reach the United States and South America at ∼8:30–9:00 UT; these TIDs have large scales and large periods, in agreement with observations. These LSTIDs can only be seen if they are not "detrended out" when processing the ionospheric data. Previous studies eliminated these LSTIDs by restricting their detrend windows, and then incorrectly suggested that Lamb waves were responsible for the TIDs they observed. Using longer detrend windows, we find good agreement between the modeled and observed TIDs. We find that the observed TIDs can be fully explained by secondary GWs, rather than by the leakage of Lamb waves into GWs. Key Points: Globally‐propagating concentric TIDs are induced by secondary GWs from the Tonga eruption with cH = 100−750 m/s and τr = 30 min to 3 hrThe fastest LSTIDs from Tonga in the far field are eliminated when detrending SAMI3 and GPS/TEC data with a 30 min windowThe fastest modeled LSTIDs from Tonga reach the US and South America at 8:30‐9:00 UT with cH = 600 m/s, in good agreement with data [ABSTRACT FROM AUTHOR]