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 c_H ≃ 100–750 m/s, horizontal wavelengths λ_H ≃ 600–6,000 km, and ground-based periods τ_r ≃ 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 c_H ≃ 680 m/s, λ_H ≃ 3,400 km, and τ_r ≃ 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 λ_H = 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.