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 similar to 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) similar or equal to 100-750 m/s, horizontal wavelengths lambda(H) similar or equal to 600-6,000 km, and ground-based periods tau(r) similar or equal to 30 min to 3 hr. The LSTID amplitudes over New Zealand are similar or equal to 2-3 TECU, but decrease sharply similar or equal to 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 similar to 8:30-9:00 UT with c(H) similar or equal to 680 m/s, lambda(H) similar or equal to 3,400 km, and tau(r) similar or equal to 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 lambda(H) = 380 km have amplitudes that are similar or equal to 2.3% that of the primary GWs at z similar or equal to 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 similar to 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.