Three‐Dimensional Numerical Modeling of Coseismic Atmospheric Dynamics and Ionospheric Responses in Slant Total Electron Content Observations

Despite routine detection of coseismic acoustic‐gravity waves (AGWs) in Global Navigation Satellite System (GNSS) total electron content (TEC) observations, models of the earthquake‐atmosphere‐ionosphere dynamics, essential for validating data‐driven studies, remain limited. We present the results of three‐dimensional numerical simulations encompassing the entire coupling from Earth's interior to the ionosphere during the Mw ${M}_{w}$ 7.8 2016 Kaikoura earthquake. Incorporating the impact of data/model uncertainties in estimating the ionospheric state, the results show a good agreement between observed and simulated slant TEC (sTEC) signals, assessed through a set of metrics. The signals exhibit intricate waveforms, resulting from the integrated nature of TEC and phase cancellation effects, emphasizing the significance of direct signal comparisons along realistic line‐of‐sight paths. By comparing simulation results initialized with kinematic and dynamic source models, the study demonstrates the quantifiable sensitivity of sTEC to AGW source specifications, pointing to their utility in the analysis of coupled dynamics. Plain Language Summary Earthquakes launch acoustic‐gravity waves (AGWs) into the atmosphere, spanning periods from seconds to minutes, that can reach the ionosphere at ∼ ${\sim} $100–400 km altitude. The majority of AGW detections in the ionosphere are performed with the use of GNSS signals collected with ground‐based receivers that nowadays comprehensively cover seismically active regions. However, the modeling of earthquake‐atmosphere‐ionosphere processes together, essential for validating and supporting data‐driven studies, remains rare. We present the outcomes of three‐dimensional numerical modeling of interconnected processes, spanning from Earth's interior to the ionosphere. We conducted a case study focused on the 2016 Mw ${M}_{w}$ 7.8 earthquake in New Zealand, renowned for its complexity and comprehensive observations of coseismic AGWs recorded with GNSS signals. Our results demonstrate a high level of accuracy of simulated GNSS signals, also revealing the high sensitivity to the chosen earthquake model and the complexity of resulting ionospheric signals, highlighting the necessity of attributing realistic geometries of GNSS TEC observations. The findings highlight the potential for using GNSS signals to investigate coseismic AGWs to infer characteristics of earthquakes. Key Points Acoustic‐gravity wave‐driven slant total electron co