Simulation of the Propagation and Effects of Gravity Waves Generated by Tonga Volcano Eruption in the Thermosphere and Ionosphere Using Nested‐Grid TIEGCM

The Hunga Tonga‐Hunga Ha'apai volcano eruption on 15 January 2022 triggered strong atmospheric gravity wave (GW) activity in the upper atmosphere, which was later detected by various observations. We perform one of the first ionosphere‐thermosphere (I‐T) model studies of the GW effects from the Tonga eruption in the ionosphere‐thermosphereI‐T system using the thermosphere‐ionosphere‐electrodynamics general circulation model (TIEGCM). We implement a high‐resolution mesh inside a regional domain (nested grid) in addition to the global low‐resolution mesh, which differs from the standard global uniform resolution setup. The nested‐grid TIEGCM (TIEGCM‐NG) successfully simulates the observed wave propagation and effects in the I‐T system by further nudging GW fields at TIEGCM lower boundaries (∼97 km) using output from the high‐resolution whole atmosphere community climate model with thermosphere and ionosphere extension simulations. The simulation results indicate that the critical parameter to simulate GW propagation is horizontal resolution. Inside the high‐resolution nested region, GWs with horizontal wavelengths of ∼400 km and periods of 10–30 min can propagate outward and upward and produce significant ionospheric disturbances close to observations. Outside the nested region, only long‐wavelength, low‐frequency waves survive. Another test indicates that GWs can be better resolved when geopotential height is nudged at TIEGCM lower boundaries. With the capability of simultaneously simulating local, small to mesoscale I‐T processes, TIEGCM‐NG is superior to global high‐resolution simulations due to its largely reduced computation cost and may find its application in the study of I‐T system regional dynamics. Plain Language Summary We develop nested‐grid thermosphere‐ionosphere‐electrodynamics general circulation model (TIEGCM‐NG) which is a nested‐grid extension of TIEGCM that embeds a high‐resolution regional mesh inside a low‐resolution global mesh. Computation costs of high‐resolution simulations are largely reduced in this way by focusing computing resources only inside the region of interest. We apply this new model to study the gravity wave (GW) effects from the Tonga eruption in the ionosphere‐thermosphere (I‐T) system. Numerical experiments indicate that the GW generates considerable wind and temperature perturbations in the high‐resolution mesh, which suggests that the resolution is essential to the propagation of GWs in the thermosphere. High‐resol