Numerical Modeling of the Concentric Gravity Wave Seeding of Low-Latitude Nighttime Medium-Scale Traveling Ionospheric Disturbances

The first-principles three-dimensional ionosphere model Naval Research Laboratory SAMI3/ESF is used to study the low-latitude nighttime medium-scale traveling ionospheric disturbances (MSTIDs) triggered by the typhoon-induced concentric gravity waves (CGWs) for the first time. Simulation results demonstrate that the electrodynamic coupling between CGWs and Perkins instability can initiate the rarely observed low-latitude nighttime MSTIDs by accelerating their growth rates. Both the simulations and observations show that the westward and westward/equatorward propagating CGWs with similar wavefront alignments to the Perkins instability could enhance the generation of MSTIDs rather than the northward propagating CGWs. The CGWs penetrating to the ionospheric F layer without severe dissipation can induce greater polarization electric fields to accelerate the Perkins instability via E x B drifts. Plain Language Summary Nighttime medium-scale traveling ionospheric disturbances (MSTIDs) are electrodynamical structures, which are primarily observed in the midlatitude ionosphere over the Asian, European, and American regions. These structures have typical wavelengths of a few hundred kilometers and propagate westward and equatorward with a unique frontal alignment along northwest-southeast and northeast-southwest in the Northern and Southern Hemispheres, respectively. Recently, low-latitude nighttime MSTIDs were observed over the Taiwan Strait when Super Typhoon Nepartak swept toward Taiwan on 7 July 2016. It is suggested that the typhoon-induced concentric gravity waves (CGWs) could play an important role to seed the low-latitude MSTIDs. To confirm this hypothesis, we used a SAMI3/ESF ionosphere model to identify the interconnection between CGWs and MSTIDs. Simulations demonstrate that the CGWs can modulate the ionospheric electrodynamics and electron density distribution through wind perturbation, leading to the generation of low-latitude nighttime MSTIDs. CGWs propagating upward into the ionosphere without severe dissipation could efficiently initiate the MSTIDs. The study confirms the impact of CGWs on the nighttime equatorial ionosphere, providing important implications for the electrodynamic coupling between the meteorological events and ionospheric instabilities.