Modeling Electrodynamics of Traveling Ionospheric Disturbances Induced by Localized Acoustic and Gravity Wave Forcing

Forcing from lower atmospheric and surface disturbances, e.g. severe weather events, earthquakes, and tsunamis, results in a spectrum of atmospheric acoustic and gravity waves (AGWs) that propagate through the overlying middle and upper atmosphere. These waves grow exponentially as they propagate upward through the rarefied atmosphere and experience a variety of dissipative, filtering, ducting, and refractive effects due to background thermal and wind structure. Ionospheric plasma density perturbations from these waves are readily detectable in GPS TEC (total electron content) as 0.1-3 TECU variations at few-60 minute periods (e.g. Nishioka et al, 2013). These result from collisional momentum transfer between the moving neutral gas and plasma along the direction of the geomagnetic field, resulting often in an observable asymmetry of perturbations that are larger in the geomagnetic equatorward direction (e.g. Zettergren and Snively, 2015). Such TEC perturbations in response to thunderstorms are well-documented and contain distinct infrasonic acoustic and gravity wave signatures (e.g. Lay and Shao, 2011).

This work seeks to address a complementary and little-explored aspect of ionospheric responses to localized lower atmospheric forcing: the generation of dynamo electric fields, currents, and associated magnetic field perturbations. We use coupled atmosphere-ionosphere models (MAGIC-GEMINI), covering altitudes from the ground to exobase/topside ionosphere to directly simulate both TEC and electromagnetic responses induced by a realistic spectrum of AGWs. Characteristics of dynamo currents, including both directional effects and production of field-aligned currents are simulated along with observable magnetic perturbations as measurable on the ground and in situ. We also examine the role of electric fields, partially mapping between hemispheres, in creating conjugate ionospheric density and magnetic fields, and discuss the implications for observations.