Geomagnetic Disturbances Due To Neutral-Wind-Driven Ionospheric Currents

Previous simulation efforts on geomagnetic disturbances (GMDs) and geomagnetically induced currents (GICs) mostly rely on global magnetohydrodynamics models, which explicitly calculate the magnetospheric currents and carry certain assumptions about the ionosphere currents. Therefore, the role of ionospheric and thermospheric processes to GMDs has not been fully evaluated. In this study, Global Ionosphere Thermosphere Model simulations for an idealized storm event have been conducted. Simply, the high-latitude electrodynamic forcing (potential pattern and particle precipitation) has been specified by empirical models. GMDs due to neutral-wind driven currents have been compared to those caused by magnetospheric convection driven currents during both the main and recovery phases. At locations where the high-latitude electric potential is dominant, neutral-wind driven currents are found to contribute to about 10%-30% of the total GMDs. During the recovery phase when the ion-convection pattern retreats to high latitudes, neutral-wind driven currents become the primary sources for GMDs at middle latitudes on the dayside due to the "flywheel" effect and the large dayside conductance. Our result strongly suggests that ionospheric and thermospheric processes should not be neglected when estimating GMDs and therefore GICs. Disturbances of magnetospheric and ionospheric current systems in the near-Earth environment can induce strong geomagnetic disturbances (GMDs) and geomagnetically induced currents at the ground level and then cause serious damage to important infrastructures, such as power grids and pipelines. Previous studies used magnetohydrodynamics models to explicitly calculate the current system in the magnetosphere and used empirical formulas to estimate the current system in the ionosphere. Such approach simplifies the ionospheric and thermospheric processes and their contribution to the ionospheric current system. In this study, an ionosphere-thermosphere model is used to simulate the ionospheric current system during an idealized event, and the main objective is to evaluate the importance of neutral-wind-driven currents. It is found that during the storm recovery phase, neutral-wind-driven currents are the primary sources for middle-latitude GMDs on the dayside. Neutral-wind-driven currents contribute to about 10%-30% of the total geomagnetic disturbances (GMDs) at locations where the high-latitude electric potential is dominant During the storm recovery phase, neutral-wind-driven currents are the primary sources for middle-latitude GMDs on the dayside At middle latitudes, the magnitude of recovery-time neutral-wind-driven GMDs is comparable to that caused by ring currents