A Time‐Dependent Two‐Dimensional Model Simulation of Lower Ionospheric Variations Under Intense SAID

Abstract

AbstractThe subauroral ion drift (SAID) denotes a latitudinally narrow channel of fast westward ion drift in the subauroral region, often observed during geomagnetically disturbed intervals. The recently recognized subauroral optical phenomena, the Strong Thermal Emission Velocity Enhancement (STEVE) and the Picket Fence, are both related to intense SAIDs. In this study, we present a 2D time‐dependent model simulation of the self‐consistent variations of the electron/ion temperature, density, and FAC, under strong SAID, with more focus in the lower ionosphere. The anomalous electron heating in the E‐region is evaluated using an empirical model. Our simulation reproduces many key features of SAID, such as the strong electron temperature enhancement in the upper F‐region, the intense ion frictional heating, and the plasma density depletion. Most importantly, the ion Pedersen drifts is found to play a crucial role in the density variations and FAC dynamics in the lower ionosphere. The transport effect of ion Pedersen drifts leads to strong density depletion in the lower ionosphere in a large portion of SAID. The FAC inside SAID is mainly downward with magnitude ≤ ∼1 μA/m2. At the poleward edge of SAID, the ion Pedersen drift leads to a pileup of the plasma density and an upward FAC. Our simulation results also corroborate the presence of strong gradients of plasma density, temperature, and flows, at the edge of SAID, which may be conducive to certain plasma instabilities. Our model provides a useful tool for the future exploration of the generation mechanisms of STEVE and Picket Fence.