Model simulation of SAID intensification in the ionosphere under a current generator: the role of ion Pedersen transport

The sub-auroral ion drift (SAID) denotes a latitudinally narrow channel of fast westward ion drift in the sub-auroral region. The recently recognized sub-auroral optical phenomenon, the Strong Thermal Emission Velocity Enhancement (STEVE), is intrinsically related to intense SAIDs. Recently, we had developed a 2D time-dependent model to study the self-consistent variations of the ionosphere under intense SAID. The present study further advances the model to a current generator scenario of SAID. By assuming magnetospheric field-aligned current (FAC) inputs based on existing knowledge and observations, we model the self-consistent variations of the ionosphere, with focus on the dynamic changes of the plasma density, the Pedersen conductance, and the electric field. We can reproduce the self-consistent evolution of an intense SAID and its associated ionospheric dynamics such as extreme heating and depletion. We illustrate that the ion Pedersen drifts can cause dynamic density variations in the lower ionosphere. Positive feedback is found to exist between the self-consistent variations of the electric field and the conductance: the ion Pedersen transport associated with the electric field leads to density depletion in the lower ionosphere, thus reducing the Pedersen conductance and further enhancing the electric field there. We conclude that such positive feedback is key to the formation of intense SAID’s in the ionosphere.