Model Simulation of SAID Intensification in the Ionosphere Under a Current Generator: The Role of Ion Pedersen Transport

During geomagnetically active intervals, latitudinally narrow channels of fast westward ion drifts were at times observed in the subauroral region. They are termed the subauroral ion drifts (SAID). The Strong Thermal Emission Velocity Enhancement (STEVE), a subauroral optical phenomenon, is intrinsically related to intense SAID. Recently, we had developed a two-dimensional (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.

Automated summary

This study uses a two-dimensional time-dependent model to investigate the ionospheric dynamics of subauroral ion drifts. The results demonstrate the importance of positive feedback in the formation of intense subauroral ion drifts.