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