A time-dependent two-dimensional model simu- lation of lower ionospheric
variations under in- tense SAID
Abstract
The 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 elec-tron/ion temperature,
density, and FAC, under strong SAID, with more focus in the lower
ionosphere. Our simulation reproduces many key features of SAID, such as
the anomalous electron heating in the E-region, 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 ï¿¿ ~1 ï¿¿A/m 2. 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.