Abstract
Space-based observations of the signatures associated with STEVE show
how this phenomenon might be closely related to an extreme version of a
SAID channel. Measurements show high velocities
($>$4km/s), high temperatures ($>$4,000
K), and very large current density drivers (up to
1$\mu$A/m$^2$). This phenomena happens in a small
range of latitudes, less than a degree, but with a large longitudinal
span. In this study, we utilize the GEMINI model to simulate an extreme
SAID/STEVE. We assume a FAC density coming from the magnetosphere as the
main driver, allowing all other parameters to adjust accordingly. We
have two main objectives with this work: show how an extreme SAID can
have velocity values comparable or larger than the ones measured under
STEVE, and to display the limitations and missing physics that arise due
to the extreme values of temperature and velocity. Changes had to be
made to GEMINI due to the extreme conditions, particularly some
neutral-collision frequencies. The importance of the temperature
threshold at which some collision frequencies go outside their
respective bounds, as well as significance of the energies that would
cause inelastic collisions and impact ionization are displayed and
discussed. We illustrate complex structures and behaviors, emphasizing
the importance of 3D simulations in capturing these phenomena.
Longitudinal structure is emphasized, as the channel develops
differently depending on MLT. However, these simulations should be
viewed as approximations due to the limited observations available to
constrain the model inputs and the assumptions made to achieve sensible
results.