  For the first time, we identify the magnetospheric driver of STEVE, east-west
aligned narrow emissions in the subauroral region. In the ionosphere, STEVE is
associated with subauroral ion drift (SAID) features of high electron
temperature peak, density gradient, and strong westward ion flow. In this
study, we present STEVE's magnetospheric driver region at a sharp plasmapause
containing: strong tailward quasi-static electric field, kinetic Alfven waves,
parallel electron acceleration, perpendicular ion drift. The observed
continuous emissions of STEVE are possibly caused by ionospheric electron
heating due to heat conduction and/or auroral acceleration process powered by
Alfven waves, both driven by the observed equatorial magnetospheric processes.
The observed green emissions are likely optical manifestations of electron
precipitations associated with wave structures traveling along the plasmapause.
The observed SAR arc at lower latitudes likely corresponds to the formation of
low-energy plasma inside the plasmapause by Coulomb collisions between ring
current ions and plasmaspheric plasma.
