Toward the Unified Theory of SAID-Linked Subauroral Arcs

We present a unified approach to subauroral arcs within intense subauroral ion drifts (SAID), which explains the observed transition of a precursor Stable Auroral Red (SAR) arc into Strong Thermal Emission Velocity Enhancement (STEVE). This approach is based on the short-circuiting concept of fasttime SAID as an integral part of a magnetospheric voltage generator between the innermost boundaries of the freshly injected plasma sheet electrons and ring current ions. Here, enhanced plasma turbulence rapidly heats the bulk plasma and accelerates suprathermal non-Maxwellian "tails." Heat and suprathermal electron transport rapidly elevate the ionospheric electron temperature-the source of a bright SAR arc. Through a substorm, the density altitude profile within the evolving ionospheric SAID channel transforms into a "fresh" F-region trough with the E-region valley. The ionospheric feedback instability within the depleted-density SAID channel generates small-scale, field-aligned currents with parallel electric fields sufficient to produce the suprathermal electron population, exciting the STEVE and Picket Fence emissions. This approach also explains the inner electromagnetic structure of intense SAID, which is consistent with fine optical structures in STEVE and Picket Fence. Nightside Stable Auroral Red (SAR) arcs emerge and follow the evolution of the fasttime subauroral ion drifts (SAID) until the ensuing emergence of Strong Thermal Emission Velocity Enhancement (STEVE)Density trough formation with the E-region valley initiates the emergence of STEVE and Picket Fence underneath of the precursor SAR arcSmall-scale parallel electric fields created by the ionospheric feedback instability in the low-density SAID channel make STEVE and Picket Fence