Toward the Unified Theory of SAID‐Linked Subauroral Arcs

Abstract

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.

Investigating the Hot Zone Developed Under Short‐Circuiting Conditions and the Coupled Magnetosphere‐Ionosphere (M‐I) System for the Subauroral Arc's Inner‐Magnetosphere Generation Environment

“…These hot Ni and hot Ne peaks are (a) associated with diamagnetic currents, (b) contribute to inner-magnetosphere heating, and (c) drive suprathermal ions and electrons (Mishin & Streltsov, 2023, 2024 in the TPBL (Mishin, 2013;Mishin & Sotnikov, 2017). In the coupled M-I-T system, these (a-c) play significant roles in fast-time SAPS/SAID development by short circuiting (Mishin & Puhl-Quinn, 2007) in the inner magnetosphere and in SAR arc development in the coupled I-T system (Mishin & Streltsov, 2019) by elevating the ionospheric Te (Mishin & Streltsov, 2023, 2024. These hot Ne and hot Ni plots show also the signatures of short circuiting: (a) with the steep gradient of hot Ne population formed tailward of the PP as the MPF-related hot electrons became stopped at the PP when the MPFs-related earthward directed polarization E field became shorted out over the PP and (b) with the earthward intruding hot Ni population as the MPF-related hot RC ions kept traveling earthward until stopped by the emerging outward SAPS/SAID E field (Mishin, 2013(Mishin, , 2023Mishin & Puhl-Quinn, 2007Mishin & Puhl-Quinn, 2007.…”

“…As the plasma density became further depleted in the RIT/MIT, a trough-in-the-trough feature (shown in Figures 3b and 4b) formed (Filippov et al, 1984;Stepanov et al, 2018), which, in turn, permitted more Pedersen currents flowing through and therefore increasing both the poleward subauroral E field and the sunward SAID/SAPS flow. Thus, the positive feedback mechanisms are significant in sustaining and regulating the SAID/SAPS flows (Mishin, 2013) via the ionospheric current generator operational (Figueiredo et al, 2004) by maintaining the input voltage generated in the inner magnetosphere by the fast-time voltage generator (VG FT : Mishin, 2023;Mishin & Streltsov, 2024).…”

“…In the seven events investigated, THEMIS observed the inner-magnetosphere drivers of plasma turbulence (appearing as narrow hot Ni and hot Ne peaks) generated during short circuiting. Overall, the narrow hot Ni and hot Ne peaks generate ion and electron diamagnetic currents, which, in turn, provide the free energy for driving plasma waves and plasma turbulence (leading to bulk plasma heating fueling the hot zone) and for accelerating downward suprathermal (200-300 eV) electrons and ions leading to ionospheric plasma heating and SAR arc development when the plasma turbulence is adequately high (Mishin & Streltsov, 2024). Intense plasma turbulence occurring in SAR and STEVE events is demonstrated with the significantly amplified narrow peaks of hot Ni (within the SAPS/SAID channel) and hot Ne (tailward of the plasmapause) while the lower-energy Ti ⊥ reached its maximum within the hot zone.…”

“…The short-circuit scenario creates a fast-time voltage generator (VG FT ;Mishin, 2023;Mishin & Streltsov, 2024) across the inner-magnetosphere plasmapause where the plasmapause serves as a power plant and converts the MPFs-related kinetic energy to electric energy (Mishin, 2013;Streltsov & Mishin, 2018). In the coupled magnetosphere-ionosphere-thermosphere (M-I-T) system, the resultant large-scale outward innermagnetosphere E field, developed on a short timescale (Mishin, 2013(Mishin, , 2023Mishin & Puhl-Quinn, 2007), maps down (along the magnetic field lines threading the plasmapause) to the subauroral ionosphere (in both hemispheres) as a poleward E field and drives the various northern-southern hemisphere conjugate subauroral plasma flows.…”

“…Both arcs develop due to suprathermal electrons that (a) excite their respective emission wavelengths (Mende et al, 2019) and (b) are produced locally at lower ionospheric heights (Mishin & Streltsov, 2022, 2024 since suprathermal electrons (transported from the topside ionosphere to lower ionospheric heights) become degraded along their paths (Khazanov et al, 2017). Local suprathermal electron production occurs in the STEVE and Picket Fence arcs' respective SAID channels and via ionospheric feedback instability (IFI) mechanisms generating small-scale field-aligned currents (FACs) and parallel E fields when the Hall conductance exceeds the Pedersen conductance (Mishin & Streltsov, 2022, 2024. SAR and STEVE arcs can develop in close proximity temporarily and spatially, but not in collocation (Chu et al, 2019;Liang et al, 2019;Martinis et al, 2021).…”