The turbulent plasmasphere boundary layer and the outer radiation belt boundary

Abstract

We report on observations of enhanced plasma turbulence and hot particle distributions in the plasmasphere boundary layer formed by reconnection-injected hot plasma jets entering the plasmasphere. The data confirm that the electron pressure peak is formed just outward of the plasmapause in the premidnight sector. Free energy for plasma wave excitation comes from diamagnetic ion currents near the inner edge of the boundary layer due to the ion pressure gradient, electron diamagnetic currents in the entry layer near the electron plasma sheet boundary, and anisotropic (sometimes ring-like) ion distributions revealed inside, and further inward of, the inner boundary. We also show that nonlinear parametric coupling between lower oblique resonance and fast magnetosonic waves significantly contributes to the VLF whistler wave spectrum in the plasmasphere boundary layer. These emissions represent a distinctive subset of substorm/storm-related VLF activity in the region devoid of substorm injected tens keV electrons and could be responsible for the alteration of the outer radiation belt boundary during (sub)storms.

Whistler Waves in the Plasmasphere Boundary Layer: Nonlinear Parametric Excitation

“…Sotnikov et al (, , ) and Mishin and Sotnikov () used equations in the spectral, ω − k , form, just enough for estimates of the sideband amplitude. In order to describe transition to the turbulent stage, equations in time‐space coordinates are required.…”

“…As the “standard” whistler generation mechanism by energetic electrons is unavailable in the TPBL, Mishin and Mishin and Sotnikov () suggested nonlinear interactions between quasi‐electrostatic LH oblique resonance (LOR) and MS waves to be the source. Indeed, as the three modes (LH, MS, and W) belong to the same branch with the cold‐plasma dispersion relation (e.g., Ganguli et al, ), but at different wavelengths and propagation angles, they can easily couple with each other.…”

“…In order to explain oblique VLF whistler waves at ω w ≥ 5 ω lhr observed in the TPBL (Mishin & Burke, , Figure 3; Mishin et al, , Figure 1; Mishin, , Figures 4 and 5), Mishin and Sotnikov () analytically explored parametric interaction of LOR at with magnetosonic waves at . This paper presents the results of numerical solution of a system of nonlinear equations describing parametric interactions between LOR and MS pump waves excited in the TPBL by the diamagnetic ion currents and hot ion ring instabilities (LaBelle & Treumann, ; Mishin & Burke, ).…”

STEVE and the Picket Fence: Evidence of Feedback‐Unstable Magnetosphere‐Ionosphere Interaction

“…The fluxes are averaged over the corresponding SAID regions. The suprathermal population between 30 and 500 eV is a typical feature of SAID resulting from nonlinear wave heating in the turbulent plasmasphere boundary layer (Mishin, ; Mishin & Sotnikov, ).…”

“…Then we show that inelastic electron collisions with molecular nitrogen, , inhibit thermal excitation of the red‐line emission in the low‐density SAID/STEVE region. Suprathermal electrons coming from the turbulent plasmasphere boundary layer (e.g., Mishin, ; Mishin & Sotnikov, ) appear to be the major excitation source. We also show that the chemiluminescent and radiative attachment reactions do not explain the short‐wavelength part of the STEVE continuum and argue that its interpretation requires vibrationally excited molecular states.…”