Double layers in the downward current region of the aurora

International audienceDirect observations of magnetic-field-aligned (parallel) electric fields in the downward current region of the aurora provide decisive evidence of naturally occurring double layers. We report measurements of parallel electric fields, electron fluxes and ion fluxes related to double layers that are responsible for particle acceleration. The observations suggest that parallel electric fields organize into a structure of three distinct, narrowly-confined regions along the magnetic field (B). In the "ramp" region, the measured parallel electric field forms a nearly-monotonic potential ramp that is localized to ~ 10 Debye lengths along B. The ramp is moving parallel to B at the ion acoustic speed (vs) and in the same direction as the accelerated electrons. On the high-potential side of the ramp, in the "beam" region, an unstable electron beam is seen for roughly another 10 Debye lengths along B. The electron beam is rapidly stabilized by intense electrostatic waves and nonlinear structures interpreted as electron phase-space holes. The "wave" region is physically separated from the ramp by the beam region. Numerical simulations reproduce a similar ramp structure, beam region, electrostatic turbulence region and plasma characteristics as seen in the observations. These results suggest that large double layers can account for the parallel electric field in the downward current region and that intense electrostatic turbulence rapidly stabilizes the accelerated electron distributions. These results also demonstrate that parallel electric fields are directly associated with the generation of large-amplitude electron phase-space holes and plasma waves

The Effects of Turbulence on Three-Dimensional Magnetic Reconnection at the Magnetopause

Two- and three-dimensional particle-in-cell simulations of a recent encounter of the Magnetospheric Multiscale Mission (MMS) with an electron diffusion region at the magnetopause are presented. While the two-dimensional simulation is laminar, turbulence develops at both the x-line and along the magnetic separatrices in the three-dimensional simulation. The turbulence is strong enough to make the magnetic field around the reconnection island chaotic and produces both anomalous resistivity and anomalous viscosity. Each contribute significantly to breaking the frozen-in condition in the electron diffusion region. A surprise is that the crescent-shaped features in velocity space seen both in MMS observations and in two-dimensional simulations survive, even in the turbulent environment of the three-dimensional system. This suggests that MMS's measurements of crescent distributions do not exclude the possibility that turbulence plays an important role in magnetopause reconnection.Comment: Revised version accepted by GR

Phase-space holes due to electron and ion beams accelerated by a current-driven potential ramp

One-dimensional open-boundary simulations have been carried out in a current-carrying plasma seeded with a neutral density depression and with no initial electric field. These simulations show the development of a variety of nonlinear localized electric field structures: double layers (unipolar localized fields), fast electron phase-space holes (bipolar fields) moving in the direction of electrons accelerated by the double layer and trains of slow alternating electron and ion phase-space holes (wave-like fields) moving in the direction of ions accelerated by the double layer. The principal new result in this paper is to show by means of a linear stability analysis that the slow-moving trains of electron and ion holes are likely to be the result of saturation via trapping of a kinetic-Buneman instability driven by the interaction of accelerated ions with unaccelerated electrons

Magnetosphere-ionosphere coupling at Jupiter:a parameter space study

Jupiter's main auroral emission is a signature of the current system that transfers angular momentum from the planet to radially outward moving Iogenic plasma. Ray et al. (2010) developed a steady state model of this current system which self-consistently included the effects of a field-aligned potential, and an ionospheric conductance modified by precipitating electrons. The presented parameter space study extends their model to explore how variations in the auroral cavity density and temperature, magnetospheric mass loading rate, and background ionospheric Pedersen conductance affect the current system and resulting auroral emission. We show that while the solutions found by Ray et al. (2010) vary with changes in the system parameters, the gross general trends remain similar to the original solutions. We find that, for an outer constraint of I100 = 86 MA, the high-latitude electron temperature and density have a lower limit of ∼1.5 keV and an upper limit of ∼0.01 cm -3, respectively, in order for solutions to be consistent with observations of Jupiter's auroral emission. For increases in the radial mass transport rate and an outer constraint of Max = 75 kV the auroral emission brightness increases

Magnetosphere-ionosphere coupling at Jupiter:Effect of field-aligned potentials on angular momentum transport

We present a time-independent model of Jupiter's rotation-driven aurora based on angular momentum conservation, including the effects of a field-aligned potential (φ∥) and an ionospheric conductivity that is modified by precipitating electrons. We argue that φ∥ arises from a limit to field-aligned current at high latitudes, and hence, we apply a current-voltage relation, which takes into account the low plasma densities at high latitudes. The resulting set of nonlinear equations that govern the behavior of angular momentum transfer is underconstrained and leads to a set of solutions, including those derived in earlier work. We show that solutions with high angular momentum transfer, large radial currents, and small mass transport rates (Ṁ ≤ 1000 kg/s) exist. Our set of solutions can reproduce many of the observed characteristics of Jupiter's main auroral oval, including the energy of the precipitating electrons, the energy flux into the ionosphere, the width of the aurora at the ionosphere, and net radial current across the field for a radial mass transport value of ∼500 kg/s

Magnetospheric Multiscale Observations Of The Electron Diffusion Region Of Large Guide Field Magnetic Reconnection

We report observations from the Magnetospheric Multiscale (MMS) satellites of a large guide field magnetic reconnection event. The observations suggest that two of the four MMS spacecraft sampled t ..

Magnetospheric Multiscale Satellites Observations Of Parallel Electric Fields Associated With Magnetic Reconnection

We report observations from the Magnetospheric Multiscale satellites of parallel electric fields (E (sub parallel)) associated with magnetic reconnection in the subsolar region of the Earth\u27s magnetopause. E (sub parallel) events near the electron diffusion region have amplitudes on the order of 100 millivolts per meter, which are significantly larger than those predicted for an antiparallel reconnection electric field. This Letter addresses specific types of E (sub parallel) events, which appear as large-amplitude, near unipolar spikes that are associated with tangled, reconnected magnetic fields. These E (sub parallel) events are primarily in or near a current layer near the separatrix and are interpreted to be double layers that may be responsible for secondary reconnection in tangled magnetic fields or flux ropes. These results are telling of the three-dimensional nature of magnetopause reconnection and indicate that magnetopause reconnection may be often patchy and/or drive turbulence along the separatrix that results in flux ropes and/or tangled magnetic fields

Fundamental length in quantum theories with PT-symmetric Hamiltonians II: The case of quantum graphs

Manifestly non-Hermitian quantum graphs with real spectra are introduced and shown tractable as a new class of phenomenological models with several appealing descriptive properties. For illustrative purposes, just equilateral star-graphs are considered here in detail, with non-Hermiticities introduced by interactions attached to the vertices. The facilitated feasibility of the analysis of their spectra is achieved via their systematic approximative Runge-Kutta-inspired reduction to star-shaped discrete lattices. The resulting bound-state spectra are found real in a discretization-independent interval of couplings. This conclusion is reinterpreted as the existence of a hidden Hermiticity of our models, i.e., as the standard and manifest Hermiticity of the underlying Hamiltonian in one of less usual, {\em ad hoc} representations ${\cal H}_j$ of the Hilbert space of states in which the inner product is local (at $j=0$) or increasingly nonlocal (at $j=1,2, ...$). Explicit examples of these (of course, Hamiltonian-dependent) hermitizing inner products are offered in closed form. In this way each initial quantum graph is assigned a menu of optional, non-equivalent standard probabilistic interpretations exhibiting a controlled, tunable nonlocality.Comment: 33 pp., 6 figure