Langmuir Turbulence in the Auroral Ionosphere: Origins and Effects

Abstract

Theory and observations of Langmuir waves and turbulence induced in the auroral ionosphere by electron beams of magnetospheric-origin are reviewed. The theoretical discussions include a brief description of the electrostatic dispersion relation, excitation of Langmuir waves by electron beams, and the stability of beam distributions. The theory of Langmuir turbulence—including the parametric decay instability and wave collapse—is also briefly discussed. The main focus of the review, however, is on the observations of Langmuir waves and turbulence in the ionosphere by in-situ and ground-based sensors. A summary of five decades of in-situ wave and particle observations is presented and combined with a collection of more recent results from ground-based instruments. The ground-based observations include signatures of Langmuir turbulence in the form of coherent echoes in incoherent scatter radar measurements; signatures of electron beams in the form of auroral morphologies recorded by high-speed, high-resolution optical imagers; and electromagnetic emissions received on the ground at high latitudes. Uniting the various observations obtained by the vastly different sensors is shown to provide further insight into the micro-scale processes that occur in the ionosphere. Also discussed in this review is the potential of the ground-based sensors to provide a broader spatial and temporal context for single-point in-situ measurements of such processes.

Resonant Alfvén Waves in the Lower Auroral Ionosphere: Evidence for the Nonlinear Evolution of the Ionospheric Feedback Instability

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Alfvén waves are fundamental features of magnetized plasmas and participate in various processes on different temporal and spatial scales. In the Earth's high-latitude ionosphere, for example, they induce, via electron acceleration, a range of intriguing micro-scale plasma processes involving high-frequency waves (e.g., Akbari et al, 2012Akbari et al, , 2020; they are thought to be responsible for the generation of fine-scale features of auroral arcs (e.g., Semeter et al, 2008); and, on larger scales, are an important component of magnetosphere-ionosphere interactions (e.g., Verkhoglyadova et al, 2018). By accelerating magnetospheric electrons (Chaston et al, 2002;Kletzing & Hu, 2001), heating ionospheric ions, and by carrying field-aligned currents and Poynting flux, Alfvén waves facilitate the exchange of mass, momentum, and energy between the ionosphere and the magnetosphere.

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Ion temperature gradient mode modulational stability analysis with cairn’s distribution

“…Cairn's et al [28], suggested a plasma system composed of nonthermal electrons with an abundance of energetic particles and cold ions to explain the density depletion observed by onboard instruments of the Freja and Viking satellites [29]. To explain the findings made by the Freja satellite, Cairn's et al, [30] proposed a nonthermal electron distribution with an abundance of energetic particles. The nonthermal distribution function for the electron is calculated as suggested by Cairn's et al [31].…”

Studying turbulence in a fluid with background damping

“…Turbulence has been observed in many natural systems with unique dissipation mechanisms, for instance, surface gravity waves [30], capillary waves on a liquid surface [31,32], quantum turbulence in two-fluid regime [33], nearwall turbulence [34], turbulence near the solar nebula [35], or solar wind turbulence [36], magnetohydrodynamics turbulence in partially ionized gas of the interstellar medium [37,38] or with snowdrift where snow particles damp the turbulence in the atmosphere [39], and even auroral ionospheric turbulence [40].…”