Dynamics of density cavities generated by frictional heating: Formation, distortion, and instability

Abstract

A simulation study of the generation and evolution of mesoscale density cavities in the polar ionosphere is conducted using a time‐dependent, nonlinear, quasi‐electrostatic model. The model demonstrates that density cavities, generated by frictional heating, can form in as little as 90 s due to strong electric fields of ∼120 mV/m, which are sometimes observed near auroral zone and polar cap arcs. Asymmetric density cavity features and strong plasma density gradients perpendicular to the geomagnetic field are naturally generated as a consequence of the strong convection and finite extent of the auroral feature. The walls of the auroral density cavities are shown to be susceptible to large‐scale distortion and gradient‐drift instability, hence indicating that arc‐related regions of frictional heating may be a source of polar ionospheric density irregularities.

Simulations of Secondary Farley‐Buneman Instability Driven by a Kilometer‐Scale Primary Wave: Anomalous Transport and Formation of Flat‐Topped Electric Fields

“…The reduced electric field causes meter‐scale waves to propagate near the plasma acoustic speed, corresponding to the near‐threshold condition and matching observations of strong, narrow coherent radar spectra observed at the magnetic equator. The results presented here may also extend to auroral density structures produced by convection, auroral precipitation, and ionospheric cavitation (Mrak et al, ; Zettergren et al, ).…”

Satellite‐Beacon Ionospheric‐Scintillation Global Model of the Upper Atmosphere (SIGMA) III: Scintillation Simulation Using A Physics‐Based Plasma Model

“…This section briefly describes the models used in the present study, GEMINI and SIGMA. A more detailed description of each code and their corresponding capability can be found in Deshpande et al (, ) and Zettergren and Snively () and Zettergren et al (). We also describe how we couple the two models together to achieve the new capability of directly simulating of GNSS scintillation from an initial mesoscale ionospheric state.…”

“…The present form of GEMINI functions in two or three dimensions and uses general orthogonal curvilinear coordinates—usually either a tilted dipole (Huba et al, ) or Cartesian system (as for the present study). GEMINI comprises a fluid system of equations (Blelly & Schunk, ; Schunk, ), describing dynamics of the ionospheric plasma, self‐consistently coupled to a quasi‐electrodynamic treatment of auroral and neutral dynamo currents (Zettergren et al, ). The fluid system is a set of mass, momentum, and energy conservation equations for each ionospheric species s relevant to the E , F , and topside regions ( ).…”

“…Recent, detailed descriptions of GEMINI (including precise statements of governing equations and assumptions) are provided in Zettergren and Snively (, Appendix A, for fluid equations) and Zettergren et al (, for the electrodynamic equation). Message passing (via OpenMPI libraries) is used in GEMINI to facilitate high‐resolution simulations (down to 200 m) covering a fairly large geographic extent (∼100 km or so), such that GEMINI can capture irregularities at Fresnel scales responsible for Global Positioning System (GPS) scintillation, while maintaining the ability to model a region of mesoscale extent.…”

“…In this work, we leverage a physics‐based model of high‐latitude ionospheric plasma instabilities, the Geospace Environment Model of Ion‐Neutral Interactions (GEMINI; Zettergren & Snively, ; Zettergren et al, ) coupled to a model of electromagnetic wave propagation through turbulent media (SIGMA; Deshpande et al, ), as illustrated in Figure . GEMINI includes both aeronomical and electrodynamic processes relevant to the formation of ionospheric fluid instabilities (viz., GDI and KHI), and SIGMA is capable of simulating scattering, diffraction, wave refraction, and reflection through an arbitrary density field—including a turbulent plasma simulated by GEMINI.…”