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Strong electric fields in the auroral and equatorial electrojets can distort the background ion distribution function away from Maxwellian. We developed a collisional plasma kinetic model using the Boltzmann equation and a simple BGK collision operator which predicts a relatively simple relationship between the intensity of the background electric field and the resulting ion distribution function. To test the model, we perform 3-D plasma particle-in-cell simulations and compare the results to the model. The simulation applies an elastic collision operator assuming a constant ion-neutral collision rate. These simulations show less ion heating in the Pedersen direction than the analytic model but show similar overall heating. The model overestimates the heating in the Pedersen direction because the simple BGK operator includes no angular collisional scattering in the ion velocity space. On the other hand, the fully-kinetic particle-in-cell code is able to capture the physics of ion scattering in 3-D and therefore heats ions more isotropically. Although the simple BGK analytic theory does not precisely model the non-Maxwellian ion distribution function, it does capture the overall momentum and energy flows and therefore can provide the basis of further analysis of E-region wave evolution., Comment: 16 pages, 4 figures, submitted to Frontiers

Models fail to reproduce observations of the coldest parts of the Sun's atmosphere, where interactions between multiple ionized and neutral species prevent an accurate MHD representation. This paper argues that a meter-scale electrostatic plasma instability develops in these regions and causes heating. We refer to this instability as the Thermal Farley-Buneman instability, or TFBI. Using parameters from a 2.5D radiative MHD Bifrost simulation, we show that the TFBI develops in many of the colder regions in the chromosphere. This paper also presents the first multi-fluid simulation of the TFBI and validates this new result by demonstrating close agreement with theory during the linear regime. The simulation eventually develops turbulence, and we characterize the resulting wave-driven heating, plasma transport, and random motions. These results all contend that effects of the TFBI contribute to the discrepancies between solar observations and radiative MHD models., Comment: 16 pages, 9 figures. Update: fix minor typos, minor grammar improvements, add citation for previously in-prep reference

During periods of strong geomagnetic activity, intense currents flow from the magnetosphere into the high-latitude E-region ionosphere along geomagnetic field lines, B. In this region, collisions between the plasma and neutral molecules allow currents to flow across B, enabling the entire magnetosphere-ionosphere current system to close. These same currents cause strong DC electric fields in the E-region ionosphere where they drive plasma instabilities, including the Farley-Buneman instability (FBI). These instabilities give rise to small-scale plasma turbulence that modifies the large-scale ionospheric conductance that, in turn, affects the evolution of the entire near-Earth plasma environment. Also, during geomagnetic storms, precipitating electrons of high energies, $\gtrsim$ 5 keV, frequently penetrate down to the same regions where intense currents and E fields develop. This research examines the effects of precipitating electrons on the generation of the FBI and shows that, under many common conditions, it can easily suppress the instability in a predictable manner. Therefore, we expect precipitation to exert a significant feedback on the magnetosphere by preventing the elevated conductivity caused by FBI driven turbulence. This suppression should be taken into account in global modeling of the magnetosphere-ionosphere coupling., Comment: 31 pages, 4 figures, uses agujournal2019.cls

Intense electric currents called electrojets occur in weakly ionized magnetized plasmas. An example occurs in the Earth's ionosphere near the magnetic equator where neutral winds drive the plasma across the geomagnetic field. Similar processes take place in the Solar chromosphere and MHD generators. This letter argues that not all convective neutral flows generate electrojets and it introduces the corresponding universal criterion for electrojet formation, $\nabla\times (\vec{U}\times\vec{B})\neq\partial\vec{B}/\partial t$, where $\vec{U}$ is the neutral flow velocity, $\vec{B}$ is the magnetic field, and $t$ is time. This criterion does not depend on the conductivity tensor, $\hat{\sigma}$. For many systems, the displacement current, $\partial\vec{B}/\partial t$, is negligible, making the criterion even simpler. This theory also shows that the neutral-dynamo driver that generates electrojets plays the same role as the DC electric current plays for the generation of the magnetic field in the Biot-Savart law., Comment: 5 pages, 2 figures, 21 references

Empirical models of the solar chromosphere show intense electron heating immediately above its temperature minimum. Mechanisms such as resistive dissipation and shock waves appear insufficient to account for the persistence and uniformity of this heating as inferred from both UV lines and continuum measurements. This paper further develops the theory of the Farley-Buneman Instability (FBI) which could contribute substantially to this heating. It expands upon the single ion theory presented by Fontenla (2005) by developing a multiple ion species approach that better models the diverse, metal-dominated ion plasma of the solar chromosphere. This analysis generates a linear dispersion relationship that predicts the critical electron drift velocity needed to trigger the instability. Using careful estimates of collision frequencies and a one-dimensional, semi-empirical model of the chromosphere, this new theory predicts that the instability may be triggered by velocities as low as 4 km s^-1, well below the neutral acoustic speed. In the Earth's ionosphere, the FBI occurs frequently in situations where the instability trigger speed significantly exceeds the neutral acoustic speed. From this, we expect neutral flows rising from the photosphere to have enough energy to easily create electric fields and electron Hall drifts with sufficient amplitude to make the FBI common in the chromosphere. If so, this process will provide a mechanism to convert neutral flow and turbulence energy into electron thermal energy in the quiet Sun., Comment: 22 pages, 4 figures, updated and published in ApJ