This project will investigate the physics underlying plasma density irregularities in the lower (E-region) ionosphere at unprecedented spatial resolution based on numerical improvements to existing, massively-parallel, kinetic plasma simulation code as well as theory. Improvements include the development of ion and electron fluid modules to enable larger scale simulations and the incorporation of electron thermal effects, non-periodic boundary conditions, and particle injection and removal for simulation of auroral and photoelectron processes having more realistic temperatures and density gradients. The proposed scientific studies are focused on low- and high-latitude plasma instabilities and also, for the first time, E-region thermal instabilities. The simulation results will be compared to observations and used to develop analytical models to improve understanding of turbulent and inhomogeneous currents and energy flows within the ionosphere. Results from this research will improve interpretation of rocket and radar monitoring of the geospace environment as well as advance upper atmospheric modeling capability.
This project supported a number of scientific projects and resulted in some interesting findings. We performed the first fully kinetic three-dimensional simulations of turbulent heating of the E-region electrojet. We have developed a theory of ionospheric turbulence with important implications for the ionospheres of other planets and the Solar chromosphere. We have developed a novel approach for measuring neutral wind velocities between 95-115 km altitudes using radar observations of long-lived meteor trails. We have worked to develop our large-scale massively parallel simulator and applied it to a study a range of issues. This work has resulted in 3 papers in the last year papers and 13 in the last 4-5 years. It has supported a number of graduate students and undergraduate students as they learn about the space environment and scientific methods. We elaborate on the specific findings below. Currents flow from the magnetosphere to the E-region ionosphere where they drive the intense currents of the auroral electrojet. The stronger of these currents develop Farley-Buneman (FB) streaming instabilities and become turbulent. This often leads to anomalous electron heating (AEH) which can raise the electron temperature from 300K to as much as 3000K and, also, modifies auroral conductivities. We have published a paper that describes the first high-resolution, 3D, fully kinetic simulations of electric field driven turbulence in the electrojet and compares the results with 2D simulations and observations. These simulations show that 3D turbulence can dramatically elevate electron temperatures and enables estimates of the magnitude of this effect. We have developed further analytic theory of the FB instability by including multiple ion species. We have derived a linear dispersion relationship that predicts the critical electron drift velocity needed to trigger the instability. We have shown that existence of several ion species with clearly distinct masses can modify dramatically the threshold conditions for the instability. This may have serious implications for other media such as ionospheres of other planets and Solar chromosphere. This resulted in a paper published in the Astrophysical Journal. Using statistical analysis of several datasets from JRO observations of long-lived non- specular meteor trails with interferometry, we have determined neutral wind velocities at the E-region altitudes in all three dimensions with unprecedented resolution. For the first time, we have shown the existence of intense wind shears~ 50-100 m/s/km. In some cases, these shears persist may persist for a few hours. Neutral winds, structured in layers, move up or, more commonly, down in the pre-dawn hours at rates of a few km/hour. All this may have serious implications for thermosphere/ionosphere modeling and aeronomy.
