Abstract.The evolution of two counter-streaming electron beams is shown by means of 2-D kinetic simulations to lead to electron distributions and coherent localized bipolar plasma wave structures with features similar to those measured by the FAST satellite in the auroral ionosphere. Electrostatic whistler waves are generated at later times when the bipolar structures begin to lose coherence and break up in the dimension transverse to the geomagnetic field.

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The nonlinear stage of the two-stream instability in a 2D magnetized plasma produces electron phase-space tubes, the counterpart of phase-space holes in a 1D plasma. These tubes align primarily perpendicular to the magnetic field B 0 and have self-consistent bipolar electric fields parallel to B 0. Such bipolar electric fields have recently been observed in four different regions of the Earth's space plasma environment. Massively parallel 2D kinetic simulations show the dynamics of tube formation, evolution, and breakup, accompanied by the generation of electrostatic whistler waves. We focus on the breakup of the tubes and describe a new numerical study of tube stability.

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Abstract.Electron phase-space holes are regions of depleted electron density commonly generated during the nonlinear stage of the two-stream instability. Recently, bipolar electric field structures a signature of electron holes have been identified in the acceleration region of the auroral ionosphere. This paper compares the evolution of electron holes in 2-D and 3-D using massively-parallel PIC simulations. In 2-D, the holes decay after hundreds of plasma periods while emitting electrostatic whistler waves. In the 3-D simulations, electron holes also go unstable and generate whistlers but, due to physical processes not present in 2-D, energy flows out of the whistlers and into highly perpendicular lower hybrid modes. As a result of this difference, 3-D holes do not decay as far as 2-D holes. The differences between 2-D and 3-D evolution may have important implications for hole longevity and wave generation in the auroral ionosphere.

[1] Radar data of non-specular meteor trails shows two clear and consistent features: (1) non-specular meteor trails are observed from a narrower altitude range than are head echoes and (2) an approximately 20 ms delay between meteor head echoes and trail radar scatter. This paper shows that both features can result from meteor trail plasma instability. Simulations have demonstrated that trails often develop Farley-Buneman/gradient-drift (FBGD) waves which become turbulent and generate field aligned irregularities (FAI). Plasma stability analysis shows that trails are only unstable within a limited altitude range, matching the observed altitudes of non-specular trails to within 1 -2 km. The simulations show that instability develops into turbulence in $20 ms and appears to be the only meteor trail process that can explain both the observed delay between head and trail echoes and generate coherent scatter at both UHF and VHF wavelengths.

Abstract. Currents flowing in the Earth's ionospheric electrojets often develop Farley-Buneman (FB) streaming instabilities and become turbulent. The resulting electron density irregularities cause these regions to readily scatter VHF and UHF radar signals. Many of the observed characteristics of these radar measurements result from the nonlinear behavior of this plasma. This paper describes a set of high-resolution, 2-D, fully kinetic simulations of electric field driven turbulence in the electrojet. These show the saturated amplitude of the waves; coupling between linearly growing modes and damped modes; the evolution of the system from dominance by shorter (1 m-5 m) to longer (10 m-200 m) wavelength modes; and the propagation of the dominant modes at phase velocities that lie below the linearly predicted phase velocity and close to but slightly above the acoustic velocity. These simulations reproduce many of the observational characteristics of type 1 waves. They provide information useful in accurately modeling FB turbulence and demonstrate the significant progress we have made in simulating the electrojet.

Abstract.Radars frequently detect meteor trails created by the ablation of micro-meteoroids between 70 and 120 km altitude in the atmosphere. Plasma simulations show that density gradients a.t the edges of meteor trails drive gradientdrift instabilities which develop into waves with perturbed electric fields often exceeding hundreds of mV/m. These waves create an anomalous cross-field diffusion that can exceed the cross-field (2_ B) ambipolar diffusion by an order of magnitude. The characteristics of the instabilities and anomalous diffusion depend on the trail altitude, latitude, and density gradient. A simple relation defines the minimum altitude at which meteor trail density gradients drive plasma instabilities and anomalous diffusion. These results impact a number of meteor radar studies, including those that use diffusion rates to determine trail altitude, and atmospheric temperature.