Double layers on auroral field lines

Time-stationary solutions to the Vlasov-Poisson equation for ion holes and double layers were examined along with particle simulations which pertain to recent observations of small amplitude (e phi)/t sub e approx. 1 electric field structures on auroral field lines. Both the time-stationary analysis and the simulations suggest that double layers evolve from holes in ion phase space when their amplitude reaches (e phi)/t sub e approx. 1. Multiple small amplitude double layers which are seen in long simulation systems and are seen to propagate past spacecraft may account for the acceleration of plasma sheet electrons to produce the discrete aurora

Weak double layers in the auroral ionosphere

Previous work on the evolution of weak double layers in a hydrogen plasma was extended to include H(+) and O(+) with relative drift. The relative drift between hydrogen and oxygen ions due to a quasi-static parallel electric field gives rise to a strong linear fluid instability which dominates the ion-acoustic mode at the bottom of the auroral acceleration region. This ion-ion instability can modify ion distributions at lower altitudes and the subsequent nonlinear evolution of weak double layers at higher altitudes in the ion-acoustic regime. Ion hole formation can occur for smaller relative electron-ion drifts than seen in previous simulations, due to the hydrogen-oxygen two-stream instability. This results in local modification of the ion distributions in phase space, and a partial filling of the valley between the hydrogen and oxygen peaks, which would be expected at higher altitudes on auroral field lines. The observed velocity diffusion does not necessarily preclude ion hole and double layer formation in hydrogen in the ion-acoustic regime. These simulation results are consistent with the experimentally measured persistence of separate hydrogen and oxygen peaks, and the observation of weak double layers above an altitude of 3000 km on auroral field lines

Nonlinear finite-Larmor-radius effects in reduced fluid models

The polarization and magnetization effects associated with the dynamical reduction leading to the nonlinear gyrokinetic Vlasov-Maxwell equations are shown to introduce nonlinear finite-Larmor-radius effects into a set of nonlinear reduced-fluid equations previously derived by Lagrangian variational method [A.J. Brizard, Phys. Plasmas 12, 092302 (2005)]. These intrinsically nonlinear FLR effects, which are associated with the transformation from guiding-center phase-space dynamics to gyrocenter phase-space dynamics, are different from the standard FLR corrections associated with the transformation from particle to guiding-center phase-space dynamics. We also present the linear dispersion relation and results from a nonlinear simulation code using these reduced-fluid equations. The simulation results (in both straight and dipole geometries) demonstrate that the equations describe the coupled dynamics of Alfven and sound waves and that the total simulation energy is conserved.Comment: 18 pages, 6 figure

Cycle-to-cycle variation of the combustion process in a diesel engine powered by different fuels

We have studied the fluctuations in mean indicated pressure (MIP) in a diesel engine powered by different fuels. Three alternative fuels and the regular diesel oil (RD) were tested. The alternative fuels are: (1) mixture of fatty acid methyl esters (FAME) and anhydrous ethanol (ET), (2) mixture of FAME and ethyl tertiary-butyl ether (ETBE), and (3) mixture of RD and ETBE. Using statistical and wavelet analyses, we investigated the cycle-to-cycle MIP variations for each fuel, at three engine speeds of 1200, 1600 and 2000 rpm. The results for the alternative fuels were compared with those for RD. At all three speeds, the MIP variations for the alternative fuels were found to exhibit strong periodicities of 64-256 cycles, and these periodicities persist over many engine cycles, whereas shorter-term periodicities at 2-32 cycles appeared to be intermittent. In the case of RD, the MIP variations with longer periodicities appeared only at the highest engine speed but intermittent fluctuations of 2-32 cycles are present at all three speeds. Among the four fuels considered, the MIP variations for the RD were found to be closest to the Gaussian white noise

Developing service promises accurate space weather forecasts in the future

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94931/1/eost10236.pd

Magnetospheric Cavity Modes Driven by Solar Wind Dynamic Pressure Fluctuations

We present results from Lyon-Fedder-Mobarry (LFM) global, three-dimensional magnetohydrodynamic (MHD) simulations of the solar wind-magnetosphere interaction. We use these simulations to investigate the role that solar wind dynamic pressure fluctuations play in the generation of magnetospheric ultra-low frequency (ULF) pulsations. The simulations presented in this study are driven with idealized solar wind input conditions. In four of the simulations, we introduce monochromatic ULF fluctuations in the upstream solar wind dynamic pressure. In the fifth simulation, we introduce a continuum of ULF frequencies in the upstream solar wind dynamic pressure fluctuations. In this numerical experiment, the idealized nature of the solar wind driving conditions allows us to study the magnetospheric response to only a fluctuating upstream dynamic pressure, while holding all other solar wind driving parameters constant. The simulation results suggest that ULF fluctuations in the solar wind dynamic pressure can drive magnetospheric ULF pulsations in the electric and magnetic fields on the dayside. Moreover, the simulation results suggest that when the driving frequency of the solar wind dynamic pressure fluctuations matches one of the natural frequencies of the magnetosphere, magnetospheric cavity modes can be energized.Comment: 2 figure

Cycle-to-cycle variation of the combustion process in a diesel engine powered by different fuels

We have studied the fluctuations in mean indicated pressure (MIP) in a diesel engine powered by different fuels. Three alternative fuels and the regular diesel oil (RD) were tested. The alternative fuels are: (1) mixture of fatty acid methyl esters (FAME) and anhydrous ethanol (ET), (2) mixture of FAME and ethyl tertiary-butyl ether (ETBE), and (3) mixture of RD and ETBE. Using statistical and wavelet analyses, we investigated the cycle-to-cycle MIP variations for each fuel, at three engine speeds of 1200, 1600 and 2000 rpm. The results for the alternative fuels were compared with those for RD. At all three speeds, the MIP variations for the alternative fuels were found to exhibit strong periodicities of 64-256 cycles, and these periodicities persist over many engine cycles, whereas shorter-term periodicities at 2-32 cycles appeared to be intermittent. In the case of RD, the MIP variations with longer periodicities appeared only at the highest engine speed but intermittent fluctuations of 2-32 cycles are present at all three speeds. Among the four fuels considered, the MIP variations for the RD were found to be closest to the Gaussian white noise

3D Magnetic Reconnection with a spatially confined X-line extent -- Implications for Dipolarizing Flux Bundles and the Dawn-Dusk Asymmetry

Using 3D particle-in-cell (PIC) simulations, we study magnetic reconnection with the x-line being spatially confined in the current direction. We include thick current layers to prevent reconnection at two ends of a thin current sheet that has a thickness on an ion inertial (di) scale. The reconnection rate and outflow speed drop significantly when the extent of the thin current sheet in the current direction is < O(10 di). When the thin current sheet extent is long enough, we find it consists of two distinct regions; an inactive region (on the ion-drifting side) exists adjacent to the active region where reconnection proceeds normally as in a 2D case. The extent of this inactive region is ~ O(10 di), and it suppresses reconnection when the thin current sheet extent is comparable or shorter. The time-scale of current sheet thinning toward fast reconnection can be translated into the spatial-scale of this inactive region; because electron drifts inside the ion diffusion region transport the reconnected magnetic flux, that drives outflows and furthers the current sheet thinning, away from this region. This is a consequence of the Hall effect in 3D. While this inactive region may explain the shortest possible azimuthal extent of dipolarizing flux bundles at Earth, it may also explain the dawn-dusk asymmetry observed at the magnetotail of Mercury, that has a global dawn-dusk extent much shorter than that of Earth.Comment: 9 pages, 9 figures, submitted to JGR on 01/23/201

The Earth: Plasma Sources, Losses, and Transport Processes

This paper reviews the state of knowledge concerning the source of magnetospheric plasma at Earth. Source of plasma, its acceleration and transport throughout the system, its consequences on system dynamics, and its loss are all discussed. Both observational and modeling advances since the last time this subject was covered in detail (Hultqvist et al., Magnetospheric Plasma Sources and Losses, 1999) are addressed