Bulletin of the American Physical Society
53rd Annual Meeting of the APS Division of Plasma Physics
Volume 56, Number 16
Monday–Friday, November 14–18, 2011; Salt Lake City, Utah
Session CM10: Mini-conference on Nonlinear Effects in Geospace Plasmas II |
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Chair: Gurudas Ganguli, Naval Research Laboratory Room: 151 ABCG |
Monday, November 14, 2011 2:00PM - 2:40PM |
CM10.00001: Macroscopic effects of E-region turbulence: Anomalous plasma heating and conductivity Yakov Dimant, Meers Oppenheim During periods of intense geomagnetic activity, strong electric fields penetrate from the Earth's magnetosphere to the high-latitude E-region ionosphere where they form electrojets and excite plasma instabilities. These instabilities give rise to plasma density turbulence coupled to electrostatic field fluctuations, causing a nonlinear current and anomalous heating. These two effects increase ionospheric conductivities that play an important role in magnetosphere-ionosphere coupling. A quantitative understanding of turbulent conductivities and energy conversion is important to accurately model magnetic storms and substorms. Our theoretical analysis, supported by fully kinetic 3-D particle-in-cell simulations, allows one to quantify energy budget in the electrojet, anomalous plasma heating and conductivities. Our recent theoretical analysis and computer simulations allow one to quantify the energy deposition in the ionosphere, particle heating, and effects of the anomalous conductivities. Our estimates show that during strong geomagnetic storms the inclusion of the instability-induced anomalous effects may nearly double the total Pedersen conductance. This helps explain why existing global MHD codes developed for predictive modeling of space weather systematically overestimate the cross-polar cap potentials by approximately a factor of two. [Preview Abstract] |
Monday, November 14, 2011 2:40PM - 3:20PM |
CM10.00002: Plasma Physics of Sub-Auroral Ion Drifts: A turbulent Plasmaspheric Boundary Layer Evgeny Mishin We present a new scenario of the subauroral ion drifts (SAID) phenomenon based on recent magnetically conjugate Cluster-DMSP-Polar satellite observations and natural analogy with plasmoids penetrating a magnetic barrier. The SAID features are explained in terms of a turbulent boundary layer formed over the plasmapause due to a short circuit of substorm-injected plasma jets (plasmoids). Nonlinear wave-particle interactions provide fast magnetic diffusion at the plasmoid leading edge and define the circuit resistivity. As in a number of laboratory and active space experiments, nonlinear plasma processes, including but not limited to gradient-drift and current-driven instabilities, define the SAID features near the outer/poleward boundary. Near the inner/equatorward boundary and next to the channel dominate anisotropic ion-driven processes. The observed level of lower hybrid/fast magnetosonic waves is in good quantitative agreement with theoretical predictions. [Preview Abstract] |
Monday, November 14, 2011 3:20PM - 4:00PM |
CM10.00003: Simulations of 3D VLF LH/whistler nonlinear interactions in the topside ionosphere Vitaly Galinsky, Valentin Shevchenko, Evgeny Mishin, Michael Starks Recent observations of the VLF waves with frequencies close to so-called lower hybrid resonance frequency have shown that amplitudes of the observed waves are 20-30 dB smaller than those obtained in VLF propagation models. Nonlinear interactions have been suggested\footnote{E. Mishin et al. {\it Geophys. Res. Lett.}, \textbf{37}, L04101, (2010)} to account for the missing mechanism of energy losses in the current propagation models. Our study\footnote{V. Galinsky et al. {\it Geophys. Res. Lett.}, \textbf{38}, (2011)} of nonlinear induced scattering in electrostatic limit based on a novel 3D code which includes so-called vector nonlinearity pinned the above nonlinear mechanism as a very likely source of this discrepancy. The results virtually reproduce the Demeter satellite observations of intense broadband lower hybrid (LH) electrostatic waves generated by whistler-mode waves from the VLF transmitter NWC. Here we present the results of the extension of the numerical model to electromagnetic (whistler) limit and discuss possible ways of doing the modeling in realistic geometry, essential for obtaining the correct spatial distribution of attenuation of the pump wave emitted from spacecraft through various latitude/longitude as well as altitude regions of the ionosphere. [Preview Abstract] |
Monday, November 14, 2011 4:00PM - 4:30PM |
CM10.00004: Nonlinear Scattering of Lower Hybrid Waves into Whistlers David Blackwell, William Amatucci, Gurudas Ganguli, Erik Tejero, Christopher Cothran, David Walker Results are presented from ongoing experimental investigations of mode conversion between lower hybrid and whistler waves. Recent theoretical results suggest that under certain conditions the direction of the wave vector can be greatly changed with only a small change in the frequency spectrum due to wave scattering from density perturbations created by the ponderomotive force of the initial wave. The experiments are performed in the NRL Space Physics Simulation Chamber facility. The waves are excited with coaxial-ring and dipole antennas which operate from a few kHz to 1 GHz in the power range of 1 milliwatt to 10's of watts. The transmitted wave signals are received by smaller electrostatic and electromagnetic antennas which can be moved in the radial and axial directions. The phase and amplitude data is Fourier analyzed over 2-D space to give perpendicular and parallel wavelengths. A controllable magnetic field profile is used run the experiment as either an infinite plasma or resonant cavity. [Preview Abstract] |
Monday, November 14, 2011 4:30PM - 5:00PM |
CM10.00005: Formation of Whistler-Mode Cavity in the Magnetosphere by Nonlinear Induced Scattering C. Crabtree, L. Rudakov, G. Ganguli, M. Mithaiwala, V. Galinsky, V. Shevchenko In the Earth's dipole magnetic field whistler-mode waves originating in the ionosphere with frequencies relevant to pitch angle scattering of relativistic electrons quickly propagate toward the hydrogen lower-hybrid resonant surface in the magnetosphere. The perpendicular wave-vector increases such that wave packets become quasi-electrostatic, experience large Landau and collisional damping, and quickly become less effective at pitch angle scattering. Recently Ganguli et al. [1] showed that through nonlinear (NL) induced scattering by thermal electrons in low $\beta$ plasmas the direction of the wave-vector of whistler-mode waves can change substantially with only a small change in the frequency. Here we apply this mechanism to demonstrate that when the turbulent whistler-mode energy density is large enough, NL scattering allows a portion of whistler-mode waves to return toward the ionosphere and reduces the perpendicular wave-vector such that the corresponding linear damping is reduced and the wave's ability to pitch angle scatter relativistic electrons is revived. Through multiple NL scatterings and ionospheric reflections a long-lived wave cavity in the Earth's magnetosphere may be formed with the appropriate properties to efficiently pitch-angle scatter trapped relativistic electrons.\\[4pt] [1] Ganguli et al. PoP (2010) [Preview Abstract] |
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