Bulletin of the American Physical Society
54th Annual Meeting of the APS Division of Plasma Physics
Volume 57, Number 12
Monday–Friday, October 29–November 2 2012; Providence, Rhode Island
Session CO6: Space Plasma Physics |
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Chair: Gregory Howes, University of Iowa Room: 555AB |
Monday, October 29, 2012 2:00PM - 2:12PM |
CO6.00001: Kinetic-Alfven turbulence in the dissipation (dispersion) range of the solar wind Stanislav Boldyrev, Jean Carlos Perez A model for strong kinetic Alfv\'en plasma turbulence at scales smaller than the ion gyroscale is proposed. It is argued that magnetic and density fluctuations are concentrated mostly at two-dimensional structures, which leads to their Fourier energy spectra $E(k_\perp)\propto k_{\perp}^{-8/3}$, where $k_\perp$ is the wave-vector component normal to the strong background magnetic field. The results are shown to be in good agreement with numerical simulations, and they may provide an explanation for recent observations of magnetic and density fluctuations in the solar wind at sub-proton scales. [Preview Abstract] |
Monday, October 29, 2012 2:12PM - 2:24PM |
CO6.00002: Model of Magnetic Discontinuities in the Solar Wind Vladimir Zhdankin, Stanislav Boldyrev, Joanne Mason The statistical properties of magnetic discontinuities, as measured by fluctuations in the magnetic field direction, are studied in the solar wind and in direct numerical simulations of incompressible magnetohydrodynamic (MHD) turbulence. We find an excellent agreement in the probability density function (pdf) of angular fluctuations for the two cases if we choose the MHD guide field to rms fluctuations ratio to be approximately $B_0/b_{rms} = 0.3$. The strong agreement between the two cases suggests that there is a similar underlying mechanism describing them, possibly associated with turbulence. We develop an analytical model to describe the observed pdfs, and we address the scalings of the resulting pdfs with the point-separation in the solar wind observations and in the numerical simulations. This work was supported by the US DoE grants DE-FG02-07ER54932, DE-SC0003888, DE-SC0001794, the NSF Grant PHY-0903872, the NSF/DOE Grant AGS-1003451, and the NSF Center for Magnetic Self-organization in Laboratory and Astrophysical Plasmas at the University of Wisconsin-Madison and the University of Chicago, as well as by an allocation of advanced computing resources at the National Institute for Computational Sciences. [Preview Abstract] |
Monday, October 29, 2012 2:24PM - 2:36PM |
CO6.00003: Pickup proton instabilities and scattering in the outer heliosheath: Hybrid simulations S. Peter Gary, Kaijun Liu, Eberhard Moebius, Dan Winske The consequences of injection of pickup protons perpendicular to a background magnetic field in a homogeneous, collisionless plasma are studied using one-dimensional hybrid simulations. Freshly ionized protons are continuously injected into the simulations at constant rates and relative speeds approaching conditions in the outer heliosheath. The pickup protons initially form a ring-velocity distribution unstable to the electromagnetic proton cyclotron instability which leads to enhanced magnetic fluctuations near and below the proton cyclotron frequency. The magnetic fluctuations first have a quiescient phase, followed by a phase of exponential growth. There is little proton scattering during the quiescient phase, but rapid pitch-angle scattering of the pickup protons toward an isotropic velocity shell distribution during the exponential growth phase. The pickup proton density at onset of rapid scattering increases with the pickup proton injection rate; scaling relations for the onset density and the subsequent scattering rate are derived from the simulations. These results suggest that significant scattering of pickup protons in the outer heliosheath occurs in a relatively limited spatial regime close to the heliopause. [Preview Abstract] |
Monday, October 29, 2012 2:36PM - 2:48PM |
CO6.00004: Using Plasma Metrics as a Diagnosis of Solar Wind Mode Composition Kristopher Klein, Gregory Howes, Jason TenBarge We present a suite of plasma metrics, including electric and magnetic field polarizations, helicities, and compression ratios, which taken together can be used as a means of identifying the presence as well as type of linear wave modes in a turbulent plasma such as the solar wind. The importance of the wavevector size and angle as well as various plasma parameters such as $\beta$ and $T_\perp/T_\parallel$ are taken into account in determining the expected behavior of these metrics. These metrics are then examined in synthetic data prepared from spectra of linear kinetic eigenmodes and non-linear gyrokinetic simulations. A comparison between synthetic and in-situ data taken from the solar wind could help to elucidate the role of linear and non-linear physics in the turbulent transfer of energy from large to small scale fluctuations. [Preview Abstract] |
Monday, October 29, 2012 2:48PM - 3:00PM |
CO6.00005: ABSTRACT WITHDRAWN |
Monday, October 29, 2012 3:00PM - 3:12PM |
CO6.00006: A Free-Electron-Laser Model for Chorus Wave Chirp in the Earth's Magnetosphere A. Rualdo Soto-Chavez, Amitava Bhattacharjee Chorus are a form of very low frequency waves that propagate in the Earth's magnetosphere. They are responsible for the acceleration of electrons in the Van Allen radiation belts and for electron scattering leading to atmospheric precipitations. One of the persistent features of chorus waves is the chirp in their frequency. Based on an extension of our recent model of chorus as a high-gain free-electron laser (Phys. Plasmas 19, 010701 (2012)), we find an analytical expression for the chorus frequency sweep (chirp) that is in agreement with observations. The new calculation yields a full asymptotic expression for the wave magnetic field and phase. We demonstrate that by considering propagation effects, that is, relative velocity differences between electrons and the radiation field, a modification on the field phase is generated. This modification is manifested as a chirp in frequency. We show that spatial inhomogeneities of the magnetic field do not play an essential role in chirp generation. [Preview Abstract] |
Monday, October 29, 2012 3:12PM - 3:24PM |
CO6.00007: In situ measurements of Alfvenic waves in the interplanetary coronal mass ejections Chijie Xiao, Honggang Wang, Qingsheng Li, Haoming Liang, Guiping Zhou, Xiaogang Wang, Zuyin Pu, Xiaoyi Yang As for the present situation of coronal mass ejection (CME) triggering models, the distributions of Alfven waves in flux ropes are different from model to model, and thus examining those distributions in interplanetary coronal mass ejection (ICME) is an effective way to connect ICME observations with these theoretical models of CME triggering. However, previous observations of Alfv\'{e}nic fluctuations in ICMEs were rare with locations ranging from 0.3 AU to 0.68 AU only, which is usually explained as rapid dissipation of those remnant waves. Here we present a preliminary statistical study of Alfven waves in magnetic clouds (MC) near 1 AU, \textit{in situ} detected by WIND. The Alfven waves, slow waves, as well as the power spectral densities of magnetic fluctuation in the MC, are identified and compare with those modes in ambient solar wind. The results will also be helpful for studies of CME theories and ICME thermodynamics. [Preview Abstract] |
Monday, October 29, 2012 3:24PM - 3:36PM |
CO6.00008: Modelling of the CHAMP satellite plasma observations within the space environment Richard Marchand, Claudia Stolle, Marcin Pilinski The interaction of CHAMP with ionospheric plasma is modelled using a particle in cell (PIC) simulation code, with a particular focus on Langmuir probe measurements. CHAMP was launched in 2000 with the mission to measure long time variations in a number of geophysical variables. It had several scientific instruments, including magnetometers, ion drift meters, an accelerometer and a large rectangular Planar Langmuir Probe (PLP). Measurements made with the PLP over the years show systematic anomalies in the estimated electron temperature at certain latitudes. A possible explanation might come from an interplay between the orientation of the magnetic field in the satellite rest frame, and wake effects from certain components of the spacecraft. This hypothesis is tested using PTetra, which uses an unstructured tetrahedral mesh, while treating all species fully kinetically, with physical charges and masses. The model accounts for satellite charging, for the possibility of relative biasing between different components and, when the satellite is exposed to solar radiation, for photoelectron emission. Simulations are carried out for a number of representative positions in orbit, and computed characteristics for the PLP are compared directly with measurements. [Preview Abstract] |
Monday, October 29, 2012 3:36PM - 3:48PM |
CO6.00009: Modeling of current characteristics of Segmented Langmuir Probe on DEMETER Nadia Imtiaz, Richard Marchand We model current characteristics of a Segmented Langmuir probe mounted on DEMETER satellite. The probe is used to measure electron density and temperature in the ionosphere on DEMETER at altitudes of 700 km.It also serves as a Mach probe and used to measure the plasma flow velocities in satellite frame of reference.The probe is partitioned into seven segments: six electrically insulated spherical caps and a Guard electrode (sphere). Comparisons are made between the model predictions and measurements for characteristics of various segments for actual ionospheric plasma conditions encountered along DEMETER orbit. Segment characteristics are computed numerically with PTetra, a 3 D PIC simulation code. The model accounts for several physical effects of importance in the interaction of spacecraft with the space environment e.g. satellite charging, photoelectron and secondary electron emission. The supersonic flow of plasma results in different characteristics for different segments of the probe. This anisotropy in turn can be used to infer the velocity of the background plasma. It is observed in that a positive bias can significantly modify plasma sheath region and wake formation around the probe.Computed characteristics and their angular anisotropy are compared with measurements. [Preview Abstract] |
Monday, October 29, 2012 3:48PM - 4:00PM |
CO6.00010: Guerilla Science: Outreach at music and art festival Mark Rosin Guerilla Science a non-profit science education organization that, since 2007, has brought live events to unconventional venues for science, such as music festivals, art galleries, banquets, department stores and theaters. Guerilla Science sets science free by taking it out of the lab and into the traditional domains of the arts. By producing events that mix science with art, music and play, they create unique opportunities for adult audiences to experience science in unorthodox ways, such as interactive events, games, live experiments, demonstrations and performances by academics, artists, musicians, actors, and professional science communicators. Much of Guerilla Science's work has focused on astrophysical and terrestrial plasmas, and this presentation will provide an overview of Guerilla Science's work in this area. Guerilla Science has produced over twenty events, receiving international media coverage, and directly reached over fifteen thousand members of the public. [Preview Abstract] |
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