Bulletin of the American Physical Society
50th Annual Meeting of the Division of Plasma Physics
Volume 53, Number 14
Monday–Friday, November 17–21, 2008; Dallas, Texas
Session PM7: Miniconference on the Plasma Physics of the Solar Wind: From Parker (1958) to the Present II |
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Chair: Gary Zank, University of Alabama in Huntsville Room: Pegasus |
Wednesday, November 19, 2008 2:00PM - 2:30PM |
PM7.00001: The Solar Wind: Then and Now Joseph Hollweg Early spacecraft data in the 1960s revealed solar wind properties which could not be well-explained by models in which the electron pressure gradient was the principal accelerating force. The Alfven waves discovered around 1970 were thought for a while to provide additional energy and momentum, but they ultimately failed to explain the rapid acceleration of the fast wind close to the Sun. By the late 1970s, various data were suggesting the importance of the ion-cyclotron resonance far from the Sun. This notion was soon applied to the acceleration region close to the Sun. The models which resulted suggested that the fast wind could be driven mainly by the proton pressure gradient. Since the mid 1990s, SOHO has provided remarkable data which have verified some of the predictions of these theories, and given impetus to studies of the ion cyclotron resonance as the principal mechanism for heating the coronal holes, and ultimately driving the fast wind. After a historical review, we discuss the basic ideas behind current research, emphasizing the particle kinetics. We discuss remaining problems, especially the source of the ion-cyclotron resonant waves and the nature of coronal turbulence. [Preview Abstract] |
Wednesday, November 19, 2008 2:30PM - 3:00PM |
PM7.00002: Kinetic Dissipation of Solar Wind Turbulence Gregory Howes, Steve Cowley, William Dorland, Gregory Hammett, Eliot Quataert, Alexander Schekochihin, Tomoya Tatsuno The identification of the key physical mechanisms by which the turbulence in the solar wind is dissipated remains a fundamental unsolved problem in heliospheric physics. I will present a theoretical model of the turbulent cascade from the large scales of energy injection, through the transition to kinetic turbulence at the scale of the ion Larmor radius, down to the electron scales at which the turbulent energy must ultimately be dissipated. Kinetic simulations of the magnetized turbulent cascade in the solar wind at the scale of the ion Larmor radius support the hypothesis that the frequencies of turbulent fluctuations in the solar wind remain well below the ion cyclotron frequency both above and below the ion gyroscale. I will present the first nonlinear kinetic simulations of kinetic Alfv\'en wave turbulence in the dissipation range from the ion to electron Larmor radius scales. [Preview Abstract] |
Wednesday, November 19, 2008 3:00PM - 3:25PM |
PM7.00003: Short-wavelength turbulence in the solar wind: whistlers vs kinetic Alfven waves S. Peter Gary The long-wavelength plasma turbulence of the inertial range has been studied in detail via both solar wind observations and MHD model computations. At relatively short wavelengths, at and beyond the proton inertial length, solar wind magnetic spectra become steeper, implying different physics. This regime has been less studied and is less well understood than the inertial range; however, short-wavelength fluctuations are the key to learning how collisionless plasma turbulence is dissipated and its energy transfered to collisionless plasmas. At present there is a controversy about the primary constituent of short-wavelength turbulence in the solar wind; some advocate high-frequency whistler fluctuations while others maintain that lower-frequency kinetic Alfv\'en waves are the major contributors. This presentation will review observational and computational results that relate to this controversy, and will provide new theoretical results which may suggest future data analysis and simulations to address this challenging problem. [Preview Abstract] |
Wednesday, November 19, 2008 3:25PM - 3:50PM |
PM7.00004: Turbulence in the Solar Corona and Solar Wind and the ``Parallel Energy Cascade'' Benjamin Chandran Observations of perpendicular ion heating and energetic particle scattering suggest that a ``parallel energy cascade'' is operating in the solar corona and solar wind, whereby wave-wave nonlinearities generate a population of small-scale fluctuations that vary more rapidly along the background-magnetic-field direction than in the directions perpendicular to the background magnetic field. This suggestion from observations is seemingly at odds with theoretical studies of incompressible MHD turbulence, which find that wave-wave nonlinearities generate small-scale structures that vary most rapidly perpendicular to the (local) background magnetic field. However, because the corona and solar wind are compressible plasmas, the energy cascade in the corona and solar wind is significantly different than in the incompressible case. In this presentation, I will discuss new results on compressible MHD turbulence that describe how Alfven waves, fast magnetosonic waves, and slow magnetosonic waves interact with one another to generate a parallel energy cascade. [Preview Abstract] |
Wednesday, November 19, 2008 3:50PM - 4:15PM |
PM7.00005: Kinetic dissipation and anisotropic heating in a turbulent collisionless plasma Michael Shay, Tulasi Parashar, Paul Cassak, Sergio Servidio The nature of the collisionless dissipation at small scales in solar wind turbulence is a problem of critical importance. To gain some insight into the nature of the dissipation, we simulate the Orszag-Tang vortex using collisionless hybrid simulations. In magnetohydrodynamics this configuration leads rapidly to broadband turbulence. At small scales, differences from magnetohydrodynamics arise, as energy dissipates into heat almost exclusively through the magnetic field. A key result is that protons are heated preferentially in the plane perpendicular to the mean magnetic field, creating a proton temperature anisotropy as is observed in the corona and solar wind. Preliminary results about the dissipation scale and the distribution of energies at different length scales are discussed. [Preview Abstract] |
Wednesday, November 19, 2008 4:15PM - 4:40PM |
PM7.00006: The Effect of Magnetic Turbulence Energy Spectra on the Heating of the Solar Wind C.S. Ng, A. Bhattacharjee, P.A. Isenberg, D. Munsi, C.W. Smith Recently, a phenomenological solar wind heating model based on a turbulent energy cascade prescribed by the Kolmogorov theory has produced reasonably good agreement with observations on proton temperatures out to distances around 70 AU, provided the effect of turbulence generation due to pickup ions is included in the model. In the present study, we have incorporated in the heating model the energy cascade rate based on Iroshnikov-Kraichnan (IK) scaling, derivable from incompressible magnetohydrodynamics. We show that the IK cascade rate can also produce good agreement with observations, with or without the inclusion of pickup ions. This effect is confirmed both by integrating the model using average boundary conditions at 1 AU, and by applying a method [Smith et al., Astrophys. J. {\bf 638}, 508 (2006)] that uses directly observed values as boundary conditions. These results suggest that if the observed proton heating rates are used to constrain theories of turbulence, there is room in the model to include spectral scalings of magnetic fluctuations varying from IK to Kolmogorov. [Preview Abstract] |
Wednesday, November 19, 2008 4:40PM - 5:05PM |
PM7.00007: Modeling the Heating of the Solar Wind: Turbulence and Electron Heat Conduction Ben Breech, William Matthaeus, Steven Cranmer, Justin Kasper We employ a turbulence transport model to explore the heating of the solar wind by turbulence. The essential effect is the deposition of internal energy associated with kinetic effects that terminate the MHD cascade at small scales. A simple transport model determines the radial dependence of three (coupled) quantities that characterize interplanetary turbulence---the energy per unit mass, the cross helicity or Alfv\'enicity, and a similarity length scale. Two other integrated quantities, the electron and proton temperatures, are modified by heat deposition through turbulent dissipation, modeled through a von Karman -- Taylor phenomenological model. The involvement of the electron temperature raises several new and interesting issues; How should the electron heat flux be modeled? How long is the collision time between protons and electrons? How much turbulence dissipation goes into heating the electrons and how much goes into heating the protons? Using Voyager and Ulysses observational data, we begin to explore these issues. We find that the inclusion of electron conduction effects provides a more complete description of the solar wind plasma and may help explain the observed temperature profiles. [Preview Abstract] |
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