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 TM7: Miniconference on the Plasma Physics of the Solar Wind: From Parker (1958) to the Present III |
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Chair: Marco Velli, Jet Propulsion Laboratory Room: Pegasus |
Thursday, November 20, 2008 9:30AM - 10:00AM |
TM7.00001: The Emerging New View of the Outer Heliosphere J.R. Jokipii In August, 2007, Voyager 2 crossed the heliospheric termination shock 84 AU from the Sun, following Voyager 1, which crossed the shock in late 2004 at 94 AU. They obtained {\it in situ} data which, combined with remote observations, have transformed our understanding of the outer heliosphere. The existence of the solar wind and heliosphere was not known prior to 50 years ago. Over the intervening decades, remote and {\it in situ} observations together with theory and modeling established the heliosphere and gradually revealed much of its structure and dynamics. The solar wind is radial and supersonic from very near the Sun out to the termination shock, where it becomes subsonic. The large-scale structure of the plasma and magnetic field {\it inside} of the shock are determined by the initial and boundary conditions near the Sun, and depend very little on the interstellar medium. Cosmic rays and neutral particles have served as invaluable probes of distant regions, permitting a reasonable picture of the global heliosphere to be assembled, but even the distance scales remained highly uncertain. The {\it in situ} measurements by the Voyagers answered many question but, inevitably, raised others. Both Voyagers are now moving further from the Sun, taking measurements in the heliosheath and heading toward the heliopause where the first {\it in situ} measurements of the interstellar plasma will be taken. In this talk I will summarize the current picture and discuss some of the new and ongoing issues. [Preview Abstract] |
Thursday, November 20, 2008 10:00AM - 10:30AM |
TM7.00002: 3D Modeling of the Interaction of the Solar Wind with the Interstellar Medium Gary Zank The presence of the interplanetary magnetic field and current sheet and the interstellar magnetic field render the interaction of the solar wind with the local interstellar medium intrinsically 3D. The inclusion of magnetic fields into the problem is therefore challenging from a simulation perspective. Furthermore, the solar wind is itself intrinsically time-dependent on a range of time scales and one has to ideally model the interaction as time variable. Finally, to further complicate matters, interstellar neutral gas, primarily H, is coupled to both LISM and interplanetary plasma through charge exchange and it has been shown in the context of simpler 2D models that neutral H can modify the global structure of the heliosphere profoundly. We discuss here the extension of earlier 2D models of the solar wind-LISM interaction to include interplanetary and interstellar magnetic fields, i.e., modeling the 3D heliosphere. We will demonstrate the profoundly important role that neutral H continues to play in determining the structure of the global heliosphere, and the corresponding back-reaction on the neutral H distribution. This will be addressed in the context of both multi-fluid and kinetic models that have been developed by our group. We will discuss the origin of energetic neutral atoms using an approach based on a kappa distribution description of interplanetary plasma. [Preview Abstract] |
Thursday, November 20, 2008 10:30AM - 10:55AM |
TM7.00003: X-ray Tomography of the Outer Heliosphere Mikhail Medvedev, T. Cravens, I. Robertson, G. Zank, V. Florinski The heliosphere is glowing in X-rays due to charge-exchange (CX) collisions between solar wind ions and neutrals from the ISM. The overall appearance of the X-ray glow is determined by the interaction of the Solar wind and the local ISM. Spectra deliver information on the Solar wind parameters (e.g., temperatures and densities of the minor species -- highly stripped ions) and the details of the Solar wind interaction with neutrals. Using numerical models for the heliosphere, we traced the CX evolution of 45 different solar wind ions along the wind stream-lines. The evolution from high- to low-ionization states is clearly seen, thus manifesting the collisional thickness effect on the outer heliosphere composition. From CX transitions, we determine the X-ray emissivity and create surface brightness and spectral maps for any viewing direction (for both the inside-out and outside view). The evolution of the wind ion-composition and the accompanying spectral changes across the heliosheath (from nose to tail) are remarkable and can serve as a diagnostic for the wind-ISM interaction. Chandra and XMM-Newton are well suited for this task. Similar models can be made for astrospheres of nearby Sun-like stars. [Preview Abstract] |
Thursday, November 20, 2008 10:55AM - 11:20AM |
TM7.00004: Physics of the energy cascade process in solar wind turbulence and comparisons between theory and observations J.J. Podesta The solar wind is the only astrophysical plasma directly accessible to in-situ plasma measurements and is an important testing ground for theories of turbulence in collisionless astrophysical plasmas. The physics of the energy cascade process and its relationship to the cross-helicity cascade and the wave-vector anisotropy in Fourier space are among the most fundamental aspects of the subject and are believed to have important practical consequences for the heating of the solar wind and the solar corona. Several different phenomenological theories of incompressible MHD turbulence have appeared in the literature and it is not known which one, if any, correctly describe the energy cascade process in the solar wind. Detailed comparison between turbulence theories and solar wind measurements is the only way to validate any theory of solar wind turbulence. In this presentation, a brief review is given of recent comparisons between phenomenological turbulence theories and solar wind measurements. Some successes and outstanding problems are highlighted. Topics to be discussed include the applicability of the Iroshnikov-Kraichnan theory for describing the energy cascade in the solar wind, the possible scale-dependent alignment between velocity and magnetic field fluctations in the inertial range, and attempts to investigate critical-balance in the solar wind as formulated by Goldreich and Sridhar. [Preview Abstract] |
Thursday, November 20, 2008 11:20AM - 11:45AM |
TM7.00005: Interaction of Energetic Particles with Discontinuities Upstream of Strong Shocks Mikhail Malkov, Patrick Diamond Acceleration of particles in strong astrophysical shocks is known to be accompanied and promoted by a number of instabilities which are driven by the particles themselves. One of them is an acoustic (also known as Drury's) instability driven by the pressure gradient of accelerated particles upstream. The generated sound waves naturally steepen into shocks thus forming a shocktrain. Similar magnetoacoustic or Alfven type structures may be driven by pick-up ions, for example. We consider the solutions of kinetic equation for accelerated particles within the shocktrain. The accelerated particles are assumed to be coupled to the flow by an intensive pitch-angle scattering on the self-generated Alfven waves. The implications for acceleration and confinement of cosmic rays in this shock environment will be discussed. [Preview Abstract] |
Thursday, November 20, 2008 11:45AM - 12:10PM |
TM7.00006: Turbulence and Solar Energetic Particles in coronal shocks Luis Gargate, Ricardo Fonseca, Robert Bingham, Luis Silva We use a kinetic ion / fluid electron numerical simulation approach (dHybrid) to study the propagation of a Coronal Mass Ejection (CME) shock in the outer corona environment. We consider a CME driving a fast magnetosonic shock, with shock parameters known to correlate well with Solar Energetic Particle (SEP) events. For these events, SEPs with energies up to several hundred MeV are commonly measured at 1 AU. Results from dHybrid show the self-consistent formation of Alfv\`{e}n waves upstream of the shock, with turbulence building up due to wave breaking, and strong particle acceleration. Energy gains of up to 110 times the maximum possible energy gain in one shock crossing are measured. For the most accelerated particles, the observed energy gain is $\sim $ quadratic in time, during the simulation time frame, consistent with surfatron acceleration, while for another less energetic set of particles the energy scales with t\^{}1/2 consistent with diffusive shock acceleration. The observed energy gain would allow for a typical solar wind proton to reach an energy of hundreds of MeV in some minutes. A thorough discussion about the observed acceleration mechanisms will be presented.~ [Preview Abstract] |
Thursday, November 20, 2008 12:10PM - 12:35PM |
TM7.00007: Using Solar Wind Data to Establish an Upper Bound on the Photon Mass D.D. Ryutov The currently accepted limit on the photon mass, $m<10^{-49}g$ (W.-M. Yao and Particle Data Group. J. Phys. G, 33, 1, 2006), has been established based on the analysis of the Solar wind structure at the Earth orbit (D.D. Ryutov. PPCF, 39, A73, 1997). This approach is based on the analysis of the additional terms that appear in the MHD equations if m is finite. By using the observed data regarding an average magnetic field of the Solar wind, one finds that, at a large-enough photon mass these additional terms make the flow pattern completely different from really observed. When applied to the Solar wind data at the Pluto orbit, the same approach leads to an improved estimate, $m<1.5\times 10^{-51}g$ (D.D. Ryutov. PPCF, 49, B429, 2007). We consider data obtained by the Voyager mission in the zone between the Pluto orbit and the termination shock to further improve the estimate and find that the upper bound can be reduced by another factor of 5. Prepared by LLNL under Contract DE-AC52-07NA27344. [Preview Abstract] |
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