Bulletin of the American Physical Society
57th Annual Meeting of the APS Division of Plasma Physics
Volume 60, Number 19
Monday–Friday, November 16–20, 2015; Savannah, Georgia
Session JM10: Mini-Conference: Nonlinear Effects in Geospace Plasmas II |
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Chair: Vladimir Sotnikov, Air Force Research Laboratory Room: 102 |
Tuesday, November 17, 2015 2:00PM - 2:20PM |
JM10.00001: Multiple Ion Beam Creation in Expanding Plasmas Earl Scime We present experimental evidence for the spontaneous formation of multiple double layers within a single divergent magnetic field structure. Downstream of the divergent magnetic field, multiple accelerated ion populations are observed. The similarity of the accelerated ion populations observed in these laboratory experiments to ion populations observed in the magnetosphere and in numerical simulations suggests that the observation of a complex ion velocity distribution alone is insufficient to distinguish between simple plasma expansion and magnetic reconnection. Further, the effective temperature of the aggregate ion population is significantly larger than the temperatures of the individual ion population components, suggesting that insufficiently resolved measurements could misidentify multiple beam creation as ion heating. Ions accelerated in randomly oriented electric fields that mimic heating would have an ion heating rate dependent on the ion charge and mass that is qualitatively consistent with recent experimental observations of ion heating during magnetic reconnection. We also discuss these results in light of recent observations of double layer formation during reconnection. [Preview Abstract] |
Tuesday, November 17, 2015 2:20PM - 2:40PM |
JM10.00002: Nonlinear Electrostatic Instability and Electron Hole Growth in the Moon's Solar Wind Wake I.H. Hutchinson, C.B. Haakonsen, C. Zhou Velocity distribution function distortions and resulting instabilities arise in the interaction of unmagnetized bodies like the moon with the solar wind. To a good approximation the physics is dominated by cross-field drift (corresponding to the perpendicular-to-B wind speed relative to the moon) and free parallel electron and ion dynamics. Analytic calculations show that the electron velocity distribution in the wake becomes unstable because of a dimple formed by ``drift-deenergization'' analogous to the ``energization'' responsible for instability in the earth's bow shock. The much more extreme two-stream distortion of the ion distribution is stable until far downstream. However, high fidelity PIC calculations show that electron holes are spawned by the dimple, and while most accelerate out of the wake without growing much, a few remain at small speeds and grow eventually large enough to disrupt the ion distributions. The nonlinear hole growth mechanism is the same de-energization. It can be reinterpreted as drift into an increasing density region. We show how this growth can be understood analytically, and time permitting will discuss related phenomena concerning ion influence on hole speed and the forewake remnants of ``shadowing.'' [Preview Abstract] |
Tuesday, November 17, 2015 2:40PM - 3:00PM |
JM10.00003: Ion heating during geomagnetic storms measured using energetic neutral atom imaging Amy Keesee, Justin Elfritz, Roxanne Katus, Earl Scime Energy from the solar wind is deposited into the magnetosphere during geomagnetic storms. Much of this energy is deposited into the plasma sheet, driving phenomena that leads to heating. The plasma sheet ions are then injected to the inner magnetosphere, driving the ring current. While ions can undergo adiabatic heating during typical drift motion, collisional and wave-particle interactions can also lead to ion heating. A technique to measure ion temperatures using energetic neutral atom (ENA) data has been developed using ENA data from the Two Wide-angle Imaging Neutral-atom Spectrometers (TWINS) mission global maps of ion temperature during the evolution of geomagnetic storms are made. These maps exhibit the location and characteristics of regions of ion heating and during which storm phase they occur. Superposed epoch analyses of such maps have demonstrated typical characteristics of ion heating during storms driven by coronal mass ejections as compared to those driven by high speed solar wind streams. The temperatures have been used to establish boundary conditions for modeling of the inner magnetosphere. We will give an overview of recent studies using TWINS ion temperature maps. [Preview Abstract] |
Tuesday, November 17, 2015 3:00PM - 3:20PM |
JM10.00004: Anomalous ionospheric conductivities caused by plasma turbulence in high-latitude E-region ionosphere Yakov Dimant, Meers Oppenheim During periods of intense geomagnetic activity, electric fields penetrating from the Earth's magnetosphere to the high-latitude E-region ionosphere drive strong currents named electrojets and excite there plasma instabilities. These instabilities give rise to plasma turbulence that induces nonlinear currents and strong anomalous electron heating. This increases the ionospheric conductances and modifies the global energy flow, affecting behavior of the entire near-Earth plasma. A quantitative understanding of anomalous conductance and global energy transfer is important for accurate modeling of the geomagnetic storm/substorm evolution. Our theoretical analysis, supported by recent 3D fully kinetic particle-in-cell simulations, shows that during strong geomagnetic storms the inclusion of anomalous conductivity can more than double the total Pedersen conductance - the crucial factor responsible for magnetosphere-ionosphere coupling through the current closure. We have started incorporating the effects of anomalous heating and nonlinear conductivity into existing global magnetosphere-ionosphere-thermosphere codes developed for predictive modeling of Space. In our presentation, we will report on the latest progress in this modeling. [Preview Abstract] |
Tuesday, November 17, 2015 3:20PM - 3:40PM |
JM10.00005: Break
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Tuesday, November 17, 2015 3:40PM - 4:00PM |
JM10.00006: Dynamics of the Earth Magnetotail, the Heliosphere Current Sheet and the Outer Planets Magnetosphere B. Coppi Magnetic reconnection occurring in the back of the Earth had been proposed [1] as the origin of the coronal substorms before the discovery of the Earth magnetotail. This discovery incentivized the theory [2] of reconnection processes and of their non-linear evolution in neutral sheet configurations that could represent that of the Earth magnetotail [2]. However, rapid acceptance of the original theories left them severely incomplete as the lack of consideration of the effects of particle temperature gradients that have been found to be important for laboratory magnetic confinement configurations. The relevance of (laboratory) experimental results on magnetic reconnection processes to the understanding of the dynamics of space entities where these processes are important is pointed out. A special consideration is given to the Heliospheric Current Sheet, its topology and its role in producing the observed high-energy particle populations that could not be associated with the Termination Shock of the Heliosphere. The possibility to extend existing theories to the more complex geometries of the magnetotails of the most distant planets is discussed.\\[4pt] [1] B. Coppi, Nature, 205 (1965) 998.\\[0pt] [2] B. Coppi, G. Laval and R. Pellat, Phys. Rev. Letters, 16, (1966) 1207. [Preview Abstract] |
Tuesday, November 17, 2015 4:00PM - 4:20PM |
JM10.00007: Process for Energy Transfer to the Electron Population at Large Distances in Gamma Ray Bubbles B. Basu, B. Coppi Resonant interaction of unmagnetized ions with lower hybrid modes that are excited by the positive slope in the distribution of magnetized electrons serves as a mechanism for transferring the longitudinal energy of electrons to the perpendicular energy of ions. This mechanism, considered originally for the explanation of the enhanced rf emission at $\omega\cong\omega_{pi}$ (ion plasma frequency) and the associated enhanced ion heating observed in Alcator [1], was also proposed by one of us (B. C.) to successfully explain the formation of ``ion conics'' in the suprauroral region [2]. The inverse process of electron energization due to resonant interaction with lower hybrid modes that are excited by an energetic ion population (e.g. a streaming ion population) could be relevant to the formation of the outer edge region of gamma ray bubbles [3]. We proposed a similar process in 1976, considering lower hybrid modes injected in a confined plasma column as the driver of an electron current [4]. \\[4pt] [1] B. Coppi, F. Pegoraro, R. Pozzoli, and G. Rewoldt, Nucl. Fusion, 16, 309 (1976).\\[0pt] [2] T. Chang and B. Coppi, Geophys. Res. Lett., 8, 1253 (1981).\\[0pt] [3] The Fermi-LAT Collaboration, Science, 328, 725 (2010).\\[0pt] [4] B. Basu and B. Coppi, RLE Report PRR-76/4, MIT, Cambridge, MA, 1976. [Preview Abstract] |
Tuesday, November 17, 2015 4:20PM - 4:40PM |
JM10.00008: Evolution of Ion Clouds in the Equatorial Ionosphere Yevgeny Petrochuk, Nathan Blaunstein, Evgeny Mishin, Todd Pedersen, Ron Caton, Al Viggiano, Nick Schuman We report on the results of 2- and 3-dimentional numerical investigations of the evolution of samarium ion clouds injected in the equatorial ionosphere, alike the recent MOSC experiments. The ambient conditions are described by a standard model of the quiet-time equatorial ionosphere from 90 to 350 km. The altitudinal distribution of the transport processes and ambient electric and magnetic fields is taken into account. The fast process of stratification of ion clouds and breaking into small plasmoids occur only during the late stage of the cloud evolution. The role of the background plasma and its depletion zones formed due to the short-circuiting currents is not as evident as in mid latitudes. It is also revealed that the altitudinal dependence of the diffusion and drift plays a minor role in the cloud evolution at the equator. Likewise, the cloud remains stable with respect to the Raleigh-Taylor and gradient-drift instabilities. These two features are defined by the equatorial near-horizontal magnetic field which leads to a strongly-elongated ellipsoid-like plasma cloud. The critical dip angle separating the stable (equatorial) and unstable (mid-latitude) cloud regimes will be defined in future simulation studies, as well as the dependence on the ambient electric field and neutral wind. $^{2}$Space Vehicles Directorate, Air Force Research Laboratory [Preview Abstract] |
Tuesday, November 17, 2015 4:40PM - 5:00PM |
JM10.00009: Relation of anomalous resistivity and current intensity in turbulent collisionless plasma cascades in the geospace Giovanni Lapenta, Koen Kemel, Pierre Henri, Francesco Califano, Stefano Markidis Using the full kinetic implicit PIC code, iPiC3D, we studied the properties of plasma kinetic turbulence, such as would be found at the interface between the solar wind and the Earth magnetosphere at low latitude during northwards periods. In this case, in the presence of a magnetic field oriented mostly perpendicular to the velocity shear, turbulence is fed by the disruption of a Kelvin-Helmholtz vortex chain via secondary instabilities, vortex pairing and non-linear interactions. We found that the magnetic energy spectral cascade between ion and electron inertial scales is in agreement with satellite observations and previous numerical simulations; however, in our case the spectrum ends with a peak beyond de due to the occurrence of the lower hybrid drift instability. The electric energy spectrum is influenced by secondary instabilities: anomalous resistivity, fed by the development of the lower hybrid drift instability, steepens the spectral decay and, depending on the alignment of B and the shear vorticity, peaks due to ion-Bernstein waves may dominate the spectrum around di. A key conclusion of the study is that the anomalous resistivity produced by these complex wave and instabilities can indeed very accurately be described in terms of a proportionality with the current. [Preview Abstract] |
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