HR: 08:00h
AN: SM51C-01    [Abstracts]
TI: Weak Bipolar Fields in the Solar Wind and Cusp: A Theoretical Interpretation*
AU: * Goldman, M V
EM: goldman@spot.colorado.edu
AF: University of Colorado at Boulder, Center for Integrated Plasma Studies, Boulder, CO 80309-0390, United States
AU: Newman, D L
EM: David.Newman@colorado.edu
AF: University of Colorado at Boulder, Center for Integrated Plasma Studies, Boulder, CO 80309-0390, United States
AU: Mangeney, A
EM: mangeney@despace.obspm.fr
AF: Observatoire de Paris, DESPA, URA 264 CNRS, Meudon, France
AB: Localized bipolar electrostatic field structures have now been measured in Earth's auroral ionosphere,¹ in conjunction with magnetic reconnection in the magnetotail,² in the vicinity of the magnetopause and cusp,³ and in the solar wind.⁴ In most of these venues the associated measured potentials, φ, often have extremely low amplitudes with ψ_m≡ eφ_max/T_e≪ 1 (sometimes with ψ_m 10^-3 or less). A systematic analytic theory of stationary bipolar fields (i.e., as viewed in their co-moving frame) is developed based on the smallness parameter ψ_m. The theory appears to explain a number of features of measured weak bipolar structures in terms of electron phase space holes, and predicts relatively simple relationships between bipolar waveforms and the corresponding distributions of passing and trapped electrons. The analytic potential obtained from theory takes the form of a hyperbolic secant raised to the fourth power for the simplest trapped electron distribution. This potential yields a good fit to bipolar waveforms measured in the solar wind and Earth's cusp region. For measurements of hundreds of weak bipolar field events in the cusp,³ the theory is shown to be consistent with the most frequently observed half-width (defined as half the distance between bipolar field peaks, which is ~2 Debye lengths). The theory is also consistent with various other features of the measured distribution of hole velocities vs hole half-widths. It is demonstrated using Vlasov simulations that a variety of the weak bipolar structures are stable over long times in one dimension, provided that they moving sufficiently fast relative to the mean velocity of the ions.
* Research supported by NSF, NASA, and DOE.
¹ Ergun, R.E., et al., Phys. Rev. Lett., 81, 826 (1998).
² Cattell, C., et al., J. Geophys. Res., 110, A01211 (2005).
³ Franz, J.R., et al., J. Geophys. Res., 110, A09212 (2005).
⁴ Mangeney, A., private communication.
DE: 2712 Electric fields (2411)
DE: 2772 Plasma waves and instabilities (2471)
DE: 7815 Electrostatic structures
DE: 7839 Nonlinear phenomena (4400, 6944)
SC: SPA-Magnetospheric Physics [SM]
MN: 2007 Joint Assembly