Magnetic moment scattering in a field reversal with nonzero BY component

We examine the nonadiabatic motion of charged particles in a field reversal with nonzero BY. We show that magnetic moment variations are organized into three categories: (1) at small equatorial pitch angles, large magnetic moment enhancements regardless of gyration phase, (2) at intermediate pitch angles, a prominent dependence upon phase with either magnetic moment enhancement or damping, and (3) at large pitch angles, negligible magnetic moment changes. This three-branch pattern of magnetic moment variations resembles that obtained for zero BY, but it is here more or less developed when particles enter above or below the field reversal. We investigate this effect using the centrifugal impulse model developed for zero BY, whereby nonadiabatic behavior is viewed as the result of perturbation of the gyromotion by an impulsive centrifugal force. We show that nonzero BY leads to a rotation of the centrifugal impulse in the gyration plane and that the nonadiabatic particle behavior is attenuated or enhanced when this rotation opposes or goes together with the gyromotion, respectively. As a consequence of this, particles with opposite charge states or originating from opposite hemispheres behave in quite distinct manners, exhibiting for instance large or negligible magnetic moment changes depending upon their direction of propagation. More generally, we demonstrate that prominent hemispherical differences are obtained as a result of nonzero BY, be it for injection inside the loss cone or gyrophase bunching near the current sheet midplane.

[1]  C. Russell,et al.  Global configuration of the magnetotail current sheet as derived from Geotail, Wind, IMP 8 and ISEE 1/2 data , 1998 .

[2]  T. Mukai,et al.  Ion dynamics in magnetic reconnection: Comparison between numerical simulation and Geotail observations , 1998 .

[3]  G. Rowlands,et al.  Are particles detrapped by constant By in static magnetic reversals , 1998 .

[4]  James Chen,et al.  Effects of a constant cross‐tail magnetic field on the particle dynamics in the magnetotail , 1996 .

[5]  J. Sauvaud,et al.  Centrifugally driven phase bunching and related current sheet structure in the near-Earth magnetotail , 1996 .

[6]  J. Sauvaud,et al.  On the nonadiabatic precipitation of ions from the near-Earth plasma sheet , 1996 .

[7]  M. Ashour‐Abdalla,et al.  Proton velocity distributions in the magnetotail: Theory and observations , 1996 .

[8]  J. Lyon,et al.  Interplanetary magnetic field control of magnetotail field: IMP 8 data and MHD model compared , 1995 .

[9]  D. Delcourt,et al.  Application of the centrifugal impulse model to particle motion in the near‐Earth magnetotail , 1994 .

[10]  T. Speiser,et al.  Effect of By on neutral line ridges and dynamical source ordering , 1994 .

[11]  M. Kivelson,et al.  Observations of nonadiabatic acceleration of ions in Earth's magnetotail , 1994 .

[12]  D. Delcourt,et al.  A simple model of magnetic moment scattering in a field reversal , 1994 .

[13]  C. Russell,et al.  Interplanetary magnetic field control of magnetotail magnetic field geometry: IMP 8 observations , 1994 .

[14]  G. Parks,et al.  Particle orbits in model current sheets with a nonzero By component , 1993 .

[15]  James Chen.  Nonlinear dynamics of charged particles in the magnetotail , 1992 .

[16]  M. Ashour‐Abdalla,et al.  Regular and chaotic aspects of charged particle motion in a magnetotail‐like field with a neutral line , 1991 .

[17]  L. Zelenyi,et al.  Sheared field tearing mode instability and creation of flux ropes in the Earth magnetotail , 1991 .

[18]  James Chen,et al.  Observational signatures of nonlinear magnetotail particle dynamics , 1990 .

[19]  C. Kennel,et al.  Ion precipitation from the inner plasma sheet due to stochastic diffusion , 1990 .

[20]  Lev M. Zelenyi,et al.  Regular and chaotic charged particle motion in magnetotaillike field reversals: 1. Basic theory of trapped motion , 1989 .

[21]  T. Engelder,et al.  Correction [to “An experimental study of permeability and fluid chemistry in an artificially jointed marble” by Chris Marone, James Rubenstone, and Terry Engelder] , 1989 .

[22]  T. Speiser,et al.  A predicted energetic ion signature of a neutral line in the geomagnetic tail , 1988 .

[23]  J. Büchner,et al.  Deterministic chaos in the dynamics of charged particles near a magnetic field reversal , 1986 .

[24]  P. Palmadesso,et al.  Chaos and nonlinear dynamics of single-particle orbits in a magnetotail-like magnetic field. Memorandum report , 1985 .

[25]  B. Tsurutani,et al.  The relationship between the IMF B(y) and the distant tail (150-238 Re) lobe and plasmasheet B(y) fields , 1984 .

[26]  T. Birmingham.  Pitch angle diffusion in the Jovian magnetodisc , 1984 .

[27]  V. A. Sergeev,et al.  Pitch-angle scattering of energetic protons in the magnetotail current sheet as the dominant source of their isotropic precipitation into the nightside ionosphere , 1983 .

[28]  W. Hughes,et al.  Observation of an IMF sector effect in the Y magnetic field component at geostationary orbit , 1983 .

[29]  T. Speiser,et al.  Evidence for current sheet acceleration in the geomagnetic tail , 1982 .

[30]  T. Speiser.  Particle trajectories in model current sheets: 1. Analytical solutions , 1965 .