Application of the centrifugal impulse model to particle motion in the near-Earth magnetotail

Details Application of the centrifugal impulse model to particle motion in the near-Earth magnetotail Application of the centrifugal impulse model to particle motion in the near-Earth magnetotail

Dec 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994jgr....9923583d&link_type=abstract

Journal of Geophysical Research (ISSN 0148-0227), vol. 99, no. A12, p. 23,583-23,590

Other

17

Centrifugal Force, Curvature, Geomagnetic Tail, Larmor Radius, Magnetic Field Configurations, Magnetic Moments, Adiabatic Conditions, Earth Magnetosphere, Geomagnetism, Particle Precipitation, Solar Terrestrial Interactions

Scientific paper

Particles traveling in the geomagnetic tail do not conserve their magnetic moment (first adiabatic invariant) due to significant field variations on the length scale of their Larmor radius. We examine the possibility of describing these magnetic moment changes by the action of an impulsive centrifugal force on the timescales of the particle cyclotron turn. Trajectory calcuations demonstrate that such a centrifugal impulse model adequately describes the nonadiabatic particle behavior for situations where the kappa parameter (defined as the square root of the monimum curvature radius-to-maximum Larmor radius ratio) is of the order of 1 to 2. In particular, it is shown that this behavior can be organized by another parameter (referred to as kappa(sub alpha), which is proportional to kappa but depends upon the particle pitch angle, namely, one obtains: systematic magnetic moment enhancements for kappa(sub alpha) much less than 1, large gyrophase effects with possibly prominent damping of the magnetic moment for kappa(sub alpha) approximately 1, and nearly constant magnetic moment for kappa (much greater than 1. More generally, we show that the centrifugl impulse approximation applies to an intermediate orbit regime at the transition between the fully adiabatic (magnetic moment conserving) regime and that regime where partcle experience meandering motions about the field minimum. It applies to ion transport in the near-Earth magnetotail where the magnetic field lines evolve from dipole to taillike configurations and where the kappa parameter nears unity. In this region of space the model predictions are in agreement with numerical results, revealing both enhanced traping (due to magnetic moment enhancement) and possible precipitation (due to magnetic moment damping) pf plasma sheets ions depending upon their pitch and phase angles.

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