PRECIPITATION OF MAGNETOSPHERIC ELECTRONS CAUSED BY RELATIVISTIC EFFECT-ENHANCED CHAOTIC MOTION IN THE WHISTLER WAVE-FIELDS

In the magnetosphere, energetic electrons in the radiation belts are t rapped by the Earth's dipole magnetic field and undergo bounce motion about the geomagnetic equator. It is shown that the trajectories of so me of the trapped particles can in the presence of a whistler wave bec ome chaotic and wander into the loss cone. Comparing the surface of se ction plots obtained from the both relativistic equations of motion an d from the nonrelativistic ones, the effect of the relativistic correc tion to the electron motion are shown. The threshold field for the com mencement of chaos in the trajectories of electrons with energies of a few hundred keV is found to be lowered by the inclusion of relativist ic effects by about an order of magnitude. Waves with these smaller ma gnetic field amplitudes (about 1% of the geomagnetic field) have been observed propagating between hemispheres. Since this chaotic scatterin g process does not have a directional preference, it offers a plausibl e explanation for the simultaneous observation of electron precipitati on into the upper atmosphere at geomagnetically conjugate regions beca use of a single lightning flash [Burgess and Inan, 1990].