tides by virtue of the dynamical interaction between the earth’s magnetosphere and the solar wind. They are depleted of such particles mainly by interaction with plasma turbulence, which tends to violate the adiabatic invariants of charged-particle motion. Such violation allows particles to escape confinement by the earth’s magnetic mirror and to precipitate (i.e., deposit their energy) in the earth’s atmosphere and ionosphere. However, the interaction of geomagnetically trapped particles with plasma turbulence is very selective, in that it is contingent upon a "resonance" between the gyration of a particle and the frequency of a wave in the turbulent spectrum (after one takes account of the Doppler shift associated with the motion of the particle through the plasma). Thus, different classes of turbulence are found to interact with different classes of particles. The energy spectrum of trapped Ar+ ions in the magnetosphere may range from 3.5 keV on down to a few eV. Thus they are properly classified as ring current and thermal particles. In order to discuss the main dynamical effects of heavy ion additions to the natural ring current (thermalized Ar+ discussed above and thermal O+ driven up from the ionosphere by heating) we must discuss the physics of electromagnetic cyclotron instability in the magnetosphere. Turbulence in a plasma can be created by various mechanisms. A main source of instability in the magnetospheric plasma is the velocity-space anisotropy intrinsic to ring-current particle distributions. Anisotropy here means that relatively more particles have larger velocity components parallel or perpendicular to the magnetic field. Thus iso-intensity contours in ([[spi:math]]) - space are no longer circular. Since the magnetic mirror points of ring-current protons and electrons are concentrated near the magnetic equator rather than being distributed uniformly along a field line, there must be relatively more energy per degree of freedom associated with particle 48
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