Ion thermalization in quasi-perpendicular shocks involving reflected ions
- Max-Planck-Inst. fuer Physik und Astrophysik, Garching (West Germany)
- Inst. Superior Tecnico, Lisbon (Portugal)
- Univ. of California, Berkeley (United States)
- Technischen Univ., Braunschweig (West Germany)
Ion thermalization mechanisms downstream of the quasi-perpendicular Earth's bow shock are examined by means of plasma and magnetic field data from the AMPTE/IRM spacecraft which include three-dimensional ion distributions, plasma fluid parameters derived every {approximately}4.3 s, and spectra of transverse and parallel magnetic fluctuations up to 16 Hz. The objects studied in detail are low-Mach number, low-{beta} shocks in which reflected-gyrating ions are present and contribute to the downstream ion temperature but where processes beyond the ramp take place slowly, so that the basic phenomenology becomes apparent. In MHD terms, most of these shocks qualify as marginally critical. Downstream of the ramp, the initially separated core and ring ions slowly merge into a joint, less anisotropic distribution possessing a high-energy tail. The ion temperature ratio, T{sub {perpendicular}}/T{sub {parallel}}, is high not only in the shock foot and ramp but also within some distance downstream; its speed of decline rises and the residual level lessens with increasing {beta}. The ions diffuse about equally fast in energy and in pitch angle. An asymmetry of the distributions with respect to the field direction is present when the shock is slightly oblique. It decays only slowly, which might indicate that the pitch angle diffusion rate near zero pitch angle is reduced. Low-frequency electromagnetic waves are present below the proton gyrofrequency; they are characterized by strong left-hand-polarized emissions and a low level of parallel fluctuations except very close to the shock. The left-hand emissions are often concentrated into a narrow frequency band but sometimes they exhibit a double-humped structure. Waves and ion distributions approach a slowly varying equilibrium some distance downstream of the shock.
- OSTI ID:
- 5103293
- Journal Information:
- Journal of Geophysical Research; (United States), Vol. 95:A5; ISSN 0148-0227
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
GENERAL PHYSICS
EARTH MAGNETOSPHERE
SOLAR WIND
IONS
ENERGY LOSSES
INTERACTIONS
ANISOTROPY
DISTRIBUTION
ELECTROMAGNETIC RADIATION
HEATING
ION TEMPERATURE
NONLINEAR PROBLEMS
REFLECTION
SATELLITES
SHOCK WAVES
CHARGED PARTICLES
EARTH ATMOSPHERE
LOSSES
RADIATIONS
SOLAR ACTIVITY
640201* - Atmospheric Physics- Auroral
Ionospheric
& Magetospheric Phenomena