Ion thermalization mechanisms downstream of the quasi-perpendicular Earth's bow shock are examined by means of plasma and magnetic field data from the AMPT•/IaM spacecraft which include three-dimensional ion distributions, plasma fluid parameters derived every ~ 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-f/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, Ti/Tii, 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 f/. 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. After extending the analysis to one supercritical shock representing the majority of bow shock encounters, we conclude that our deductions are more generally valid, although the thermalization is faster, usually, and appears to involve nonlinear processes which tend to obscure most of the features noted. 1. sipated at the bow shock. In quasi-perpendicular shocks, the dominant dissipation process is ion heating. For shocks above a certain Mach number, a consistent model of the ion heating mechanism has evolved in the course of the last 20 years from the results of laboratory experiments, theoretical studies, computer simulations, and observations in space. But several details of the downstream thermalization still are unsupported by direct observations. It is the purpose of this paper to present and discuss such observations.The essential element of the ion heating mechanism in higher-Mach number, quasi-perpendicular shocks is the initial reflection of some of the incident ions off the shock surface. The majority of the ions (• 80 %) are directly transmitted through the shock. Their temperature rises by more than the adiabatic rate that corresponds to the magnetic field compression. A similar, or even higher contribution to the total ion temperature is provided by the refl...

By means of an energy conservation approach, this paper analyzes the growth rates of whistlers with arbitrary frequency and direction of propagation in a cold plasma permeated by a dilute energetic electron population. Numerical results are obtained for whistler frequencies and plasma characteristics prevailing at the onset of artificially stimulated emissions (ω/Ω ∼ 0.5, ωp/Ω ∼ 10, the energetic electron population with varying energy and pitch angle). It is found that the growth rates do not in general maximize for propagation along the static magnetic field, and a criterion for the existence of maximal growth at this direction is derived. An application to artificially stimulated emissions is discussed.

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We review the effect of finite amplitude circularly polarized waves on the behavior of linear ion-beam plasma instabilities. It has been shown that left-hand polarized waves can stabilize linear right-handed instabilities [1]. It has also been shown that for beam velocities capable of destabilizing left-handed waves, left-hand polarized large amplitude waves can also stabilize these waves. On the other hand, when the large amplitude wave is right-hand polarized, they can either stabilize or destabilize right-handed instabilities depending on the wave frequency and beam speed [2]. Finally, we show that the presence of large amplitude left-hand polarized waves can also trigger electrostatic ion-acoustic instabilities by forcing the phase velocities of two ion acoutic waves to become equal, above a threshold amplitude value.

Here we demonstrate that introduction of SNG in a particle population of an otherwise stable magnetoplasma can (1) bring about unstable linear mode coupling among the parallel eigenmod.es for finite perpendicular currents (as was the case for TNG distributions) albeit now without the frequency shifts, and (2) stimulate nonoscillatory purely growing waves (zero real frequency within a finite wavenumber band) in nongyrotropic environments that only couple parallel electromagnetic waves (zero unperturbed perpendicular current), behavior not encountered in TNG media.