Vicinity Of Interplanetary Shocks Research Articles

Fluctuations of cosmic rays and IMF in the vicinity of interplanetary shocks

Fluctuations of cosmic rays and interplanetary magnetic field upstream of interplanetary shocks are studied using data of ground-based polar neutron monitors as well as measurements of energetic particles and solar wind plasma parameters aboard the ACE spacecraft. It is shown that coherent cosmic ray fluctuations in the energy range from 10 keV to 1 GeV are often observed at the Earth’s orbit before the arrival of interplanetary shocks. This corresponds to an increase of solar wind turbulence level by more than the order of magnitude upstream of the shock. We suggest a scenario where the cosmic ray fluctuation spectrum is modulated by fast magnetosonic waves generated by flux of low-energy cosmic rays which are reflected and/or accelerated by an interplanetary shock.

Langmuir Waves in the Vicinity of interplanetary Shocks and the Consequences for Type II Burst Models

The in situ wave data obtained by the Ulysses Unified Radio And Plasma wave experiment in the vicinity of a large number of interplanetary shocks show that Langmuir waves (1) are observed in only ~15% of the interplanetary shocks, (2) occur mostly in the upstream regions, and (3) are produced in the vicinity of both quasi-parallel Q|| and quasi-perpendicular Q⊥ shocks and that (4) Langmuir wave-producing shocks are supercritical. Since Langmuir waves are the essential ingredients for the solar and interplanetary type II burst excitation, these observations imply that (1) the shock responsible for type II emission can be either Q|| with a shock normal angle, θB, n ≤ π/4, or Q⊥ with θB, n > π/4, (2) type II bursts are excited in the upstream regions, (3) the θB, n need not be close to ~π/2 for either the excitation or the clumpiness of the type II bursts, and (4) type II shocks are mostly supercritical.

OBLIQUE EMISSION OF WHISTLER-MODE WAVES AROUND INTERPLANETARY SHOCKS

We present a study of whistler-mode wave generation and wave particle interaction in the vicinity of interplanetary shocks as observed by the Ulysses spacecraft. Generally the whistler-mode waves (measured in the frequency range 0.22–448 Hz) are observed downstream of the shocks where they persist for some hours. From the electron distribution functions (EDF) in the energy range 1.6 to 862 eV measured by the spacecraft, we compute the wave growth rate of the electromagnetic electron cyclotron and Landau instabilities for the case of oblique propagation of the waves with respect to the interplanetary magnetic field (IMF) B. In general, in agreement with the wave measurements, the instability grows mostly downstream of the shock fronts. Following the wave activity, velocity space diffusion of the electrons results in a marginally stable state with some sporadic fluctuations.

Whistler‐mode wave generation around interplanetary shocks in and out of the ecliptic plane

We present a study of whistler‐mode wave generation and wave particle interaction in the vicinity of interplanetary shocks in and out of the ecliptic plane, as observed by the Ulysses spacecraft. We focus here on one shock in the ecliptic plane as a reference and three shocks obtained at −30, −54 and −55.4 degrees of heliographic latitude respectively. Generally the whistler‐mode waves (measured in the frequency range 0.22–448 Hz) are observed downstream of the shocks where they persist for some hours. From the electron distribution functions in the energy range 1.6 to 862 eV, we compute the temperature anisotropy and the wave growth rate of the electromagnetic electron cyclotron instability for the case of parallel propagation of the waves with respect to the interplanetary magnetic field (IMF) B. In general, in agreement with the wave measurements, the instability grows only downstream of the shock fronts. Following the wave activity, velocity space diffusion of the electrons results in a marginally stable state with some sporadic fluctuations. Broadening of the wave reduced frequency range of the instability and an increase of the temperature anisotropy with latitude are observed.

Interaction between whistler-mode waves and electrons in the vicinity of interplanetary shocks as seen by Ulysses: A preleminary study

Interaction between whistler-mode waves and electrons in the vicinity of interplanetary shocks as seen by Ulysses: A preleminary study

Ion injection and acceleration at quasi‐perpendicular shocks

We present and discuss results of a new model for ion injection and acceleration at quasi‐perpendicular collisionless shocks. We use the one‐dimensional hybrid simulation (kinetic ions/fluid electrons) and impose an assumption on the ion motion so that diffusion across the magnetic field (normal to the shock front) is possible. These motions are otherwise suppressed by both one‐ and two‐dimensional simulations. We find that, even in strictly perpendicular shocks, when scattering normal to the field is included, a fraction of the incident ions are accelerated to suprathermal energies. When reasonable scattering times are considered, only pickup ions are injected, whereas thermal solar wind ions are not. The acceleration of these ions is very rapid. We have found that a few of the initially low‐energy pickup ions can reach many tens to a few hundred times the plasma ramming energy in less than 100 gyroperiods. Furthermore, highly field aligned energetic ions are found to exist upstream of the slightly oblique shock. The most direct application of this study is toward the interpretation of observations of both solar wind and interstellar pickup ion distributions in the vicinity of interplanetary shocks which are most often quasi‐perpendicular. This work also directly addresses a fundamental issue with regard to our current understanding of the anomalous component of cosmic rays.