Upstream waves, shocklets, short large-amplitude magnetic structures and the cyclic behavior of oblique quasi-parallel collisionless shocks
- Max-Planck-Institut fuer Extraterrestrische Physik, Garching (Germany)
The re-formation process of more oblique quasi-parallel shocks is investigated using one-dimensional hybrid simulations. Several types of simulations were performed. The simulation of a shock with a magnetic field-shock normal angle of 30[degrees] shows that a more oblique quasi-parallel shock exhibits reformation cycles with a larger length scale (about 20 ion inertial lengths). This is considerably larger than the distance specularly reflected ions are able to propagate, so that their velocity in the shock normal direction is nearly zero. These cycles are due to changes of upstream waves into pulsationlike structures when they are convected into the region of strongly increasing diffuse ion density immediately upstream of the shock. When the steepening wave packet crashes into the shock, the shock ramp dispersively radiates whistler waves into the region between the shock ramp and the approaching wave, while the steepening of the pulsation leads to phase standing whistler waves on the upstream side. Entropy production occurs either at the shock ramp or at the upstream edge of the pulsation. In order to analyze the wave steepening, upstream waves have been isolated, and their subsequent interaction with a hot, tenuous ion beam representing the diffuse backstreaming ions has been studied. Similar results are obtained when a counterstreaming beam of hot ions is injected into a solar wind not initially containing a wave field. The strong density increase of hot beam ions in these simulations is due to the steady injection of beam ions in a solar wind with an embedded field inclined relative to the solar wind direction. In the shock simulation the shock itself is the steady source of the hot backstreaming ions. These simulations suggest that upstream waves, shocklets, and short large-amplitude magnetic structures are all the same entity in different stages of their development and play a crucial role in re-forming oblique quasi-parallel shocks. 29 refs., 10 figs.
- OSTI ID:
- 6900921
- Journal Information:
- Journal of Geophysical Research; (United States), Vol. 98:A1; ISSN 0148-0227
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
GENERAL PHYSICS
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
MAGNETIC FIELDS
SIMULATION
SHOCK WAVES
SOLAR WIND
ACCELERATORS
ION DENSITY
IONS
VELOCITY
CHARGED PARTICLES
SOLAR ACTIVITY
661320* - Auroral
Ionospheric
& Magnetospheric Phenomena- (1992-)
662390 - Electromagnetic Processes & Properties- (1992-)