Structure of medium Mach number quasi-parallel shocks: Upstream and downstream waves

Journal Article · Tue Oct 01 00:00:00 EDT 1991 · Journal of Geophysical Research; (United States)

DOI:https://doi.org/10.1029/91JA01545· OSTI ID:5813982

Krauss-Varban, D; Omidi, N ^[1]

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1. Univ. of California, San Diego, La Jolla (United States)

Satellite observations of quasi-parallel collisionless shocks document a complex behavior that has proven to be extraordinarily difficult to analyze and interpret. Recent data analyses and computer simulations, however, have revealed that these shocks can be unsteady and cyclically reforming, and have shed some light on the processes that are involved. To understand the transition from steady low Mach number to unsteady high Mach number shocks, the authors have performed large-scale one-dimensional hybrid code simulations at increasing Mach numbers. They find that fast-mode waves with wavelengths longer than phase-standing whistlers are excited upstream from the shock by backstreaming ions. At increasing Mach numbers, the phase and group velocities of the dominant waves are reduced until they point back toward the shock. When there is sufficient energy flux in these waves, they lead to unsteady shock behavior and eventually to shock re-formation. For typical solar wind conditions and an angle of {theta}{sub Bn} = 30{degree} between the shock normal and the upstream magnetic field, the authors find the shock to become unsteady at M{sub A} {approximately} 2.3. Various spectral diagnostics are employed to investigate the properties of the excited upstream and downstream waves. Fast-mode wave energy that is convected through the shock is partially mode converted into downstream Alfven and slow-mode fluctuations. This mechanism may be responsible for some of the turbulence observed downstream of the Earth's quasi-parallel bow shock.

• OSTI ID: 5813982
• Journal Information: Journal of Geophysical Research; (United States), Journal Name: Journal of Geophysical Research; (United States) Vol. 96:A10; ISSN JGREA; ISSN 0148-0227
• Country of Publication: United States
• Language: English

Related Subjects

661320* -- Auroral
Ionospheric
& Magnetospheric Phenomena-- (1992-)
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ALFVEN WAVES
COLLISIONLESS PLASMA
COMPUTERIZED SIMULATION
CONVECTION
DATA ANALYSIS
EARTH ATMOSPHERE
EARTH MAGNETOSPHERE
ELECTROMAGNETIC RADIATION
ENERGY TRANSFER
HEAT TRANSFER
HYDROMAGNETIC WAVES
INTERACTIONS
MACH NUMBER
MASS TRANSFER
NOISE
PLASMA
RADIATIONS
RADIO NOISE
RADIOWAVE RADIATION
REFLECTION
SATELLITES
SHOCK WAVES
SIMULATION
SOLAR ACTIVITY
SOLAR WIND
STANDING WAVES
TURBULENCE
VELOCITY
WHISTLERS