A magnetized, spherical plasma expansion in an inhomogeneous plasma: Transition from super- to sub-Alfvénic

• Published in: Geophysical research letters Vol. 36; no. 15; pp. L15105 - n/a
• Main Authors: Brecht, Stephen H., Hewett, Dennis W., Larson, David J.
• Format: Journal Article
• Language: English
• Published: Washington, DC American Geophysical Union 16.08.2009; Blackwell Publishing Ltd; John Wiley & Sons, Inc
• Subjects: ALFVEN WAVES; Atmospheric sciences; Auroral phenomena; CLASSICAL AND QUANTUMM MECHANICS, GENERAL PHYSICS; Coherence; Density; Earth sciences; Earth, ocean, space; ELECTROMAGNETIC RADIATION; Electromagnetic waves; Exact sciences and technology; Geophysics; INHOMOGENEOUS PLASMA; Ionosphere; Magnetic fields; Magnetism; Magnetohydrodynamics; Magnetospheric configuration and dynamics; Magnetospheric Physics; PLASMA EXPANSION; Plasma waves and instabilities; plasmas; polarized; SHEAR; shocks; Spherical plasmas; Three dimensional; VELOCITY; polarized; plasmas; shocks; coupling; electromagnetic waves; magnetic field; interfaces; shear; density; Plasma expansion; Alfven wave; Inhomogeneous plasma; velocity; energy
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2009GL038393

In this letter the transition of a strong 3‐D collisionless shock into sub‐Alfvénic waves is numerically. The transition occurs due to changes in the background plasma parameters. The Alfvén speed eventually exceeds the shock speed; the shock does not run out of energy. At this velocity transition, the shock disassembles into two types of waves: the usual compressional Alfvén wave and a left‐hand polarized electromagnetic shear Alfvén wave. This latter wave shows remarkable 3‐D coherence, and preliminary analysis suggests that there are two possible sources of energy: one is coupling to the strong electromagnetic waves that exist within the collisionless shock and the other is the density and magnetic field gradients at the interface.