Open AccessNonstationarity of a two‐dimensional perpendicular shock: Competing mechanisms
Author(s) -
Lembège Bertrand,
Savoini Philippe,
Hellinger Petr,
Trávníček Pavel M.
Publication year - 2009
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2008ja013618
Subject(s) - whistler , physics , amplitude , shock wave , shock (circulatory) , plane (geometry) , computational physics , perpendicular , front (military) , supercritical fluid , plasma , mechanics , optics , meteorology , geometry , nuclear physics , medicine , mathematics , thermodynamics
Two‐dimensional particle‐in‐cell (PIC) simulations are used for analyzing in detail different nonstationary behaviors of a perpendicular supercritical shock. A recent study by Hellinger et al. (2007) has shown that the front of a supercritical shock can be dominated by the emission of large‐amplitude whistler waves. These waves inhibit the self‐reformation driven by the reflected ions; then, the shock front appears almost “quasi‐stationary.” The present study stresses new complementary results. First, for a fixed β i value, the whistler waves emission (WWE) persists for high M A above a critical Mach number (i.e., M A ≥ M A WWE ). The quasi‐stationarity is only apparent and disappears when considering the full 3‐D field profiles. Second, for lower M A , the self‐reformation is retrieved and becomes dominant as the amplitude of the whistler waves becomes negligible. Third, there exists a transition regime in M A within which both processes compete each other. Fourth, these results are observed for a strictly perpendicular shock only as B 0 is within the simulation plane. When B 0 is out of the simulation plane, no whistler waves emission is evidenced and only self‐reformation is recovered. Fifth, the occurrence and disappearance of the nonlinear whistler waves are well recovered in both 2‐D PIC and 2‐D hybrid simulations. The impacts on the results of the mass ratio (2‐D PIC simulations), of the resistivity and spatial resolution (2‐D hybrid simulations), and of the size of the simulation box along the shock front are analyzed in detail.