Full particle simulations of short large‐amplitude magnetic structures (SLAMS) in quasi‐parallel shocks

Abstract

Dynamics of SLAMS (short large‐amplitude magnetic structures) is investigated by the use of one‐dimensional, full particle electromagnetic simulations. As previous hybrid simulations and analysis of experimental observations suggested, present results confirm that the SLAMS patterns result from the steepening of long wavelength magnetosonic waves which are excited by diffuse ions (representing the field‐aligned reflected ion beam) interacting with the upstream ambient plasma. Five successive phases have been identified in the SLAMS dynamics: ULF wave growth and symmetric, asymmetric, spiky, and late SLAMS. The present accessibility to high‐resolution (electron) scales leads to the following new features: (1) the leading edge of the SLAMS steepens over a spatial scale from which a large‐amplitude whistler precursor is emitted; (2) this whistler departs from the SLAMS edge and behaves as a new shock front; (3) the spiky SLAMS phase is characterized by the build‐up of a strong spiky electrostatic field (its width is about 0.5 ion inertial length) within the whistler precursor and is intermittent with a lifetime less than one inverse ion gyroperiod; (4) the new shock front suffers a local self‐reformation typical of a quasi‐perpendicular shock in supercritical regime during the late‐SLAMS phase. The features of the spiky SLAMS phase can be used as a typical signature in the time history of the SLAMS dynamics. Spatial/time scales of SLAMS have been measured throughout the different phases and are found in good agreement with results issued from previous hybrid simulations and with experimental measurements made by AMPTE UKS/IRM satellites; these are also compared with recent results from Cluster‐2 space mission.