Paradigmatic flow for small-scale magnetohydrodynamics: Properties of the ideal case and the collision of current sheets

作     者：E. Lee M. E. Brachet A. Pouquet P. D. Mininni D. Rosenberg 

作者机构：Geophysical Turbulence Program National Center for Atmospheric Research P.O. Box 3000 Boulder Colorado 80307-3000 USA Department of Applied Physics and Applied Mathematics Columbia University 500 W. 120th Street New York New York 10027 USA École Normale Supérieure 24 Rue Lhomond 75231 Paris France Departamento de Física Facultad de Ciencias Exactas y Naturales Universidad de Buenos Aires Ciudad Universitaria 1428 Buenos Aires Argentina 

出 版 物：《Physical Review E》 (物理学评论E辑：统计、非线性和软体物理学)

年 卷 期：2008年第78卷第6期

页      面：066401-066401页

核心收录：

学科分类：07[理学] 070203[理学-原子与分子物理] 0702[理学-物理学] 

基　　金：National Science Foundation, NSF, (0421498, 0420873, 0420985) National Science Foundation, NSF 

主　　题：Paradigmatic small-scale magnetohydrodynamics Collisions model cars magnetic field Spatial resolution grid point Ideal magnetohydrodynamics direction of rotation Exponential Decay current sheet Magnetic pressure CPU time Flow acceleration energy spectra 

摘      要：We propose two sets of initial conditions for magnetohydrodynamics (MHD) in which both the velocity and the magnetic fields have spatial symmetries that are preserved by the dynamical equations as the system evolves. When implemented numerically they allow for substantial savings in CPU time and memory storage requirements for a given resolved scale separation. Basic properties of these Taylor-Green flows generalized to MHD are given, and the ideal nondissipative case is studied up to the equivalent of 20483 grid points for one of these flows. The temporal evolution of the logarithmic decrements δ of the energy spectrum remains exponential at the highest spatial resolution considered, for which an acceleration is observed briefly before the grid resolution is reached. Up to the end of the exponential decay of δ, the behavior is consistent with a regular flow with no appearance of a singularity. The subsequent short acceleration in the formation of small magnetic scales can be associated with a near collision of two current sheets driven together by magnetic pressure. It leads to strong gradients with a fast rotation of the direction of the magnetic field, a feature also observed in the solar wind.