“Complexity” and anomalous transport in space plasmas

Abstract

“Complexity” has become a hot topic in nearly every field of modern physics. Space plasma is of no exception. In this paper, it is demonstrated that the sporadic and localized interactions of magnetic coherent structures are the origin of “complexity” in space plasmas. The intermittent localized interactions, which generate the anomalous diffusion, transport, and evolution of the macroscopic state variables of the overall dynamical system, may be modeled by a triggered (fast) localized chaotic growth equation of a set of relevant order parameters. Such processes would generally pave the way for the global system to evolve into a “complex” state of long-ranged interactions of fluctuations, displaying the phenomenon of forced and/or self-organized criticality. An example of such type of anomalous transport and evolution in a sheared magnetic field is provided via two-dimensional magnetohydrodynamic simulations. The coarse-grained dissipation due to the intermittent triggered interactions among the magnetic coherent structures induces a “fluctuation-induced nonlinear instability” that reconfigures the sheared magnetic field into an X-point magnetic geometry (in the mean field sense), leading to the anomalous acceleration of the magnetic coherent structures. A phenomenon akin to such type of anomalous transport and acceleration, the so-called bursty bulk flows, has been commonly observed in the plasma sheet of the Earth’s magnetotail.