A Microscopic View of Magnetic Reconnection in the Magnetosphere

Michael Hesse
NASA GSFC

Magnetic reconnection provides the energy conversion engine that
drives the dynamical evolution of most space plasmas. Magnetic
reconnection requires the decoupling of ions and electrons from
the magnetic field, in a localized diffusion region. This
localized dissipation process enables large-scale plasma transport
and energy conversion that affects the entire evolution of the
space and astrophysical system. In recent years, much progress has
been made in the understanding of the dissipation processes that
facilitate magnetic decoupling for ions and electrons inside the
diffusion region. While final consensus is still outstanding,
particle-in-cell simulations have consistently supported the view
that the decoupling mechanism is based on thermal particle
inertia, which manifests itself in form of nongyrotropic pressure
tensors. In this paper, we will analyze how thermal particle inertia
effects control the dissipation process. We will focus on an
analysis of the differences between the reconnection of
anti-parallel magnetic fields, and of magnetic field with a shear
angle different from 180 degrees. In both cases, we will discuss
the physical mechanism responsible for particle scattering, and derive
scaling relations for the width of the central diffusion region.