The role that microscale plasma kinetics can play in structuring macroscale phenomena is well illustrated by the formation upwind of the magnetosphere of a high Mach number bow shock created entirely by non-collisional processes. One facet regarding global magnetospheric behavior has reached a level of at least empirical understanding where it is now being incorporated into operational space weather forecasting. The solar wind affects the internal state of the magnetosphere primarily through the action of the magnetic field it brings with it from the sun. The solar wind's magnetic field brushes against the magnetosphere's magnetic field all along the magnetopause. Here, over a finite volume, the fields can merge together, giving the solar wind access to the magnetosphere.
Magnetospheric convection is the main mode of energy transfer in global magnetospheric dynamics.
Understanding the processes by which magnetic fields merge at the magnetopause is, therefore, a topic of central importance to magnetospheric physics. Unfortunately it is also one of the deepest, and accordingly, it is the object of intense theoretical studies. At issue is an apparent conflict between the time dependence of field line merging seen at the magnetopause and the time independence of the effects of merging seen at the ionospheric footprint of the field lines that merge at the magnetopause. Newell surveys recent work to arrive at a reconciliation. On its inside, the magnetotail owes its distinctive geometrical and dynamical properties to the equatorial current sheet, which bisects the magnetotail cylinder from east to west and divides it into a northern half where magnetic field lines point toward the earth and a southern half where they point the other way.