An amended magnetohydrodynamic equation which predicts field-aligned current sheets (Q1094246)

A derivation of the physical conditions for magnetohydrodynamic equilibrium from first principles establishes a set of equations which differ slightly from the usual ones. The difference is only relevant in the special case when the current is parallel to the magnetic field. What is noteworthy is that these modified equations predict that the simplest magnetohydrodynamic equilibria can only exist in regions of field-aligned current sheets. This prediction is entirely consistent with the observed large-scale structures in the Earth's magnetosphere.