From Glossary of Meteorology


A magnetic field in a (zero resistivity) electrically conducting fluid (
or plasma), so named because when the plasma moves, the magnetic lines of force may be said to move with it.

The field lines are fixed within the plasma. Because a plasma is an electrical conductor, when it moves in a magnetic field an electric current results, which in turn produces a magnetic field that adds to the existing field. The net field (assuming negligible resistivity) is as if the existing field lines had moved with the plasma.