Small-scale nonequilibrium of the magnetopause and its consequences

The tangential motion of the solar wind along the magnetopause produces currents in the boundary layer that generate a magnetic field in the boundary layer transverse to the tangential motion. A simplified example is presented to illustrate the growth of the transverse field. The transverse field is approximately as strong as the geomagnetic field at the magnetopause. There is no evidence for sufficiently large electron and/or magnetic pressures to confine the transverse field, so the transverse layer apparently expands outward into the wind. This nonequilibrium enhances the mixing of geomagnetic lines of force with the solar wind plasma, thereby contributing to the ‘viscous’ drag of the wind on the magnetopause. It is estimated that the effect may replenish the lines of force in the geomagnetic tail in 10³–105 seconds.