Electric currents in the solar wind

Abstract

The electric currents in the solar wind are described for the particular case of Parker's model, in which the sun's magnetic field is a dipole located at the center of the sun and inclined at an arbitrary angle to the sun's axis of rotation. The current consists of two components. The density of one depends only upon the sun's dipole moment, and that of the other depends upon the solar wind velocity and the sun's angular velocity as well as its dipole moment. The latter component flows in heliographic meridional planes. The electromagnetic forces of this component tend to accelerate the plasma in the leading half of a magnetic sector and to decelerate it in the following half. If the angle λ between the sun's spin axis and the dipole axis is different from either 0° or 90°, the electromagnetic force near the equatorial plane has a southward component in the positive sector and a northward component in the negative sector. The generalization to a more complicated solar magnetic field is discussed. The electromagnetic torque on the sun slows its rotation and for λ ≠ 0° or 90° also has oscillating components in the two directions perpendicular to the spin axis. These components tend to increase λ, indicating that the stable configuration is λ = 90°. For a given dipole moment, λ = 90° is also the orientation that maximizes the electromagnetic braking. Possible electromagnetic contributions to the sun's differential rotation are also considered.