Relationship between changes in the interplanetary magnetic field and variations in the magnetic field at the Earth's surface

Abstract

Hourly average values of solar wind velocity and the components of the interplanetary magnetic field obtained by IMP 1 were combined to obtain the interplanetary electric field as measured in a coordinate system with one axis parallel to the earth's magnetic dipole axis. The hourly values of the azimuthal component of the interplanetary electric field were related to the different types of magnetic activity observed at a worldwide chain of stations. It is found that a positive increment in the azimuthal electric field (enhancement of the southward directed interplanetary magnetic field) is strongly related to the initiation of magnetic bay and storm activity, and that establishment of a negative (or less positive) azimuthal electric field during the course of a storm or bay is associated with the start of the recovery phase. Sudden impulses are shown to be equally often associated with negative and positive increments in the azimuthal electric field and are found to be the most common event observed in this study. The combinations of solar-terrestrial parameters that appear to determine the different types of magnetic activity are discussed in the light of the results presented in this paper.