A New Source for the Large-scale Electric Fields in the Magnetosphere

Abstract

ALFVEN1 has pointed out that no real understanding of the properties of the magnetosphere is possible without a knowledge of the electric field. Large scale electric fields in the magnetosphere so far discussed in the literature have been confined mainly to the following three categories2: first, the electric field due to the polarization of the ambient plasma in the vicinity of the magnetopause through the frictional interaction with the solar wind; second, the electric field due to the polarization of energetic particles caused by differential drift motions of these charged particles in the Earth's magnetic field; and third, the penetration of the interplanetary electric field into the magnetosphere. But electric fields induced by variations of the magnetic field have not been reported until very recently. In 1971 Ferraro3,4 reported that inductive electric fields are unimportant during the growth of the ring current and Wang and Kim5 pointed out that the electric fields induced by a decaying ring current during the recovery phase of a magnetic storm are quite substantial and should not be ignored. Here we show, using model calculations, that a decaying ring current is capable of producing the large scale electric fields in the magnetosphere.