On the distribution of electric fields in the magnetosphere

The magnetic storm theories of Alfvén, Axford and Hines, and Dungey imply that an electrostatic potential difference exists across the magnetosphere. The detailed distribution of the resulting electric fields is, as yet, unknown. The present study is an attempt to solve this problem, assuming that a plasma with continuous energy spectrum is injected, by some unknown mechanism, into the magnetosphere. It is shown that space charges will occur owing to the different forbidden regions for particles of different charge and energy. The space charges will tend to suppress the applied potential and to push the field toward the outer parts of the magnetosphere, leaving a field-free region in the center. The size of the field-free region depends on the applied potential and the density and spectrum of the injected particles. The field-free region may be identified with the region containing the whistler medium. Outside this region the thermal plasma is swept away by the electric fields. In a first tentative approximation the auroral zone is found to be situated at an L value 52% larger than the L value of the field-free boundary.