Electrodynamics of rotating planetary plasmaspheres in a dipole magnetic field

Abstract

As a model of the actual structure of the planetary plasmasphere, we consider the electrodynamical problem of electric field and current generation by a planet with a dipole magnetic field corotating with the plasma envelope. The plasma envelope is characterized by the conductivity and angular velocity of the magnetospheric plasma as functions of the distance τ from the planet center and the angle ϑ measured from the rotation axis. The exact solutions of the Maxwell equations are obtained in the axially symmetric case within the framework of unipole electrodynamics when the rotational and magnetic axes coincide. These solutions describe the possible distributions of electric fields, currents, and charges in the rotating plasma envelope surrounding the magnetized planet. As an exmple, we constructed, using the theory proposed, the exact solution corresponding to the following structure of the plasmasphere:

• 1) the plasmasphere region corotating with the planet and located between L-shells (L=τ/Rsin ² ϑ, where R is the radius of the planet) from L=1 to L=L_*;

• 2) the polar region with differential, spherically symmetric rotation;

• 3) the transient region of the plasmasphere rotating differentially with the angular velocity dependent on the L-number and located between L-shells from L=L_* to L=L_*+L₀;

• 4) the external (vacuum) region.

Analysis of the multipole expansion of the electrostatic potential showed that the electric field potential is equal to zero in the external region (L>L_*+L₀), independently of the number of the boundary L-shell. This solution can serve as a basis for simulation of the plasmasphere formation processes, taking into account the actual conditions in the near-planetary plasma envelopes.