Radial Transport of Io Plasma From the Inner Magnetosphere to the Tail

The solar wind-Jovian magnetosphere-ionosphere interaction is studied from the global magnetohydrodynamic simulation. The calculation considers the high-speed solar wind, Io plasma emission, high-speed rotation, ionospheric ions, and precession of magnetic field, and consequently reproduces the confinement of Jovian magnetic field, distributions of O+ and H+, supply of H+ by the polar wind, the interchange instability, and the current system that maintains co-rotation. The radial transport process of plasma generated from Io is traceable from this solution, such that the transport mechanism gradually changes from the Io torus to the distant tail. In the transport of Io plasma, the precession plus interchange instability is effective near 10-15 Rj, interchange instability is predominant around 15-20 Rj, and the centrifugal force is predominant beyond 25 Rj. The current system supplies torque from the planet to co-rotating plasma beyond 25 Rj to compensate the rotation delay. The associated upward field-aligned current (FAC) is connected to the main emission (ME) in the ionosphere. The polar emission (PE) position coincides with that of downward feedback current of upward FAC causing the ME. High-speed polar wind develops in the ME and in the polar cap, while slow polar wind develops in lower latitudes. In the middle of transport, Io plasma is mixed around 15 Rj with H+ supplied from the ionosphere by the low-speed polar wind. Afterward, mixed plasma diffuses outward. The equatorial diffuse emission occurs in the projected position of the plasma mixing process.