Radial diffusion of iogenic plasma in a centrifugally-driven turbulence
Abstract
A quantitative model of plasma diffusion from the Io torus, driven by the centrifugal force of Jupiter's rotation, is developed. It is argued that the unstable mode of perturbation, which would lead to a system of deterministic motion of plasma, should be dominated by a more turbulent mode of motion in order to effect a longer trapping time of the Iogenic plasma as implied by the observations. The energy of the turbulent motion is derived internally from the centrifugal potential of the planetary rotation. The length scale of the turbulence cells is determined by the interaction between the magnetospheric plasma and the dissipative ionosphere, and found to be of order 0.1 RJ for the Jovian magnetosphere. Since the cells are smaller than the dimension of the system, the transport of the plasma can be studied as a problem of eddy diffusion, governed by the Fokker-Planck equation. A specific model is established based on the above considerations. Investigation of this model shows that the nominal L-5 dependence of plasma density can be reproduced in an appropriate limit. Other details of the density distribution (e.g. the density ramp located at L = 7.5) can be attributed to the spatial variation of the ionospheric Pedersen conductance. The density ramp implies a conductivity peak in its magnetically conjugate ionosphere. The conductivity profile consistent with the observed density distribution is solved. The inward expansion of the Io torus effected by fringing electric field of the outer torus is also briefly discussed.
- Publication:
-
Planetary and Space Science
- Pub Date:
- August 1990
- DOI:
- 10.1016/0032-0633(90)90044-Q
- Bibcode:
- 1990P&SS...38..995L
- Keywords:
-
- Centrifugal Force;
- Io;
- Planetary Ionospheres;
- Planetary Rotation;
- Plasma Currents;
- Plasma Turbulence;
- Density Distribution;
- Ionospheric Propagation;
- Jupiter (Planet);
- Lunar and Planetary Exploration