Four-Dimensional Empirical Model for the Peak Density Structure of the Io Plasma Torus

Author: Charles A. Peterson and William H. Smyth
Date: 
July 7, 2008
Type: 
Journal Article
Venue: 
Bulletin of the American Astronomical Society
Citation: 

Peterson, C.A. and W.H. Smyth (2008) Four-Dimensional Empirical Model for the Peak Density Structure of the Io Plasma Torus, BAAS 40, 476-477.

A four-dimensional (dipole L, magnetic latitude, magnetic longitude, and local-time) empirical model is being developed to describe more accurately the peak density structure of the plasma torus electrons and heavy ions that occurs radially near and inside of Io's orbit. Based upon suitable physical scenarios, the model can determine the L-shell latitudinal distribution of ions for plasma conditions measured in the plasma torus at one 4-D location and map it to its corresponding L-shell distribution at another 4-D location. Consequently, the model can be used to compare and investigate physical torus conditions for both in situ and remote ion emission observations acquired at different epochs and for various local-times and System III longitudes. The current model includes System III longitudinal and local-time asymmetries in the location of the peak density structure and in the ion and electron temperatures. The local-time asymmetries are created by the dawn-dusk electric field that is constructed to be equipotential along the magnetic field lines and is adjustable in overall magnitude and vector direction (i.e., not necessarily directed along the dawn-dusk line) in Jupiter's inertial frame. In the corotating magnetic coordinate frame, the dawn-dusk electric field is therefore time dependent and causes a small but important ExB drift of the plasma across magnetic field lines as it moves in local time about Jupiter. The plasma drift path is determined numerically for an adopted offset-tilted dipole description for Jupiter's magnetic field. Model calculations for in situ and remote ion emission images will be compared with selected spacecraft and ground-based measurements.