A time dependent model of the Jovian current sheet

Abstract

From analysis of vector helium magnetometer measurements obtained during the Pioneer 10 outbound pass through the Jovian magnetosphere it is argued that the average location of the near‐equatorial current sheet is a surface whose shape is determined by the velocity at which the magnetic perturbations produced by a rotating tilted dipole propagate to large radial distances. The equation of the surface in Jovigraphic spherical polar coordinates is cos[ϕ s +Ω (r s ‐r o )/v r + cot λ cot θ s = 0, where Ω is the angular velocity of planetary rotation ϕ s = −Ω(t‐t o ), λ is the angle between Ω and the planetary magnetic moment, v r is an effective velocity for the radial transport of magnetic perturbations, and r o is the Jovicentric distance to the source of the field. This surface rotates rigidly with the planet and so is time independent in a rotating coordinates system, a feature of the model which would change if the obvious asymmetry of external boundary conditions were considered. For appropriately defined v r and r o the expression is applicable to either of the basic models which have been discussed for the outer magnetosphere, i.e., an outflow model or a quasi‐static disk model. Fits to the data are used to evaluate the parameters, and the values v r = 43 R J /h and r o = 14 R J are obtained from the least squares fit to the averages of observed current sheet crossings.