HR: 0800h
AN: SM31A-02    [Abstracts]
TI: Field-Line (Euler-Potential) Model of the Ring Current
AU: * Schulz, M
EM: mike.schulz@lmco.com
AF: Lockheed Martin Advanced Technology Center, Dept ADCS, Bldg 255, 3251 Hanover Street, Palo Alto, CA 94304, United States
AU: Chen, M W
EM: margaret.w.chen@aero.org
AF: Space Science Applications Laboratory, The Aerospace Corporation, M2-260, PO Box 92957, Los Angeles, CA 90009, United States
AB: The equation of a magnetic field line in Dungey's model magnetosphere (dipole field plus uniform southward ΔB parallel to the dipole axis) is r = La[1 + (r³/2b³)]sin²θ, where r is the radial distance from the point dipole, a is the planetary radius, θ is the magnetic colatitude, and b (~ 12a, but possibly time-dependent) is the radius of the circular neutral line in Dungey's model. The dimensionless parameter L is inversely proportional to the amount of magnetic flux enclosed by the corresponding magnetic shell. The model for B thus described is curl-free and therefore current-free. In the present work we explore a formally similar B-field model in which the parameter b is allowed to vary spatially with L and possibly with φ (magnetic local time), so that the added field is no longer uniform nor even necessarily unidirectional. Our purpose is to simulate (in an analytically controllable way) the outward stretching of magnetic field lines associated with the presence of a mainly azimuthal ring current. To obtain a definite result and thereby test the model for reasonableness, we apply this method to the equatorial ring-current field model of Schulz [JGR, 102, 14149~14154, 1997], for which the amount of magnetic flux enclosed (a quantity inversely proportional to L) is expressible analytically as a function of equatorial radial distance r₀. This approach yields the parameter b as a function of L for a specified model of equatorial ΔB. It thereby yields the Euler potential α (directly proportional to 1/L) as a function of r₀, and therefore (from the equation of a generic field line) as a function of r and θ throughout the model magnetosphere. Moreover, since magnetic field lines are considered to lie in meridional planes for purposes of this construction, the magnetic field B itself is given by B = grad α × grad φ. Representative field-line configurations will be shown graphically for selected values of Dst.
DE: 2704 Auroral phenomena (2407)
DE: 2740 Magnetospheric configuration and dynamics
DE: 2778 Ring current
DE: 2788 Magnetic storms and substorms (7954)
DE: 2794 Instruments and techniques
SC: SPA-Magnetospheric Physics [SM]
MN: 2007 Joint Assembly