Physics
Scientific paper
May 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agusmsm44b..04s&link_type=abstract
American Geophysical Union, Fall Meeting 2007, abstract #SM44B-04
Physics
2704 Auroral Phenomena (2407), 2716 Energetic Particles: Precipitating, 2740 Magnetospheric Configuration And Dynamics, 2778 Ring Current, 2788 Magnetic Storms And Substorms (7954)
Scientific paper
The equation of a magnetic field line (labeled L) in Dungey's model magnetosphere (dipole field plus uniform southward ΔB) is r = La[1 + (r3/2b3)]sin2θ, where r denotes geocentric distance, θ denotes magnetic colatitude, a is the Earth's radius, and b is the radius of the field model's equatorial neutral line. This model can be generalized (e.g., to accommodate a ring current) by treating b as a function of L and φ (magnetic local time) rather than as a constant, so as to yield measured or calculated values of the equatorial magnetic field B0. (In this generalization the equatorial neutral line has a radius b*(φ) = (3a/2)L*(φ) for some particular φ-dependent value of L called L*.) This approach yields an estimate for how a specified distortion of equatorial B0 might map to higher latitudes. It also allows for analytical calculation of the current density J = (c/4π)(curl B) at arbitrary latitude. Since charged particles (of scalar momentum p) scattered strongly in pitch angle satisfy an adiabatic invariant λ = p3Ψ, where Ψ is the flux-tube volume (per unit magnetic flux), it is of interest to approximate (as well as possible the flux-tube volume Ψ as a function of L and φ. By generalizing the calculation of Schulz [JGR, 103, 61-67, 1998], we have found such an analytical approximation of Ψ for arbitrarily non-constant b and are proceeding to use it in bounce-averaged transport simulations of diffuse auroral electrons.
Chen Margaret W.
Schulz Michael
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