Angular momentum transfer at Jupiter: boundary conditions required by field-aligned potential

Details Angular momentum transfer at Jupiter: boundary conditions required by field-aligned potential Angular momentum transfer at Jupiter: boundary conditions required by field-aligned potential

Dec 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufmsm11c..10v&link_type=abstract

American Geophysical Union, Fall Meeting 2009, abstract #SM11C-10

Physics

[2704] Magnetospheric Physics / Auroral Phenomena, [2721] Magnetospheric Physics / Field-Aligned Currents And Current Systems, [2736] Magnetospheric Physics / Magnetosphere/Ionosphere Interactions, [2756] Magnetospheric Physics / Planetary Magnetospheres

Scientific paper

The partial corotation of plasma in the magnetospheres of Jupiter and Saturn is closely connected with angular momentum transfer from the planet to the magnetosphere and particularly at Jupiter may also produce the main part of the aurora, by the action of Birkeland (magnetic-field-aligned) currents. In the classical theory of the inertial limit to corotation (T. W. Hill, 1979), the radial profile of azimuthal plasma flow is derived as the solution of a first-order differential equation, which requires one boundary condition, usually taken as full corotation at the low-latitude boundary. With the aurora ascribed to electrons accelerated by electric fields parallel to the magnetic field, field-aligned potential differences (neglected in the classical theory) need to be considered. These are expressed as functions of Birkeland current density, most commonly by some version of the formula introduced by S. Knight (1973). The resulting differential equation is of third order and hence requires three boundary conditions. The specification and physical meaning of the two additional boundary conditions (besides full corotation at the inner boundary) will be discussed, and previous treatments (invoking some ad hoc assumption, or simply evading the question) will be critically examined. Since the plasma flow in the ionosphere is no longer assumed equal to the flow mapped from the magnetosphere, the flow equation in the ionosphere — a second-order elliptic equation — enters explicitly; hence a specific assumption about what happens at the high-latitude well as at the low-latitude boundary must be made. The requirement that the discontinuity of the Knight formula at the critical value of Birkeland current density not lead to non-removable discontinuities of any quantity that is differentiated in the basic equations (in particular, no jumps of the parallel potential) may also imply a boundary condition.

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