Na. Tsyganenko et Dp. Stern, MODELING THE GLOBAL MAGNETIC-FIELD OF THE LARGE-SCALE BIRKELAND CURRENT SYSTEMS, J GEO R-S P, 101(A12), 1996, pp. 27187-27198
Quantitative models are developed for representing the global distribu
tion of the average magnetic field produced by the region 1 and 2 Birk
eland current systems. The problem is solved in four following steps:
(1) constructing a realistic hit-dependent model of the Birkeland curr
ent sheets, based on the formalism of Euler potentials, (2) numericall
y computing their field at a large number of points within the modelin
g region, (3) finding a best-fit analytical approximation for that fie
ld, and (4) adding a current-free shielding held which confines the Bi
rkeland held within the model magnetopause. At low altitudes the model
field-aligned currents reach the ionosphere along eccentric ovals, wh
ich fit the observed region I and 2 zones of Iijima and Potemra, and t
hey continue there as horizontal currents. At larger distances the nig
htside region I currents map to the plasma sheet boundary layer and ar
e then diverted toward the tail flanks, while currents in the dawn-dus
k and dayside sectors connect directly to the higher-latitude magnetop
ause. The region 2 current closes azimuthally near the equator, formin
g a spread-out partial ring current system. The described approach all
ows a great flexibility in the geometry of the Birkeland currents, mak
ing it feasible to infer their properties from spacecraft data.