Y. Mei et al., CUSP CURRENTS FROM IONOSPHERIC VORTICITY GENERATED BY GASDYNAMIC AND MERGING FLOW-FIELDS AT THE MAGNETOPAUSE, J GEO R-S P, 100(A5), 1995, pp. 7641-7647
Cusp currents that arise from ionospheric vorticity generated by the c
ombined merging outflow and gasdynamic flow fields at the magnetopause
, as proposed by Saunders (1989), are quantified and compared with tho
se calculated by Mei et al. (1994) from vorticity, generated by mappin
g the solar wind electric field into a limited cusp region of the pola
r cap, as proposed in the synthesis view of Banks et al. (1984). The r
esults are essentially identical for strong interplanetary magnetic fi
eld (IMF) B-y, thus demonstrating equivalence,between mechanical and e
lectrical descriptions of reconnection-driven convection. For southwar
d IMF, however, the mechanical description yields weak cusp currents w
ith dawn-dusk bipolarity, as deduced from early observations by Iijima
and Potemra (1976), whereas the electrical description yields none. T
he bipolar currents arise from the diverging pattern of gasdynamic flo
w. The currents become unipolar as B-y increases and the asymmetry of
the merging outflow dominates. Additional cusp currents in both models
arise at kinks in the flow contours (additional ionospheric vorticity
) around the border of the cusp region, owing to limiting the area of
mapping from the magnetopause. The border currents form a bipolar pair
that rotates around the circumference of the cusp as the IMF rotates
in clock angle. They dominate the currents arising from vorticity with
in the cusp.