Magnetosphere-ionosphere coupling in the Harang region

Octav Marghitu (1), Costel Bunescu (1), Tomas Karlsson (2), Berndt Klecker (3)

(1) Institute for Space Sciences, Bucharest, Romania
(2) Space and Plasma Physics, Royal Institute of Technology, Stockholm, Sweden
(3) Max Planck Institute for Extraterrestrial Physics, Garching, Germany

The current configuration in the Harang region (HR), between the
evening and morning sectors of the auroral oval, is believed to
consist typically of one upward field-aligned current (FAC) sheet, fed
from the sides, via meridional Pedersen currents, by downward FAC
sheets. We present FAST observations indicating that the ionospheric
current closure in the HR is sometimes dominated by the longitudinal
coupling of FAC sheets with electrojet currents. The current
configuration at ionospheric level suggests azimuthal current closure
in the magnetosphere, contributing to the asymmetry of the ring
current in the dusk sector, and to the cancellation of the cross-tail
current at substorm onset. The auroral current circuit appears to be a
mix of the 'Type 1' and 'Type 2' configurations introduced by Bostrom
(1964), and may represent a relevant M-I coupling mode in the HR. In
the upward current region, if the divergence of the electrojet is
related primarily to the variation of the conductance, the FAC--EJ
coupling is realized mainly by Hall currents for a wide energy range
of the precipitating electrons. In this case the Joule effect has
little contribution to the energy dissipation in the ionosphere, which
is achieved mainly by collisions of the accelerated electrons.