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Ann. Geophys., 24, 203-214, 2006
www.ann-geophys.net/24/203/2006/
© European Geosciences Union 2006
Ionospheric characteristics of the dusk-side branch of the two-cell aurora
J.-H. Shue1, P. T. Newell2, K. Liou2, C.-I. Meng2, M. R. Hairston3, and F. J. Rich4
1Institute of Space Science and Dept. of Atmospheric Sciences, National Central University, Jhongli, Taoyuan 32001, Taiwan
2The Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, MD 20723, USA
3Center of Space Science, University of Texas in Dallas, POB 830688, Richardson, TX 75083, USA
4Air Force Research Laboratory/VSBXP, 29 Randolph Road, Hanscom AFB, MA 01731, USA
Abstract. The two-cell aurora is characterized by azimuthally elongated
regions of enhanced auroral brightness
over extended local times in the dawn and dusk sectors.
Its association with the convection, particle
precipitation, and field-aligned currents under various
phases of substorms has not been fully
understood. With Polar Ultraviolet Imager auroral images
in conjunction with Defense Meteorological Satellite Program (DMSP)
F12 spacecraft on the dusk-side branch of the two-cell aurora, we are
able to investigate an association of the auroral emissions with
the electric fields, field-aligned currents, and energy flux
of electrons. Results show that the substorm expansion onset
does not significantly change the orientation of the dusk-side branch of
the two-cell aurora. Also, the orientation of the magnetic
deflection vector produced by the region 1 field-aligned current
changed from 73±1° to the DMSP trajectory
during the substorm growth phase, to 44±6°
to the DMSP trajectory during the substorm expansion phase.
With a comparison between the orientation of the dusk-side branch of
the two-cell aurora and the orientation of the magnetic deflection
vector, it is found that the angular difference between
the two orientations is 28±5°
during the substorm growth phase, and 13±6°
during the substorm expansion phase.
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