Abstract
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.
Highlights
The coupling between the solar wind, magnetosphere, and ionosphere is an important subject in the field of solarterrestrial physics. Dungey (1961) postulated an open magnetosphere in which the southward interplanetary magnetic field (IMF) merges with the Earth’s dipole magnetic field
The orientation of the two-cell aurora determined by the tangent to the locus of the maximum emission as one moves azimuthally along the region of auroral emissions was at an angle of ∼49◦ to the Defense Meteorological Satellite Program (DMSP) trajectory
We have found that the orientation of the magnetic deflection vector produced by the region 1 field-aligned current changed from the growth phase to the substorm expansion phase
Summary
The coupling between the solar wind, magnetosphere, and ionosphere is an important subject in the field of solarterrestrial physics. Dungey (1961) postulated an open magnetosphere in which the southward interplanetary magnetic field (IMF) merges with the Earth’s dipole magnetic field. Some of the other part of the solar wind energy is stored in the magnetotail and released into the ionosphere during the substorm expansion phase. The electrojet system can be separated into two categories according to signatures determined with data from ground-based magnetometer stations These two categories are commonly denoted as disturbance polar of the first type (DP 1) and disturbance polar of the second type (DP 2) (Nishida, 1968). The DP 1 system represents the loading-unloading process, while the DP 2 system represents the direct-driven process in the solar wind-magnetosphere coupling. The former is related to a sudden energy release, which is denoted as the substorm electrojet. The relative importance of the convection and substorm electrojets to the electric field and conductance depends on the locations of the electrojets and the phase of substorms (Kamide, 1982; Kamide and Kokubun, 1996)
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