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Three DMSP 31 (Defense Meteorological Satellite Program) auroral photographs are presented to show that there is a particular type of polar cap auroral arc which lies parallel to oval arcs in the evening sector and which bends away from the oval to the usual sun-earth line direction near the poleward boundary of the oval in the midnight sector. The occurrence of this type of polar cap arc is, however, not common.
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Meng et al. (1976) studied this question.
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