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Enhancement of optical aurora triggered by the solar wind negative pressure impulse (SI−)

A geomagnetic negative sudden impulse (SI−) occurred on 3 August 1997 in association with a sudden decrease of solar wind dynamic pressure. The discrete auroras observed by an all‐sky TV imager at Zhongshan in Antarctica (magnetic latitude is ∼74.5°S) suddenly enhanced their luminosity and moved poleward at the time of the SI−. Following the primary enhancement, three cycles of quasi‐periodic luminosity pulsations were observed with periods of about 10–14 min and their average position drifted equatorward. The luminosity pulsations showed one‐to‐one correspondence with the magnetic pulsations, with the characteristic features of a field‐line resonance. The low‐altitude DMSP‐F13 satellite was almost directly over Zhongshan and observed accelerated electron precipitation with an inverted ‘V' structure and an upward field‐aligned current. These signatures suggest that the solar wind negative pressure impulse triggered a field‐line resonance of the geomagnetic field. The resonance caused the upward and downward field‐aligned current sheets, and the field‐aligned electron acceleration.