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.