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 as sociation with a sudden decrease of solar wind dynamic pressure. The discre te auroras observed by an all-sky TV imager at Zhongshan in Antarctica (mag netic latitude is similar to 74.5 degreesS) suddenly enhanced their luminos ity and moved poleward at the time of the SI-. Following the primary enhanc ement, three cycles of quasi-periodic luminosity pulsations were observed w ith periods of about 10-14 min and their average position drifted equatorwa rd. The luminosity pulsations showed one-to-one correspondence with the mag netic pulsations, with the characteristic features of a field-line resonanc e, The low-altitude DMSP-F13 satellite was almost directly over Zhongshan a nd observed accelerated electron precipitation with an inverted 'V' structu re and an upward field-aligned current. These signatures suggest that the s olar wind negative pressure impulse triggered a field-lint resonance of the geomagnetic field. The resonance caused the upward and downward field-alig ned current sheets, and the field-aligned electron acceleration.