References

J. Geophys. Res., VOL.105, NO.A8, PAGES 18,835-18,846, AUGUST 1, 2000

Geomagnetic Negative Sudden Impulse due to
a Magnetic Cloud Observed on May 13, 1995

T. Takeuchi, T. Araki, H. Luehr, O. Rasmussen,
J. Watermann, D. K. Milling, I. R. Mann,
K. Yumoto, K. Shiokawa, and T. Nagai



Abstract


A geomagnetic negative sudden impulse (SI-) observed on May 13, 1995, was examined using magnetic field data from ETS VI and GOES 7 in the magnetosphere and ground geomagnetic observation networks. The SI- was caused by a sudden decrease in the solar wind dynamic pressure at the front boundary of a magnetic cloud embedded in a density enhancement region. The amplitude and the fall time at Kakioka geomagnetic observatory (magnetic latitude 26.9, magnetic longitude 208.3) were 26 nT and 10 min, respectively. Although SI- has been considered to be the mirror image of geomagnetic positive sudden impulse (SI+) or sudden commencement (SC), we found the polarization distribution of the SI- consistent with that of SC. We suggest that the contribution from the longitudinal movement of a twin vortex ionospheric current system is the dominant factor to produce the polarization of SC and SI-. We also discuss the relationship between the angle at which discontinuities in the solar wind impinge upon the magnetosphere and the geomagnetic response.



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