Abstract
Abstract. We analyzed observations of the solar activities and the solar wind parameters associated with large geomagnetic storms near the maximum of solar cycle 23. This analysis showed that strong southward interplanetary magnetic fields (IMFs), formed through interaction between an interplanetary disturbance, and background solar wind or between interplanetary disturbances are an important factor in the occurrence of intense geomagnetic storms. Based on our analysis, we seek to improve our understanding of the physical processes in which large negative Bz's are created which will lead to improving predictions of space weather. Key words. Interplanetary physics (Flare and stream dynamics; Interplanetary magnetic fields; Interplanetary shocks)
Highlights
According to Tsurutani and Gonzalez (1997 and references therein), interplanetary events with interplanetary magnetic fields (IMFs), Bz, of less than −10 nT and a duration longer than three hours, tend to cause intense geomagnetic storms
We studied the interplanetary disturbances with strong southward IMF near the maximum of solar cycle 23
Southward IMF is an important factor in the intensity and duration of geomagnetic disturbances
Summary
According to Tsurutani and Gonzalez (1997 and references therein), interplanetary events with interplanetary magnetic fields (IMFs), Bz, of less than −10 nT and a duration longer than three hours, tend to cause intense geomagnetic storms. Tsurutani et al (1988) have made a study of the causes of the southward Bz component responsible for major geomagnetic storms near the previous solar maximum (1978–1979). From their analysis of 10 cases they concluded that the negative Bz was caused by internal fields of ejecta for only four cases. Cyr (2000) studied all halo/partial, halo coronal mass ejections (CMEs) detected by the LASCO coronagraphs on board the SOHO spacecraft during 1996–1999 and compared them to geomagnetic storms They noted that the southward IMF associated with ejecta determined mainly their geo-effectiveness, regardless of whether ejecta was a magnetic cloud structure or not.
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