HR: 1330h
AN: SH42A-0478    [PDF]
TI: A Statistical Study on the Geoeffectiveness of Magnetic Clouds During High Solar Activity Years
AU: * Zhang, J
EM: jichunz@engin.umich.edu
AF: Space Physics Research Laboratory(SPRL), University of Michigan, Ann Arbor, Space Research Building(SRB) 2455 Hayward St., Ann Arbor, MI 48109-2143 United States
AU: Liemohn, M W
EM: liemohn@engin.umich.edu
AF: Space Physics Research Laboratory(SPRL), University of Michigan, Ann Arbor, Space Research Building(SRB) 2455 Hayward St., Ann Arbor, MI 48109-2143 United States
AU: Kozyra, J U
EM: jukozyra@umich.edu
AF: Space Physics Research Laboratory(SPRL), University of Michigan, Ann Arbor, Space Research Building(SRB) 2455 Hayward St., Ann Arbor, MI 48109-2143 United States
AU: Lynch, B J
EM: lynchb@umich.edu
AF: Space Physics Research Laboratory(SPRL), University of Michigan, Ann Arbor, Space Research Building(SRB) 2455 Hayward St., Ann Arbor, MI 48109-2143 United States
AU: Zurbuchen, T H
EM: thomasz@umich.edu
AF: Space Physics Research Laboratory(SPRL), University of Michigan, Ann Arbor, Space Research Building(SRB) 2455 Hayward St., Ann Arbor, MI 48109-2143 United States
AB: Using the Dst* index and solar wind IMF \& plasma data from 1998.001 to 2002.127 in which solar activities are high, we have statistically examined the relationship of 270 storms (Dst*­š-30nT) to 104 magnetic clouds. It is found that most of the magnetic clouds can result in geomagnetic storms, but only about 30% of storms are due to magnetic clouds. A storm can be induced by the sheath, the leading, the axial, the trailing field, both the leading and trailing fields, or both the sheath and leading or trailing fields of a cloud with 9.6%, 22.1%, 8.7%, 12.5%, 1.0%, 16.4%, 5.8% occurrence percentages, respectively. However, different levels of geomagnetic activity have different occurrence percentages due to different cloud fields. The occurrence percentage of intense storms caused by clouds is 72%, which is much higher than the around 20% occurrence percentage of smaller storms caused by clouds. It is also shown that Unipolar Bz and Bipolar Bz clouds have different geoeffectiveness percentages and the long-known hypothesis of southward Bz control of magnetic activity is supported by the results of this study. Because multiple-step development storms can result not only from both sheath and cloud fields but also from different fields within a cloud, the geoeffectiveness of the fields within the clouds are statistically studied in more detail than before.
UR: http://www-personal.engin.umich.edu/~jichunz/
DE: 2111 Ejecta, driver gases, and magnetic clouds
DE: 2700 MAGNETOSPHERIC PHYSICS
DE: 2731 Magnetosphere--outer
DE: 2784 Solar wind/magnetosphere interactions
DE: 2788 Storms and substorms
SC: SPA - Solar and Heliospheric Physics [SH]
MN: 2003 Fall Meeting