HR: 1340h
AN: SH53B-0307    [Abstracts]
TI: A statistical comparison of solar wind sources of intense and moderate geomagnetic storms at solar maximum and minimum
AU: * Zhang, J
EM: jichunz@umich.edu
AF: Space Physics Research Laboratory, 2455 Hayward St., Universtiy of Michigan, Ann Arbor, MI 48109-2143 United States
AU: Liemohn, M W
EM: liemohn@umich.edu
AF: Space Physics Research Laboratory, 2455 Hayward St., Universtiy of Michigan, Ann Arbor, MI 48109-2143 United States
AU: Kozyra, J U
EM: jichunz@umich.edu
AF: Space Physics Research Laboratory, 2455 Hayward St., Universtiy of Michigan, Ann Arbor, MI 48109-2143 United States
AU: Thomsen, M F
EM: mthomsen@lanl.gov
AF: Los Alamos National Laboratory, P.O. Box 1663, Los Alamos, NM 87545 United States
AB: Superposed epoch analyses of 153 storms are performed to make a comparison of solar wind typical features of geomagnetic storm events at solar minimum (January, 1995 - June, 1997) and solar maximum (July, 1999 - June, 2002). In this study, geomagnetic storms are defined by the pressure corrected Dst (Dst$^{*}$) and classified into intense storms and moderate storms. After the seasonal distribution of storms in each category is shown,the average values of interplanetary magnetic fields (IMF), solar wind plasma, NOAA/POES Hemispheric Power, Kp and Dst$^{*}$ are analyzed and compared among different storm categories. Occurrence peak shiftings between intense storms and moderate storms are found in the storm seasonal distributions. It is shown that the peak of solar wind density leads minimum Dst* by 5.2-7.3 hours, which is longer than the peak time difference (0.5-1.0 hour) between IMF B$_{z}$ and Dst$^{*}$$_{min}$. During intense storms, it is found that much higher solar wind density and lower solar wind bulk flow speed at solar minimum than at solar maximum. The results obtained also show that the average interplanetary cause of intense storms is IMF B$_{s}$ ­Y 10 nT lasting for over 3 hours with longer duration and less fluctuations at solar maximum than at solar minimum. As for moderate storms, the primary cause is IMF B$_{s}$ ­Y 5 nT lasting for over 2 hours with almost no average value difference among solar wind parameters at solar maximum and minimum, except for higher solar wind temperature during moderate storms at solar minimum than at solar maximum. The interplanetary and solar origins of storms in different categories are also discussed.
DE: 7536 Solar activity cycle (2162)
DE: 2134 Interplanetary magnetic fields
DE: 2164 Solar wind plasma
DE: 2784 Solar wind/magnetosphere interactions
DE: 2788 Storms and substorms
SC: SPA-Solar and Heliospheric Physics [SH]
MN: 2004 AGU Fall Meeting