HR: 15:09h
AN: SM23B-06    [Abstracts]
TI: Periodic magnetospheric substorms and the effect of solar wind
AU: * Huang, C
EM: cshuang@haystack.mit.edu
AF: MIT Haystack Observatory, Route 40, Westford, MA 01886 United States
AU: Foster, J
AF: MIT Haystack Observatory, Route 40, Westford, MA 01886 United States
AU: Reeves, G
AF: Los Alamos National Laboratory, NIS-1, Los Alamos, NM 87545 United States
AU: Le, G
AF: NASA Goddard Space Flight Center, Laboratory for Extraterrestrial Physics, Greenbelt, MD 20771 United States
AU: Chau, J
AF: Radio Observatorio de Jicamarca, Instituto Geofisico del Peru, Lima, 13-0207 Peru
AU: Yumoto, K
AF: Kyushu University, 6-10-1 Hakozaki, Fukuoka, 812-8581 Japan
AB: Periodic magnetospheric substorms can last for 6-10 cycles with a nearly constant period of ~3 hours. The characteristics of the substorms include periodic magnetic reconnection onsets in the near tail between X = -20 and -30 Re, sawtooth-like injections of energetic charged plasma fluxes from the tail into the inner magnetosphere, periodic intensifications of the auroral electrojet, and other periodic variations in the magnetosphere and ionosphere. An outstanding problem is whether the period of the substorms is determined by the solar wind or by the magnetosphere. We will show that periodic substorms can occur when the IMF is continuously southward or fluctuating between southward and northward. The period of the substorms during fluctuating IMF is nearly the same as that during continuously southward IMF. The substorms have a narrow spectrum with a strong peak at periods of ~3 hours, while the solar wind has a broad spectrum and does not have the same peak as the substorms. Large sudden changes in the solar wind (northward IMF turning or solar wind pressure impulses) after an interval of southward IMF do not necessarily trigger substorm onsets. Periodic variations in some geomagnetic indices (such as Dst and polar cap index) during periodic substorms are caused by the substorms but not by solar wind pressure fluctuations. The observations show that the period of substorms is not controlled either directly by fluctuations in the solar wind or indirectly by the energy transferred to the magnetosphere from the solar wind. We suggest that a sudden change in the solar wind can trigger a substorm onset if and only if the magnetosphere has reached a state conducive to the generation of substorms. Substorms will occur every ~3 hours, no matter whether the IMF is continuously southward or fluctuating between southward and northward. The period of the substorms is determined by some internal processes of the magnetosphere.
DE: 2435 Ionospheric disturbances
DE: 2712 Electric fields (2411)
DE: 2740 Magnetospheric configuration and dynamics
DE: 2788 Storms and substorms
SC: SPA-Magnetospheric Physics [SM]
MN: 2004 AGU Fall Meeting