HR: 1330h
AN: SM32A-1135    [PDF]
TI: Investigation of IMF Trigger Structure of Substorms by Using Multi-Satellites Observations
AU: * Hsu, T
EM: thsu@igpp.ucla.edu
AF: IGPP/UCLA, 405 Hilgard Ave., Los Angeles, CA 90066 United States
AU: McPherron, R L
EM: rmcpherr@igpp.ucla.edu
AF: IGPP/UCLA, 405 Hilgard Ave., Los Angeles, CA 90066 United States
AB: To understand the magnetospheric substorm, it is necessary to determine whether substorm onset is always externally triggered by the interplanatery magnetic field (IMF) or whether substorm onset sometimes occurs spontaneously as a result of internal processes. Lyons [1995; 1996] argued that substorms must be triggered by external changes in the IMF and/or the solar wind. Specifically, Lyons [1996] argued that events without apparent triggers were likely to be a non-substorm disturbance such as a convection bay [Pytte et al., 1978]. The hypothesis that most or perhaps all substorms are triggered has initiated considerable interest in substorm triggering studies. Over the past decade, several studies have demonstrated that a majority of substorms (~60%) appear to be triggered by the IMF. However, 40% of all substorms appear to begin without obvious IMF perturbations. A stasitical analysis determining the average characteristics of triggered and non-triggered substorm in the magnetotail and geosynchronous orbit was performed by Hsu and McPherron [2003]. It was found that the average response in the tail field and plasma suggests no qualitative difference between the two classes of events. However, the magnitude of the response is different. Triggered substorms exhibit a larger response than non-triggered ones. This surprising result has been suggested to be a manifestation of undetected small scale structures in the IMF. Small structures are suggested to have weak driving fields of short duration and hence transfer less energy to the magnetosphere. To investigate this hypothesis, multi-satellite observations are required to eliminate the possibility of missing IMF trigger structures. In this study the authors will use multi-satellite observations to examine how frequently different IMF structure are observed at different locations in the solar wind. Specifically, data from 1977 to 1984 when at least two of the ISEE1, ISEE2, ISEE 3 and IMP8 spacecraft were in the solar wind will be used to examine the size and scale of the structures that trigger substorm onsets.
DE: 2744 Magnetotail
DE: 2784 Solar wind/magnetosphere interactions
DE: 2788 Storms and substorms
SC: SPA - Magnetospheric Physics [SM]
MN: 2003 Fall Meeting