HR: 14:25h
AN: SM33B-04    [Abstracts]
TI: Estimation of the Substorm-Related Variation of the Ring Current Intensity from the Sym-H Index
AU: * Ohtani, S
EM: ohtani@jhuapl.edu
AF: The Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Rd., Laurel, MD 20723-6099 United States
AU: Ukhorskiy, A Y
EM: UKHORAY1@jhuapl.edu
AF: The Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Rd., Laurel, MD 20723-6099 United States
AU: C:son Brandt, P
EM: BRANDPC1@jhuapl.edu
AF: The Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Rd., Laurel, MD 20723-6099 United States
AU: Mitchell, D G
EM: MITCHDG1@jhuapl.edu
AF: The Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Rd., Laurel, MD 20723-6099 United States
AB: The development of magnetospheric storms has been conventionally addressed in terms of the Sym-H(Dst) index, which is ideally regarded as a measure of the ring current intensity. However, it is highly likely that a considerable fraction (~25%) of storm-time Sym-H reduction can be actually attributed to the tail current. Furthermore, the results of previous studies strongly suggest that the substorm-associated variations of the tail current and the ring current have opposite effects on Sym-H, and that the former overcompensates the latter. Thus, for the substorm timescale, using the Sym-H index as a measure of the ring current intensity is misleading with regard not only to the intensity of the ring current but also to the timing of the ring current development and decay. In the present study we address this issue by decomposing storm-time variations of Sym-H into {\it low-frequency} and {\it high-frequency} components. It is inferred that the {\it low-frequency} component is driven mostly by magnetospheric convection, whereas the {\it high-frequency} component includes most of substorm-related variations. Using the total energetic neutral atom (ENA) flux measured by the IMAGE/HENA instrument as a proxy of the ring current intensity, we quantitatively address how this {\it high-frequency} component is related to the variation of the ring-current intensity.
DE: 2708 Current systems (2409)
DE: 2720 Energetic particles, trapped
DE: 2722 Forecasting
DE: 2778 Ring current
DE: 2788 Storms and substorms
SC: SPA-Magnetospheric Physics [SM]
MN: 2004 AGU Fall Meeting