HR: 0830h
AN: SM51A-11    [Abstracts]
TI: Failure of Dst index fields to represent a ring current
AU: * Campbell, W H
EM: bcampbel@colorado.edu
AF: Solar-Terrestrial Physics Division of NGDC/NOAA, 325 S.Broadway, Boulder, CO 80305 United States
AB: Two geomagnetic storms were chosen for their size, isolation, seasonal difference, and global data availability. For these storm periods, records from all available stations, within the latitude range of Dst contributors, were collected to choose those pairs having similar longitude. Four-hour average fields centered at local noon and midnight were compared. The 1/Cos(theta) factor, used for the Dst derivation, was applied to the paired data to determine if a Ring Current adjustment was worthwhile. Results indicate that the local station measurements behave not like Ring Current fields, but more like those from other current sources, such as the ionosphere and field-aligned currents. The cosine factor, used to adjust station fields for the magnetospheric ring current effect, typically fails. I also verified the daytime ionospheric enhancement of the disturbance field at the magnetic dip equator. The lognormal form of the Dst, a result of multi-source Dst behavior, was verified. The Dst appellation "Equatorial Ring Current Index" is clearly a misnomer.
DE: 1555 Time variations--diurnal to secular
DE: 1599 General or miscellaneous
DE: 2415 Equatorial ionosphere
DE: 2708 Current systems (2409)
DE: 2736 Magnetosphere/ionosphere interactions
SC: SPA-Magnetospheric Physics [SM]
MN: 2005 Joint Assembly