HR: 10:35h
AN: SM42A-02    [Abstracts]
TI: Semiannual Variation of Geomagnetic Activity: Protons or Photons?
AU: * Svalgaard, L
EM: agu@leif.org
AF: Easy Toolkit, Inc., 6927 Lawler Ridge, Houston, TX 77055-7010 United States
AU: * Svalgaard, L
EM: agu@leif.org
AF: STEL, Nagoya University, Honorara 3-13, Toyokawa, 442-8507 Japan
AU: Schulz, M
EM: mike@stelab.nagoya-u.ac.jp
AF: STEL, Nagoya University, Honorara 3-13, Toyokawa, 442-8507 Japan
AU: Schulz, M
EM: mike@stelab.nagoya-u.ac.jp
AF: Lockheed Martin Advanced Technology Center, Hanover Street, Palo Alto, CA 94304 United States
AU: Cliver, E W
EM: Edward.Cliver@hanscom.af.mil
AF: Space Vehicle Directorate, AFRL, Hanscom AFB, MA 01731 United States
AB: The cause(s) of the semiannual variation (SAV) of geomagnetic activity is a problem of long standard ($\sim$100 years). The various mechanisms put forward can be divided into 'excitations' and 'modulations'. Using 45 years of the am-index, we show that the SAV is a modulation of existing activity. The modulation is a function of the angle between the Earth's dipole moment and either (1) the aberrated solar wind velocity and/or (2) the sun-Earth line, causing both time of year and time of day (UT) variations. Here we examine the correlation of geomagnetic activity with directions (1) and (2). Mechanisms involving interaction between the solar wind and the magnetopause would correlate best with direction (1). Mechanisms involving ionospheric conductance would correlate best with direction (2).
DE: 7899 General or miscellaneous
DE: 2708 Current systems (2409)
DE: 2731 Magnetosphere--outer
DE: 2740 Magnetospheric configuration and dynamics
DE: 1555 Time variations--diurnal to secular
SC: SPA-Magnetospheric Physics [SM]
MN: 2004 AGU Fall Meeting