HR: 1340h
AN: SM43A-1135    [Abstracts]
TI: Earth-ionosphere transmission line model for an impulsive geomagnetic disturbance at the dayside geomagnetic equator
AU: * Kikuchi, T
EM: kikuchi@nict.go.jp
AF: National Institute of Information and Communications Technology, 4-2-1, Nukui-Kitamachi, Koganei, Tok 184-8795 Japan
AB: The near instantaneous onset of a geomagnetic impulse such as the preliminary reverse impulse (PRI) of the geomagnetic sudden commencement at high latitude and at the dayside geomagnetic equator has been explained by means of the TM0 mode waves in the Earth-ionosphere waveguide (Kikuchi and Araki, J. Atmosph. Terrest. Phys., 41, 927-936, 1979). There is, on the other hand, a time lag of the order of 10 sec in the peak amplitude of the magnetic impulse at the dayside equator. To explain these two temporal aspects, we examine transmission of the TM0 mode in a finite-length Earth-ionosphere transmission line composed of a finitely conducting ionosphere and the perfectly conducting Earth, with a fixed electric potential at one end and null potential at the other end of the transmission line, corresponding to the foot of a field-aligned current on the dawn- or dusk-side in the polar cap and middle point on the noon-midnight meridian at low latitude, respectively. Successive transmission and reflection in the bounded transmission line lead to that the ionospheric currents start to grow instantaneously, but reach a steady state with a relaxation time proportional to the length of the transmission line and the ionospheric conductivity. The relaxation time is of the order of 10 sec when we give high conductivity applicable to the equatorial ionosphere, which matches the observed time lag in the peak amplitude of the equatorial geomagnetic impulse. Consequently, the TM0 mode in the finite-length Earth-ionosphere transmission line explains both the instantaneous onset and time lag in the peak amplitude of the geomagnetic impulse at the dayside geomagnetic equator.
DE: 2407 Auroral ionosphere (2704)
DE: 2409 Current systems (2708)
DE: 2411 Electric fields (2712)
DE: 2415 Equatorial ionosphere
DE: 2487 Wave propagation (6934)
SC: SPA-Magnetospheric Physics [SM]
MN: 2004 AGU Fall Meeting