Transmission line model for the near‐instantaneous transmission of the ionospheric electric field and currents to the equator

Abstract

The simultaneous onset of the preliminary impulse (PI) of the geomagnetic sudden commencement at high latitude and dayside dip equator is explained by means of the TM 0 mode waves propagating at the speed of light in the Earth-ionosphere waveguide (EIW) [Kikuchi et al., 1978]. A couple of issues remain to be addressed in the EIW model: (1) How is the TM 0 mode wave excited by the field-aligned currents (FACs) in the polar region? (2) How are the quasi-steady ionospheric currents achieved by the TM 0 mode waves? (3) How simultaneous or delayed are the onset and peak of the equatorial PI with respect to the high-latitude PI? To address these issues, we examine the TEM (TM 0 ) mode wave propagation in the finite-length transmission lines replacing the pair of FACs (magnetosphere-ionosphere (MI) transmission line) and the Earth-ionosphere waveguide (ionosphere-ground (IG) transmission line). The issue (1) is addressed by showing that a fraction of the TEM mode wave is transmitted from the MI to IG transmission lines through the polar ionosphere. To address the issues (2) and (3), we examine the properties of the finite-length IG transmission line with finite ionospheric conductivity. It is shown that the ionospheric currents start to grow instantaneously and continue to grow gradually with time constants of 1-10 s depending on the ionospheric conductivity. The MIG transmission line enables us to explain the instantaneous onset and delayed peak time of the equatorial PI and quick electric field response of the low-latitude ionosphere and inner magnetosphere.

Evolution of the current system during solar wind pressure pulses based on aurora and magnetometer observations

“…The initiation of both PI and MI magnetic field variations is considered to occur simultaneously across the entire latitude range including the magnetic equator, and this is attributed to rapid changes in large-scale electric fields (Boudouridis et al 2011) and their instantaneous penetration to lower latitudes (Araki 1977;Kikuchi 1986). Recently, Kikuchi (2014) presented a comprehensive model of signal transmission from the magnetosphere to the equatorial ionosphere through the ionosphere-ground waveguide.…”

Transmission of the electric fields to the low latitude ionosphere in the magnetosphere-ionosphere current circuit

“…(from Fig. 6 of Kikuchi et al 2008) terminated by the fully ionized magnetosphere (Kikuchi 2014). The positive electric potential (+V 0 ) is transmitted with the downward FAC (thick arrow) to the left end of the waveguide, providing the vertical electric field, E zV in the waveguide, which excites the TM 0 mode wave propagating with the horizontal Poynting flux, S xV , at the speed of light.…”

“…8 of Kikuchi et al 2008) dashed line at noon, on which downward and upward currents of the same amount are supposed to take part in the duskside and dawnside current circuits driven by the positive and negative potentials, respectively. Replacing the waveguide with the finite-length parallel plane transmission line, Kikuchi (2014) calculated the electric potential and currents in the ionosphere and showed that the ionospheric currents grow to the steady-state value with the time constant of a few to 10s of seconds, depending on the ionospheric conductivity. The transmission line model well explains the instantaneous onset of the PI at all latitudes and delayed peak at the equator by 20 s (Takahashi et al 2015).…”

“…However, the electric field is strong enough to be detected by the HF Doppler sounder (Kikuchi 1986). The electric field associated with the ionospheric currents is transmitted by the Alfven wave upward into the F-region ionosphere and the inner magnetosphere (Kikuchi 2014), which leads to the coherent variations of the ground magnetic field and ionospheric motion at the geomagnetic equator, as observed by the HF Doppler sounders (Abdu et al 1988) and by the Jicamarca incoherent scatter radar (Kikuchi et al 2003). The upward transmission of the Poynting flux into the inner magnetosphere has been observed by the satellites (Nishimura et al 2010), causing the quick development of the electric field in the inner magnetosphere (Nishimura et al 2009), ring current (Hashimoto et al 2002), and so on.…”

Interhemispheric Asymmetry in Response of Low‐Latitude Ionosphere to Perturbation Electric Fields in the Main Phase of Geomagnetic Storms

“…These interactions channelize the plasma into different magnetospheric regions like plasma sheet and ring currents eventually transporting it through reconnection in the magnetotail toward polar latitudes in the Northern and Southern Hemispheres (Baumjohann et al, 2010;Hasegawa et al, 2004;Heikkila, 2011;Kamide & Baumjohann, 1993;Ohtani et al, 2000). The electric field of interplanetary origin can instantaneously penetrate to equatorial and low latitudes (Kikuchi, 2014;Kikuchi & Hashimoto, 2016 and references therein), whereas delayed effects of high-latitude Joule heating and associated perturbation winds and traveling atmospheric disturbances (TADs) arrive after more than 8-10 hr to days (Bauske & Prölss, 1997;Dashora et al, 2009;Ding et al, 2007;Hajkowicz, 1990;Hocke & Schlegel, 1996;Hunsucker, 1982;Nicolls et al, 2004). The electric field of interplanetary origin can instantaneously penetrate to equatorial and low latitudes (Kikuchi, 2014;Kikuchi & Hashimoto, 2016 and references therein), whereas delayed effects of high-latitude Joule heating and associated perturbation winds and traveling atmospheric disturbances (TADs) arrive after more than 8-10 hr to days (Bauske & Prölss, 1997;Dashora et al, 2009;Ding et al, 2007;Hajkowicz, 1990;Hocke & Schlegel, 1996;Hunsucker, 1982;Nicolls et al, 2004).…”