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

Abstract

The solar wind energy is transmitted to low latitude ionosphere in a current circuit from a dynamo in the magnetosphere to the equatorial ionosphere via the polar ionosphere. During the substorm growth phase and storm main phase, the dawn-to-dusk convection electric field is intensified by the southward interplanetary magnetic field (IMF), driving the ionospheric DP2 currents composed of two-cell Hall current vortices in high latitudes and Pedersen currents amplified at the dayside equator (EEJ). The EEJ-Region-1 field-aligned current (R1 FAC) circuit is completed via the Pedersen currents in midlatitude. On the other hand, the shielding electric field and the Region-2 FACs develop in the inner magnetosphere, tending to cancel the convection electric field at the mid-equatorial latitudes. The shielding often causes overshielding when the convection electric field reduces substantially and the EEJ is overcome by the counter electrojet (CEJ), leading to that even the quasi-periodic DP2 fluctuations are contributed by the overshielding as being composed of the EEJ and CEJ. The overshielding develop significantly during substorms and storms, leading to that the mid and low latitude ionosphere is under strong influence of the overshielding as well as the convection electric fields. The electric fields on the day-and night sides are in opposite direction to each other, but the electric fields in the evening are anomalously enhanced in the same direction as in the day. The evening anomaly is a unique feature of the electric potential distribution in the global ionosphere. DP2-type electric field and currents develop during the transient/short-term geomagnetic disturbances like the geomagnetic sudden commencements (SC), which appear simultaneously at high latitude and equator within the temporal resolution of 10 s. Using the SC, we can confirm that the electric potential and currents are transmitted near-instantaneously to low latitude ionosphere on both day-and night sides, which is explained by means of the light speed propagation of the TM 0 mode waves in the Earth-ionosphere waveguide.© 2016 Kikuchi and Hashimoto. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

Flux Enhancements of > 30 keV Electrons at Low Drift Shells L < 1.2 During Last Solar Cycles

“…We can assume that higher ionospheric conductivity due to higher illumination promotes effective penetration of perturbations in the electric field at high latitudes into the inner magnetosphere (e.g., Kikuchi & Araki, ; see also Kikuchi & Hashimoto, for references). Coupling of the magnetosphere with the high‐latitude ionosphere is provided by field‐aligned currents, the intensity of which at dayside is strongly controlled by the solar illumination‐induced conductivity (e.g., Wang, Lühr, & Ma, ).…”

Shrinking equatorial plasma bubbles

“…In such a case, the vertical drifts in equatorial region will vary with altitudes as well. Especially during geomagnetically disturbed conditions, the penetration of polar electric fields primarily occur in the bottomside of the equatorial ionosphere where Pedersen conductivities are higher [ Kikuchi and Araki , ; Kikuchi and Hashimoto , ]. Therefore, the events like that on 3 February 2008 (Figures and ) are possible wherein the bottomside ionosphere is being lifted up due to penetration electric fields while the topside drifts are downward as they are connected to nocturnal westward fields in off‐equatorial latitudes through geomagnetic field lines.…”

Geomagnetic and ionospheric response to the interplanetary shock on January 24, 2012

“…The propagation of the PI from high to low latitudes is often interpreted as an instantaneous transmission of atmospheric TH o mode along the ionosphere-ground waveguide (Kikuchi and Hashimoto 2016), though some researchers (e.g., Yumoto et al 1997;Chi et al 2001) consider this mechanism questionable because of the observed finite time delay between the PI detected at separated sites. Engebretson et al (1999) revealed dispersive propagation of the PI in early morning hours at speeds decreasing from ~150 to ~50 km/s directly away from a source near the cusp using ground observatories in the Arctic and Antarctic regions.…”