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 TM0 mode waves in the Earth-ionosphere waveguide.
Highlights
This article reviews the transmission of the electric field and currents from the dynamos in the magnetosphere down to the equatorial ionosphere to better understand the ionospheric and geomagnetic disturbances at mid and low latitudes during substorms and storms
The convection electric field is transmitted by the Alfven wave from the dynamo in the outer magnetosphere to the polar ionosphere, accompanying the Region-1 field-aligned current (R1 FAC) and driving the DP2 currents composed of ionospheric Hall currents at high latitude and the Pedersen currents amplified by the Cowling effect at the dip equator
The convection electric field is transmitted to low latitude near-instantaneously by the TM0 mode waves in the Earth-ionosphere waveguide, resulting in high correlation of the DP2 fluctuations between high latitudes and equator during storm and substorms
Summary
Introduction This article reviews the transmission of the electric field and currents from the dynamos in the magnetosphere down to the equatorial ionosphere to better understand the ionospheric and geomagnetic disturbances at mid and low latitudes during substorms and storms. The evening anomaly is a unique feature of the global distribution of the electric potential as calculated by the potential solver with an input of the field-aligned currents in the polar ionosphere (Senior and Blanc 1984; Fig. 4 (top, thick solid curves) Vertical drift of the F-region ionosphere observed with the HF Doppler sounder over the equator (KODAIKANAL), which is well correlated with the DP2 magnetic fluctuations at the (middle) dayside equator (ALCANTARA) and (bottom) afternoon high latitude (NURMIJARVI).
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