Penetration of the Magnetospheric Electric Fields to the Low Latitude Ionosphere

The solar wind magnetosphere interaction activates a dynamo in the outer magnetosphere, providing the dawn-to-dusk convection electric field and Region-1 field-aligned currents (FACs) to the polar ionosphere. The polar electric field is transmitted near-instantaneously to the equator, driving ionospheric plasma motions at low latitudes and global DP2 (type-2 magnetic disturbances of polar origin) currents extending to the equator. The convection electric field is transported into the inner magnetosphere where the shielding electric field and Region-2 FACs are generated, providing dusk-to-dawn electric field at low latitude and counterelectrojet (CEJ) at the dayside equator. Overshielding occurs when the R1 FACs reduce substantially because of the northward turning of the IMF, or when the R2 FACs are intensified by substorms. The penetration electric fields in the evening are anomalously enhanced with the same direction as in the day. The evening anomaly is a unique feature of the electric potential in the global ionosphere. The ionospheric electric potential is transmitted near-instantaneously to low latitude by the zeroth-order transverse magnetic (TM0) mode waves in the Earth-ionosphere waveguide. We review magnetometer and radar/sounder observations of the convection and overshielding electric fields and the Earth-ionosphere waveguide/transmission line model, explaining the prompt penetration of the magnetospheric electric fields to the low latitude ionosphere.