Observational evidence indicates that high‐latitude magnetic activity can be causally related to fluctuations and reversals of the equatorial electric field. Using Birkeland currents as the driving forces, we have made numerical calculations of the ionospheric electric fields and currents that distribute globally. Our calculations utilize a fairly realistic empirical ionospheric conductivity model and the field‐aligned current distribution inferred from TRIAD measurements. The results presented here demonstrate that the field‐aligned currents observed during disturbed periods can account for the equatorial fluctuations and reversals in electric field and associated magnetic disturbances noted during such times. In this way, magnetospheric dynamics has a direct and significant influence on the equatorial ionosphere through the ionospheric conductivity.

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The propagation of a geomagnetic sudden impulse (si) and the magnetic field pulsations excited by it in the magnetosphere is traced from the bow shock in the solar wind, through the magnetosphere, to the ground. Within the magnetosphere the impulse appears as a compressive magnetohydrodynamic (MHD) impulse that travels rapidly (-•1500 km/s) tailward. A resonant oscillation observed both in space and on the ground is excited near geostationary orbit. The effect of the si is enhanced by a factor of at least 5 on the ground near the geomagnetic equator. We suggest that discontinuities in the solar wind may be a more important source of exciting dayside pulsations than has been commonly assumed.