Relation of Field‐Aligned Currents Measured by the Network of Iridium® Spacecraft to Solar Wind and Substorms

The strength of field‐aligned currents coupling the magnetosphere to the ionosphere was obtained by the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) using the network of Iridium® spacecraft. The distribution of current was integrated giving total current in and out of the ionosphere on the dayside and nightside of the Earth in both hemispheres. The onset of auroral zone negative bays and midlatitude positive bays corresponds to an increase in nightside upward current. The total outward current tends toward saturation with increasing solar wind driver strength. The optimum solar wind coupling function for AL index predicts ~73% of the variance in nightside upward current. The dayside and nightside predictors of upward current rise to a peak at 30–45 min and decay slowly over 2.5 hr. Nightside response is delayed relative to dayside.