Net field-aligned currents observed by Triad

The existence of a net current flowing into or away from the ionosphere in the current layer is inferred from the Triad-satellite magnetometer observation of a steplike level shift in the east-west component of the magnetic field at 800 km altitude. The current direction is toward the ionosphere on the morning side and away from it on the afternoon side. The current layer is identified as the same layer that was observed by the Ogo 5 satellite at much higher altitudes. Thus, the field-aligned currents observed by Triad must be considered to be an important element in the electrodynamical coupling between the distant magnetosphere and the ionosphere.