Field-aligned currents and the auroral electrojet in the morning sector

On the basis of magnetic field data for four events taken from the Triad satellite and simultaneous ground magnetic data from the Alaska meridian chain of observatories the location of field-aligned currents in the morning sector (0600–1200 MLT) is examined with respect to the auroral electrojet. It is found that (1) the downward field-aligned currents in the poleward half of the auroral oval are more intense than the upward currents in the equatorward half of the oval in the morning sector and (2) during substorm periods, both the downward and the upward field-aligned currents generally occur inside the westward electrojet region. The observed inequality of the intensities of the upward and downward field-aligned currents suggests that their closure in the ionosphere cannot be completed in the same meridian and must have a large westward component in the morning sector. It is also suggested that this westward ionospheric current constitutes a part of the westward auroral electrojet.