The equatorward extent of auroral activity during 1973-1974

The equatorward boundary of auroral activity during 1973-1974 has been derived from DMSP photographs and their associated auroral analysis records. On a time scale of days, the equatorward position of the northern auroral oval varied in phase with the average level of geomagnetic activity. In general, this variation was associated with the occurrence of solar flares and coronal holes. On a time scale of hours, the equatorward position of the oval correlated with the AE index of substorm activity and with the strength of the southward component of the interplanetary magnetic field.