The morphology of the auroral displays of 1957-1958: 1. Statistical analyses of Alaska data

A study of the variation of auroral phenomena with local time and geomagnetic latitude has been made using data from a meridional array of all-sky cameras located in Alaska. It is found that the form of the diurnal variation is dependent upon the criteria of auroral activity used: those criteria that are based on the counting of forms peak near local midnight, whereas those based on the total luminosity in the sky show high activity in the morning hours. The maximum incidence of aurora is found to occur near 66½°N geomagnetic latitude, and the distribution of aurora with latitude between 60° and 70°N is determined. Although the southern extent of auroras retreat northward after local magnetic midnight, the southward motion of the individual forms observed south of the auroral zone peak predominates over the northward motion throughout the night.