The morphology of the auroral displays of 1957-1958: 2. Detail analyses of Alaska data and analyses of high-latitude data

Abstract

This study is based on the all-sky camera records obtained during the IGY 1957–1958 from a close-spaced network of stations in Alaska and from an array of stations extending from Choteau, Montana, northward across Canada to Thule, Greenland. The aspects of auroral morphology discussed here include the time and latitude dependency of the incidence, azimuthal alignment, and direction of horizontal motion of auroral forms, and the relation of these aspects to magnetic disturbance. The diurnal variation of auroral incidence at geomagnetic latitudes 60° to 68° has a single maximum. Near latitude 70° three maxima appear, while farther north, at and above 75°, two maxima occur; these maxima merge into a single peak at the geomagnetic pole. The azimuthal alignment of auroral forms is nearly geomagnetic east-west at geomagnetic latitudes 55° to 68°, and is approximately in the direction of the sun at latitudes above 80°; at latitudes 68° to 80° the azimuthal alignment is transitional between that at lower latitudes and that near the geomagnetic pole. At the auroral zone, horizontal auroral motions are in the longitudinal direction—westward in the evening, and eastward in the morning—whereas meridional motions are primarily southward throughout the night. The reversal from westward to eastward auroral motion occurs rather abruptly on any night, but its time of occurrence varies from night to night. Detailed analyses of individual auroral displays and the concurrent magnetic disturbance indicate detailed association of the alignment and direction of motion of auroral forms with the magnitude and direction of ionospheric currents. The ionospheric current is generally parallel to the alignment of auroral forms and is opposite in direction to the observed motion within the forms. Patterns representing the average incidence, alignment, and direction of motion of the aurora throughout the polar region are deduced from the results of the analysis. These patterns are centered about the boreal geomagnetic pole and are fixed with respect to the direction toward the sun.