The morphology of the IQSY auroral oval: 2. Auroral alignments in and near the auroral oval

Abstract

The azimuths of extended auroral features have been measured on all-sky camera photographs from Barrow, Alaska (dp [dipole] 68°) and T-3 Ice Island (dp 78°) during the IQSY period 1964–1965. The arc alignments measured at Barrow during the IQSY period are parallel for all hours to the Barrow arc alignments during IGY. This suggests that auroral alignments are independent of solar cycle. The T-3 arc alignments, when plotted in polar diagram form with previous alignment data from several IGY stations show two separate alignment functions during nighttime hours. This bimodal behavior is interpreted to show that dp 78° is near the transition region between generally east-west-aligned auroral features of the statistical auroral zone and earth-sun-oriented auroral arcs and bands in the auroral cap. On the nightside region both the IQSY and IGY auroral ovals are situated near the statistical auroral zone (dp 66°), but on the dayside the IQSY auroral oval is situated very near dp 78°. For several hours near noon, when the IQSY auroral oval includes the high-latitude day-side aurora near dp 78°, the arc alignment, while generally east-west, is best described as perpendicular to the earth-sun vector.