Conjugacy of rapid motions and small-scale deformations of discrete auroras by all-sky TV observations

摘要

Simultaneous observations of discrete auroras were made on 26 September 1984 by means of all-sky TV cameras at a geomagnetically conjugate pair of sites : Syowa Station in Antarctica and Husafell in Iceland. A comparison of the data obtained at the two places gives the following characteristics regarding the conjugacy of discrete auroras under a geomagnetically weakly disturbed condition (ΔH=-50nT) : Before the onset of a small substorm conjugate faint discrete auroras were identified in both conjugate areas despite a small displacement (0.5°) in invariant latitude (the southern aurora is 0.5° higher than the northern one). A striking dissimilarity of the conjugate auroras is noted in small-scale structures within the auroras. That is, the northern discrete aurora was rather homogeneous, whereas the southern one was a rayed aurora. During the substorm the east-west movement and/or extension of discrete auroras was quite conjugate and simultaneous. However, the vortexlike structures such as folds on the discrete auroras were not always simultaneously observed at the both places. Even if they appeared simultaneously, their sizes seemed to be different between the conjugate regions. These results would suggest that the large-scale structures and their movements are mainly controlled by some conditions in the magnetosphere, perhaps near the equatorial region, but the small-scale structures such as vortices are greatly due to local acceleration processes between the magnetosphere and the ionosphere.