Magnetic conjugacy of northern and southern auroral beads

Auroral beads, i.e., azimuthally arrayed bright spots resembling a pearl necklace, have recently drawn attention as a possible precursor of auroral substorms. We used simultaneous, ground‐based, all‐sky camera observations from a geomagnetically conjugate Iceland‐Syowa Station pair to demonstrate that the auroral beads, whose wavelength is ∼30–50 km, evolve synchronously in the northern and southern hemispheres and have remarkable interhemispheric similarities. In both hemispheres: 1) they appeared almost at the same time; 2) their longitudinal wave number was similar ∼300–400, corresponding bead separation being ∼1° in longitude; 3) they started developing into a larger scale spiral form at the same time; 4) their propagation speeds and their temporal evolution were almost identical. These interhemispheric similarities provide strong evidence that there is a common driver in the magnetotail equatorial region that controls the major temporal evolution of the auroral beads; thus, the magnetosphere plays a primary role in structuring the initial brightening arc in this scale size. Key Points Simultaneous observations of northern and southern auroral beads Remarkable interhemispheric similarities in the characteristics of auroral beads Two‐step evolution of auroral beads