Azimuthal Motion of Poleward Moving Auroral Forms

Poleward moving auroral forms (PMAFs), the most common dayside auroral structure, images the process of energy and particle transport from the solar wind to the magnetosphere via magnetic reconnection. This form of aurora moves not only poleward, but also in the azimuthal (dawn-dusk) direction. However, the underlying mechanism responsible for the azimuthal motion of PMAFs are not thoroughly investigated. Here based on all-sky imager observations in the southern hemisphere, we statistically determine that the azimuthal motion of PMAFs is highly dependent on the dawn-dusk component of the interplanetary magnetic field (IMF B-y). Using three-dimensional (3-D) global hybrid simulations, we demonstrate that IMF B-y controls the azimuthal motion of PMAFs through plasma flow derived from magnetic tension of magnetopause flux ropes. Our study, by focusing on the azimuthal motion of PMAFs, allows a better understanding of space weather, especially from a 3-D perspective.