Formation of Electron Zebra Stripes Observed on 8 September 2017

Abstract

Zebra stripes are the characteristic structures having repeated hills and valleys in the electron flux intensities observed below L = 3. We delineate the fundamental properties and evolution of electron zebra stripes by modeling advection using time-dependent electric fields provided by a global magnetohydrodynamics simulation. At the beginning of the simulation, the electrons were uniformly distributed in longitude. Some electrons moved inward due to enhanced westward electric field transients in the premidnight-postdawn region. The inwardly displaced electrons were confined in a narrow longitudinal range and underwent grad-B and curvature drifts. For any specific fixed position, the electrons periodically passed through the point with an energy dependent period, giving rise to the hills and valleys in the electron differential flux also known as zebra stripes. The valleys of the zebra stripes are composed of the electrons that underwent outward displacement, or no significant radial displacement. On the nightside, the duskside convection cell is skewed toward dawn in the equatorward of the auroral oval, and the westward electric field becomes dominant in the postdawn region, which results in the inward motion of the electrons. The spatial distribution of the westward electric field is consistent with observation. Zebra stripes are a mixture of the electrons that have and have not experienced inward transport due to solar wind-inner magnetosphere coupling by way of the ionosphere.