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.

Intensification of the Electron Zebra Stripes in the Earth's Inner Magnetosphere During Geomagnetic Storms

“…In the current study, we propose that enhanced FACs trigger magnetospheric convection, subsequently causing the inward drift of electrons influenced by the westward E ϕ , as shown by Pandya et al. (2023), ultimately leading to the intensification of zebra stripes.…”

“…Alternatively, Ukhorskiy et al (2014) proposed a hypothesis involving electric fields induced by electromagnetic oscillations related to Earth's rotation and dipole tilt. In the current study, we propose that enhanced FACs trigger magnetospheric convection, subsequently causing the inward drift of electrons influenced by the westward E ϕ , as shown by Pandya et al (2023), ultimately leading to the intensification of zebra stripes.…”

“…As illustrated in Figure 9 of Pandya et al. (2023), the eastward electric field intensifies in the midnight‐dawn sector rather than the dusk‐midnight sector, for the reasons mentioned. Therefore, the observed skewness of the perturbed electric field, as shown in Figure 9 of Lejosne and Mozer (2020), can be reasonably attributed to significant contributions from the ionosphere, supporting the outlined scenario.…”

“…Additionally, the electric field is not necessarily symmetric relative to the noon-midnight meridian, owing to the asymmetric distribution of FACs and the discontinuous nature of the ionospheric Hall current. As illustrated in Figure 9 of Pandya et al (2023), the eastward electric field intensifies in the midnight-dawn sector rather than the dusk-midnight sector, for the reasons mentioned. Therefore, the observed skewness of the perturbed electric field, as shown in Figure 9 of Lejosne and Mozer (2020), can be reasonably attributed to significant contributions from the ionosphere, supporting the outlined scenario.…”

“…Megha Pandya 1,2,3 , Yusuke Ebihara 1 , Takashi Tanaka 4 , Jerry W. Manweiler 5 , and Sarah K. Vines 6 This study builds upon earlier research on electron zebra stripes conducted by Pandya et al (2023). Their work focused on modeling the evolution of electron zebra stripes through advection, using time-dependent electric fields generated from global magnetohydrodynamic (MHD) simulations.…”