Zebra Stripe Patterns in Energetic Ion Spectra at Saturn

• Published in: Geophysical research letters Vol. 49; no. 4
• Main Authors: Sun, Y. X., Hao, Y.‐X., Roussos, E., Zong, Q.‐G., Liu, Y., Zhou, X. Z., Yue, C., Krupp, N.
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 28.02.2022
• Subjects: Charged particles; Convection; convection electric field; Dipoles; Drift; Earth; Electric field; Electric fields; electron; Electron radiation; Energetic particles; Energy; Ions; Jupiter; Magnetic field; Magnetic fields; Particle physics; Planetary magnetic fields; Planetary magnetospheres; Planetary rotation; Planets; Protons; Radial flow; Radiation; radiation belt; Radiation belts; Saturn; Spectrograms; Transport; zebra stripe
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2021GL097691

Magnetospheric convective electric fields that could radially transport particles adiabatically, may leave their imprints in the form of energy‐time dispersed patterns termed ”zebra stripes”. Inspired by comprehensive studies on zebra stripes in Earth's electron radiation belts, similar electron signatures were found and explained in Saturn's inner magnetosphere. Using Cassini Magnetosphere Imaging Instrument observations, we demonstrate that the zebra‐stripes in proton and water group ion spectrograms at the energy range from 30 keV to ∼1 MeV, which coexist with electron zebra‐stripes, can be traced to the same electric field, even though the associated radial flows were originally thought to be too slow to disturb the fast azimuthal energetic ion drift. The simultaneous observations of zebra stripes in electrons and ions further establish the importance of the planet's noon‐midnight electric field as a regulator of radiation belt dynamics. Plain Language Summary Planets with an intense intrinsic magnetic field, such as Earth, Saturn, and Jupiter, could trap energetic charged particles, including electrons and ions. These particles drift around the planets under the control of the dipole‐like magnetic field. And when a global uniform convection electric field exists, the particles will show a banded pattern in the spectrogram of energy versus distance to the planet as a result of radial transport. Such a link has been established on Earth and recently also on Saturn with electron observation. In this paper, we report that ions also have a similar pattern. This is unexpected since the convection electric field was thought to be powerless on ions as they drift so fast compared to the radial flow associated with the electric field. This result gives hints on how the convection electric field modulates the energetic particle environment of fast‐rotating giant planets. Key Points Simultaneous energy‐time dispersed zebra‐stripes of ions and electrons at Saturn are analyzed Both proton and water group ion fluxes are modulated by the magnetospheric noon‐midnight electric field Test‐particle model under convection electric field reproduces both proton and electron stripes