Experimental Determination of the Conditions Associated with “Zebra
Stripe” Pattern Generation in the Earth’s Inner Radiation Belt
Abstract
The “zebra stripes” are peaks and valleys commonly present in the
spectrograms of energetic particles trapped in the Earth’s inner belt.
Several theories have been proposed over the years to explain their
generation, structure and evolution. Yet, the plausibility of various
theories has not been tested due to a historical lack of ground-truth,
including in-situ electric field measurements. In this work, we leverage
the new visibility offered by the database of NASA Van Allen Probes
electric drift measurements to reveal the conditions associated with the
generation of zebra stripe patterns. Energetic electron flux
measurements by the Radiation Belt Storm Probes Ion Composition
Experiment between January 1, 2013 and December 31, 2015 are
systematically analyzed to determine 370 start times associated with the
generation of zebra stripes. Statistical analyses of these events reveal
that the zebra stripes are usually created during substorm onset, a time
at which prompt penetration electric fields are present in the
plasmasphere. All the pieces of experimental evidence collected are
consistent with a scenario in which the prompt penetration electric
field associated with substorm onset leads to a sudden perturbation of
the trapped particle drift motion. Subsequent inner belt drift echoes
constitute the zebra stripes. This study exemplifies how the analysis of
trapped particle dynamics in the inner belt and slot region provides
complimentary information on the dynamics of plasmaspheric electric
fields. It is the first time that the signature of prompt penetration
electric fields is detected in near‐equatorial electric field
measurements below L=3.