Drift Phase Structure Implications for Radiation Belt Transport. Issue 8 (10th August 2022)

• Record Type: Journal Article
• Authors: O'Brien, T. P.; Green, J. C.; Halford, A. J.; Kwan, B. P.; Claudepierre, S. G.; Ozeke, Louis G.
• Is Part Of: Journal of geophysical research. Volume 127:Issue 8(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-08-10
• Subjects: radiation belts -- radial transport -- radial diffusion -- drift resonance -- ULF waves; Magnetospheric physics -- Periodicals; Space environment -- Periodicals; Cosmic physics -- Periodicals; Planets -- Atmospheres -- Periodicals; Heliosphere (Astrophysics) -- Periodicals; Geophysics -- Periodicals; 523.01
• DOI: 10.1029/2022JA030331
• Languages: English
• ISSNs: 2169-9380

Abstract

Abstract: We examine drift phase structure in the electron radiation belt observations to differentiate radial transport mechanisms. Impulsive electrostatic or electromagnetic fields can cause radial transport and produce drift echoes (periodic drift phase structures with energy‐dependent period). Narrow‐band standing electromagnetic wave fields can also cause radial transport, while producing energy‐independent periodic drift phase structures. Broad‐band, random‐phase electromagnetic wave fields can cause radial transport, but do not necessarily produce drift phase structure. We present results of three case studies showing little association between drift phase structure and approximately MeV electron flux enhancements in the outer belt. We estimate the amplitude of drift phase structures expected for impulsive or narrow‐band interactions to compete with broad‐band, random‐phase waves. We show that the observed drift phase structure is typically much smaller than would be present if either impulses or narrow‐band waves were the dominant cause of radial transport. We conclude that radial transport is primarily consistent with the broad‐band, random‐phase, small perturbations assumed in quasilinear diffusion theory, although we cannot rule out the unlikely possibility that radial transport plays little role in radiation belt dynamics. Plain Language Summary: Radial motion of electrons is one of the most significant processes in the dynamics of the Earth's electron radiation belts. We examine the ripples in the time series of radiation belt electron flux observations to determine how the electrons move radially in space. Different kinds of radial motion leave different signatures in these time series ripples. Large ripples are rare enough that much of the radial reshaping of the radiation belts occurs independent of their influence. Established radial transport theory, known as quasilinear theory, is consistent with many small ripples, but our analysis cannot rule out the unlikely alternative that the small ripples indicate that there is little or no radial transport happening in the radiation belts. Key Points: Some radial transport mechanisms produce drift phase structure Drift phase structure is not strongly associated with electron belt enhancements Drift resonance with random‐phase broadband waves appears to dominate