Models of monochromatic Pc5 (2–7 mHz) ultralow frequency (ULF) wave interactions with high energy (greater than ∼1 MeV) electrons predict drift resonant interactions that can cause rapid radial transport and acceleration. There are few reports of electron drift resonance at energies greater than ∼1 MeV, in contrast to lower energies; moreover, all previous reports occur in the aftermath of interplanetary shocks. These two facts are difficult to reconcile with theory and numerical simulations predicting that greater than ∼1 MeV drift resonances should occur more often and in a wider variety of driving conditions. In this study, we show that a combination of observational sampling biases and nominal radial phase space density gradients is one explanation for this discrepancy between theory and observations. In particular, we examine electron dynamics in two case studies with very similar satellite coverage, solar wind conditions, and Pc5 wave properties, yet with different radial phase space density profiles. Using global wave and particle observations, we show that the events have vastly different particle responses despite having similar wave properties. Placing these results in context with past studies, we further show that nominal radial PSD gradients near geostationary orbit can mask the expected drift resonance particle response and explain (1) the small number of past greater than ∼1 MeV drift resonance reports and (2) the restriction of these reports to interplanetary shock events. We argue that future observational studies characterizing radial transport via drift resonance should examine global particle dynamics, including observations of the radial phase space density profile.
Bibliographical noteFunding Information:
M. D. Hartinger was supported by NASA 80NSSC18K1613 and LANL‐CSES. Work at The Aerospace Corporation was supported by RBSPECT funding provided by JHU/APL Contract 967399 under NASA's Prime contract NAS501072. X.‐J. Zhang was supported by NASA Grant 80NSSC18K1112. We thank I. R. Mann, D. K. Milling, and the rest of the CARISMA team for data. CARISMA is operated by the University of Alberta, funded by the Canadian Space Agency. We acknowledge NASA contract NAS5‐02099 and V. Angelopoulos for use of data from the THEMIS Mission. We thank the NASA Space Science Data facility for the use of solar wind data and geomagnetic activity indices.
M.?D. Hartinger was supported by NASA 80NSSC18K1613 and LANL-CSES. Work at The Aerospace Corporation was supported by RBSPECT funding provided by JHU/APL Contract 967399 under NASA's Prime contract NAS501072. X.-J. Zhang was supported by NASA Grant 80NSSC18K1112. We thank I.?R. Mann, D.?K. Milling, and the rest of the CARISMA team for data. CARISMA is operated by the University of Alberta, funded by the Canadian Space Agency. We acknowledge NASA contract NAS5-02099 and V. Angelopoulos for use of data from the THEMIS Mission. We thank the NASA Space Science Data facility for the use of solar wind data and geomagnetic activity indices.
All ground magnetometer data are publicly available on the CARISMA website ( http://www.carisma.ca/ ). Processing and analysis of the MagEIS and REPT data were supported by Energetic Particle, Composition, and Thermal Plasma (RBSP‐ECT) investigation funded under NASA's Prime Contract No. NAS5‐01072. We acknowledge Dan Baker for use of REPT data. All RBSP data except phase space densities were accessed via NASA CDAWeb and are publicly available there ( https://cdaweb.sci.gsfc.nasa.gov/index.html/ ). The phase space density data were accessed directly from the RBSP‐ECT Science and Data Portal and are publicly available there ( https://rbsp‐ect.lanl.gov/data_pub/PSD/ ). All THEMIS data were accessed via the SPEDAS software and are publicly available at the THEMIS Berkeley data repository http://themis.ssl.berkeley.edu/data_products/ ). The THEMIS phase space densities were obtained using the method described in section 2.2 and are publicly available at this Zenodo repository ( https://doi.org/10.5281/zenodo.3668319 ). The LANL‐GEO data used in this study are publicly available at the above Zenodo repository. The geomagnetic activity indices and solar wind parameters are publicly available at the NASA Space Science Data Facility ( https://omniweb.gsfc.nasa.gov/ ). The final data used to generate the figures in this manuscript, as well as the IDL software for plotting the figures, are publicly available on the Zenodo repository listed above. The SPEDAS software package used for plotting can be obtained from the THEMIS website ( http://themis.ssl.berkeley.edu/index.shtml ).
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- ULF wave
- drift resonance
- phase space density
- radial diffusion
- radiation belts