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Abstract Earth's slot region, lying between the outer and inner radiation belts, has been identified as due to a balance between inward radial diffusion and pitch angle (PA) scattering induced by waves. However, recent satellite observations and modeling studies indicate that cosmic ray albedo neutron decay (CRAND) may also play a significant role in energetic electron dynamics in the slot region. In this study, using a drift‐diffusion‐source model, we investigate the relative contribution of all significant waves and CRAND to the dynamics of energetic electrons in the slot region during July 2014, an extended period of quiet geomagnetic activity. The bounce‐averaged PA diffusion coefficients from three types of waves (hiss, lightning‐generated whistlers [LGW], and very low frequency [VLF] transmitters) are calculated based on quasi‐linear theory, while the CRAND source follows the results in Xiang et al. (2019,https://doi.org/10.1029/2018GL081730). The simulation results indicate that both LGW and VLF transmitter waves can enhance loss and weaken the top hat PA distribution induced by hiss waves. For 470 keV electrons atL = 2.5, simulation results without CRAND show a much quicker decrease than observations from the Van Allen Probes. After including CRAND, simulated electron flux variations reproduce satellite observations, suggesting that CRAND is an important source for hundreds of keV electrons in the slot region during quiet times. The balance between the CRAND source and loss due to wave‐particle interactions provides a lower limit to relativistic electron fluxes in the slot region, which can act as an important reference point for instrument calibration when a true background level is warranted.
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Quasi‐Trapped Electron Fluxes Induced by NWC Transmitter and CRAND: Observations and Simulations
Abstract Signals from the NWC ground‐based very low frequency (VLF) transmitter can leak into the magnetosphere and scatter trapped energetic electrons into drift loss cones. Recent studies also suggest that cosmic ray albedo neutron decay (CRAND) is probably an important source for quasi‐trapped electrons in the inner belt. To investigate their relative contributions, this study comprehensively analyzes the long‐term variations of quasi‐trapped 206 keV electrons atL = 1.7, which is roughly the L shell where NWC is located. Furthermore, a drift‐diffusion‐source model is used to reproduce longitudinal distributions of quasi‐trapped electrons and investigate sensitivities of simulation results to VLF transmitter intensities. These results suggest that CRAND is the main source of quasi‐trapped hundreds of keV electrons when the NWC station is at dayside. In contrast, pitch angle diffusions become the main source mechanism of these quasi‐trapped electrons when the NWC station operates at nightside with more VLF transmitter energy leaking into the magnetosphere.
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- Award ID(s):
- 1834971
- PAR ID:
- 10444006
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Geophysical Research Letters
- Volume:
- 49
- Issue:
- 5
- ISSN:
- 0094-8276
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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