Energetic (≳50 keV) electron precipitation from the magnetosphere to the ionosphere during substorms can be important for magnetosphere‐ionosphere coupling. Using conjugate observations between the THEMIS, ELFIN, and DMSP spacecraft during a substorm, we have analyzed the energetic electron precipitation, the magnetospheric injection, and the associated plasma waves to examine the role of waves in pitch‐angle scattering plasma sheet electrons into the loss cone. During the substorm expansion phase, ELFIN‐A observed 50–300 keV electron precipitation from the plasma sheet that was likely driven by wave‐particle interactions. The identification of the low‐altitude extent of the plasma sheet from ELFIN is aided by DMSP global auroral images. Combining quasi‐linear theory, numerical test particle simulations, and equatorial THEMIS measurements of particles and fields, we have evaluated the relative importance of kinetic Alfvén waves (KAWs) and whistler‐mode waves in driving the observed precipitation. We find that the KAW‐driven bounce‐averaged pitch‐angle diffusion coefficients
Electron cyclotron harmonic (ECH) waves, potential drivers for diffuse aurora precipitation, have been extensively investigated for decades. The generation mechanism of ECH waves, however, remains an open question. Theoretical work in 1970s has demonstrated that ECH waves can be excited by loss cone distributions of hot plasma sheet electrons. Recent THEMIS spacecraft observations, however, indicate that the waves can also be excited by low energy electron beams. Utilizing interferometry techniques to analyze the phase difference between electric potentials measured by individual probes on Electric Field Instrument antenna pairs on THEMIS spacecraft, we compute the wavenumber of both beam‐driven ECH waves and loss‐cone‐driven ECH waves. These wavenumber measurements as well as other wave properties obtained from spacecraft measurements prove to be consistent with expectation from linear instability analysis. This provides us with independent verification of the generation mechanism and linear dispersion relation of beam‐driven and loss‐cone‐driven ECH waves. Our statistical results demonstrate that the median value of the wave vectors of beam‐driven ECH waves, characterized by wave normal angles (
- Award ID(s):
- 2026375
- NSF-PAR ID:
- 10444611
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Space Physics
- Volume:
- 127
- Issue:
- 7
- ISSN:
- 2169-9380
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract near the edge of the loss cone are ∼10−6–10−5s−1for these energetic electrons. The due to parallel whistler‐mode waves, observed at THEMIS ∼10‐min after the ELFIN observations, are ∼10−8–10−6s−1. Thus, at least in this case, the observed KAWs dominate over the observed whistler‐mode waves in the scattering and precipitation of energetic plasma sheet electrons during the substorm injection. -
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