Evidence of Nonlinear Interactions Between Magnetospheric Electron Cyclotron Harmonic Waves. Issue 16 (21st August 2020)

• Record Type: Journal Article
• Authors: Gao, Zhonglei; Zuo, Pingbing; Feng, Xueshang; Wang, Yi; Jiang, Chaowei; Wei, Fengsi
• Is Part Of: Geophysical research letters. Volume 47:Issue 16(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-08-21
• Subjects: ECH -- wave‐wave interaction -- nonlinear interaction -- frequency spectrum broadening -- electron Bernstein mode -- generalized Bernstein mode; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2020GL088452
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: Electron cyclotron harmonic (ECH) waves play an important role in the magnetosphere‐ionosphere coupling. They are usually considered to be generated by the Bernstein‐mode instability with electron loss cone distributions. By analyzing the Van Allen Probes wave data, we present the direct evidence of the nonlinear interactions between ECH waves in the magnetosphere. Substorm‐injected electrons excite primary ECH waves in a series of structureless bands between multiples of the electron gyrofrequency. Nonlinear interactions between the primary ECH waves produce secondary waves at sum‐ and difference‐frequencies of the primary waves. Our results suggest that the nonlinear wave‐wave interactions can redistribute the primary ECH wave energy over a broader frequency range and hence potentially affect the magnetospheric electrons over a broader range of pitch angles and energies. Plain Language Summary: Electron cyclotron harmonic (ECH) waves significantly contribute to the magnetosphere‐ionosphere coupling via resonating with hot electrons. The resonance effect strongly depends on the wave frequency distributions. Both theoretical studies and laboratory experiments made the point that nonlinear wave‐wave interactions can contribute to the frequency spectrum broadening of ECH waves. However, whether such nonlinear interactions occur in the magnetospheric plasma environment remains to be investigated. In this letter, we present, for the first time, the direct evidence of the nonlinear interactions between magnetospheric ECH waves. The nonlinear wave‐wave interactions redistribute the primary ECH wave energy over a broader frequency range. Hence, these waves are expected to have the ability to resonate with the electrons over a broader range of pitch angles and energies. Key Points: We present the direct evidence of the nonlinear interactions between electron cyclotron harmonic (ECH) waves in the magnetosphere Primary ECH waves are generated by the Bernstein‐mode instability of substorm‐injected electrons Sum‐ and difference‐frequency interactions between the primary ECH waves can redistribute wave energy over a broader frequency range