Chorus Wave Modulation of Langmuir Waves in the Radiation Belts. Issue 23 (7th December 2017)

• Record Type: Journal Article
• Authors: Li, Jinxing; Bortnik, Jacob; An, Xin; Li, Wen; Thorne, Richard M.; Zhou, Meng; Kurth, William S.; Hospodarsky, George B.; Funsten, Herbert O.; Spence, Harlan E.
• Is Part Of: Geophysical research letters. Volume 44:Issue 23(2017)
• Page Start: 11, 713
• Page End: 11, 721
• Publication Date: 2017-12-07
• Subjects: chorus wave -- Langmuir wave -- nonlinear interaction -- Landau resonance -- radiation belt -- wave modulation; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1002/2017GL075877
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: Using high‐resolution waveforms measured by the Van Allen Probes, we report a novel observation in the radiation belts. Namely, we show that multiband, discrete, rising‐tone whistler mode chorus emissions exhibit a one‐to‐one correlation with Langmuir wave bursts. Moreover, the periodic Langmuir wave bursts are generally observed at the phase location where the chorus wave E || component is oriented opposite to its propagation direction. The electron measurements show a beam in phase space density at the particle velocity that matches the parallel phase velocity of the chorus waves. Based on this evidence, we conclude that the chorus waves accelerate the suprathermal electrons via Landau resonance and generate a localized electron beam in phase space density. Consequently, the Langmuir waves are excited locally and are modulated by the chorus wave phase. This microscale interaction between chorus waves and high‐frequency electrostatic waves provides a new insight into the nonlinear wave‐particle interaction process. Plain Language Summary: The Earth's space is filled with energetic particles and various waves. One very fascinating wave is named chorus wave, which is discrete like birds' chirping, and another wave is Langmuir wave, which is related with electron's oscillation along the magnetic field lines. A novel phenomenon is discovered in the radiation belt: during some geomagnetic storm time, the Langmuir waves occur together with the discrete rising‐tone chorus waves, and the high‐resolution data show that they are modulated by chorus waves. By analyzing the electron distribution and evaluating the wave‐particle interactions, we found that the Langmuir waves are always generated at a certain place where the electrons are accelerated locally by the chorus waves, and therefore, they are modulated by chorus waves. Since the close correlation between these two waves has also been observed in the interplanetary space and Earth's outer magnetosphere, our theory has broad implication in understanding the microscopic nonlinear interactions in space. Key Points: Langmuir waves are modulated by multiband rising‐tone whistler mode chorus waves Observations suggest that electrons are accelerated via Landau resonance with chorus waves Langmuir waves are excited locally where the electrons are accelerated by chorus waves