skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


Title: First Observation of Mini Harmonic Structure in Magnetosonic Waves
Abstract We recently reported the finding of elementary rising‐tone emissions embedded within each harmonic of magnetosonic waves, by investigating wave electric field waveforms measured by Van Allen Probes. The present study further uncovers a new set of fine structures of magnetosonic waves, namely, each elementary rising‐tone may consist of a series of mini harmonics spaced around the O+gyrofrequency. The measured ion distributions suggest that the proton ring distribution provides free energy to excite the waves, whilst the O+ions suppress the wave growth around multiples of O+gyrofrequency, resulting in the formation of mini harmonics. Further investigation suggests that the warm plasma dispersion relation, that is, the ion Bernstein mode instabilities, may contribute to the formation of mini harmonics. The mini harmonic structure implies a new mechanism of energy redistribution among ion species in space plasmas, potentially providing a new acceleration mechanism for O+ions in the magnetosphere.  more » « less
Award ID(s):
2225445
PAR ID:
10599548
Author(s) / Creator(s):
 ;  ;  ;  ;  ;  ;  ;  ;  
Publisher / Repository:
DOI PREFIX: 10.1029
Date Published:
Journal Name:
Geophysical Research Letters
Volume:
52
Issue:
11
ISSN:
0094-8276
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; ; ; ; ; ; ; ; et al (, Journal of Geophysical Research: Space Physics)
    Abstract The present study uncovers the fine structures of magnetosonic waves by investigating the EFW waveforms measured by Van Allen Probes. We show that each harmonic of the magnetosonic wave may consist of a series of elementary rising‐tone emissions, implying a nonlinear mechanism for the wave generation. By investigating an elementary rising‐tone magnetosonic wave that spans a wide frequency range, we show that the frequency sweep rate is likely proportional to the wave frequency. We studied compound rising‐tone magnetosonic waves, and found that they typically consist of multiple harmonics in the source region, and may gradually become continuous in frequency as they propagate away from source. Both elementary and compound rising‐tone magnetosonic waves last for ∼1 min which is close to the bounce period of the ring proton distribution, but their relation is not fully understood. 
    more » « less
  2. ; ; ; (, Journal of Geophysical Research: Space Physics)
    Abstract We report plasma wave observations of equatorial magnetosonic waves at integer harmonics of the local gyrofrequency of doubly ionized helium (). The waves were observed by Van Allen Probe A on 08 Feb 2014 when the spacecraft was in the afternoon magnetic local time sector nearinside of the plasmasphere. Analysis of the complementary in‐situ energetic ion measurements (1–300 keV) reveals the presence of a helium ion ring distribution centered near 30 keV. Theoretical linear growth rate calculations suggest that the local plasma and field conditions can support the excitation of the magnetosonic waves from the unstable ring distribution. This represents the first report of the generation of magnetosonic equatorial noise via a ring distribution in energeticions in the near‐Earth space plasma environment. 
    more » « less
  3. ; ; ; ; ; (, Geophysical Research Letters)
    Abstract Recent observations have reported that magnetosonic waves can exhibit rising‐tone structures in the frequency‐time spectrogram. However, the generation mechanism has not been identified yet. In this paper, we investigate the generation of rising‐tone magnetosonic waves in the terrestrial magnetosphere using 1‐D particle‐in‐cell (PIC) simulations, in which the plasma consists of three components: cool electrons, cool protons and ring distribution protons. We find that the magnetosonic waves excited by the ring distribution protons can form a rising‐tone structure with frequency of the structure ranging from about0.5Ωlhto nearlyΩlh, whereΩlhis the lower hybrid frequency. It is further demonstrated that the rising frequency of magnetosonic waves can be accounted for by the scattering of ring distribution protons. Moreover, the rising‐tone timescale obtained by PIC simulation is compared with the satellite observation. Our findings provide some new insights to understand the nonlinear evolution of plasma waves in the Earth's magnetosphere. 
    more » « less
  4. ; ; (, Geophysical Research Letters)
    Abstract Electron cyclotron harmonic (ECH) waves are known to precipitate plasma sheet electrons into the upper atmosphere and generate diffuse aurorae. In this study, we report quasiperiodic rising (3 events) and falling tone (22 events) ECH waves observed by Van Allen Probes and evaluate their properties. These rising and falling tone ECH waves prefer to occur during quiet geomagnetic conditions over the dusk to midnight sector in relatively high‐density (10–80 cm−3) regions. Their repetition periods increase with increasingLshell atL < 6, ranging from ∼60 to 110 s. The wave element duration varies from 10 to 130 s peaking at ∼40 s and the chirping rate peaks at ∼50 (∼−50) Hz/s for rising (falling) tones. Our findings reveal intriguing features of the ECH wave properties, which provide new insights into their generation and potential effects on electron precipitation. 
    more » « less
  5. ; ; ; ; ; ; ; ; ; ; et al (, Geophysical Research Letters)
    Abstract Electromagnetic ion cyclotron (EMIC) waves are commonly observed in the Earth's magnetosphere and play a significant role in regulating relativistic electron fluxes. The waveform of EMIC waves comprises amplitude‐modulated wave packets, known as “subpackets.” Despite their prevalence, the underlying physics and associated particle dynamics for subpacket formation remain poorly understood. In this study, using Van Allen Probe A observations, we present several rising‐tone EMIC wave events to reveal the downward frequency chirping between adjacent subpackets. By performing a hybrid simulation, we demonstrate for the first time that these wave properties are associated with the oscillation of proton holes in the wave gyrophase space induced by cyclotron resonance. The oscillation modulates the energy transfer between waves and particles, establishing a direct link between subpacket formation in cyclotron waves and nonlinear wave‐particle interactions. This new understanding advances our knowledge of subpacket formation in general and its broader implications in space plasma physics. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email