Journal article
Magnetospheric Line Radiation: Temporal Modulation Corresponding to a Bouncing Wave
Geophysical research letters, Vol.51(19), e2024GL111477
10/16/2024
DOI: 10.1029/2024GL111477
Abstract
Abstract Magnetospheric line radiation (MLR) is a peculiar type of whistler‐mode emissions formed by several similarly spaced spectral lines, whose frequencies may vary with time. These emissions typically occur at frequencies between about 1 and 8 kHz and are observed in both ground‐based and satellite measurements. However, their origin and source locations are not yet understood, as their detection by spacecraft instruments is challenging due to the limited frequency resolution of onboard wave measurements. We use high‐resolution multicomponent wave data obtained by the Van Allen Probes to demonstrate that, in addition to the frequency modulation, MLR events possess a temporal modulation with periods on the order of seconds, which may be related to the wave bouncing between hemispheres. Observed modulation periods are used to estimate a tentative source L‐shell. The modulation periods are shorter for events with larger frequency spacing, and the estimated source L‐shells correlate with model plasmapause locations.
Plain Language Summary Electromagnetic waves with frequencies of a few kHz observed in the near‐Earth space, the magnetosphere, sometimes exhibit distinct frequency modulation. When represented in traditional frequency‐time spectrograms, with wave intensity color‐coded as a function of frequency and time, these waves appear as several nearly equidistant spectral lines. They are called magnetospheric line radiation (MLR). Although they have been observed by both ground‐based and spacecraft instruments, their origin is still not understood. We use high‐resolution data obtained by the Van Allen Probes spacecraft to show that MLR intensity is modulated not only in frequency but also in time, with modulation periods on the order of seconds. The available wave measurements allow us to determine not only wave intensity but also propagation directions. This is used to demonstrate that the observed temporal modulation corresponds, with some uncertainties, to a wave element bouncing back and forth between hemispheres. Using the theory of wave propagation in plasma, the bouncing periods can be used to calculate the distance of the magnetic field line where the wave bounces, that is, the distance of a tentative wave source. Our results help to understand possible generation mechanisms and source locations of these peculiar emissions.
Key Points Magnetospheric line radiation may have a fine temporal structure related to the wave bouncing between hemispheres Analysis of the corresponding modulation periods allows estimation of the L‐shell of a tentative source Tentative source locations of analyzed events with the fine temporal structure correlate with the model plasmapause locations
Details
- Title: Subtitle
- Magnetospheric Line Radiation: Temporal Modulation Corresponding to a Bouncing Wave
- Creators
- F. Němec - Charles UniversityO. Santolík - Charles UniversityG. B. Hospodarsky - University of IowaW. S. Kurth - University of Iowa
- Resource Type
- Journal article
- Publication Details
- Geophysical research letters, Vol.51(19), e2024GL111477
- Publisher
- AMER GEOPHYSICAL UNION
- DOI
- 10.1029/2024GL111477
- ISSN
- 0094-8276
- eISSN
- 1944-8007
- Grant note
- CNES: 21-01813S GACR: LUAUS23152
We thank the engineers from CNES and scientific laboratories (CBK, IRAP, LPC2E, LPP, and SSD of ESTEC) who largely contributed to the success of the DEMETER mission. F. N. and O. S. acknowledge the support of GACR Grant 21-01813S and MSMT Grant LUAUS23152.
- Language
- English
- Date published
- 10/16/2024
- Academic Unit
- Physics and Astronomy
- Record Identifier
- 9984721113702771
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