Journal article
Global Survey and Empirical Model of Fast Magnetosonic Waves Over Their Full Frequency Range in Earth's Inner Magnetosphere
Journal of geophysical research. Space physics, Vol.124(12), pp.10270-10282
12/2019
DOI: 10.1029/2019JA027407
Abstract
We investigate the global distribution and provide empirical models of fast magnetosonic waves using the combined observations by the magnetometer and waveform receiver on board Van Allen Probes. The magnetometer measurements of magnetosonic waves indicate a significant wave power within the frequency range from the helium gyrofrequency to 20 Hz at L ≥ 4 in the afternoon sector, both inside and outside the plasmapause. The waveform receiver measurements indicate a significant wave power from 20 Hz to the lower hybrid resonance frequency at L ≤ 5.5 near the dayside outside the plasmapause or in the afternoon sector inside the plasmapause. The sum of the wave powers from the two instruments provides the wave power distribution over the complete frequency range. The most significant root‐mean‐square wave amplitude of magnetosonic waves is typically 100–200 pT inside or outside the plasmapause with a magnetic local time coverage of 30–50% during geomagnetically active times when AE* > 500 nT. The magnetosonic wave frequency increases with decreasing L shell following the trend of the proton gyrofrequency outside the plasmapause, indicating a close relation with the local wave generation. Inside the plasmapause, the dependence of wave frequency on L shell is weaker, and the wave frequency is more stable across L shells, indicating the wave propagation effects from the source located at higher L shells. We have performed polynomial fits of the global magnetosonic wave distribution and wave frequency spectra, which are useful in future radiation belt simulations.
Plain Language Summary
Magnetosonic waves are highly oblique electromagnetic emissions, naturally occurring in the Earth's magnetosphere. Using combined measurements made by different instruments on board Van Allen Probes, we survey the magnetosonic wave power and its frequency spectrum in a complete frequency range in the inner magnetosphere. The averaged wave amplitude reaches 100–200 pT inside and outside the plasmapause during disturbed geomagnetic conditions, with extensive coverage in magnetic local time. The wave frequency increases with decreasing L shell outside the plasmapause, and the wave frequency spectrum exhibits the effects of propagation across L shells inside the plasmapause. The global distribution and frequency spectrum of the wave power are fitted using polynomial functions. Our survey provides empirical models of magnetosonic waves in the inner magnetosphere, which are useful in future radiation belt modeling.
Key Points
We combine the magnetosonic wave power spectrogram measured by the magnetometer and waveform receiver on board Van Allen Probes
The global distributions of magnetosonic waves from fcHe to fLHR are constructed and fitted to provide empirical models
We present the statistical frequency spectra of magnetosonic waves from fcHe to fLHR and perform empirical fitting
Details
- Title: Subtitle
- Global Survey and Empirical Model of Fast Magnetosonic Waves Over Their Full Frequency Range in Earth's Inner Magnetosphere
- Creators
- Q. Ma - Boston UniversityW. Li - Boston UniversityJ. Bortnik - University of California, Los AngelesC. A. Kletzing - University of IowaW. S. Kurth - University of IowaG. B. Hospodarsky - University of IowaJ. R. Wygant - University of Minnesota
- Resource Type
- Journal article
- Publication Details
- Journal of geophysical research. Space physics, Vol.124(12), pp.10270-10282
- DOI
- 10.1029/2019JA027407
- ISSN
- 2169-9380
- eISSN
- 2169-9402
- Number of pages
- 13
- Grant note
- NASA (NNX14AI18G; NNX14AN85G; NNX15AI96G; NNX16AG21G; NAS5‐01072; 80NSSC20K0196) AFOSR (FA9550‐15‐1‐0158) DOD | USAF | AFMC | Air Force Office of Scientific Research (AFOSR) Alfred P. Sloan Research Fellowship (FG‐2018‐10936) NSF (AGS‐1847818) JHU/APL (921647; 967399) JHU | Applied Physics Laboratory, Johns Hopkins University (APL, JHU)
- Language
- English
- Date published
- 12/2019
- Academic Unit
- Physics and Astronomy
- Record Identifier
- 9984428829702771
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