Determining the Mode, Frequency, and Azimuthal Wave Number of ULF Waves During a HSS and Moderate Geomagnetic Storm

Ultralow frequency (ULF) waves play a fundamental role in the dynamics of the inner magnetosphere and outer radiation belt during geomagnetic storms. Broadband ULF wave power can transport energetic electrons via radial diffusion, and discrete ULF wave power can energize electrons through a resonant...

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Bibliographic Details
Published in:Journal of geophysical research. Space physics 2018-08, Vol.123 (8), p.6457-6477
Main Authors: Murphy, Kyle R., Inglis, Andrew R., Sibeck, David G., Rae, I. Jonathan, Silveira, Marcos, Plaschke, Ferdinand, Claudepierre, Seth G., Nakamura, Rumi
Format: Article
Language:English
Subjects:
Activation
azimuthal wave number
Broadband
Electron radiation
Evolution
Extremely low frequencies
Geomagnetic storms
Geomagnetism
Instability
Instruments and Techniques
Ionosphere
Jupiter
Kelvin-Helmholtz instability
Magnetic fields
Magnetic resonance
Magnetic Storms
Magnetic Storms and Substorms
Magnetosphere
Magnetospheres
Magnetospheric Physics
mode structure
Natural Hazards
Outer radiation belt
Plasma Waves and Instabilities
Radiation
Radiation Belts
Resonant interactions
Solar wind
Solar wind velocity
Solar Wind/Magnetosphere Interactions
Space Radiation
Space Weather
Spacecraft
Stability analysis
Storms
Topology
ULF waves
Wave power
Wavelengths
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Summary:Ultralow frequency (ULF) waves play a fundamental role in the dynamics of the inner magnetosphere and outer radiation belt during geomagnetic storms. Broadband ULF wave power can transport energetic electrons via radial diffusion, and discrete ULF wave power can energize electrons through a resonant interaction. Using observations from the Magnetospheric Multiscale mission, we characterize the evolution of ULF waves during a highspeed solar wind stream (HSS) and moderate geomagnetic storm while there is an enhancement of the outer radiation belt. The Automated Flare Inference of Oscillations code is used to distinguish discrete ULF wave power from broadband wave power during the HSS. During periods of discrete wave power and utilizing the close separation of the Magnetospheric Multiscale spacecraft, we estimate the toroidal mode ULF azimuthal wave number throughout the geomagnetic storm. We concentrate on the toroidal mode as the HSS compresses the dayside magnetosphere resulting in an asymmetric magnetic field topology where toroidal mode waves can interact with energetic electrons. Analysis of the mode structure and wave numbers demonstrates that the generation of the observed ULF waves is a combination of externally driven waves, via the KelvinHelmholtz instability, and internally driven waves, via unstable ion distributions. Further analysis of the periods and toroidal azimuthal wave numbers suggests that these waves can couple with the core electron radiation belt population via the drift resonance during the storm. The azimuthal wave number and structure of ULF wave power (broadband or discrete) have important implications for the inner magnetospheric and radiation belt dynamics.
ISSN:2169-9402
2169-9380
2169-9402
DOI:10.1029/2017ja024877