Global mode ULF pulsations in a magnetosphere with a nonmonotonic Alfvén velocity profile

Zhu, Xiaoming; Kivelson, M. G.

doi:10.1029/ja094ia02p01479

Cited by 116 publications

(92 citation statements)

References 19 publications

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“…Yet the ionosphere is a significant energy sink for ULF waves. Furthermore, it is known that some wave energy can cross the plasmapause into the inner magnetosphere (Takahashi et al, 1990), a result that has also been explained theoretically (Allan et al, 1986b;Zhu and Kivelson, 1989). Neither the real plasmapause, nor the real magnetopause are the ideal reflectors assumed in the simulation, nor is the real magnetosphere azimuthally symmetric as assumed in the model.…”

Section: Comparison With Computer Simulationsmentioning

confidence: 82%

“…Computer simulations and numerical solutions use simplified models (Allan et al, 1985(Allan et al, , 1986aInhester, 1987;Lee and Lysak, 1989;Zhu and Kivelson, 1989) but they reveal various important features of cavity eigenmode oscillations. A comparison of our observations with previous analyses of the global mode support our interpretation of the wave mode present in our data.…”

Section: Comparison With Computer Simulationsmentioning

confidence: 99%

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A Possible Signature of Magnetic Cavity Mode Oscillations in ISEE Spacecraft Observations.

Kivelson

Cao

McPherron

et al. 1997

J. geomagn. geoelec

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The structure of magnetohydrodynamic waves in the terrestrial magnetosphere is controlled by the dispersion relations of the wave modes, the inhomogeneities of the system and the boundary conditions. If the waves are confined within the magnetospheric cavity with proper boundary conditions, two types of spectra are predicted by MHD theory. One is a discrete compressional spectrum and the other is a continuous shear Alfven spectrum. The discrete spectrum refers to compressional eigenmodes with spatially constant eigenfrequencies. The continuous shear Alfven spectrum corresponds to field line resonances with spatially varying resonant frequencies. There have been many reports of observations consistent with the theoretical predictions for shear Alfven waves. However, only a few spacecraft observations of the global cavity eigenmodes or the coupling between the two modes have been reported. Here we report an observation using ISEE 1 and 2 spacecraft magnetometer data. On a quiet day with low solar wind dynamic pressure and low geomagnetic activity, the ISEE 1 and 2 spacecraft identified a compressional wave with constant frequency throughout most of its inbound orbit in the outer magnetosphere. Multiple harmonics of shear Alfven waves with spatially varying frequencies were observed in the azimuthal component. Evidence of the coupling between these two waves in found. Comparing our observations with the results of a computer simulation in a dipole field, we find qualitative (not quantitative) agreement. We also consider why so few examples of radially-extended monochromatic compressional oscillations have been found. We conclude that the exceptional circumstances required for development and identification of these wave structures occur very rarely.

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Section: Comparison With Computer Simulationsmentioning

confidence: 82%

Section: Comparison With Computer Simulationsmentioning

confidence: 99%

A Possible Signature of Magnetic Cavity Mode Oscillations in ISEE Spacecraft Observations.

Kivelson

Cao

McPherron

et al. 1997

J. geomagn. geoelec

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“…The modelling work of Allan et al (1986) and Zhu and Kivelson (1989) suggests that lowfrequency spectral peaks can occur at low latitude if a realistic plasmapause structure is included when modelling the magnetosphere. If the fundamental eigenfrequency of the magnetospheric cavity/waveguide is ∼ 1.3 mHz, as suggested by Samson et al (1992), then 1.6 mHz is a plausible frequency for such a mode (Allan et al, 1986;Zhu and Kivelson, 1989). The low-latitude peak could thus be evidence of such a compressional mode, or could be a field-line resonance driven by the cavity mode within the plasmasphere at the lower latitude of the Wick radar field of view.…”

Section: Discussionmentioning

confidence: 99%

A comparison of field-line resonances observed at the Goose Bay and Wick radars

Provan

Yeoman

1997

Ann. Geophys.

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Abstract. Previous observations with the Goose Bay HF coherent-scatter radar have revealed structured spectral peaks at ultra-low frequencies. The frequencies of these spectral peaks have been demonstrated to be extremely consistent from day to day. The stability of these spectral peaks can be seen as evidence for the existence of global magnetospheric cavity modes whose resonant frequencies are independent of latitude. Fieldline resonances occur when successive harmonics of the eigenfrequency of the magnetospheric cavity or waveguide match either the first harmonic eigenfrequency of the geomagnetic field lines or higher harmonics of this frequency. Power spectra observed at the SABRE VHF coherent-scatter radar at Wick, Scotland, during night and early morning are revealed to show similarly clearly structured spectral peaks. These spectral peaks are the result of local field-line resonances due to Alfvén waves standing on magnetospheric field lines. A comparison of the spectra observed by the Goose Bay and Wick radars demonstrate that the frequencies of the field-line resonances are, on average, almost identical, despite the different latitudinal ranges covered by the two radars. Possible explanations for the similarity of the signatures on the two radar systems are discussed.

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“…When there is a sharp inward density gradient at the plasmapause, a cavity mode localized within the plasmasphere can be established. Quantitative analyses of the mode have been presented using a box magnetosphere (Zhu and Kivelson, 1989), a cylindrical magnetosphere (Allan et al, 1986b) and, most recently, a dipole magnetosphere (Fujita and Glassmeier, 1995;Lee, 1996). The simulation by Lee (1996), shown in Fig.…”

Section: Pc 3±4 Wavesmentioning

confidence: 99%

ULF waves: 1997 IAGA division 3 reporter review

Takahashi

1998

Ann Geophysicae

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Abstract. Highlights of studies of ULF waves from 1995 to early 1997 are presented. The subjects covered include (1) Pc 3±5 waves excited by sources in the solar wind, with emphasis on the role of the magnetospheric cavity in modifying the external source and establishing its own resonances, and the role of the plasmapause in magnetohydrodynamic wave propagation; (2) Pi 2 waves, with emphasis on the plasmaspheric resonances and possible alternative excitation by plasmasheet source waves; (3) the spatial structure of internally excited long-period waves, including a kinetic theory for radially con®ned ring current instability and groundbased multipoint observation of giant pulsations; (4) amplitude-modulated Pc 1±2 waves in the outer magnetosphere (Pc 1±2 bursts) and in the inner magnetosphere (structured Pc 1 waves or pearls); and (5) the source region of the quasi-periodic emissions. Theory and observations are compared, and controversial issues are highlighted. In addition, some future directions are suggested.

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Global mode ULF pulsations in a magnetosphere with a nonmonotonic Alfvén velocity profile

Cited by 116 publications

References 19 publications

A Possible Signature of Magnetic Cavity Mode Oscillations in ISEE Spacecraft Observations.

A Possible Signature of Magnetic Cavity Mode Oscillations in ISEE Spacecraft Observations.

A comparison of field-line resonances observed at the Goose Bay and Wick radars

ULF waves: 1997 IAGA division 3 reporter review

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