Storm time occurrence and spatial distribution of Pc4 poloidal ULF waves in the inner magnetosphere: A Van Allen Probes statistical study

Dai, Lei; Takahashi, Kazue; Lysak, R. L.; Wang, Chi; Wygant, J. R.; Kletzing, C. A.; Bonnell, J. W.; Cattell, C. A.; Smith, Charles W.; MacDowall, R. J.; Thaller, S. A.; Breneman, A. W.; Tang, Xiangwei; Tao, X.; Chen, Lunjin

doi:10.1002/2015ja021134

Cited by 68 publications

(102 citation statements)

References 72 publications

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“…Only weak spectral features are seen in the compressional B z component. Some pulsations observed during the three orbits might be categorized as compressional ones based on the classification of Dai et al (2015). They consider pulsations to be compressional for even very weak B p , i.e., for abs (B p /B r ) > 0.2.…”

Section: Spectral Characteristic Of the Pc4 Pulsationsmentioning

confidence: 99%

“…Schäfer et al (2007Schäfer et al ( , 2008 reported that sometimes high-m Pc4 waves were actually seen near the plasmapause and suggested that they may be due to harmonics of poloidal mode eigen oscillations in a radially confined Alfvén resonance region at the inner or outer edges of the plasmapause. Dai et al (2015) noted that the effect of the plasmapause on the radial transmission of the poloidal waves is caused by the fact that the Alfvén speed changes rapidly across the radial direction. Eriksson et al (2005) reported three cases of poloidal Pc5 pulsations with large azimuthal number (m = 100) waves observed by Cluster that occurred in the dayside magnetosphere during magnetically quiet times from L = 4 to L = 6.…”

Section: Introductionmentioning

confidence: 99%

“…Motoba et al (2015) reported one-to-one associations of these pulsations with auroral pulsations around the ionospheric footprint of the magnetic field line and suggested that an auroral undulation event is closely linked to the generation of second-harmonic poloidal waves. Dai et al (2015) presented a comprehensive statistical study of poloidal Pc4 pulsations observed by Van Allen Probes spacecraft. To get more information on the free-energy wave source for the inner magnetosphere they sorted the pulsations into compressional and non-compressional waves based on the ratio of radial (B r ) to compressional (B p ) components.…”

Section: Introductionmentioning

confidence: 99%

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Multipoint spacecraft observations of long-lasting poloidal Pc4 pulsations in the dayside magnetosphere on 1–2 May 2014

et al. 2016

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Abstract. We use magnetic field and plasma observations from the Van Allen Probes, Time History of Events and Macroscale Interactions during Substorms (THEMIS) and Geostationary Operational Environmental Satellite system (GOES) spacecraft to study the spatial and temporal characteristics of long-lasting poloidal Pc4 pulsations in the dayside magnetosphere. The pulsations were observed after the main phase of a moderate storm during low geomagnetic activity. The pulsations occurred during various interplanetary conditions and the solar wind parameters do not seem to control the occurrence of the pulsations. The most striking feature of the Pc4 magnetic field pulsations was their occurrence at similar locations during three of four successive orbits. We used this information to study the latitudinal nodal structure of the pulsations and demonstrated that the latitudinal extent of the magnetic field pulsations did not exceed 2 Earth radii (R E ). A phase shift between the azimuthal and radial components of the electric and magnetic fields was observed from Z SM = 0.30 R E to Z SM = −0.16 R E . We used magnetic and electric field data from Van Allen Probes to determine the structure of ULF waves. We showed that the Pc4 magnetic field pulsations were radially polarized and are the secondmode harmonic waves. We suggest that the spacecraft were near a magnetic field null during the second orbit when they failed to observe the magnetic field pulsations at the local times where pulsations were observed on previous and successive orbits. We investigated the spectral structure of the Pc4 pulsations. Each spacecraft observed a decrease of the dominant period as it moved to a smaller L shell (stronger magnetic field strength). We demonstrated that higher frequencies occurred at times and locations where Alfvén velocities were greater, i.e., on Orbit 1. There is some evidence that the periods of the pulsations increased during the plasmasphere refilling following the storm.

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Section: Spectral Characteristic Of the Pc4 Pulsationsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Multipoint spacecraft observations of long-lasting poloidal Pc4 pulsations in the dayside magnetosphere on 1–2 May 2014

et al. 2016

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“…Solar wind dynamic pressure fluctuations can be a substantial source for magnetosphere ULF wave power [Kessel, 2008;Takahashi and Ukhorskiy, 2007;Dai et al, 2015]. Solar wind dynamic pressure fluctuations can be a substantial source for magnetosphere ULF wave power [Kessel, 2008;Takahashi and Ukhorskiy, 2007;Dai et al, 2015].…”

Section: Introductionmentioning

confidence: 99%

Modulation of chorus intensity by ULF waves deep in the inner magnetosphere

Xia

Chen

Dai

et al. 2016

Geophysical Research Letters

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Previous studies have shown that chorus wave intensity can be modulated by Pc4‐Pc5 compressional ULF waves. In this study, we present Van Allen Probes observation of ULF wave modulating chorus wave intensity, which occurred deep in the magnetosphere. The ULF wave shows fundamental poloidal mode signature and mirror mode compressional nature. The observed ULF wave can modulate not only the chorus wave intensity but also the distribution of both protons and electrons. Linear growth rate analysis shows consistence with observed chorus intensity variation at low frequency (f <∼ 0.3fce), but cannot account for the observed higher‐frequency chorus waves, including the upper band chorus waves. This suggests the chorus waves at higher‐frequency ranges require nonlinear mechanisms. In addition, we use combined observations of Radiation Belt Storm Probes (RBSP) A and B to verify that the ULF wave event is spatially local and does not last long.

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“…Furthermore, motivated by a recent direct observation of poloidal standing Alfvén waves in Earth's magnetosphere by Dai et al (2013) (see also Dai et al, 2015;Takahashi et al, 2013;Liu et al, 2013Liu et al, , 2011, we extend our investigation to examine the poloidal-mode waves as well. In the case of a transverse poloidal mode, we show that the wave equation can also be cast as a KG form along a field line.…”

Section: Introductionmentioning

confidence: 99%

Hydromagnetic waves in a compressed-dipole field via field-aligned Klein–Gordon equations

Zheng¹,

Hu²,

Webb³

et al. 2016

Ann. Geophys.

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Abstract. Hydromagnetic waves, especially those of frequencies in the range of a few millihertz to a few hertz observed in the Earth's magnetosphere, are categorized as ultra low-frequency (ULF) waves or pulsations. They have been extensively studied due to their importance in the interaction with radiation belt particles and in probing the structures of the magnetosphere. We developed an approach to examining the toroidal standing Aflvén waves in a background magnetic field by recasting the wave equation into a Klein-Gordon (KG) form along individual field lines. The eigenvalue solutions to the system are characteristic of a propagation type when the corresponding eigenfrequency is greater than a critical frequency and a decaying type otherwise. We apply the approach to a compressed-dipole magnetic field model of the inner magnetosphere and obtain the spatial profiles of relevant parameters and the spatial wave forms of harmonic oscillations. We further extend the approach to poloidalmode standing Alfvén waves along field lines. In particular, we present a quantitative comparison with a recent spacecraft observation of a poloidal standing Alfvén wave in the Earth's magnetosphere. Our analysis based on the KG equation yields consistent results which agree with the spacecraft measurements of the wave period and the amplitude ratio between the magnetic field and electric field perturbations.

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Storm time occurrence and spatial distribution of Pc4 poloidal ULF waves in the inner magnetosphere: A Van Allen Probes statistical study

Cited by 68 publications

References 72 publications

Multipoint spacecraft observations of long-lasting poloidal Pc4 pulsations in the dayside magnetosphere on 1–2 May 2014

Multipoint spacecraft observations of long-lasting poloidal Pc4 pulsations in the dayside magnetosphere on 1–2 May 2014

Modulation of chorus intensity by ULF waves deep in the inner magnetosphere

Hydromagnetic waves in a compressed-dipole field via field-aligned Klein–Gordon equations

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