PC 4 giant pulsations in the morning sector

Rostoker, G.; Lam, Hing-Lan; Olson, John V.

doi:10.1029/ja084ia09p05153

Cited by 56 publications

(36 citation statements)

References 25 publications

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“…These nearly monochromatic waves are usually observed during quite geomagnetic conditions, when the plasmapause lies somewhere at L ∼ 5.5 − 6, and giant pulsations (Pg) are recorded just there. Rostoker et al (1979) were the first to notice this. The assumption that Pg are resonator modes on the outer edge of the plasmapause is consistent with the strong localization of Pg across magnetic shells accompanied by a phase change by 180 degrees (Green, 1979;Rostoker et al, 1979;Glassmeier, 1980), and the amplitude distribution in L is described by the Gaussian function with the halfwidth of about 1 R E (Chisham et al, 1997), and this is indeed expected for the fundamental radial harmonic within the resonator on the outer edge of the plasmapause.…”

Section: On the Observation Of Toroidal And Poloidal Alfvén Waves In mentioning

confidence: 90%

Toroidal and poloidal Alfvén waves with arbitrary azimuthal wavenumbers in a finite pressure plasma in the Earth's magnetosphere

Klimushkin

Mager

Glaßmeier³

2004

Ann. Geophys.

124

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Abstract. In this paper, in terms of an axisymmetric model of the magnetosphere, we formulate the criteria for which the Alfvén waves in the magnetosphere can be toroidally and poloidally polarized (the disturbed magnetic field vector oscillates azimuthally and radially, respectively). The obvious condition of equality of the wave frequency ω to the toroidal (poloidal) eigenfrequency T N ( P N ) is a necessary and sufficient one for the toroidal polarization of the mode and only a necessary one for the poloidal mode. In the latter case we must also add to it a significantly stronger condition, where m is the azimuthal wave number, and N is the longitudinal wave number. In cold plasma (the plasma to magnetic pressure ratio β = 0) the left-hand side of this inequality is too small for the routinely recorded (in the magnetosphere) second harmonic of radially polarized waves, therefore these waves must have nonrealistically large values of m. By studying several models of the magnetosphere differing by the level of disturbance, we found that the left-hand part of the poloidality criterion can be satisfied by taking into account finite plasma pressure for the observed values of m ∼ 50 − 100 (and in some cases, for even smaller values of the azimuthal wave numbers). When the poloidality condition is satisfied, the existence of two types of radially polarized Alfvén waves is possible. In magnetospheric regions, where the function P N is a monotonic one, the mode is poloidally polarized in a part of its region of localization. It propagates slowly across magnetic shells and changes its polarization from poloidal to toroidal. The other type of radially polarized waves can exist in those regions where this function reaches its extreme values (ring current, plasmapause). These waves are standing waves across magnetic shells, having a poloidal polarization throughout the region of its existence. Waves of this type are likely to be exemplified by giant pulsations. If the poloidality condition is not satisfied, then the mode is toroidally polarized throughout the region of its existence. Furthermore, itCorrespondence to: D. Yu. Klimushkin (klimush@iszf.irk.ru) has a resonance peak near the magnetic shell, the toroidal eigenfrequency of which equals the frequency of the wave.

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Section: On the Observation Of Toroidal And Poloidal Alfvén Waves In mentioning

confidence: 90%

Toroidal and poloidal Alfvén waves with arbitrary azimuthal wavenumbers in a finite pressure plasma in the Earth's magnetosphere

Klimushkin

Mager

Glaßmeier³

2004

Ann. Geophys.

124

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“…However, Rostoker et al (1979) reported ground magnetometer observations of highly monochromatic Pc4 giant pulsations in the auroral zone that reoccurred on successive days during quiet geomagnetic conditions. They suggested that the Pc4 pulsations may be due to the occurrence of field line resonances at the plasmapause in the region where the electric field changes its azimuthal direction from westward to eastward.…”

Section: Introductionmentioning

confidence: 99%

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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“…They are characterised by their large amplitudes, and their striking quasi-monochromatic wave form with periods of typically 100 s. Giant pulsations have been studied intensively in the past by e.g. Annexstad and Wilson (1968), Green (1979), Rostoker et al (1979), Glassmeier (1980), and more recently by Chisham and Orr (1991), Chisham et al (1992), Takahashi et al (1992), Chisham and Orr (1994), Chisham (1996), and Chisham et al (1997).…”

Section: Introductionmentioning

confidence: 99%

Concerning the generation of geomagnetic giant pulsations by drift-bounce resonance ring current instabilities

et al. 1999

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Abstract. Giant pulsations are nearly monochromatic ULF-pulsations of the Earth's magnetic ®eld with periods of about 100 s and amplitudes of up to 40 nT. For one such event ground-magnetic observations as well as simultaneous GEOS-2 magnetic and electric ®eld data and proton¯ux measurements made in the geostationary orbit have been analysed. The observations of the electromagnetic ®eld indicate the excitation of an odd-mode type fundamental ®eld line oscillation. A clear correlation between variations of the proton¯ux in the energy range 30±90 keV with the giant pulsation event observed at the ground is found. Furthermore, the proton phase space density exhibits a bump-on-the-tail signature at about 60 keV. Assuming a drift-bounce resonance instability as a possible generation mechanism, the azimuthal wave number of the pulsation wave ®eld may be determined using a generalized resonance condition. The value determined in this way, m À21 AE 4, is in accord with the value m À27 AE 6 determined from ground-magnetic measurements. A more detailed examination of the observed ring current plasma distribution function f shows that odd-mode type eigenoscillations are expected for the case df ad b 0, much as observed. This result is dierent from previous theoretical studies as we not only consider local gradients of the distribution function in real space, but also in velocity space. It is therefore concluded that the observed giant pulsation is the result of a driftbounce resonance instability of the ring current plasma coupling to an odd-mode fundamental standing wave. The generation of the bump-on-the-tail distribution causing df ad b 0 can be explained due to velocity dispersion of protons injected into the ring current. Both this velocity dispersion and the necessary substorm activity causing the injection of protons into the nightside magnetosphere are observed.

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PC 4 giant pulsations in the morning sector

Cited by 56 publications

References 25 publications

Toroidal and poloidal Alfvén waves with arbitrary azimuthal wavenumbers in a finite pressure plasma in the Earth's magnetosphere

Toroidal and poloidal Alfvén waves with arbitrary azimuthal wavenumbers in a finite pressure plasma in the Earth's magnetosphere

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

Concerning the generation of geomagnetic giant pulsations by drift-bounce resonance ring current instabilities

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