STARE and SABRE observations of a Pc 5 pulsation with large azimuthal wave number during a storm period

Data from three instruments, the magnetometer, the charge‐energy‐mass spectrometer, and the medium‐energy particle, analyzer onboard the Active Magnetospheric Particle Tracer Explorers/Charge Composition Explorer (CCE) spacecraft have been used to study a compressional Pc 5 wave observed at 1925–2200 UT on day 202 (July 21) of 1986 at a radial distance of ≃8 RE in the postmidnight sector near the beginning of minor geomagnetic activity. The wave exhibited harmonically related transverse and compressional magnetic oscillations, modulation of the flux of medium energy protons (E ≳ 10 keV), and a large azimuthal wave number (m ∼ 65). These properties are similar to those of compressional Pc5 waves observed previously at geostationary orbit. The unique observations associated with the CCE event are the occurrence in the postmidnight sector, the eastward (or sunward) propagation with respect to the spacecraft, and the left‐handed polarization of the perturbed magnetic field. These are opposite to previous geostationary observations. We propose that the unique propagation and polarization are caused by a dawn‐to‐dusk dc electric field which convects the plasma sunward. The wave, probably propagating westward in the plasma rest frame, appears to propagate eastward to the observer because the electric field drift velocity is larger than the wave phase velocity.

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“…. Similar observations have been made with ground-based radar [Walker et al, 1982;Allan et al, 1982;Misra et al, 1985].…”

supporting

confidence: 83%

An eastward propagating compressional Pc 5 wave observed by AMPTE/CCE in the postmidnight sector

Takahashi¹,

López²,

McEntire³

et al. 1987

J. Geophys. Res.

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“…The characteristic feature of Pc5 waves must be the large azimuthal wave numbers and velocity of wave propagation of the order of the ion drift velocity. Pc5 waves with such features were repeatedly observed using radar systems and satellites during magnetic storms (for example, see Misra et al, 1985 and references therein).…”

Section: Discussionmentioning

confidence: 99%

Characteristics of Pc1-2 and IPDP Geomagnetic Pulsations during Large-Scale Undulations on the Evening Diffuse Auroral Boundary.

Baishev

Solovyev

1994

J. geomagn. geoelec

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In this paper, the properties of Pcl-2 and IPDP geomagnetic pulsations in the evening sector using the Yakut chain data and satellite measurements are described. It is shown that maximum intensity of Pc 1-2 type geomagnetic pulsations is observed at latitudes of peak precipitating proton fluxes and the pulsation amplitude is modulated with periods of 2-7 min. The large-scale undulations observed by the DMSP satellites on the equatorward diffuse auroral boundary, are formed during motion of the pulsation excitation region and a centre of the eastward electroj et to lower latitudes and during a growth of Pcl-2 pulsation frequency. The oscillation periods of the undulation boundary are in agreement with' modulation periods of Pc 1-2 amplitude, taking into account the observed wavelengths and assuming that the azimuthal velocity of their propagation is about 1-2 km/s. The results are interpreted in terms of the mechanism of spatial modulation of magnetically drifting and precipitating auroral protons.

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“…Another reason is that we wish to eliminate the polarization reversal of the transverse magnetic field perturbation which can result from a component-dependent standing wave structure [Nagano and Araki, 1983;Takahashi et al, 1985bTakahashi et al, , 1987a. One reason for this is to find out how often and where such events are observed.…”

Section: Datamentioning

confidence: 99%

Observation and theory of Pc 5 waves with harmonically related transverse and compressional components

et al. 1990

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The properties of 23 magnetic pulsation events observed by the AMPTE CCE spacecraft are studied. These events are selected on the basis of the field magnitude which oscillated at the second harmonic of a simultaneously present transverse oscillation. The events have a second harmonic period of 80–600 s (roughly the Pc 5 range), are observed in cluster in the dawn (0300–0800 magnetic local time, MLT) and dusk (1600–2100 MLT) sectors, and are localized near the magnetic equator. Although the azimuthal wave number, m, estimated from an ion finite Larmor radius effect, is generally large (|m| ∼ 50), there is a marked difference between the events observed in the dawn and dusk sectors. In the dawn sector the waves have low frequencies (1–5 mHz), indicate left‐hand polarization with respect to the ambient magnetic field, and propagate eastward with respect to the spacecraft. In the dusk sector the waves have high frequencies (5–15 mHz), indicate right‐hand polarization, and propagate westward. We suggest that the waves are all westward propagating in the plasma rest frame and that local‐time‐dependent Doppler shift is the reason for the local time dependence of the wave properties. The drift mirror instability is considered to be the mechanism for exciting the westward propagating waves. An analytical formula for the ion flux oscillations is derived on the basis of the nonlinear gyrokinetic theory. The observed correlation between the ion flux and the parallel magnetic field perturbation δB∥ can be adequately explained with this analytical formula.

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STARE and SABRE observations of a Pc 5 pulsation with large azimuthal wave number during a storm period

Cited by 8 publications

References 55 publications

An eastward propagating compressional Pc 5 wave observed by AMPTE/CCE in the postmidnight sector

An eastward propagating compressional Pc 5 wave observed by AMPTE/CCE in the postmidnight sector

Characteristics of Pc1-2 and IPDP Geomagnetic Pulsations during Large-Scale Undulations on the Evening Diffuse Auroral Boundary.

Observation and theory of Pc 5 waves with harmonically related transverse and compressional components

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