Spectral characteristics of magnetic Pi 2 pulsations in the auroral region and lower latitudes

Kuwashima, Masayuki; Saito, Takao

doi:10.1029/ja086ia06p04686

Cited by 37 publications

(25 citation statements)

References 56 publications

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“…On the other hand, since VA has a sharp gradient just inside the plasmapause where the Pit amplitude appears to show a secondary maximum (e.g., Kuwashima and Saito, 1981), the excitation of 6jljust inside the plasmapause will be primarily due to the effect of inhomogeneity. Further, the excitation will be more intense just inside the plasmapause than in the regions which surround the plasmapause.…”

Section: Discussionmentioning

confidence: 99%

The Excitation of Shear Alfven Wave and the Associated Modulation of Compressional Wave in the Inner Magnetosphere.

Itonaga

Yoshikawa

1996

J. geomagn. geoelec

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Two basic but novel equations directly describing the generation of shear Alfven and compressional waves in the inner magnetosphere filled with a cold magnetized plasma are derived. The shear Alfven wave is characterized by the field-aligned current and the compressional wave by the compressional component of the magnetic field. Such a generation arises from the effects of inhomogeneous Alfven speed and curvilinear field line. Around the magnetic equator, if the Alfven speed is inversely proportional to a power of the geocentric distance, these effects have magnitudes of the same order and their signs are identical.Considered in the present study is a situation that the earthward propagating compressional wave is launched from a large scale oscillating current wedge centered at midnight and symmetric about the magnetic equator. Then, it is found that the field-aligned current excited around the equator by the compressional wave has opposite senses in direction in the northern and southern hemispheres, in the pre-and post-midnight sectors as well as just inside the plasmapause and in its surrounding regions. As a result of the excitation of shear Alfven wave, two types of oscillations appear on a field line: One is a forced oscillation and the other is an eigenoscillation. Although a modulation of the compressional wave may be caused locally (or microscopically) around the equator by the eigenoscillation of field line, the modulation can be globally (or macroscopically) neglected. So far as the propagation along the source longitude (source-earth line) around the equator is concerned, the coupling between compressional and shear Alfven waves can be almost neglected and so one-dimensional response of the inner magnetosphere around the equator plays a significant role in the compressional oscillation.

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Section: Discussionmentioning

confidence: 99%

The Excitation of Shear Alfven Wave and the Associated Modulation of Compressional Wave in the Inner Magnetosphere.

Itonaga

Yoshikawa

1996

J. geomagn. geoelec

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“…The amplitude of Pi2 pulsations has the primary maximum around the auroral electrojet latitudes and the secondary maximum near the foot point of the plasmapause (e.g., Kuwashima and Saito, 1981). This secondary maximum is not always observed since it is weak and narrow in latitude.…”

Section: Introductionmentioning

confidence: 99%

Local time dependence of the dominant frequency of Pi2 pulsations at mid- and low-latitudes

et al. 2014

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We carried out a statistical analysis of Pi2 pulsations using the geomagnetic field data obtained at three ground stations. A local time dependence of the dominant frequency of Pi2 was found on the nightside. The frequency of mid-latitude Pi2 pulsations is lower on the dusk side than that on the dawn side. This tendency is attributed to the shape of the plasmasphere which bulges out to the dusk side. It was confirmed that the Pi2 frequency depends also on the geomagnetic activity measured with Kp index. During the disturbed periods, Pi2 pulsations have higher frequency than that in the quiet periods. This dependence is interpreted to be caused by the size of the plasmapause which is smaller under the disturbed conditions than that under the quiet conditions. The dominant frequency of Pi2 pulsations at lower latitudes has a peak in post-midnight, and a Kp dependence similar to that at mid-latitudes is also observed. However, the result for low-latitude Pi2's is different from that for mid-latitude Pi2. We consider that the dominant mechanism of mid-latitude Pi2 is the plasmaspheric surface wave. In order to examine the idea that the surface wave on the plasmapause is the dominant mechanism of Pi2 pulsations at mid-latitudes, we estimated the resonance frequency of the surface wave on the plasmapause using a plasmaspheric model which includes the effect of the plasmaspheric bulge. The estimated frequency of the surface wave is higher on the dawn side than that on the dusk side, which is essentially consistent with the observational results. The predicted frequency under quiet conditions (Kp ≤ 3) is nearly equal to the observed Pi2 frequency at mid-latitudes. These results suggest that the dominant frequency of Pi2 pulsations at mid-latitudes depends on the structure of the plasmapause.

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“…Pi 2 pulsations at higher latitudes (L >-4) on the nightside have been generally interpreted to be either a transient standing resonance of the auroral field line excited at substorm expansion onset (Maltsev et al, 1974;Saito et al, 1976;Olson and Rostoker, 1977;Kuwashima, 1978) or oscillating localized fieldaligned currents in the substorm current wedge (and/or in the head of the westward traveling surge) (Pashin et al, 1982;Samson and Rostoker, 1983;Sakurai and McPherron, 1983;Glassmeier, 1988;Glassmeier et al, 1988).…”

Section: Introductionmentioning

confidence: 99%

Correlation of High- and Low-Law-Latitude Pi 2 Magnetic Pulsations Observed at 210.DEG. Magnetic Meridian Chain Stations.

Yumoto

Osaki

Fukao

et al. 1994

J. geomagn. geoelec

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Spectral characteristics of magnetic Pi 2 pulsations in the auroral region and lower latitudes

Cited by 37 publications

References 56 publications

The Excitation of Shear Alfven Wave and the Associated Modulation of Compressional Wave in the Inner Magnetosphere.

The Excitation of Shear Alfven Wave and the Associated Modulation of Compressional Wave in the Inner Magnetosphere.

Local time dependence of the dominant frequency of Pi2 pulsations at mid- and low-latitudes

Correlation of High- and Low-Law-Latitude Pi 2 Magnetic Pulsations Observed at 210.DEG. Magnetic Meridian Chain Stations.

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