Pulsations at the Substorm Onset

Southwood, D. J.; Stuart, W.F.

doi:10.1007/978-94-009-9519-2_17

Cited by 33 publications

(29 citation statements)

References 45 publications

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“…Thus, the source mechanism of mid-latitude Pi 2 pulsations might be associated with the surface waves at the plasmapause (Sutcliffe, 1975;Southwood and Stuart, 1980). On the other hand, early observations (e.g., Samson and Rostoker, 1972) reported that Pi 2 pulsations had the characteristics of discrete spectrum and suggested that there might exist global cavity modes.…”

Section: Introductionmentioning

confidence: 99%

Spectral power of low-latitude Pi 2 pulsations at the 210° magnetic meridian stations and plasmaspheric cavity resonances

2014

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Pi 2 pulsations at low latitudes are examined with magnetic fields data at the 210• magnetic meridian (MM) stations in 1991. Due to high degree of coherence over most latitudes, 68 low-latitude Pi 2 events at the 210• MM stations are identified with reference to same waveforms on the magnetogram at Lunping (189.5• MM, L = 1.06). With spectral power analysis, the ratio of the first four harmonic frequencies of low-latitude Pi 2 pulsations is about 1 : (1.7 ± 0.1) : (2.3 ± 0.1) : (2.9 ± 0.1). By using a box model for the inner magnetosphere, the cold linearized MHD wave equations are studied with realistic Alfven speed profile for nonuniform ambient magnetic fields. With appropriate parameters to depict the magnetospheric environments during the aforementioned period, numerical results are acquired with the fourth order Runge-Kutta method. It is found that the ratio of the first four harmonic frequencies of plasmaspheric cavity resonances is about 1 : 1.7 : 2.4 : 3.1 that is consistent with data analysis. This suggests that low-latitude Pi 2 pulsations at the 210• MM stations may be plasmaspheric cavity resonances driven by fast compressional waves owing to the impulsive source at the magnetotail.

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Section: Introductionmentioning

confidence: 99%

Spectral power of low-latitude Pi 2 pulsations at the 210° magnetic meridian stations and plasmaspheric cavity resonances

2014

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“…The azimuthal wave number for Pi2 events manifests a pronounced latitudinal dependence, with |m| as large as 20 at high latitudes, but decreasing to less than 1 close to the equator (Yumoto, 1986 pendence, with |m| as large as 20 at high latitudes, but decreasing to less than 1 close to the equator (Yumoto, 1986). Southwood and Stuart (1980) found that the coherence between ground stations was highest in the midnight sector and observed small m, typically 4. MierJedrzejowicz and Southwood (1979) found |m| 6 in the 8-25 mHz band, and m ∼ 2 for a Pi2 event.…”

Section: Discussionmentioning

confidence: 98%

“…While the pulsations are well defined at lower latitudes, closer to the poles they are irregular and complex, contaminated by a pronounced level of background noise, particularly in the Pi1 band (Stuart and Booth, 1974;Rostoker and Olson, 1978;Southwood and Stuart, 1980). Yeoman et al (1991) showed that Pi2 are predominantly transverse at auroral latitudes and compressional at lower latitudes.…”

Section: Introductionmentioning

confidence: 99%

“…These uniform spectral features have been attributed to transient surface waves propagating on the plasmapause (Sutcliffe, 1975;Southwood and Stuart, 1980), or temporal fluctuations of bursty bulk flows with similar spectral content (Kepko and Kivelson, 1999). However, the most established explanation invokes cavity or fast mode resonances (FMRs), which are compressional waves trapped in cavities formed within the magnetosphere (Lin et al, 1991;Sutcliffe and Yumoto, 1991;Takahashi et al, 1995;Allan et al, 1996;Pekrides et al, 1997).…”

Section: Introductionmentioning

confidence: 99%

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Evidence of standing waves during a Pi2 pulsation event observed on Cluster

et al. 2006

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Abstract.Observations of Pi2 pulsations at middle and low latitudes have been explained in terms of cavity mode resonances, whereas transients associated with field-aligned currents appear to be responsible for the high latitude Pi2 signature.Data from Cluster are used to study a Pi2 event observed at 18:09 UTC on 21 January 2003, when three of the satellites were within the plasmasphere (L=4.7, 4.5 and 4.6) while the fourth was on the plasmapause or in the plasmatrough (L=6.6). Simultaneous pulsations at ground observatories and the injection of particles at geosynchronous orbit corroborate the occurrence of a substorm.Evidence of a cavity mode resonance is established by considering the phase relationship between the orthogonal electric and magnetic field components associated with radial and field-aligned standing waves. The relative phase between satellites located on either side of the geomagnetic equator indicates that the field-aligned oscillation is an odd harmonic. Finite azimuthal Poynting flux suggests that the cavity is effectively open ended and the azimuthal wave number is estimated as m∼13.5.

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“…Pi 2 magnetic pulsations (damped oscillations with periods of 40-150 s) associated with substorm expansion onset have been widely investigated, and the basic morphological pictures were established in the 1960s and 1970s (Saito, 1969;Jacobs, 1970;On, 1973;Lanzerotti and Fukunishi, 1974;Southwood and Stuart, 1980;McPherron, 1980). Pi 2 magnetic pulsations at high latitude (L > 4) on the nightside have generally been interpreted to be atransient standing resonance of the aurora] field line excited at substorm expansion onset (Maltsev et al, 1974;Saito et al, 1976;Olson and Rostoker, 1977;Kuwashima, 1978) or to be oscillating localized field-aligned currents (FACs) in the substorm current wedge connected to the head of the westward traveling surge (Pashin et al, 1982;Lester et al, 1983;Samson and Rostoker, 1983;Sakurai and McPhenon, 1983;Gelpi et al, 1987;Glassmeier, 1988;Glassmeier et al, 1988).…”

Section: Introductionmentioning

confidence: 99%

A Comparison of the Occurrence of Very-Low-Latitude Pi 2 Pulsations with Magnetic-Field and Energetic-Particle Flux Variations (30-300 keV) at Geosynchronous Altitudes.

Saka

Watanabe

Shinohara

et al. 1996

J. geomagn. geoelec

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The occurrence of Pi 2 pulsations (20-150 s) at very-low-latitude stations is compared with the energetic-particle andmagnetic-field variations at geosynchronous orbit duringthe PROMIS (PolarRegion and Outer Magnetosphere International Study) period (March 10-June 16,1986). Ground magnetometer data from Huancayo, Peru (dip equator, 75°W), and Kuju, Japan (L = 1.2,1350E), are utilized to monitor the magnetic pulsations, while the particles (electron, 30-300 keV; proton, 145-560 keV) and magnetic fields in space are monitored by geosynchronous satellites S/C1982-019, S/C1984-129, S/C1984-037, GOES-5, and GOES-6. Of 175 Pi 2 events surveyed during the PROMIS period, 110 events are accompanied by electron flux enhancement, and 51 events have a concurrent onset of the field-aligned current (FAQ. The FAC events correlated with ground Pi 2 pulsations indicate a local time change in polarities. If currents are assumed to flow along the field lines tailward of the geosynchronous orbit, the polarities are upward in the premidnight sector and downward in the postmidnight sector. We classified Pi 2 events in the nightside sector in several different ways. The results imply that if Pi 2 events in the present study can be assumed to be of substorm origin, then 47% of Pi 2 events occur in regions close to geosynchronous altitude.

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Pulsations at the Substorm Onset

Cited by 33 publications

References 45 publications

Spectral power of low-latitude Pi 2 pulsations at the 210° magnetic meridian stations and plasmaspheric cavity resonances

Spectral power of low-latitude Pi 2 pulsations at the 210° magnetic meridian stations and plasmaspheric cavity resonances

Evidence of standing waves during a Pi2 pulsation event observed on Cluster

A Comparison of the Occurrence of Very-Low-Latitude Pi 2 Pulsations with Magnetic-Field and Energetic-Particle Flux Variations (30-300 keV) at Geosynchronous Altitudes.

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