Multi-instrument observations of a large scale Pc4 pulsation

Clausen, L. B. N.; Yeoman, T. K.; Behlke, R.; Lucek, E.

doi:10.5194/angeo-26-185-2008

Cited by 10 publications

(16 citation statements)

References 33 publications

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“…The density changes by about 2 orders of magnitude. The band‐pass‐filtered magnetic field magnitudes shown in Figure (middle row) reveal the bursty nature of the observed wave activity, which is in agreement with observations of upstream waves penetrating into the inner magnetosphere [ Clausen et al , , ]. Two wave bursts were observed, one prior to the plasmapause crossing and one afterward.…”

Section: Observationssupporting

confidence: 87%

“…Another way of using MHD waves, albeit at much lower frequencies, to identify the plasmapause is described in Menk et al [] who study the latitudinal variation of magnetic field line eigenfrequencies using closely spaced ground‐based magnetometers. In the case of field line eigenfrequencies, the wave period is dependent on the Alfvén velocity along the magnetic field line [e.g., Cummings et al , ], and hence, a sudden change in plasma density results in a sudden change of the observed eigenfrequency [ Menk et al , ; Clausen et al , ].…”

Section: Introductionmentioning

confidence: 99%

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Enhancement of ultralow frequency wave amplitudes at the plasmapause

Clausen

Glaßmeier

2014

JGR Space Physics

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We present measurements of ultralow frequency (ULF) wave amplitudes measured by the Time History of Events and Macroscale Interactions during Substorms (THEMIS) probes while crossing the plasmapause. During one crossing on 24 June 2007 which we study in detail, all three probes of which data that were obtained show an increase in the ULF compressional wave amplitude between 10 and 50 mHz by about 30%. These results are confirmed by a statistical study that examines the ULF compressional wave amplitude in the same frequency range averaged over 132 sharp plasmapause crossings between June 2007 and December 2007 made by THEMIS C, D, and E. Sharp plasmapause crossings are defined as those where the density increases by more than a factor of 50 over a spatial scale of 500 km. We find that assuming that the plasmapause can be approximated by a tangential MHD discontinuity, a ULF wave amplitude enhancement of 30% is in good agreement with theoretical transmission coefficient calculations if the plasma density increases from about 4 cm −3 on the magnetospheric trough side to about 540 cm −3 on the plasmaspheric side while simultaneously the magnetic field magnitude increases from 250 nT to 350 nT. These results might have important implications for the detection of global fast modes by satellites as their amplitude is hence expected to be higher inside the plasmasphere than outside.

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Section: Observationssupporting

confidence: 87%

Section: Introductionmentioning

confidence: 99%

Enhancement of ultralow frequency wave amplitudes at the plasmapause

Clausen

Glaßmeier

2014

JGR Space Physics

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“…The equatorial plane location and the magnetic field values for the Alfvén velocities came from the T96 model using disturbance storm time index DST = 2.5 nT, SW dynamic pressure p = 1.4 nPa, IMF B y = 3.5 nT GSM, and IMF B z = −0.5 nT GSM. Particle density was determined using THM-D measurements and a R −3 dependence from the center of the Earth [Clausen et al, 2008]. This results in a total transit time of 80 s. The observed first pulsation maximum at THM-D occurred at 0437:14 UT while the corresponding first maximum at BKS occurred at 0438:32 UT, giving an observed transit time of 78 s. This agrees well with our estimate.…”

Section: Discussionsupporting

confidence: 83%

First radar observations in the vicinity of the plasmapause of pulsed ionospheric flows generated by bursty bulk flows

Frissell

Baker

Ruohoniemi

et al. 2011

Geophys. Res. Lett.

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Recent expansion of the SuperDARN network to mid‐latitudes and the addition of a new high‐time resolution mode provides new opportunities to observe mid‐latitude ultra‐low frequency waves and other ionospheric sub‐auroral features at high temporal resolution. On 22 February 2008, the Blackstone SuperDARN radar and THEMIS ground magnetometers simultaneously observed substorm Pi2 pulsations. Similarities in measurements from the Blackstone radar and a magnetometer at Remus suggest a common generating mechanism. Cross‐phase analysis of magnetometer data places these measurements at the ionospheric projection of the plasmapause, while fine spatial and temporal details of the radar data show evidence of field line compressions. About 1 min prior to ground Pi2 observation, 2 Earthward‐moving Bursty Bulk Flows (BBFs) were observed by THEMIS probes D and E in the near‐Earth plasma sheet. We conclude that the first 2 pulses of the Pi2s observed at Blackstone and Remus result from compressional energy generated by BBFs braking against the magnetospheric dipolar region.

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“…It has commonly been found that eigenfrequencies decrease with increasing magnetic latitude (e.g., Baransky et al, 1989;Clausen et al, 2008;Samson et al, 1971;Wharton et al, 2018). This has been attributed to the lengthening of the field lines toward the magnetic poles.…”

Section: Variations With Geomagnetic Latitude and Mltmentioning

confidence: 99%

The Variation of Resonating Magnetospheric Field Lines With Changing Geomagnetic and Solar Wind Conditions

et al. 2019

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Standing ultralow frequency waves redistribute energy and momentum around the Earth's magnetosphere. The eigenfrequencies of these standing waves can be measured by applying the cross‐phase technique to ground magnetometer data. To make a detection, the flux tubes in the vicinity of the magnetometers must all be driven at their local eigenfrequencies by a source with a sufficient frequency width. Therefore, successful measurement of the local eigenfrequencies indicates that a broadband source is exciting the flux tubes. We have analyzed 10 years of magnetometer data with an automated cross‐phase algorithm and used correlations with the OMNI data set to understand under what conditions broadband excitation occurs and how the conditions affect the eigenfrequency values. This is the largest such survey of its kind to date. We found that lower eigenfrequencies at higher latitudes (L>5) and higher eigenfrequencies at lower latitudes (L<4) were excited under different conditions. It was also possible to directly compare the first and third harmonics at midlatitudes. The lower eigenfrequencies were excited during more disturbed conditions, and we suggest that these harmonics are driven by solar wind pressure pulses or the Kelvin‐Helmholtz instability at the magnetopause. The higher eigenfrequencies were excited when the magnetosphere was relatively quiet, and we suggest that the cause was waves generated upstream of the Earth's bow shock. The eigenfrequencies were observed to decrease in the middle magnetosphere during disturbed intervals. This is because the intensification of the ring current weakens the magnetic field. Variations in magnetic local time and latitude were also investigated.

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Multi-instrument observations of a large scale Pc4 pulsation

Cited by 10 publications

References 33 publications

Enhancement of ultralow frequency wave amplitudes at the plasmapause

Enhancement of ultralow frequency wave amplitudes at the plasmapause

First radar observations in the vicinity of the plasmapause of pulsed ionospheric flows generated by bursty bulk flows

The Variation of Resonating Magnetospheric Field Lines With Changing Geomagnetic and Solar Wind Conditions

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