Magnetotelluric Sounding of the Crust and Hydrodynamic Monitoring of the Magnetosphere with the Use of ULF Waves

Pilipenko, V. A.; Fedorov, E. N.

doi:10.1029/gm081p0283

Cited by 24 publications

(22 citation statements)

References 21 publications

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“…The data hodograph is too far away from a simple circular shape to make it meaningful enough to calculate f R (x) using the hodograph method. To think about the reason of this separation of the two curves, we have applied APGM (Pilipenko and Fedorov, 1994;Kawano et al, 2002) to the raw data of the amplitude ratio and the cross phase, and the result is shown in Fig. 12.…”

Section: Discussion and Summarymentioning

confidence: 99%

“…As shown by Pilipenko (1990), Pilipenko and Fedorov (1994), and (see also references therein), the solution to the above equation can be asymptotically decomposed, and its leading term is expressed as follows (its valid range will be discussed later in the main text and in Appendix A):…”

Section: Overviewmentioning

confidence: 99%

“…−1 (e.g., Menk et al, 1994;Pilipenko and Fedorov, 1994;Waters et al, 1994). The sign of the gradient of f R (x), and correspondingly δ, determines the direction of an apparent phase velocity in the resonant region.…”

Section: Overviewmentioning

confidence: 99%

“…Then we go further, apply the hodograph method to an adjacent station pair, and compare the results. Furthermore, in this paper we apply the "amplitude-phase gradient method" (APGM below) (Pilipenko and Fedorov, 1994;Kawano et al, 2002) (Section 5); this is the first time in literature that the hodograph method and the APGM are applied to the same dataset. We note here that APGM is different from the hodograph method: They are based on the same equation Eq.…”

Section: Introductionmentioning

confidence: 99%

“…To examine the validity and usefulness of the hodograph method, we apply it to a Pc 4 event observed by the Scandinavian BEAR array. We also apply the amplitude-phase gradient method (Pilipenko and Fedorov, 1994;Kawano et al, 2002) to the same event, and compare the results; this is the first article applying the both methods to the same dataset. …”

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confidence: 99%

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Hodograph method to estimate the latitudinal profile of the field-line resonance frequency using the data from two ground magnetometers

2013

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The hodograph method enables estimating the latitudinal profile of the field-line resonance (FLR) frequency ( f R ) using the data from two ground magnetometers. This paper provides the full details of this method for the first time, and uses a latitudinal chain of ground magnetometers to examine its validity and usefulness. The hodograph method merges the widely-used amplitude-ratio and cross-phase methods in a sense that the hodograph method uses both the amplitude ratio and the phase difference in a unified manner; further than that, the hodograph method provides f R at any latitude near those of the two ground magnetometers. It is accomplished by (1) making a complex number by using the amplitude ratio (phase difference) as its real (imaginary) part; (2) drawing thus obtained complex numbers (one number for one frequency) in the complex plane to make a hodograph; and (3) fitting to thus obtained hodograph a model satisfying the FLR condition, which is a circle with the assumption that the resonance width is independent of the latitude. To examine the validity and usefulness of the hodograph method, we apply it to a Pc 4 event observed by the Scandinavian BEAR array. We also apply the amplitude-phase gradient method (Pilipenko and Fedorov, 1994;Kawano et al., 2002) to the same event, and compare the results; this is the first article applying the both methods to the same dataset.

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Section: Discussion and Summarymentioning

confidence: 99%

Section: Overviewmentioning

confidence: 99%

Section: Overviewmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

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Hodograph method to estimate the latitudinal profile of the field-line resonance frequency using the data from two ground magnetometers

2013

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Mode number calculations of ULF field‐line resonances using ground magnetometers and THEMIS measurements

Sarris

Liu

et al. 2013

JGR Space Physics

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[1] Using multiple pairs of International Monitor for Auroral Geomagnetic Effects ground magnetometers together with simultaneous measurements from two of the Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft constellation, when they were flying over the magnetometers in magnetic conjunction and in close azimuthal separation, we are able to calculate the phase differences of Ultra Low Frequency Field-Line Resonances, and, through that, their azimuthal mode number, wavelength and propagation characteristics. A cross-wavelet technique is applied, that exposes the times and frequencies of common power between time series from azimuthally aligned magnetometers in space or on the ground, yielding their relative phase. Using the amplitude ratio and phase differences between ground stations with similar longitudes that are separated in latitude, a correction to the mode number calculation is demonstrated, accounting for the phase differences that arise from the L shell separation of the THEMIS probes.

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Externally driven plasmaspheric ULF waves observed by the Van Allen Probes

et al. 2015

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We analyze data acquired by the Van Allen Probes on 8 November 2012, during a period of extended low geomagnetic activity, to gain new insight into plasmaspheric ultralow frequency (ULF) waves. The waves exhibited strong spectral power in the 5–40 mHz band and included multiharmonic toroidal waves visible up to the eleventh harmonic, unprecedented in the plasmasphere. During this wave activity, the interplanetary magnetic field cone angle was small, suggesting that the waves were driven by broadband compressional ULF waves originating in the foreshock region. This source mechanism is supported by the tailward propagation of the compressional magnetic field perturbations at a phase velocity of a few hundred kilometers per second that is determined by the cross‐phase analysis of data from the two spacecraft. We also find that the coherence and phase delay of the azimuthal components of the magnetic field from the two spacecraft strongly depend on the radial separation of the spacecraft and attribute this feature to field line resonance effects. Finally, using the observed toroidal wave frequencies, we estimate the plasma mass density for L = 2.6–5.8. By comparing the mass density with the electron number density that is estimated from the spectrum of plasma waves, we infer that the plasma was dominated by H+ ions and was distributed uniformly along the magnetic field lines. The electron density is higher than the prediction of saturated plasmasphere models, and this “super saturated” plasmasphere and the uniform ion distribution are consistent with the low geomagnetic activity that prevailed.

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Magnetotelluric Sounding of the Crust and Hydrodynamic Monitoring of the Magnetosphere with the Use of ULF Waves

Cited by 24 publications

References 21 publications

Hodograph method to estimate the latitudinal profile of the field-line resonance frequency using the data from two ground magnetometers

Hodograph method to estimate the latitudinal profile of the field-line resonance frequency using the data from two ground magnetometers

Mode number calculations of ULF field‐line resonances using ground magnetometers and THEMIS measurements

Externally driven plasmaspheric ULF waves observed by the Van Allen Probes

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