ULF waves in the outer magnetosphere: Geotail observation 1 transverse waves

Kokubun, S.

doi:10.5047/eps.2012.12.013

Cited by 15 publications

(20 citation statements)

References 61 publications

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“…We note that we are not the first to report the dawn-dusk asymmetry in satellite observations. Qualitatively the same asymmetry has been reported using observations with AMPTE/CCE (L < 9) [Anderson et al, 1990], DE 1 (polar orbit covering a wide range of Ls) [Nosé et al, 1995], and Geotail (L > 8) [Kokubun, 2013;Takahashi et al, 2014]. However, we believe that our analyses provide by far the most quantitative evaluation of the asymmetry because we used a large amount of data and a technique to detect T1 waves in a consistent manner.…”

Section: Dawn-dusk Asymmetry Of T1 Wave Detection Rate and Amplitudesupporting

confidence: 80%

A statistical study of fundamental toroidal mode standing Alfvén waves using THEMIS ion bulk velocity data

et al. 2015

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We have studied the statistical properties of toroidal mode standing Alfvén waves with a fundamental eigenmode structure along the field line, denoted T1 waves, in the L range 7–12, using THEMIS‐D data for 2008–2013. T1 wave events were identified in hourly data segments using an automated procedure that detects narrowband oscillations in the azimuthal component of the ion bulk velocity. For each event we determined the frequency, amplitude, ellipticity, and the orientation angle of the polarization ellipse, and we examined the L and magnetic local time dependence of the detection rate and physical properties of the T1 waves. Confirming previous observations in space and on the ground, we found a pronounced dawn‐dusk asymmetry in the wave detection rate and amplitude. The detection rate in the dawn sector is approximately twice as high as that in the dusk sector, and the amplitude in the dawn sector is larger by ∼50%. The same asymmetry is also evident in the velocity amplitude averaged in the fixed Pc5 band (1.7–6.7 mHz) and in the amplitude of the electric field and field line displacement that are derived from the velocity amplitude. The ellipticity and the orientation angle of the polarization ellipse are organized by local time, in accordance with the theoretical prediction of toroidal mode waves excited by field line resonance with tailward propagating waves in the magnetosphere, which are in turn driven by external sources. Although infrequently, T1 waves are also detected in the midnight sector, suggesting magnetotail sources for this subset of events.

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Section: Dawn-dusk Asymmetry Of T1 Wave Detection Rate and Amplitudesupporting

confidence: 80%

A statistical study of fundamental toroidal mode standing Alfvén waves using THEMIS ion bulk velocity data

et al. 2015

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“…It should be noted that comparable, possibly quasi‐steady, discrete frequencies have been reported in a number of studies [ Fenrich et al , ; Chisham and Orr , ; Francia and Villante , ; Villante et al , ; Kokubun , ]. These have been attributed to different modes, depending on the circumstances of the observations (location, solar wind conditions, etc.…”

Section: Introductionmentioning

confidence: 62%

What frequencies of standing surface waves can the subsolar magnetopause support?

Archer

Plaschke

2015

JGR Space Physics

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It is has been proposed that the subsolar magnetopause may support its own eigenmode, consisting of propagating surface waves which reflect at the northern/southern ionospheres forming a standing wave. While the eigenfrequencies of these so‐called Kruskal‐Schwarzschild (KS) modes have been estimated under typical conditions, the potential distribution of frequencies over the full range of solar wind conditions is not known. Using models of the magnetosphere and magnetosheath applied to an entire solar cycle's worth of solar wind data, we perform time‐of‐flight calculations yielding a database of KS mode frequencies. Under nonstorm times or northward interplanetary magnetic field (IMF), the most likely fundamental frequency is calculated to be 0.64−0.12+0.03 mHz, consistent with previous estimates and indirect observational evidence for such standing surface waves of the subsolar magnetopause. However, the distributions exhibit significant spread (of order ±0.3 mHz) demonstrating that KS mode frequencies, especially higher harmonics, should vary considerably depending on the solar wind conditions. The implications of such large spread on observational statistics are discussed. The subsolar magnetopause eigenfrequencies are found to be most dependent on the solar wind speed, southward component of the IMF, and the Dst index, with the latter two being due to the erosion of the magnetosphere by reconnection and the former an effect of the expression for the surface wave phase speed. Finally, the possible occurrence of KS modes is shown to be controlled by the dipole tilt angle.

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“…In the scientific literature, the analysis of magnetospheric fluctuations has been often performed, for individual events (Clausen et al, ; Du et al, ; Eriksson, Blomberg, & Glassmeier, ; Eriksson, Blomberg, Walker, et al, ; Eriksson et al, ; Ren et al, ; Sarris et al, ; Wang et al, ; Waters et al, ; Zhao et al, ; Zong et al, , ) and for statistical analysis (Kokubun, ; Yumoto et al, ), after having rotated the original measurements (SE coordinates, in the present case) in the field‐aligned coordinates (MFA), at each point along the spacecraft trajectory. In MFA N coordinates (see also Appendix ),

\overset{μ}{true}

is along the average field, as defined by the N min vector running average;

\overset{φ}{true}

, perpendicular to

\overset{μ}{true}

and to the spacecraft position vector (

\overset{r}{true}

), is directed eastward; and

\overset{ν}{true}

completes the orthogonal system.…”

Section: The Influence Of the Data Rotation On The Spectral Analysismentioning

confidence: 99%

The Identification of Waves at Discrete Frequencies at the Geostationary Orbit: The Role of the Data Analysis Techniques and the Comparison With Solar Wind Observations

Matteo

Villante

2018

JGR Space Physics

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Following a recent investigation in which we examined the performance of two methods (the Welch method and the multitaper windowing and F test) on the identification of fluctuations of the solar wind dynamic pressure in streams following interplanetary shocks, we extend our analysis to the magnetospheric field fluctuations detected at the geostationary orbit after the occurrence of the related sudden impulses. First, we show that a contamination of the experimental results, dramatic in statistical investigations, might come from the rotation of measurements in the field‐aligned coordinates when the field direction is determined, point by point, by the running averages: this procedure creates spurious events at frequencies related to the length of the running average window. These aspects do not appear in a fixed coordinate system, as determined by evaluating the average field vector for the entire interval. In this system, we examined 124 magnetospheric structures following sudden impulses: the Welch method/multitaper windowing and F test agreement in the wave identification and frequency estimate was achieved for ≈50% of events, and some evidence for higher percentages of events occurs at f ≈ 1.5–1.7, f ≈ 2.2–2.4, ≈3.9–4.2, and, more explicitly, at f ≈ 4.2–4.7 mHz. Oscillation modes with the same characteristics at different local times were rarely observed. An analysis of case events reveals that fluctuations of the solar wind pressure may drive magnetospheric fluctuations at the same frequencies; in addition, the manifestation of modes, not appearing in the solar wind, might be related to the magnetospheric compression or to other processes triggered by the shock arrival.

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ULF waves in the outer magnetosphere: Geotail observation 1 transverse waves

Cited by 15 publications

References 61 publications

A statistical study of fundamental toroidal mode standing Alfvén waves using THEMIS ion bulk velocity data

A statistical study of fundamental toroidal mode standing Alfvén waves using THEMIS ion bulk velocity data

What frequencies of standing surface waves can the subsolar magnetopause support?

The Identification of Waves at Discrete Frequencies at the Geostationary Orbit: The Role of the Data Analysis Techniques and the Comparison With Solar Wind Observations

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