Compressional waves in the Earth's neutral sheet

Volwerk, M.; Baumjohann, W.; Glaßmeier, Karl‐Heinz; Nakamura, R.; Zhang, T. L.; Runov, A.; Vörös, Z.; Klecker, B.; Treumann, R. A.; Bogdanova, Y. V.; Eichelberger, Hans; Balogh, A.; Rème, H.

doi:10.5194/angeo-22-303-2004

Cited by 31 publications

(30 citation statements)

References 29 publications

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“…The spectral index changes around f 1 ∼ 0.01-0.08 Hz (100-13 s). The observed scaling indices are α 1 ∼ 0.5-1.5 for f < f 1 and α 2 ∼ 1.7-3 when f > f 1 (Milovanov et al, 2001;Volwerk et al, 2003Volwerk et al, , 2004a. For frequencies higher than f 2 ∼ 1 Hz (time scales smaller than 1 s) dissipation and kinetic effects start to be important.…”

Section: Turbulence Spectramentioning

confidence: 86%

Bursty Bulk Flow Driven Turbulence in the Earth’s Plasma Sheet

et al. 2006

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During the last several years significant progress has been made in understanding MHD turbulence in the Earth's plasma sheet. Due to the statistically transitory properties of fluctuations, finite size and boundary effects, however, issues of fundamental importance remain unresolved. Here we concentrate on such intrinsic features of plasma sheet turbulence as its origin and dynamical nature. In particular, we investigate bursty bulk flow driven multi-scale transfer of energy towards the dissipation scale, and provide evidence for the presence of non-linear interactions. We show that, in contrast with previous results, Alfvénic fluctuations together with 2D eddy interactions may appear as important constituents of turbulence in the plasma sheet.

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Section: Turbulence Spectramentioning

confidence: 86%

Bursty Bulk Flow Driven Turbulence in the Earth’s Plasma Sheet

et al. 2006

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“…It is also known from 3‐D MHD simulations of turbulence that for β ∼1, variance anisotropy is significant; however, over β >40 the anisotropy disappears [ Matthaeus et al , 1996]. The power of compressional fluctuations over MHD scales is known to be larger than the power of right‐hand and left‐hand polarized waves in the near‐Earth plasma sheet [ Volwerk et al , 2004]. More importantly, plasma β varied between 1 and 10 during the activation periods, which can explain the appearance of variance anisotropy at the position of Cluster spacecraft.…”

Section: Spectral Analysis Of Magnetic Fluctuationsmentioning

confidence: 99%

Study of reconnection‐associated multiscale fluctuations with Cluster and Double Star

et al. 2008

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[1] The objective of the paper is to asses the specific spectral scaling properties of magnetic reconnection associated fluctuations/turbulence at the earthward and tailward outflow regions observed simultaneously by the Cluster and Double Star (TC-2) spacecraft on 26 September 2005. Systematic comparisons of spectral characteristics, including variance anisotropy and scale-dependent spectral anisotropy features in wave vector space were possible due to the well-documented reconnection events, occurring between the positions of Cluster (X = À14-16 R e ) and TC-2 (X = À6.6 R e ). Another factor of key importance is that the magnetometers on the spacecraft are similar. The comparisons provide further evidence for asymmetry of physical processes in earthward/tailward reconnection outflow regions. Variance anisotropy and spectral anisotropy angles estimated from the multiscale magnetic fluctuations in the tailward outflow region show features which are characteristic for magnetohydrodynamic cascading turbulence in the presence of a local mean magnetic field. The multiscale magnetic fluctuations in the earthward outflow region are not only exhibiting more power, lack of variance, and scale-dependent anisotropies but also are having larger anisotropy angles. In this region the magnetic field is more dipolar and the main processes driving turbulence are flow breaking/ mixing, perhaps combined with turbulence ageing and noncascade-related multiscale energy sources.

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“…The spectral index changes around f c 1 ∼0.01–0.08 Hz. The observed scaling indices are α 1 ∼ 0.5–1.5 for f < f c 1 and α 2 ∼ 1.7–2.9 when f > f c 1 [ Milovanov et al , 2001; Volwerk et al , 2003, 2004]. The uncertainty of the estimated values of α 1 and α 2 can be explained by slightly different frequency ranges studied by various authors and by the occurrence of spatially inhomogeneous, intermittent, and transitory mechanisms involved in the generation of the observed scalings.…”

Section: Introductionmentioning

confidence: 99%

Magnetic turbulence in the plasma sheet

et al. 2004

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[1] Small-scale magnetic turbulence observed by the Cluster spacecraft in the plasma sheet is investigated by means of a wavelet estimator suitable for detecting distinct scaling characteristics even in noisy measurements. The spectral estimators used for this purpose are affected by a frequency-dependent bias. The variances of the wavelet coefficients, however, match the power-law shaped spectra, which makes the wavelet estimator essentially unbiased. These scaling characteristics of the magnetic field data appear to be essentially nonsteady and intermittent. The scaling properties of bursty bulk flow (BBF) and non-BBF associated magnetic fluctuations are analyzed with the aim of understanding processes of energy transfer between scales. Small-scale ($0.08-0.3 s) magnetic fluctuations having the same scaling index a $ 2.6 as the large-scale ($0.7-5 s) magnetic fluctuations occur during BBF-associated periods. During non-BBF associated periods the energy transfer to small scales is absent, and the large-scale scaling index a $ 1.7 is closer to Kraichnan or Iroshnikov-Kraichnan scalings. The anisotropy characteristics of magnetic fluctuations show both scale-dependent and scale-independent behavior. The former can be partly explained in terms of the Goldreich-Sridhar model of MHD turbulence, which leads to the picture of Alfvénic turbulence parallel and of eddy turbulence perpendicular to the mean magnetic field direction. Nonetheless, other physical mechanisms, such as transverse magnetic structures, velocity shears, or boundary effects can contribute to the anisotropy characteristics of plasma sheet turbulence. The scaleindependent features are related to anisotropy characteristics which occur during a period of magnetic reconnection and fast tailward flow.

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Compressional waves in the Earth's neutral sheet

Cited by 31 publications

References 29 publications

Bursty Bulk Flow Driven Turbulence in the Earth’s Plasma Sheet

Bursty Bulk Flow Driven Turbulence in the Earth’s Plasma Sheet

Study of reconnection‐associated multiscale fluctuations with Cluster and Double Star

Magnetic turbulence in the plasma sheet

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