Spectral Law and Polarization Properties of the Low‐Frequency Waves at the Magnetopause

Rezeau, Laurence; Belmont, Gérard; Cornilleau‐Wehrlin, N.; Reberac, F.; Briand, Cyril

doi:10.1029/1999gl900060

Cited by 23 publications

(28 citation statements)

References 23 publications

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“…These spectra are found in this case to follow a f −α power law (Fig. 5), as already observed (Rezeau et al, 1999). A calculation of the parameter α in the magnetosheath and at the magnetopause gives values between 2.3 and 2.9, depending on the spacecraft and on the interval studied.…”

Section: Small-scale Fluctuationssupporting

confidence: 54%

A case study of low-frequency waves at the magnetopause

Rezeau¹,

Sahraoui

d’Humières

et al. 2001

Ann. Geophys.

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Abstract. We present the study of one of the first magnetopause crossings observed by the four Cluster spacecraft simultaneously, on 10 December 2000. Although the delays between the crossings are very short, the features of the boundary appear quite different as seen by the different spacecraft, strongly suggesting the presence of a local curvature of the magnetopause at that time. The small-scale fluctuations observed by the STAFF search-coil experiment are placed in relation to this context. A preliminary investigation of their behaviour on the boundary and in the neighbourhood magnetosheath is performed in comparison with the theoretical model of Belmont and Rezeau (2001), which describes the interaction of waves with the boundary.

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Section: Small-scale Fluctuationssupporting

confidence: 54%

A case study of low-frequency waves at the magnetopause

Rezeau¹,

Sahraoui

d’Humières

et al. 2001

Ann. Geophys.

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“…This allows to deal with a smooth spectrum resulting by averaging over the whole number of FFTs. Furthermore, to avoid any inaccuracy in the phase determination due to boundary effect [ Rezeau et al , 1999], each data segment corresponding to a time interval of length T 0 is multiplied by a cos 3 ( t ) window function before computing the FFTs.…”

Section: The K‐filtering Techniquementioning

confidence: 99%

ULF wave identification in the magnetosheath: The k‐filtering technique applied to Cluster II data

Sahraoui¹

2003

J. Geophys. Res.

110

116

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[1] The magnetic fluctuations in the magnetosheath are studied, thanks to Cluster II data. The k-filtering technique is applied to explore ULF magnetic fluctuations using STAFF (Spatio-Temporal Analysis of a Field Fluctuations) data. Based on multipoint measurements, the k-filtering technique allows, for the first time, to estimate the Magnetic Field Energy Distribution (MFED) in both the angular frequency and wave vector space. We show how the localisation of the magnetic energy in the (w, k) domain can be used to identify the linear modes that can propagate in the magnetosheath. A comparison between k-filtering results and prediction of the linear theory is performed. For the frequencies examined the magnetic energy seems to be distributed over the low frequency modes: mirror, Alfvén, and slow modes. Estimation of Doppler shift shows that each frequency observed is the superposition of different frequencies in the plasma frame. This ''mixture of modes'' at a given observed frequency explains why the fluctuations are generally not observed to be polarized, as shown in previous studies. Some other implications on a weak turbulence approach of the magnetic fluctuations in the magnetosheath are discussed.

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“…Rezeau et al (1999) find a power law f −3.4 above f ci in an interval close to the magnetopause. For intervals close to the bow shock, Czaykowska et al (2001) find power laws around f −1 below f ci , and f −2.6 above f ci .…”

Section: Spectral Shapementioning

confidence: 99%

“…The power law spectra ∼f −5/3 , typical of the solar wind inertial range at f <f ci , have not been observed in the magnetosheath. However, as in the solar wind, the energy of the magnetic fluctuations follows a power law close to ∼f −3 at frequencies f >f ci (Rezeau et al, 1999;Czaykowska et al, 2001).…”

Section: Introductionmentioning

confidence: 99%

Spectra and anisotropy of magnetic fluctuations in the Earth's magnetosheath: Cluster observations

2008

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Abstract. We investigate the spectral shape, the anisotropy of the wave vector distributions and the anisotropy of the amplitudes of the magnetic fluctuations in the Earth's magnetosheath within a broad range of frequencies [10 −3 , 10] Hz which corresponds to spatial scales from ∼10 to 10 5 km. We present the first observations of a Kolmogorov-like inertial range of Alfvénic fluctuations δB 2 ⊥ ∼f −5/3 in the magnetosheath flanks, below the ion cyclotron frequency f ci . In the vicinity of f ci , a spectral break is observed, like in solar wind turbulence. Above the break, the energy of compressive and Alfvénic fluctuations generally follows a power law with a spectral index between −3 and −2. Concerning the anisotropy of the wave vector distribution, we observe a clear change in its nature in the vicinity of ion characteristic scales: if at MHD scales there is no evidence for a dominance of a slab (k k ⊥ ) or 2-D (k ⊥ k ) turbulence, above the spectral break, (f >f ci , kc/ω pi >1) the 2-D turbulence dominates. This 2-D turbulence is observed in six selected one-hour intervals among which the average ion β varies from 0.8 to 10. It is observed for both the transverse and compressive magnetic fluctuations, independently on the presence of linearly unstable modes at low frequencies or Alfvén vortices at the spectral break. We then analyse the anisotropy of the magnetic fluctuations in a time dependent reference frame based on the field B and the flow velocity V directions. Within the range of the 2-D turbulence, at scales [1, 30]kc/ω pi , and for any β we find that the magnetic fluctuations at a given frequency in the plane perpendicular to B have more energy along the B×V direction. This non-gyrotropy of the fluctuations at a fixed frequency is consistent with gyrotropic fluctuations at a given wave vector, with k ⊥ k , which suffer a different Doppler shift along and perpendicular to V in the plane perpendicular to B.

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Spectral Law and Polarization Properties of the Low‐Frequency Waves at the Magnetopause

Cited by 23 publications

References 23 publications

A case study of low-frequency waves at the magnetopause

A case study of low-frequency waves at the magnetopause

ULF wave identification in the magnetosheath: The k‐filtering technique applied to Cluster II data

Spectra and anisotropy of magnetic fluctuations in the Earth's magnetosheath: Cluster observations

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