Discontinuity observations with cluster

Knetter, T.; Neubauer, F. M.; Horbury, T. S.; Balogh, A.

doi:10.1016/s0273-1177(03)00335-1

Cited by 55 publications

(83 citation statements)

References 15 publications

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“…By contrast, Cluster multiple spacecraft observations suggest that the fluctuations in the examined intervals are highly oblique (Sahraoui et al 2010;Narita et al 2011). Another analysis of the Cluster spacecraft data found that the normal directions of the solar wind magnetic field discontinuities are nearly perpendicular to the magnetic field (Knetter et al 2004). This was argued to be the result of turbulence-generated coherent structures (Matthaeus & Montgomery 1980;Vasquez et al 2007;Greco et al 2010;Osman et al 2011).…”

Section: Introductionmentioning

confidence: 89%

Statistical Analysis of the Magnetic Helicity Signature of the Solar Wind Turbulence at 1 Au

Markovskii

Vasquez

Smith

2015

ApJ

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The absolute value of the magnetic helicity spectrum of the solar wind turbulence often has a peak at kinetic scales. This helicity signature is important for understanding the mechanism of the turbulent cascade. In this paper, a statistical analysis of the magnetic helicity is performed. For this purpose, a database of the solar wind intervals with the helicity signature was assembled using Wind spacecraft magnetic and plasma data. New statistically significant correlations between the magnetic helicity and the properties of the background plasma are found. The position of the signature within the spectrum depends on the proton gyroscale and the proton inertial scale. Possible mechanisms responsible for the observed trends are discussed. The helicity peak is interpreted as a result of two competing processes, one of which generates the helicity and the other one eliminates it.

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Section: Introductionmentioning

confidence: 89%

Statistical Analysis of the Magnetic Helicity Signature of the Solar Wind Turbulence at 1 Au

Markovskii

Vasquez

Smith

2015

ApJ

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“…In a survey, Knetter et al (2003Knetter et al ( , 2004) applied multispacecraft timing methods to a number of discontinuities observed by Cluster in the solar wind, and concluded that most of the observed discontinuities could be classified as TDs. Also, in a recent publication, Weimer and King (2008), adapted the MVAB-0 method, and performed a thorough check of the method, and basically confirmed its usefulness for propagation delay calculations.…”

Section: Constrained Minimum Variance -Mvab-0mentioning

confidence: 99%

What is the best method to calculate the solar wind propagation delay?

2008

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Abstract. We present a statistical study of propagation times of solar wind discontinuities between Advanced Composition Explorer (ACE) spacecraft orbiting the L1 libration point and the Cluster quartet of spacecraft near the Earth's magnetopause. The propagation times for almost 200 events are compared with the predicted times from four different models. The simplest model assumes a constant convective motion of solar wind disturbances along the Sun-Earth line, whereas more sophisticated models take the orientation of the discontinuity as well as the real positions of the solar wind monitor and target into account. The results show that taking orientation and real position of the solar wind monitor and target into account gives a more precise time delay estimation in most cases. In particular, we show that recent modifications to the minimum variance technique can improve the estimation of propagation times of solar wind discontinuities.

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“…Many single-spacecraft studies of DDs in the solar wind have been published (e.g., Burlaga 1969;Smith 1973;Martin et al 1978;Tsurutani & Smith 1979;Mariani et al 1983;Neugebauer 1989;Soding et al 2001): in most cases RDs or TDs have been found to be prevalent in fast-speed or in slow-speed streams, respectively. Using multiple (three or more) spacecraft data allows for determining the normal direction by considering the times of crossing the DD for each spacecraft (Burlaga & Ness 1969;Horbury et al 2001;Knetter et al 2003Knetter et al , 2004. Unlike what is found by minimum variance analisys, the multiple-spacecraft technique indicates a prevalence of EDs in the population of DDs with respect to the other kinds of discontinuities (Knetter et al 2003(Knetter et al , 2004.…”

Section: Introductionmentioning

confidence: 99%

Alfvén waves in coronal holes: formation of discontinuities in inhomogeneous magnetic fields

Malara

2012

A&A

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Context. Solar wind fluctuations are characterized by discontinuities. The nature and properties of these structures have been largely studied in the literature, and different mechanisms have been proposed to explain their formation. Aims. We investigate the evolution of Alfvénic perturbations propagating in the inhomogeneous magnetic field of a coronal open-field region, in order to study both the way that small-scale structures are generated and the possible formation of discontinuities. Methods. We constructed a model for the equilibrium magnetic field in a coronal hole. The model represents a potential field with a complex structure: regions of opposite polarity or of only the dominant polarity are present at low or high altitudes, respectively. The evolution of small-amplitude Alfvén waves in the inhomogeneous structure is studied by employing a WKB approach that describes how the perturbation wavevector and the wave phase vary along magnetic lines. Results. We find that small-scale structures form in the perturbation at relatively low altitudes (∼3 × 10 4 km) above the coronal base. An initially monochromatic perturbation develops a steep power-law spectrum with slope α 2.3, which is strongly anisotropic with a predominance of quasi-perpendicular wavevectors. Small-scale structures are localized around separatrices of the magnetic structures. In many cases they contain quasi-perpendicular rotational discontinuities that can propagate to the upper corona, eventually reaching the solar wind. Conclusions. The considered mechanism could be responsible for forming a fraction of the population of discontinuities detected in the solar wind.

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Discontinuity observations with cluster

Cited by 55 publications

References 15 publications

Statistical Analysis of the Magnetic Helicity Signature of the Solar Wind Turbulence at 1 Au

Statistical Analysis of the Magnetic Helicity Signature of the Solar Wind Turbulence at 1 Au

What is the best method to calculate the solar wind propagation delay?

Alfvén waves in coronal holes: formation of discontinuities in inhomogeneous magnetic fields

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