Rapid Alignment of Velocity and Magnetic Field in Magnetohydrodynamic Turbulence

Matthaeus, W. H.; Pouquet, A.; Mininni, Pablo D.; Dmitruk, P.; Breech, B.

doi:10.1103/physrevlett.100.085003

Cited by 114 publications

(124 citation statements)

References 23 publications

(28 reference statements)

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“…The local emergence of Beltrami states was found [48][49][50] to lead to a statistical depression of nonlinearity in turbulence not associated with driving by a dominant large-scale shear flow (in other words, freely relaxing turbulence rather than driven turbulence.) Somewhat later, it was discovered numerically [51,52] (see also [53]) that Alfvénic correlations in MHD turbulence occur spontaneously in patches. Simulation subsequently showed [54] that all three types of correlations-Alfvénic, Beltrami and force free-occur spontaneously, concurrently and rapidly in MHD turbulence.…”

Section: Dynamical Relaxation Cellularization and Intermittencymentioning

confidence: 99%

Intermittency, nonlinear dynamics and dissipation in the solar wind and astrophysical plasmas

Matthaeus

Wan

Servidio

et al. 2015

Phil. Trans. R. Soc. A.

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177

139

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Section: Dynamical Relaxation Cellularization and Intermittencymentioning

confidence: 99%

Intermittency, nonlinear dynamics and dissipation in the solar wind and astrophysical plasmas

Matthaeus

Wan

Servidio

et al. 2015

Phil. Trans. R. Soc. A.

Self Cite

177

139

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“…This is expected since the transverse component of the magnetic field is amplified by the converging velocity field. However, it is known that in magnetized flows the velocity and magnetic fields tend to align (Boldyrev 2006;Matthaeus et al 2008;Banerjee et al 2009). This effect is due in part to the Lorentz force which vanishes along the magnetic field and therefore is expected to be smaller when the magnetic and velocity fields are parallel.…”

Section: Alignment Of Velocity and Magnetic Fieldsmentioning

confidence: 99%

Structure distribution and turbulence in self-consistently supernova-driven ISM of multiphase magnetized galactic discs

Iffrig

Hennebelle

2017

A&A

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Context. Galaxy evolution and star formation are two multi-scale problems tightly linked to each other. Aims. We aim to describe simultaneously the large-scale evolution widely induced by the feedback processes and the details of the gas dynamics that controls the star formation process through gravitational collapse. This is a necessary step in understanding the interstellar cycle, which triggers galaxy evolution. Methods. We performed a set of three-dimensional high-resolution numerical simulations of a turbulent, self-gravitating and magnetized interstellar medium within a 1 kpc stratified box with supernova feedback correlated with star-forming regions. In particular, we focussed on the role played by the magnetic field and the feedback on the galactic vertical structure, the star formation rate (SFR) and the flow dynamics. For this purpose we have varied their respective intensities. We extracted properties of the dense clouds arising from the turbulent motions and compute power spectra of various quantities. Results. Using a distribution of supernovae sufficiently correlated with the dense gas, we find that supernova explosions can reproduce the observed SFR, particularly if the magnetic field is on the order of a few µG. The vertical structure, which results from a dynamical and an energy equilibrium is well reproduced by a simple analytical model, which allows us to roughly estimate the efficiency of the supernovae in driving the turbulence in the disc to be rather low, of the order of 1.5%. Strong magnetic fields may help to increase this efficiency by a factor of between two and three. To characterize the flow we compute the power spectra of various quantities in 3D but also in 2D in order to account for the stratification of the galactic disc. We find that within our setup, the compressive modes tend to dominate in the equatorial plane, while at about one scale height above it, solenoidal modes become dominant. We measured the angle between the magnetic and velocity fields and we conclude that they tend to be well aligned particularly at high magnetization and lower feedback. Finally, the dense structures present scaling relations that are reminiscent of the observational ones. The virial parameter is typically larger than 10 and shows a large spread of masses below 1000 M . For masses larger than 10 4 M , its value tends to a few. Conclusions. Using a relatively simple scheme for the supernova feedback, which is self-consistently proportional to the SFR and spatially correlated to the star formation process, we reproduce a stratified galactic disc that presents reasonable scale height, SFR as well as a cloud distribution with characteristics close to the observed ones.

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“…Cross-helicity has only recently become an object of systematic study, as it become clear that it plays a fundamental role in driven MHD turbulence [14,15,17,18,19,20,21,22,23].…”

mentioning

confidence: 99%

Role of Cross-Helicity in Magnetohydrodynamic Turbulence

2009

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Strong incompressible three-dimensional magnetohydrodynamic turbulence is investigated by means of high resolution direct numerical simulations. The simulations show that the configuration space is characterized by regions of positive and negative cross-helicity, corresponding to highly aligned or anti-aligned velocity and magnetic field fluctuations, even when the average cross-helicity is zero. To elucidate the role of cross-helicity, the spectra and structure of turbulence are obtained in 'imbalanced' regions where cross-helicity is non-zero. When averaged over regions of positive and negative cross-helicity, the result is consistent with the simulations of balanced turbulence. An analytical explanation for the obtained results is proposed.

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Rapid Alignment of Velocity and Magnetic Field in Magnetohydrodynamic Turbulence

Cited by 114 publications

References 23 publications

Intermittency, nonlinear dynamics and dissipation in the solar wind and astrophysical plasmas

Intermittency, nonlinear dynamics and dissipation in the solar wind and astrophysical plasmas

Structure distribution and turbulence in self-consistently supernova-driven ISM of multiphase magnetized galactic discs

Role of Cross-Helicity in Magnetohydrodynamic Turbulence

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