Theory and observation of double discontinuities

Whang, Y. C.

doi:10.5194/npg-11-259-2004

Cited by 5 publications

(5 citation statements)

References 21 publications

(19 reference statements)

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“…Finally, the properties of the second TG flow (corresponding to the conducting case) will also be examined in a future work. Since rotational structures, including double discontinuities [33], have been observed in interplanetary space in a much more complex environment involving compressibility and Hall currents, the flows proposed here may prove useful in understanding the interplay between turbulent eddies, waves, and small-scale structures in interplanetary space and the heliosphere.…”

Section: Discussionmentioning

confidence: 98%

Paradigmatic flow for small-scale magnetohydrodynamics: Properties of the ideal case and the collision of current sheets

et al. 2008

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We propose two sets of initial conditions for magnetohydrodynamics (MHD) in which both the velocity and the magnetic fields have spatial symmetries that are preserved by the dynamical equations as the system evolves. When implemented numerically they allow for substantial savings in CPU time and memory storage requirements for a given resolved scale separation. Basic properties of these Taylor-Green flows generalized to MHD are given, and the ideal nondissipative case is studied up to the equivalent of 2048;{3} grid points for one of these flows. The temporal evolution of the logarithmic decrements delta of the energy spectrum remains exponential at the highest spatial resolution considered, for which an acceleration is observed briefly before the grid resolution is reached. Up to the end of the exponential decay of delta , the behavior is consistent with a regular flow with no appearance of a singularity. The subsequent short acceleration in the formation of small magnetic scales can be associated with a near collision of two current sheets driven together by magnetic pressure. It leads to strong gradients with a fast rotation of the direction of the magnetic field, a feature also observed in the solar wind.

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Section: Discussionmentioning

confidence: 98%

Paradigmatic flow for small-scale magnetohydrodynamics: Properties of the ideal case and the collision of current sheets

et al. 2008

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“…Observations of compound discontinuities with the RD downstream the SS are reported in Wind and Geotail data and explained within the ideal MHD framework as RD/SS interaction where a RD approaches a SS from the postshock side [Whang et al, 1998;Whang, 2004].…”

Section: 1002/2017gl073092mentioning

confidence: 99%

Switch‐off slow shock/rotational discontinuity structures in collisionless magnetic reconnection: What to look for in satellite observations

Innocenti

Cazzola

Mistry

et al. 2017

Geophysical Research Letters

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In Innocenti et al. (2015) we have observed and characterized for the first time Petschek‐like switch‐off slow shock/rotational discontinuity (SO‐SS/RD) compound structures in a 2‐D fully kinetic simulation of collisionless magnetic reconnection. Observing these structures in the solar wind or in the magnetotail would corroborate the possibility that Petschek exhausts develop in collisionless media as a result of single X point collisionless reconnection. Here we highlight their signatures in simulations with the aim of easing their identification in observations. The most notable signatures include a four‐peaked ion current profile in the out‐of‐plane direction, associated ion distribution functions, increased electron and ion anisotropy downstream the SS, and increased electron agyrotropy downstream the RDs.

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“…It has been shown recently (Dar et al, 2001, Alexakis et al, 2005, Debliquy et al, 2005) that such interactions are noticeably more nonlocal than in the fluid case, involving widely separated scales. More-over, several recent in situ observations in the magnetosphere and in the solar wind show the occurence of highly energetic events due to reconnection of magnetic field lines (Hasegawa et al, 2004, Sundkvist et al, 2005, Nykyry et al, 2006, Phan et al, 2006, Retinò et al, 2007, as well as rotational discontinuities (Whang, 2004). It thus becomes important to be able to study in detail multi-scale interactions in MHD, a pre-requisite to which is to have sufficient scale separation in the fluid with high kinetic and magnetic Reynolds numbers.…”

Section: Introductionmentioning

confidence: 99%

The dynamics of unforced turbulence at high Reynolds number for Taylor–Green vortices generalized to MHD

Pouquet

Lee

Brachet

et al. 2010

Geophysical & Astrophysical Fluid Dynamics

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We study decaying magnetohydrodynamics (MHD) turbulence stemming from the evolution of the Taylor-Green (TG) flow generalized recently to MHD, with equal viscosity and magnetic resistivity and up to equivalent grid resolutions of 2048 3 points. A pseudo-spectral code is used in which the symmetries of the velocity and magnetic fields have been implemented, allowing for sizable savings in both computer time and usage of memory at a given Reynolds number. The flow is non-helical, and at initial time the kinetic and magnetic energies are taken to be equal and concentrated in the large scales. After testing the validity of the method on grids of 512 3 points, we analyze the data on the large grids up to Taylor Reynolds numbers of ≈ 2200. We find that the global temporal evolution is accelerated in MHD, compared to the corresponding neutral fluid case. We also observe an interval of time when such configurations have quasiconstant total dissipation, time during which statistical properties are determined after averaging over of the order of two turn-over times. A weak turbulence spectrum obtains which is also given in terms of its anisotropic components. Finally, we contrast the development of small-scale eddies with two other initial conditions for the magnetic field and briefly discuss the structures that develop, and which display a complex array of current and vorticity sheets with clear rolling-up and folding.

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Theory and observation of double discontinuities

Cited by 5 publications

References 21 publications

Paradigmatic flow for small-scale magnetohydrodynamics: Properties of the ideal case and the collision of current sheets

Paradigmatic flow for small-scale magnetohydrodynamics: Properties of the ideal case and the collision of current sheets

Switch‐off slow shock/rotational discontinuity structures in collisionless magnetic reconnection: What to look for in satellite observations

The dynamics of unforced turbulence at high Reynolds number for Taylor–Green vortices generalized to MHD

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