scholarly journals Three-dimensional simulations of turbulent spectra in the local interstellar medium

2007 ◽  
Vol 14 (4) ◽  
pp. 351-359 ◽  
Author(s):  
D. Shaikh ◽  
G. P. Zank
Keyword(s):  
Interstellar Medium ◽  
Three Dimensional ◽  
Density Fluctuations ◽  
Spectral Energy ◽  
Local Interstellar Medium ◽  
Laboratory Plasmas ◽  
Self Consistent ◽  
Supersonic Plasma ◽  
Turbulent Spectra ◽  
Three Dimensional Simulations

Abstract. Three-dimensional time dependent numerical simulations of compressible magnetohydrodynamic fluids describing super-Alfvénic, supersonic and strongly magnetized space and laboratory plasmas show a nonlinear relaxation towards a state of near incompressibility. The latter is characterized essentially by a subsonic turbulent Mach number. This transition is mediated dynamically by disparate spectral energy dissipation rates in compressible magnetosonic and shear Alfvénic modes. Nonlinear cascades lead to super-Alfvénic turbulent motions decaying to a sub-Alfvénic regime that couples weakly with (magneto)acoustic cascades. Consequently, the supersonic plasma motion is transformed into highly subsonic motion and density fluctuations experience a passive convection. This model provides a self-consistent explaination of the ubiquitous nature of incompressible magnetoplasma fluctuations in the solar wind and the interstellar medium.

The Three‐dimensional Structure of the Warm Local Interstellar Medium. I. Methodology

2000 ◽  
Vol 528 (2) ◽  
pp. 756-766 ◽  
Author(s):  
Jeffrey L. Linsky ◽  
Seth Redfield ◽  
Brian E. Wood ◽  
Nikolai Piskunov
Keyword(s):  
Interstellar Medium ◽  
Three Dimensional ◽  
Dimensional Structure ◽  
Local Interstellar Medium ◽  
Three Dimensional Structure

Heliosphere in the magnetized local interstellar medium: Results of a three-dimensional MHD simulation

1998 ◽  
Vol 103 (A2) ◽  
pp. 1889-1904 ◽  
Author(s):  
Timur J. Linde ◽  
Tamas I. Gombosi ◽  
Philip L. Roe ◽  
Kenneth G. Powell ◽  
Darren L. DeZeeuw
Keyword(s):  
Interstellar Medium ◽  
Three Dimensional ◽  
Local Interstellar Medium ◽  
Mhd Simulation

scholarly journals Turbulent spectra in the solar wind plasma

2009 ◽  
Vol 76 (2) ◽  
pp. 183-191 ◽  
Author(s):  
DASTGEER SHAIKH ◽  
G. P. ZANK
Keyword(s):  
Solar Wind ◽  
Three Dimensional ◽  
Solar Wind Plasma ◽  
Density Fluctuations ◽  
Magnetized Plasma ◽  
Density Spectrum ◽  
Turbulent Spectrum ◽  
Extended Length ◽  
Turbulent Spectra ◽  
Magnetohydrodynamic Fluid

AbstractObservations of interstellar scintillations at radio wavelengths reveal a Kolmogorov-like scaling of the electron density spectrum with a spectral slope of −5/3 over six decades in wavenumber space. A similar turbulent density spectrum in the solar wind plasma has been reported. The energy transfer process in the magnetized solar wind plasma over such extended length scales remains an unresolved paradox of modern turbulence theories, raising the especially intriguing question of how a compressible magnetized solar wind exhibits a turbulent spectrum that is a characteristic of an incompressible hydrodynamic fluid. To address these questions, we have undertaken three-dimensional time-dependent numerical simulations of a compressible magnetohydrodynamic fluid describing super-Alfvénic, supersonic and strongly magnetized plasma. It is shown that the observed Kolmogorov-like (−5/3) spectrum can develop in the solar wind plasma by supersonic plasma motions that dissipate into highly subsonic motion that passively convect density fluctuations.

scholarly journals Study of the LISM Using Pulsar Scintillation

1997 ◽  
Vol 166 ◽  
pp. 211-214
Author(s):  
N.D.R. Bhat ◽  
Y. Gupta ◽  
A.P. Rao
Keyword(s):  
Interstellar Medium ◽  
Radio Telescope ◽  
Density Fluctuations ◽  
Solar Neighborhood ◽  
Dispersion Measure ◽  
Low Density ◽  
Local Interstellar Medium ◽  
Local Bubble ◽  
Scattering Material ◽  
Scattering Strength

AbstractWe present here the results from an extensive scintillation study of twenty pulsars in the dispersion measure (DM) range 3 – 35 pc cm−3 carried out using the Ooty Radio Telescope, to investigate the distribution of ionized material in the local interstellar medium (LISM). Our analysis reveals several anomalies in the scattering strength, which suggest that the distribution of scattering material in the solar neighborhood is not uniform. Our model suggests the presence of a low density bubble surrounded by a shell of much higher density fluctuations. We are able to put some constraints on geometrical and scattering properties of such a structure, and find it to be morphologically similar to the local bubble known from other studies.

Spectra and energy transfer in stably stratified turbulence

1989 ◽  
Vol 207 ◽  
pp. 419-452 ◽  
Author(s):  
E. C. Itsweire ◽  
K. N. Helland
Keyword(s):  
Energy Transfer ◽  
Spectral Characteristics ◽  
Water Channel ◽  
Three Dimensional ◽  
Density Fluctuations ◽  
Buoyancy Flux ◽  
Spectral Energy ◽  
Small Scale ◽  
Two Dimensional ◽  
Buoyancy Forces

The influence of stabilizing buoyancy forces on the spectral characteristics and spectral energy transfer of grid-generated turbulence was studied in a ten-layer closed-loop stratified water channel. The results are compared to the limiting ideal cases of the three-dimensional turbulence and two-dimensional turbulence theories. The velocity power spectra evolve from a classical isotropic shape to a shape of almost k−2 after the suppression of the net vertical mixing. This final spectral shape is rather different from the k−3 to k−4 predicted by the theory of two-dimensional turbulence and could result from the interaction between small-scale internal waves and quasi-two-dimensional turbulent structures as well as some Doppler shift of advected waves. Several lengthscales are derived from the cospectra of the vertical velocity and density fluctuations and compared with the buoyancy, overturning and viscous lengthscales measured in previous studies, e.g. Stillinger, Helland & Van Atta (1983) and Itsweire, Helland & Van Atta (1986). The smallest turbulent scale, defined when the buoyancy flux goes to zero, can be related to the peak of the cospectra of the buoyancy flux. This new relationship can be used to provide a measure of the smallest turbulent scale in cases where the buoyancy flux never goes to zero, i.e. a growing turbulent stratified shear flow. Finally, the one-dimensional energy transfer term computed from the bispectra shows evidence of a reverse energy cascade from the small scales to the large scales far from the grid where buoyancy forces dominate inertial forces. The observed reverse energy transfer could be produced by the development of quasi-two-dimensional eddies as the original three-dimensional turbulence collapses.

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