Observation of Turbulent Fluctuations in the Interstellar Plasma Density and Magnetic Field on Spatial Scales of 0.01 to 100 Parsecs

1996 ◽  
Vol 458 ◽  
pp. 194 ◽  
Author(s):  
Anthony H. Minter ◽  
Steven R. Spangler
Keyword(s):  
Magnetic Field ◽  
Plasma Density ◽  
Spatial Scales ◽  
Turbulent Fluctuations ◽  
Interstellar Plasma

Inverse cascades in incompressible fluid and magnetofluid turbulence

1996 ◽  
Vol 56 (3) ◽  
pp. 467-491
Author(s):  
Murshed Hossain
Keyword(s):  
Magnetic Field ◽  
Incompressible Fluid ◽  
Uniform Magnetic Field ◽  
Spatial Scales ◽  
Three Dimensional ◽  
Self Organization ◽  
Anisotropic Fluid ◽  
Uniform Rotation ◽  
Fluid Turbulence ◽  
Turbulent Fluctuations

Absolute equilibrium statistical theory and numerical simulations are reviewed in the context of inverse cascades in two- and three-dimensional incompressible fluid and magnetofluid turbulence. Turbulent fluctuations of physically interesting quantities undergo inverse cascade to larger spatial scales, leading to self-organization under certain circumstances. In particular, most systems with more than one quadratic ideal invariant, or, having some kind of imposed anisotropy, exhibit inverse cascades. Anisotropic fluid turbulence in the presence of a uniform rotation and magnetofluid turbulence in the presence of a uniform magnetic field are considered.

scholarly journals Computer Simulations of Electromagnetic Emissions Produced via Injection of Electron Beam into a Plasma with Strong Transverse Density Gradients

2019 ◽  
Vol 14 (4) ◽  
pp. 5-16
Author(s):  
V. V. Glinskiy ◽  
I. V. Timofeev ◽  
V. V. Annenkov ◽  
A. V. Arzhannikov
Keyword(s):  
Magnetic Field ◽  
Plasma Density ◽  
Plasma Frequency ◽  
Spatial Scales ◽  
Longitudinal Direction ◽  
Magnetized Plasma ◽  
Density Gradients ◽  
The Real ◽  
Particle In Cell ◽  
Strong Transverse

Recent experiments on the injection of kiloampere electron beams into a magnetized plasma at the GOL-PET facility have shown that the power of sub-terahertz radiation escaping from the plasma along the magnetic field increases by more than an order of magnitude if strong transverse density gradients are preliminarily created in the plasma. In this paper, the influence of transverse in homogeneities of plasma density on the efficiency of electromagnetic radiation generation near the harmonics of the plasma frequency is studied using particle-in-cell simulations. Simulations performed for the real relative density of the beam and the real spatial scales of the in homogeneity show that the beam instability develops only in the density wells, and the small transverse size of its localization comparable with the wavelength contributes to a more efficient conversion of unstable oscillations into electromagnetic ones. Despite the fact that radiation at the plasma frequency is blocked across the leading magnetic field, it can leave the generation region with the decrease of the plasma density in the longitudinal direction.

scholarly journals Energetics of magnetic transients in a solar active region plage

2019 ◽  
Vol 623 ◽  
pp. A176 ◽  
Author(s):  
L. P. Chitta ◽  
A. R. C. Sukarmadji ◽  
L. Rouppe van der Voort ◽  
H. Peter
Keyword(s):  
Magnetic Field ◽  
Active Region ◽  
Magnetic Flux ◽  
Numerical Simulations ◽  
Extreme Ultraviolet ◽  
Spatial Scales ◽  
Coronal Loops ◽  
The Sun ◽  
Flux Emergence ◽  
Transient Events

Context. Densely packed coronal loops are rooted in photospheric plages in the vicinity of active regions on the Sun. The photospheric magnetic features underlying these plage areas are patches of mostly unidirectional magnetic field extending several arcsec on the solar surface. Aims. We aim to explore the transient nature of the magnetic field, its mixed-polarity characteristics, and the associated energetics in the active region plage using high spatial resolution observations and numerical simulations. Methods. We used photospheric Fe I 6173 Å spectropolarimetric observations of a decaying active region obtained from the Swedish 1-m Solar Telescope (SST). These data were inverted to retrieve the photospheric magnetic field underlying the plage as identified in the extreme-ultraviolet emission maps obtained from the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO). To obtain better insight into the evolution of extended unidirectional magnetic field patches on the Sun, we performed 3D radiation magnetohydrodynamic simulations of magnetoconvection using the MURaM code. Results. The observations show transient magnetic flux emergence and cancellation events within the extended predominantly unipolar patch on timescales of a few 100 s and on spatial scales comparable to granules. These transient events occur at the footpoints of active region plage loops. In one case the coronal response at the footpoints of these loops is clearly associated with the underlying transient. The numerical simulations also reveal similar magnetic flux emergence and cancellation events that extend to even smaller spatial and temporal scales. Individual simulated transient events transfer an energy flux in excess of 1 MW m−2 through the photosphere. Conclusions. We suggest that the magnetic transients could play an important role in the energetics of active region plage. Both in observations and simulations, the opposite-polarity magnetic field brought up by transient flux emergence cancels with the surrounding plage field. Magnetic reconnection associated with such transient events likely conduits magnetic energy to power the overlying chromosphere and coronal loops.

scholarly journals Sequential modelling of the Earth’s core magnetic field

2020 ◽  
Vol 72 (1) ◽  
Author(s):  
Guillaume Ropp ◽  
Vincent Lesur ◽  
Julien Baerenzung ◽  
Matthias Holschneider
Keyword(s):  
Magnetic Field ◽  
Prior Information ◽  
Spatial Scales ◽  
Model Parameters ◽  
International Geomagnetic Reference Field ◽  
The Earth ◽  
Temporal And Spatial ◽  
Different Sources ◽  
Original Approach ◽  
Modelling Approach

Abstract We describe a new, original approach to the modelling of the Earth’s magnetic field. The overall objective of this study is to reliably render fast variations of the core field and its secular variation. This method combines a sequential modelling approach, a Kalman filter, and a correlation-based modelling step. Sources that most significantly contribute to the field measured at the surface of the Earth are modelled. Their separation is based on strong prior information on their spatial and temporal behaviours. We obtain a time series of model distributions which display behaviours similar to those of recent models based on more classic approaches, particularly at large temporal and spatial scales. Interesting new features and periodicities are visible in our models at smaller time and spatial scales. An important aspect of our method is to yield reliable error bars for all model parameters. These errors, however, are only as reliable as the description of the different sources and the prior information used are realistic. Finally, we used a slightly different version of our method to produce candidate models for the thirteenth edition of the International Geomagnetic Reference Field.

Plasma density accumulation on a conical surface for diffusion along a diverging magnetic field

2014 ◽  
Vol 21 (4) ◽  
pp. 043502 ◽  
Author(s):  
S. K. Saha ◽  
S. Chowdhury ◽  
M. S. Janaki ◽  
A. Ghosh ◽  
A. K. Hui ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Plasma Density ◽  
Conical Surface

Turbulence changes from magnetic fields in a stationary plasma

2010 ◽  
Vol 77 (4) ◽  
pp. 537-545 ◽  
Author(s):  
A. B. ALEXANDER ◽  
C. T. RAYNOR ◽  
D. L. WIGGINS ◽  
M. K. ROBINSON ◽  
C. C. AKPOVO ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Field Strength ◽  
Magnetic Field Strength ◽  
Axial Magnetic Field ◽  
Turbulent Energy ◽  
Dominant Mode ◽  
Dc Glow Discharge ◽  
Turbulent Fluctuations ◽  
Stationary Plasma

AbstractWhen the krypton plasma in a DC glow discharge tube is exposed to an axial magnetic field, the turbulent energy and the characteristic dominant mode in the turbulent fluctuations are systematically and unexpectedly reduced with increasing magnetic field strength. When the index measuring the rate of transfer of energy through fluctuation scales is monitored, a lambda-like dependence on turbulent energy is routinely observed in all magnetic fields. From this, a critical turbulent energy is identified, which also decreases with increasing magnetic field strength.

A MODEL HIERARCHY FOR IONOSPHERIC PLASMA MODELING

2004 ◽  
Vol 14 (03) ◽  
pp. 393-415 ◽  
Author(s):  
CHRISTOPHE BESSE ◽  
PIERRE DEGOND ◽  
FABRICE DELUZET ◽  
JEAN CLAUDEL ◽  
GÉRARD GALLICE ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Plasma Density ◽  
Maxwell Equations ◽  
Ionospheric Plasma ◽  
Practical Interest ◽  
Plasma Modeling ◽  
Model Hierarchy ◽  
Great Practical Interest ◽  
Two Fluid ◽  
Insight Into

This paper deals with the modeling of the ionospheric plasma. Starting from the two-fluid Euler–Maxwell equations, we present two hierarchies of models. The MHD hierarchy deals with large plasma density situations while the dynamo hierarchy is adapted to lower density situations. Most of the models encompassed by the dynamo hierarchy are classical ones, but we shall give a unified presentation of them which brings a new insight into their interrelations. By contrast, the MHD hierarchy involves a new (at least to the authors) model, the massless-MHD model. This is a diffusion system for the density and magnetic field which could be of great practical interest. Both hierarchies terminate with the "classical" Striation model, which we shall investigate in detail.

Plasma Density Fluctuations in a Magnetic Field

1961 ◽  
Vol 122 (6) ◽  
pp. 1663-1674 ◽  
Author(s):  
E. E. Salpeter
Keyword(s):  
Magnetic Field ◽  
Plasma Density ◽  
Density Fluctuations

scholarly journals Saturn's Plasma Density Depletions Along Magnetic Field Lines Connected to the Main Rings

2018 ◽  
Vol 45 (16) ◽  
pp. 8104-8110 ◽  
Author(s):  
W. M. Farrell ◽  
L. Z. Hadid ◽  
M. W. Morooka ◽  
W. S. Kurth ◽  
J.‐E. Wahlund ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Plasma Density ◽  
Field Lines

scholarly journals Spatial scales and locality of magnetic helicity

2020 ◽  
Vol 635 ◽  
pp. A95 ◽  
Author(s):  
C. Prior ◽  
G. Hawkes ◽  
M. A. Berger
Keyword(s):  
Magnetic Field ◽  
Active Region ◽  
Spectral Methods ◽  
Wavelet Decomposition ◽  
Spatial Scales ◽  
Solar Interior ◽  
Magnetic Helicity ◽  
Clear Correlation ◽  
Arbitrary Boundary ◽  
The Magnetic Field

Context. Magnetic helicity is approximately conserved in resistive magnetohydrodynamic models. It quantifies the entanglement of the magnetic field within the plasma. The transport and removal of helicity is crucial in both dynamo development in the solar interior and active region evolution in the solar corona. This transport typically leads to highly inhomogeneous distributions of entanglement. Aims. There exists no consistent systematic means of decomposing helicity over varying spatial scales and in localised regions. Spectral helicity decompositions can be used in periodic domains and is fruitful for the analysis of homogeneous phenomena. This paper aims to develop methods for analysing the evolution of magnetic field topology in non-homogeneous systems. Methods. The method of multi-resolution wavelet decomposition is applied to the magnetic field. It is demonstrated how this decomposition can further be applied to various quantities associated with magnetic helicity, including the field line helicity. We use a geometrical definition of helicity, which allows these quantities to be calculated for fields with arbitrary boundary conditions. Results. It is shown that the multi-resolution decomposition of helicity has the crucial property of local additivity. We demonstrate a general linear energy-topology conservation law, which significantly generalises the two-point correlation decomposition used in the analysis of homogeneous turbulence and periodic fields. The localisation property of the wavelet representation is shown to characterise inhomogeneous distributions, which a Fourier representation cannot. Using an analytic representation of a resistive braided field relaxation, we demonstrate a clear correlation between the variations in energy at various length scales and the variations in helicity at the same spatial scales. Its application to helicity flows in a surface flux transport model show how various contributions to the global helicity input from active region field evolution and polar field development are naturally separated by this representation. Conclusions. The multi-resolution wavelet decomposition can be used to analyse the evolution of helicity in magnetic fields in a manner which is consistently additive. This method has the advantage over more established spectral methods in that it clearly characterises the inhomogeneous nature of helicity flows where spectral methods cannot. Further, its applicability in aperiodic models significantly increases the range of potential applications.

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