scholarly journals Heating of coronal loops: weak MHD turbulence and scaling laws

2007 ◽  
Author(s):  
A. F. Rappazzo ◽  
M. Velli ◽  
G. Einaudi
Keyword(s):  
Scaling Laws ◽  
Coronal Loops ◽  
Mhd Turbulence

Siphon Flows in Stratified Coronal Loops

1994 ◽  
Vol 144 ◽  
pp. 185-187
Author(s):  
S. Orlando ◽  
G. Peres ◽  
S. Serio
Keyword(s):  
Heat Flux ◽  
Scaling Laws ◽  
Flow Model ◽  
Supersonic Flows ◽  
Coronal Loops ◽  
Characteristic Parameters

AbstractWe have developed a detailed siphon flow model for coronal loops. We find scaling laws relating the characteristic parameters of the loop, explore systematically the space of solutions and show that supersonic flows are impossible for realistic values of heat flux at the base of the upflowing leg.

scholarly journals Coronal Heating, Weak MHD Turbulence, and Scaling Laws

2007 ◽  
Vol 657 (1) ◽  
pp. L47-L51 ◽  
Author(s):  
A. F. Rappazzo ◽  
M. Velli ◽  
G. Einaudi ◽  
R. B. Dahlburg
Keyword(s):  
Scaling Laws ◽  
Coronal Heating ◽  
Mhd Turbulence

scholarly journals A Study of the Decay Phase of an X-Ray Flare on Algol

1989 ◽  
Vol 104 (2) ◽  
pp. 123-126
Author(s):  
R. Mewe ◽  
G.H.J. van den Oord ◽  
J. Jakimiec
Keyword(s):  
Decay Time ◽  
Scaling Laws ◽  
Decay Phase ◽  
Coronal Loops ◽  
Unique Determination ◽  
X Ray ◽  
Additional Heating ◽  
Loop Volume ◽  
The Common

AbstractWe have re-analyzed the X-ray flare on Algol which was observed with EXOSAT (White et al. (1986)). The common practice of estimating loop volume and length from the decay time of the flare is discussed extensively. We show that during the decay phase of the flare both scaling laws for coronal loops are valid. This implies a unique determination of loop volume and length and allows a check whether additional heating occurs in the decay phase of a flare.

scholarly journals Phenomenologies of intermittent Hall MHD turbulence

2021 ◽  
Vol 0 (0) ◽  
pp. 0
Author(s):  
Mimi Dai
Keyword(s):  
Hall Effect ◽  
Scaling Laws ◽  
Structure Functions ◽  
Energy Spectra ◽  
Mhd Turbulence ◽  
Hall Mhd

<p style='text-indent:20px;'>We introduce the concept of intermittency dimension for the magnetohydrodynamics (MHD) to quantify the intermittency effect. With dependence on the intermittency dimension, we derive phenomenological laws for intermittent MHD turbulence with and without the Hall effect. In particular, scaling laws of dissipation wavenumber, energy spectra and structure functions are predicted. Moreover, we are able to provide estimates for energy spectra and structure functions which are consistent with the predicted scalings.</p>

scholarly journals Can magnetized turbulence set the mass scale of stars?

2020 ◽  
Vol 496 (4) ◽  
pp. 5072-5088 ◽  
Author(s):  
Dávid Guszejnov ◽  
Michael Y Grudić ◽  
Philip F Hopkins ◽  
Stella S R Offner ◽  
Claude-André Faucher-Giguère
Keyword(s):  
Star Formation ◽  
Scaling Laws ◽  
Initial Conditions ◽  
Mass Function ◽  
Stellar Mass ◽  
Mass Scale ◽  
Initial Mass Function ◽  
Mhd Turbulence ◽  
Numerical Resolution ◽  
Stellar Masses

ABSTRACT Understanding the evolution of self-gravitating, isothermal, magnetized gas is crucial for star formation, as these physical processes have been postulated to set the initial mass function (IMF). We present a suite of isothermal magnetohydrodynamic (MHD) simulations using the gizmo code that follow the formation of individual stars in giant molecular clouds (GMCs), spanning a range of Mach numbers found in observed GMCs ($\mathcal {M} \sim 10\!-\!50$). As in past works, the mean and median stellar masses are sensitive to numerical resolution, because they are sensitive to low-mass stars that contribute a vanishing fraction of the overall stellar mass. The mass-weighted median stellar mass M50 becomes insensitive to resolution once turbulent fragmentation is well resolved. Without imposing Larson-like scaling laws, our simulations find $M_\mathrm{50} \,\, \buildrel\propto \over \sim \,\,M_\mathrm{0} \mathcal {M}^{-3} \alpha _\mathrm{turb}\, \mathrm{SFE}^{1/3}$ for GMC mass M0, sonic Mach number $\mathcal {M}$, virial parameter αturb, and star formation efficiency SFE = M⋆/M0. This fit agrees well with previous IMF results from the ramses, orion2, and sphng codes. Although M50 has no significant dependence on the magnetic field strength at the cloud scale, MHD is necessary to prevent a fragmentation cascade that results in non-convergent stellar masses. For initial conditions and SFE similar to star-forming GMCs in our Galaxy, we predict M50 to be $\gt 20 \, \mathrm{M}_{\odot }$, an order of magnitude larger than observed ($\sim 2 \, \mathrm{M}_\odot$), together with an excess of brown dwarfs. Moreover, M50 is sensitive to initial cloud properties and evolves strongly in time within a given cloud, predicting much larger IMF variations than are observationally allowed. We conclude that physics beyond MHD turbulence and gravity are necessary ingredients for the IMF.

scholarly journals An Observational Test for Coronal Heating Models

2004 ◽  
Vol 219 ◽  
pp. 473-477
Author(s):  
Lidia van Driel-Gesztelyi ◽  
Pascal Démoulin ◽  
Cristina H. Mandrini ◽  
Louise K. Harra ◽  
James A. Klimchuk
Keyword(s):  
Magnetic Flux ◽  
Flux Density ◽  
Scaling Laws ◽  
Emission Measure ◽  
Coronal Heating ◽  
Mhd Waves ◽  
Magnetic Flux Density ◽  
Coronal Loops ◽  
Coronal Emission ◽  
The Mean

We correlate the evolution of the mean X-ray flux, emission measure and temperature (Yohkoh SXT & BCS) with the magnetic flux density (SOHO/MDI) in active region NOAA 7978 from its birth throughout its decay, for five solar rotations. We show that these plasma parameters together with other quantities deduced from them, such as the density and the pressure, follow power-law relationships with the mean magnetic flux density (B). We derive the dependence of the mean coronal heating rate on the magnetic flux density. We use the obtained scaling laws of coronal loops in thermal equilibrium to derive observational estimates of the scaling of the coronal heating with B. These results are used to test the validity of coronal heating models. We find that models based on the dissipation of stressed, current-carrying magnetic fields are in better agreement with the observations than models that attribute coronal heating to the dissipation of MHD waves injected at the base of the corona. This confirms, with smaller error bars, previous results obtained for individual coronal loops, as well as for the global coronal emission of the Sun and cool stars.

scholarly journals On Active Stars, Coronal Loops, Magnetic Braking and All That

1986 ◽  
Vol 7 ◽  
pp. 467-470
Author(s):  
Osmi Vilhu
Keyword(s):  
Scaling Laws ◽  
Coronal Loops ◽  
X Ray ◽  
Active Stars ◽  
Magnetic Braking

AbstractCoronal scaling laws and magnetic braking are discussed. The importance of future EUV and X-ray spectroscopy missions is emphasized.

scholarly journals Exact scaling laws and the local structure of isotropic magnetohydrodynamic turbulence

2007 ◽  
Vol 575 ◽  
pp. 111-120 ◽  
Author(s):  
T. A. YOUSEF ◽  
F. RINCON ◽  
A. A. SCHEKOCHIHIN
Keyword(s):  
Scaling Laws ◽  
Linear Scaling ◽  
Mhd Turbulence ◽  
Third Order ◽  
Magnetohydrodynamic Turbulence ◽  
Kolmogorov Turbulence ◽  
Non Local ◽  
Prandtl Numbers ◽  
The Magnetic Field ◽  
Exact Scaling

This paper examines the consistency of the exact scaling laws for isotropic magnetohydrodynamic (MHD) turbulence in numerical simulations with large magnetic Prandtl numbers Pm and with Pm = 1. The exact laws are used to elucidate the structure of the magnetic and velocity fields. Despite the linear scaling of certain third-order correlation functions, the situation is not analogous to the case of Kolmogorov turbulence. The magnetic field is adequately described by a model of a stripy (folded) field with direction reversals at the resistive scale. At currently available resolutions, the cascade of kinetic energy is short-circuited by the direct exchange of energy between the forcing-scale motions and the stripy magnetic fields. This non-local interaction is the defining feature of isotropic MHD turbulence.

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