scholarly journals Three-Dimensional MHD Simulations of a Subcluster Plasma Moving in Turbulent ICM

2006 ◽  
Vol 2 (S235) ◽  
pp. 189-189
Author(s):  
N. Asai ◽  
N. Fukuda ◽  
R. Matsumoto
Keyword(s):  
Heat Conduction ◽  
Magnetic Fields ◽  
Three Dimensional ◽  
Cold Fronts ◽  
Mhd Simulations ◽  
Anisotropic Heat Conduction ◽  
Magnetohydrodynamic Simulations

AbstractWe carried out 3D magnetohydrodynamic simulations of a subcluster moving in turbulent ICM by including anisotropic heat conduction. Since magnetic fields stretched along the subcluster surface suppress the heat conduction across the front, cold fronts are formed and sustained.

scholarly journals Can Multi-threaded Flux Tubes in Coronal Arcades Support a Magnetohydrodynamic Avalanche?

Solar Physics ◽  
2021 ◽  
Vol 296 (8) ◽  
Author(s):  
J. Threlfall ◽  
J. Reid ◽  
A. W. Hood
Keyword(s):  
Magnetic Fields ◽  
Three Dimensional ◽  
Coronal Loops ◽  
Flux Tubes ◽  
Single Thread ◽  
Mhd Instabilities ◽  
Mhd Instability ◽  
Mhd Simulations ◽  
Ideal Mhd ◽  
Model Geometry

AbstractMagnetohydrodynamic (MHD) instabilities allow energy to be released from stressed magnetic fields, commonly modelled in cylindrical flux tubes linking parallel planes, but, more recently, also in curved arcades containing flux tubes with both footpoints in the same photospheric plane. Uncurved cylindrical flux tubes containing multiple individual threads have been shown to be capable of sustaining an MHD avalanche, whereby a single unstable thread can destabilise many. We examine the properties of multi-threaded coronal loops, wherein each thread is created by photospheric driving in a realistic, curved coronal arcade structure (with both footpoints of each thread in the same plane). We use three-dimensional MHD simulations to study the evolution of single- and multi-threaded coronal loops, which become unstable and reconnect, while varying the driving velocity of individual threads. Experiments containing a single thread destabilise in a manner indicative of an ideal MHD instability and consistent with previous examples in the literature. The introduction of additional threads modifies this picture, with aspects of the model geometry and relative driving speeds of individual threads affecting the ability of any thread to destabilise others. In both single- and multi-threaded cases, continuous driving of the remnants of disrupted threads produces secondary, aperiodic bursts of energetic release.

scholarly journals Global 3D radiation magnetohydrodynamic simulations for FU Ori’s accretion disc and observational signatures of magnetic fields

2020 ◽  
Vol 495 (3) ◽  
pp. 3494-3514 ◽  
Author(s):  
Zhaohuan Zhu ◽  
Yan-Fei Jiang ◽  
James M Stone
Keyword(s):  
Magnetic Fields ◽  
Accretion Rate ◽  
Mass Loss Rate ◽  
Global Radiation ◽  
Surface Region ◽  
Accretion Disc ◽  
Near Ir ◽  
Mhd Simulations ◽  
Fu Ori ◽  
Magnetohydrodynamic Simulations

ABSTRACT FU Ori is the prototype of FU Orionis systems that are outbursting protoplanetary discs. Magnetic fields in FU Ori’s accretion discs have previously been detected using spectropolarimetry observations for Zeeman effects. We carry out global radiation ideal MHD simulations to study FU Ori’s inner accretion disc. We find that (1) when the disc is threaded by vertical magnetic fields, most accretion occurs in the magnetically dominated atmosphere at z ∼ R, similar to the ‘surface accretion’ mechanism in previous locally isothermal MHD simulations. (2) A moderate disc wind is launched in the vertical field simulations with a terminal speed of ∼300–500 km s−1 and a mass-loss rate of 1–10 per cent the disc accretion rate, which is consistent with observations. Disc wind fails to be launched in simulations with net toroidal magnetic fields. (3) The disc photosphere at the unit optical depth can be either in the wind launching region or the accreting surface region. Magnetic fields have drastically different directions and magnitudes between these two regions. Our fiducial model agrees with previous optical Zeeman observations regarding both the field directions and magnitudes. On the other hand, simulations indicate that future Zeeman observations at near-IR wavelengths or towards other FU Orionis systems may reveal very different magnetic field structures. (4) Due to energy loss by the disc wind, the disc photosphere temperature is lower than that predicted by the thin disc theory, and the previously inferred disc accretion rate may be lower than the real accretion rate by a factor of ∼2–3.

scholarly journals Feedback Regulated Turbulence, Magnetic Fields, and Star Formation Rates in Galactic Disks

2015 ◽  
Vol 11 (S315) ◽  
pp. 38-41
Author(s):  
Chang-Goo Kim ◽  
Eve C. Ostriker
Keyword(s):  
Star Formation ◽  
Magnetic Fields ◽  
Formation Rate ◽  
Three Dimensional ◽  
Vertical Direction ◽  
Quasi Equilibrium ◽  
Galactic Disks ◽  
Heating Rates ◽  
Mhd Simulations ◽  
Vertical Support

AbstractWe use three-dimensional magnetohydrodynamic (MHD) simulations to investigate the quasi-equilibrium states of galactic disks regulated by star formation feedback. We incorporate effects from massive-star feedback via time-varying heating rates and supernova (SN) explosions. We find that the disks in our simulations rapidly approach a quasi-steady state that satisfies vertical dynamical equilibrium. The star formation rate (SFR) surface density self-adjusts to provide the total momentum flux (pressure) in the vertical direction that matches the weight of the gas. We quantify feedback efficiency by measuring feedback yields, ηc≡ Pc/ΣSFR (in suitable units), for each pressure component. The turbulent and thermal feedback yields are the same for HD and MHD simulations, ηth ~ 1 and ηturb ~ 4, consistent with the theoretical expectations. In MHD simulations, turbulent magnetic fields are rapidly generated by turbulence, and saturate at a level corresponding to ηmag,t ~ 1. The presence of magnetic fields enhances the total feedback yield and therefore reduces the SFR, since the same vertical support can be supplied at a smaller SFR. We suggest further numerical calibrations and observational tests in terms of the feedback yields.

scholarly journals Three-Dimensional Global MHD Simulations of Magnetised Accretion Disks and Jets

1997 ◽  
Vol 163 ◽  
pp. 443-447 ◽  
Author(s):  
R. Matsumoto ◽  
K. Shibata
Keyword(s):  
Surface Layer ◽  
Magnetic Fields ◽  
Accretion Disks ◽  
Large Scale ◽  
Three Dimensional ◽  
Maximum Speed ◽  
Jet Formation ◽  
Mhd Simulations ◽  
Avalanche Flow ◽  
Magnetic Braking

AbstractWe carried out three-dimensional global MHD simulations of jet formation from an accretion disk threaded by large-scale magnetic fields. Numerical results show that bipolar jets with maximum speed υjet ~ υKepler are created. The surface layer of the disk accretes faster than the equatorial part because magnetic braking most effectively affects that layer. Accretion proceeds along spiral channels which correspond to the surface avalanche flow appearing in previous axisymmetric simulations. Spirally shaped low β (= Pgas/Pmag < 1) regions appear in the innermost part of accretion disks where toroidal magnetic fields become dominant.

scholarly journals Three-dimensional MHD simulations of molecular cloud fragmentation regulated by gravity, ambipolar diffusion, and turbulence

2008 ◽  
Vol 4 (S259) ◽  
pp. 115-116
Author(s):  
Takahiro Kudoh ◽  
Shantanu Basu
Keyword(s):  
Star Formation ◽  
Magnetic Fields ◽  
Time Scale ◽  
Molecular Cloud ◽  
Molecular Clouds ◽  
Three Dimensional ◽  
Core Formation ◽  
Mhd Simulations ◽  
Dimensional Simulation

AbstractWe find that the star formation is accelerated by the supersonic turbulence in the magnetically dominated (subcritical) clouds. We employ a fully three-dimensional simulation to study the role of magnetic fields and ion-neutral friction in regulating gravitationally driven fragmentation of molecular clouds. The time-scale of collapsing core formation in subcritical clouds is a few ×107 years when starting with small subsonic perturbations. However, it is shortened to approximately several ×106 years by the supersonic flows in the clouds. We confirm that higher-spacial resolution simulations also show the same result.

scholarly journals Validation of Coronal Mass Ejection Arrival-time Forecasts by Magnetohydrodynamic Simulations Based on Interplanetary Scintillation Observations

2020 ◽  
Author(s):  
Kazumasa Iwai ◽  
Daikou Shiota ◽  
Munetoshi Tokumaru ◽  
Ken'ichi Fujiki ◽  
Mitsue Den ◽  
...  
Keyword(s):  
Solar Wind ◽  
Arrival Time ◽  
Interplanetary Space ◽  
Three Dimensional ◽  
Space Environment ◽  
Environmental Research ◽  
Interplanetary Scintillation ◽  
Arrival Times ◽  
Mhd Simulations ◽  
Magnetohydrodynamic Simulations

Abstract Coronal mass ejections (CMEs) cause various disturbances of the space environment; therefore, forecasting their arrivaltime is very important.However,forecasting accuracy is hindered by limited CME observations in interplanetary space. This study investigates the accuracy of CME arrivaltimesat the Earth forecasted by three-dimensional(3D) magnetohydrodynamic (MHD) simulations based on interplanetary scintillation (IPS) observations. In this system, CMEs are approximated as spheromakswith various initial speeds. TenMHD simulations with different CME initial speed are tested, and the density distributions derived from each simulation run are compared with IPS data observed by the Institute for Space-Earth Environmental Research (ISEE), Nagoya University.The CME arrivaltime of the simulation run that most closelyagrees with the IPS data is selected as the forecasted time. We then validate the accuracy of this forecast using 12 halo CME events. The average absolute arrival-time error of theIPS-based MHD forecast is approximately 5.0 h, which is one of the most accurate predictions that ever been validated, whereasthat of MHD simulations without IPS data, in which the initial CME speed isderived from white-light coronagraph images, is approximately6.7 h. This suggests that the assimilation of IPS data into MHD simulations can improve the accuracy of CME arrival-time forecasts. The average predicted arrivaltimes are earlier than the actual arrival times. These early predictions may be duetooverestimation of the magnetic field included in the spheromak and/or underestimation of the drag force from the background solar wind, the latter of which could be related to underestimation of CME size or background solar wind density.

scholarly journals Validation of Coronal Mass Ejection Arrival-Time Forecasts by Magnetohydrodynamic Simulations based on Interplanetary Scintillation Observations

2020 ◽  
Author(s):  
Kazumasa Iwai ◽  
Daikou Shiota ◽  
Munetoshi Tokumaru ◽  
Ken'ichi Fujiki ◽  
Mitsue Den ◽  
...  
Keyword(s):  
Solar Wind ◽  
Arrival Time ◽  
Interplanetary Space ◽  
Three Dimensional ◽  
Space Environment ◽  
Environmental Research ◽  
Interplanetary Scintillation ◽  
Arrival Times ◽  
Mhd Simulations ◽  
Magnetohydrodynamic Simulations

Abstract Coronal mass ejections (CMEs) cause various disturbances of the space environment; therefore, forecasting their arrival time is very important. However, forecasting accuracy is hindered by limited CME observations in interplanetary space. This study investigates the accuracy of CME arrival times at the Earth forecasted by three-dimensional (3D) magnetohydrodynamic (MHD) simulations based on interplanetary scintillation (IPS) observations. In this system, CMEs are approximated as spheromaks with various initial speeds. Ten MHD simulations with different CME initial speed are tested, and the density distributions derived from each simulation run are compared with IPS data observed by the Institute for Space-Earth Environmental Research (ISEE), Nagoya University. The CME arrival time of the simulation run that most closely agrees with the IPS data is selected as the forecasted time. We then validate the accuracy of this forecast using 12 halo CME events. The average absolute arrival-time error of the IPS-based MHD forecast is approximately 5.0 h, which is one of the most accurate predictions that ever been validated, whereas that of MHD simulations without IPS data, in which the initial CME speed is derived from white-light coronagraph images, is approximately 6.7 h. This suggests that the assimilation of IPS data into MHD simulations can improve the accuracy of CME arrival-time forecasts. The average predicted arrival times are earlier than the actual arrival times. These early predictions may be due to overestimation of the magnetic field included in the spheromak and/or underestimation of the drag force from the background solar wind, the latter of which could be related to underestimation of CME size or background solar wind density.

scholarly journals Three Dimensional MHD Simulations of Parker Instability in Differentially Rotating Disk

1997 ◽  
Vol 163 ◽  
pp. 766-767 ◽  
Author(s):  
T. Matsuzaki ◽  
R. Matsumoto ◽  
T. Tajima ◽  
K. Shibata
Keyword(s):  
Magnetic Fields ◽  
Magnetic Flux ◽  
Accretion Disks ◽  
Three Dimensional ◽  
Rotating Disk ◽  
Saturation Level ◽  
Nonlinear Growth ◽  
Magnetic Viscosity ◽  
Mhd Simulations

AbstractNonlinear growth of the Parker instability (PI) and the Balbus & Hawley instability (BHI) in accretion disks have been studied by local three-dimensional magnetohydrodynamic (MHD) simulations. In high-β disks (β = Pgas/Pmag > 1), the PI has only minor effects on the saturation level of BHI. In low β disks (β ≤ 1), the disk stays in a low-β state because magnetic flux cannot escape fast enough to convert the disk into a high-β state. We found that even in low-β disk the BHI generates fluctuating magnetic fields. The effective magnetic viscosity αB(= –⟨BrBΦ/4πP0⟩) is O(0.1) when β ~ 1.

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