scholarly journals Global Non-ideal Magnetohydrodynamic Simulations of Protoplanetary Disks with Outer Truncation

2021 ◽  
Vol 922 (2) ◽  
pp. 201
Author(s):  
Haifeng Yang ◽  
Xue-Ning Bai
Keyword(s):  
Magnetic Flux ◽  
Large Scale ◽  
Protoplanetary Disks ◽  
Outer Radius ◽  
Poloidal Magnetic Field ◽  
Disk Evolution ◽  
Flux Loops ◽  
Magnetohydrodynamic Simulations ◽  
Ideal Magnetohydrodynamic

Abstract It has recently been established that the evolution of protoplanetary disks is primarily driven by magnetized disk winds, requiring a large-scale magnetic flux threading the disks. The size of such disks is expected to shrink with time, as opposed to the conventional scenario of viscous expansion. We present the first global 2D non-ideal magnetohydrodynamic simulations of protoplanetary disks that are truncated in the outer radius, aiming to understand the interaction of the disk with the interstellar environment, as well as the global evolution of the disk and magnetic flux. We find that as the system relaxes, the poloidal magnetic field threading the disk beyond the truncation radius collapses toward the midplane, leading to a rapid reconnection. This process removes a substantial amount of magnetic flux from the system and forms closed poloidal magnetic flux loops encircling the outer disk in quasi-steady state. These magnetic flux loops can drive expansion beyond the truncation radius, corresponding to substantial mass loss through a magnetized disk outflow beyond the truncation radius analogous to a combination of viscous spreading and external photoevaporation. The magnetic flux loops gradually shrink over time, the rates of which depend on the level of disk magnetization and the external environment, which eventually governs the long-term disk evolution.

Towards Realistic Understandings of Gas Dynamics in Protoplanetary Disks

2018 ◽  
Vol 14 (S345) ◽  
pp. 102-105
Author(s):  
Xue-Ning Bai
Keyword(s):  
Gas Dynamics ◽  
Large Scale ◽  
Planet Formation ◽  
Protoplanetary Disks ◽  
Poloidal Magnetic Field ◽  
Weakly Ionized ◽  
Disk Evolution ◽  
Microphysical Processes ◽  
Ideal Magnetohydrodynamic ◽  
Almost All

AbstractThe gas dynamics of protoplanetary disks (PPDs) plays a crucial role in almost all stages of planet formation, yet it is far from being well understood largely due to the complex interplay among various microphysical processes. Primarily, PPD gas dynamics is likely governed by magnetic fields, and their coupling with the weakly ionized gas is described by non-ideal magnetohydrodynamic (MHD) effects. Incorporating these effects, I will present the first fully global simulations of PPDs that include the most realistic disk microphysics. Accretion and disk evolution is primarily driven by magnetized disk winds with significant mass loss comparable to accretion rate. The overall disk gas dynamics strongly depends on the polarity of large-scale poloidal magnetic field threading the disk owing to the Hall effect. The flow structure in the disk is highly unconventional with major implications on planet formation.

scholarly journals Local semi-analytic models of magnetic flux transport in protoplanetary discs

2019 ◽  
Vol 487 (4) ◽  
pp. 5155-5174 ◽  
Author(s):  
Philip K C Leung ◽  
Gordon I Ogilvie
Keyword(s):  
Magnetic Flux ◽  
Large Scale ◽  
Vertical Structure ◽  
Vertical Direction ◽  
Governing Equations ◽  
Magnetorotational Instability ◽  
Flux Transport ◽  
Poloidal Magnetic Field ◽  
Ideal Magnetohydrodynamic ◽  
Analytic Models

Abstract The evolution of a large-scale poloidal magnetic field in an accretion disc is an important problem because it determines the launching of winds and the feasibility of the magnetorotational instability to generate turbulence or channel flows. Recent studies, both semi-analytical calculations and numerical simulations, have highlighted the crucial role non-ideal magnetohydrodynamic effects (Ohmic resistivity, Hall drift, and ambipolar diffusion), relevant in the protoplanetary disc context, might play in magnetic flux evolution in the disc. We investigate the flux transport in discs through the use of two 1D semi-analytic models in the vertical direction, exploring regimes where different physical source terms and effects dominate. The governing equations for both models are derived by performing an asymptotic expansion in the limit of a thin disc, with the different regimes isolated through setting the relative order of the leading terms between variables. Flux transport rates and vertical structure profiles are calculated for a range of diffusivities and disc magnetizations. We found that Ohmic and ambipolar diffusivities drive radially outward flux transport with an outwardly inclined field. A wind outflow drives inward flux transport, which is significantly enhanced in the presence of Hall drift in the positive polarity case, $\eta _\mathrm{ H} (\boldsymbol{B}_\mathrm{ z} \cdot \boldsymbol{\Omega }) \gt 0$, an effect which has only been briefly noted before. Coupled only with outward inclination, the Hall effect reduces the flux transport given by a background Ohmic and/or ambipolar diffusivity, but drives no flux transport when it is the only non-ideal effect present.

scholarly journals Large scale magnetic helicity fluxes estimated from MDI magnetic synoptic charts

2012 ◽  
Vol 8 (S294) ◽  
pp. 157-158
Author(s):  
Shangbin Yang ◽  
Hongqi Zhang
Keyword(s):  
Solar Cycle ◽  
Magnetic Flux ◽  
Solar Disk ◽  
Large Scale ◽  
Magnetic Helicity ◽  
Local Correlation ◽  
Solar Cycles ◽  
23Rd Solar Cycle ◽  
Term Evolution

AbstractTo investigate the characteristics of large scale and long term evolution of magnetic helicity with solar cycles, we use the method of Local Correlation Tracking (LCT) to estimate the magnetic helicity evolution over the 23rd solar cycle from 1996 to 2009 by using 795 MDI magnetic synoptic charts. The main results are: the hemispheric helicity rule still holds in general, i.e. the large-scale negative (positive) magnetic helicity dominates the northern (southern) hemisphere. However, the large scale magnetic helicity fluxes show the same sign in both hemispheres around 2001 and 2005. The global, large scale magnetic helicity flux over the solar disk changes from negative value at the beginning of the 23rd solar cycle to positive value at the end of the cycle, which also shows the similar trend from the normalized magnetic flux by using the magnetic flux. The net accumulated magnetic helicity is negative in the period between 1996 and 2009.

scholarly journals HMI observations of two types of ephemeral regions

2013 ◽  
Vol 8 (S300) ◽  
pp. 470-472
Author(s):  
Shuhong Yang ◽  
Jun Zhang ◽  
Yang Liu
Keyword(s):  
Magnetic Flux ◽  
Large Scale ◽  
Active Regions ◽  
The Self ◽  
The Sun ◽  
Number Density ◽  
Flux Loops ◽  
Background Fields

AbstractUsing the magnetograms observed with the Helioseismic and Magnetic Imager, we statistically study the ephemeral regions (ERs) of the Sun. we notice that the areas with locations around S15° and N25° have larger ER number density, implying that the generation of ERs may be affected by the large-scale background fields from dispersed active regions. According to their evolution, the ERs can be classified into two types, i.e., normal ERs (2798 ones) and self-canceled ERs (190 ones). Submergence of initial magnetic flux loops connecting the opposite dipolar polarities may lead to the self-cancellation.

Evolutionary Characteristics of Large-Scale Magnetic and Velocity Fields

1993 ◽  
Vol 141 ◽  
pp. 495-499
Author(s):  
Pavel Ambrož
Keyword(s):  
Magnetic Flux ◽  
Large Scale ◽  
Flux Distribution ◽  
Active Regions ◽  
Giant Cells ◽  
Velocity Fields ◽  
Magnetized Plasma ◽  
Horizontal Flow ◽  
Term Evolution

AbstractLong-term evolution of solar large-scale magnetic fields in relation to the local active phenomena is studied. The changes of the magnetic flux distribution are influenced by the horizontal transport of magnetized plasma. The whole system of magnetic field changes is interpreted as a global process which is controlled by the large-scale convective patterns. The large-scale horizontal velocity field of transporting motions is determined in various approaches with similar results. Regions with positive divergence in the field of horizontal flow field are found to be closely connected with the occurrence of solar active regions. The process of the horizontal flow was analysed by the “cork” method. The corks reveal a pattern of giant cells which are persistent for several solar rotations. These large cells are interpreted as giant convective elements. Occurrence of new strong magnetic flux in regions of positive divergence is then interpreted as a result of emergence of flux in the upflowing parts of that pattern.

scholarly journals Large-scale poloidal magnetic field dynamo leads to powerful jets in GRMHD simulations of black hole accretion with toroidal field

2020 ◽  
Vol 494 (3) ◽  
pp. 3656-3662 ◽  
Author(s):  
M Liska ◽  
A Tchekhovskoy ◽  
E Quataert
Keyword(s):  
Magnetic Field ◽  
Magnetic Flux ◽  
Large Scale ◽  
Ambient Medium ◽  
Theoretical Models ◽  
Toroidal Field ◽  
Poloidal Magnetic Field ◽  
Scale Free ◽  
General Relativistic

ABSTRACT Accreting black holes (BHs) launch relativistic collimated jets, across many decades in luminosity and mass, suggesting the jet launching mechanism is universal, robust, and scale-free. Theoretical models and general relativistic magnetohydrodynamic (GRMHD) simulations indicate that the key jet-making ingredient is large-scale poloidal magnetic flux. However, its origin is uncertain, and it is unknown if it can be generated in situ or dragged inward from the ambient medium. Here, we use the GPU-accelerated GRMHD code h-amr to study global 3D BH accretion at unusually high resolutions more typical of local shearing box simulations. We demonstrate that turbulence in a radially extended accretion disc can generate large-scale poloidal magnetic flux in situ, even when starting from a purely toroidal magnetic field. The flux accumulates around the BH till it becomes dynamically important, leads to a magnetically arrested disc (MAD), and launches relativistic jets that are more powerful than the accretion flow. The jet power exceeds that of previous GRMHD toroidal field simulations by a factor of 10 000. The jets do not show significant kink or pinch instabilities, accelerate to γ ∼ 10 over three decades in distance, and follow a collimation profile similar to the observed M87 jet.

scholarly journals A ‘Rosetta Stone’ for Protoplanetary Disks: The Synergy of Multi-Wavelength Observations

2016 ◽  
Vol 33 ◽  
Author(s):  
A. Sicilia-Aguilar ◽  
A. Banzatti ◽  
A. Carmona ◽  
T. Stolker ◽  
M. Kama ◽  
...  
Keyword(s):  
Adaptive Optics ◽  
Large Scale ◽  
Protoplanetary Disks ◽  
Open Problems ◽  
Disk Radius ◽  
Disk Structure ◽  
Rosetta Stone ◽  
Multi Wavelength ◽  
Disk Evolution ◽  
Spectrally Resolved

AbstractRecent progress in telescope development has brought us different ways to observe protoplanetary disks: interferometers, space missions, adaptive optics, polarimetry, and time- and spectrally-resolved data. While the new facilities have changed the way we can tackle open problems in disk structure and evolution, there is a substantial lack of interconnection between different observing communities. Here, we explore the complementarity of some of the state-of-the-art observing techniques, and how they can be brought together to understand disk dispersal and planet formation.This paper was born at the ‘Protoplanetary Discussions’ meeting in Edinburgh, 2016. Its goal is to clarify where multi-wavelength observations converge in unveiling disk structure and evolution, and where they challenge our current understanding. We discuss caveats that should be considered when linking results from different observations, or when drawing conclusions from limited datasets (in terms of wavelength or sample). We focus on disk properties that are currently being revolutionized, specifically: the inner disk radius, holes and gaps and their link to large-scale disk structures, the disk mass, and the accretion rate. We discuss how their connections and apparent contradictions can help us to disentangle the disk physics and to learn about disk evolution.

Evolution of Large-Scale Coronal Structures

1994 ◽  
Vol 144 ◽  
pp. 29-33
Author(s):  
P. Ambrož
Keyword(s):  
Magnetic Field ◽  
Field Line ◽  
Large Scale ◽  
Coronal Magnetic Field ◽  
Source Surface ◽  
Solar Cycles ◽  
Characteristic Relationship ◽  
The Magnetic Field ◽  
Coronal Structures

AbstractThe large-scale coronal structures observed during the sporadically visible solar eclipses were compared with the numerically extrapolated field-line structures of coronal magnetic field. A characteristic relationship between the observed structures of coronal plasma and the magnetic field line configurations was determined. The long-term evolution of large scale coronal structures inferred from photospheric magnetic observations in the course of 11- and 22-year solar cycles is described.Some known parameters, such as the source surface radius, or coronal rotation rate are discussed and actually interpreted. A relation between the large-scale photospheric magnetic field evolution and the coronal structure rearrangement is demonstrated.

Large-scale Motion of Solar Filaments

2000 ◽  
Vol 179 ◽  
pp. 205-208
Author(s):  
Pavel Ambrož ◽  
Alfred Schroll
Keyword(s):  
Magnetic Flux ◽  
Proper Motion ◽  
Time Scale ◽  
Large Scale ◽  
Accuracy Of Measurements ◽  
Solar Filaments ◽  
General Movement ◽  
Scale Motion ◽  
Velocity Scatter

AbstractPrecise measurements of heliographic position of solar filaments were used for determination of the proper motion of solar filaments on the time-scale of days. The filaments have a tendency to make a shaking or waving of the external structure and to make a general movement of whole filament body, coinciding with the transport of the magnetic flux in the photosphere. The velocity scatter of individual measured points is about one order higher than the accuracy of measurements.

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