The role of partial ionization effects in the chromosphere

The energy for the coronal heating must be provided from the convection zone. However, the amount and the method by which this energy is transferred into the corona depend on the properties of the lower atmosphere and the corona itself. We review: (i) how the energy could be built in the lower solar atmosphere, (ii) how this energy is transferred through the solar atmosphere, and (iii) how the energy is finally dissipated in the chromosphere and/or corona. Any mechanism of energy transport has to deal with the various physical processes in the lower atmosphere. We will focus on a physical process that seems to be highly important in the chromosphere and not deeply studied until recently: the ion–neutral interaction effects in the chromosphere. We review the relevance and the role of the partial ionization in the chromosphere and show that this process actually impacts considerably the outer solar atmosphere. We include analysis of our 2.5D radiative magnetohydrodynamic simulations with the Bifrost code (Gudiksen et al. 2011 Astron. Astrophys. 531 , A154 ( doi:10.1051/0004-6361/201116520 )) including the partial ionization effects on the chromosphere and corona and thermal conduction along magnetic field lines. The photosphere, chromosphere and transition region are partially ionized and the interaction between ionized particles and neutral particles has important consequences on the magneto-thermodynamics of these layers. The partial ionization effects are treated using generalized Ohm's law, i.e. we consider the Hall term and the ambipolar diffusion (Pedersen dissipation) in the induction equation. The interaction between the different species affects the modelled atmosphere as follows: (i) the ambipolar diffusion dissipates magnetic energy and increases the minimum temperature in the chromosphere and (ii) the upper chromosphere may get heated and expanded over a greater range of heights. These processes reveal appreciable differences between the modelled atmospheres of simulations with and without ion–neutral interaction effects.

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MAGNETIC FIELD AMPLIFICATION BY RELATIVISTIC SHOCKS IN AN INHOMOGENEOUS MEDIUM

International Journal of Modern Physics Conference Series ◽

10.1142/s2010194512004904 ◽

2012 ◽

Vol 08 ◽

pp. 364-367

Author(s):

YOSUKE MIZUNO ◽

MARTIN POHL ◽

JACEK NIEMIEC ◽

BING ZHANG ◽

KEN-ICHI NISHIKAWA ◽

...

Keyword(s):

Magnetic Field ◽

Inhomogeneous Medium ◽

Magnetic Energy ◽

Small Scale ◽

Two Dimensional ◽

Filamentary Structure ◽

Field Amplification ◽

Relativistic Shocks ◽

Field Lines ◽

Magnetohydrodynamic Simulations

We perform two-dimensional relativistic magnetohydrodynamic simulations of a mildly relativistic shock propagating through an inhomogeneous medium. We show that the postshock region becomes turbulent owing to preshock density inhomogeneity, and the magnetic field is strongly amplified due to the stretching and folding of field lines in the turbulent velocity field. The amplified magnetic field evolves into a filamentary structure in two-dimensional simulations. The magnetic energy spectrum is flatter than the Kolmogorov spectrum and indicates that the so-called small-scale dynamo is occurring in the postshock region. We also find that the amplitude of magnetic-field amplification depends on the direction of the mean preshock magnetic field.

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A New View of the Solar Interface Region from the Interface Region Imaging Spectrograph (IRIS)

Solar Physics ◽

10.1007/s11207-021-01826-0 ◽

2021 ◽

Vol 296 (5) ◽

Author(s):

Bart De Pontieu ◽

Vanessa Polito ◽

Viggo Hansteen ◽

Paola Testa ◽

Katharine K. Reeves ◽

...

Keyword(s):

Solar Atmosphere ◽

Resonant Absorption ◽

Interface Region ◽

Machine Learning Techniques ◽

Small Scale ◽

Wide Range ◽

Field Lines ◽

Far Ultraviolet ◽

Imaging Spectrograph

AbstractThe Interface Region Imaging Spectrograph (IRIS) has been obtaining near- and far-ultraviolet images and spectra of the solar atmosphere since July 2013. IRIS is the highest resolution observatory to provide seamless coverage of spectra and images from the photosphere into the low corona. The unique combination of near- and far-ultraviolet spectra and images at sub-arcsecond resolution and high cadence allows the tracing of mass and energy through the critical interface between the surface and the corona or solar wind. IRIS has enabled research into the fundamental physical processes thought to play a role in the low solar atmosphere such as ion–neutral interactions, magnetic reconnection, the generation, propagation, and dissipation of waves, the acceleration of non-thermal particles, and various small-scale instabilities. IRIS has provided insights into a wide range of phenomena including the discovery of non-thermal particles in coronal nano-flares, the formation and impact of spicules and other jets, resonant absorption and dissipation of Alfvénic waves, energy release and jet-like dynamics associated with braiding of magnetic-field lines, the role of turbulence and the tearing-mode instability in reconnection, the contribution of waves, turbulence, and non-thermal particles in the energy deposition during flares and smaller-scale events such as UV bursts, and the role of flux ropes and various other mechanisms in triggering and driving CMEs. IRIS observations have also been used to elucidate the physical mechanisms driving the solar irradiance that impacts Earth’s upper atmosphere, and the connections between solar and stellar physics. Advances in numerical modeling, inversion codes, and machine-learning techniques have played a key role. With the advent of exciting new instrumentation both on the ground, e.g. the Daniel K. Inouye Solar Telescope (DKIST) and the Atacama Large Millimeter/submillimeter Array (ALMA), and space-based, e.g. the Parker Solar Probe and the Solar Orbiter, we aim to review new insights based on IRIS observations or related modeling, and highlight some of the outstanding challenges.

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Role of Z-pinches in magnetic reconnection in space plasmas

Journal of Plasma Physics ◽

10.1017/s0022377814000725 ◽

2014 ◽

Vol 81 (1) ◽

Cited By ~ 4

Author(s):

Vyacheslav Olshevsky ◽

Giovanni Lapenta ◽

Stefano Markidis ◽

Andrey Divin

Keyword(s):

Magnetic Reconnection ◽

Magnetic Energy ◽

Large Fraction ◽

Three Dimensional ◽

Space Plasmas ◽

Particle In Cell ◽

Cell Simulation ◽

Field Lines ◽

Three Dimensional Configuration

A widely accepted scenario of magnetic reconnection in collisionless space plasmas is the breakage of magnetic field lines in X-points. In laboratory, reconnection is commonly studied in pinches, current channels embedded into twisted magnetic fields. No model of magnetic reconnection in space plasmas considers both null-points and pinches as peers. We have performed a particle-in-cell simulation of magnetic reconnection in a three-dimensional configuration where null-points are present initially, and Z-pinches are formed during the simulation along the lines of spiral null-points. The non-spiral null-points are more stable than spiral ones, and no substantial energy dissipation is associated with them. On the contrary, turbulent magnetic reconnection in the pinches causes the magnetic energy to decay at a rate of ~1.5% per ion gyro period. Dissipation in similar structures is a likely scenario in space plasmas with large fraction of spiral null-points.

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The role of thermal pressure in jet launching

Proceedings of the International Astronomical Union ◽

10.1017/s1743921307009556 ◽

2007 ◽

Vol 3 (S243) ◽

pp. 195-202 ◽

Cited By ~ 2

Author(s):

Noam Soker

Keyword(s):

Kinetic Energy ◽

Internal Energy ◽

Accretion Rate ◽

Magnetic Energy ◽

Acceleration Process ◽

Relativistic Jets ◽

High Speeds ◽

Field Lines ◽

Very High

AbstractI present and discuss a unified scheme for jet launching that is based on stochastic dissipation of the accretion disk kinetic energy, mainly via shock waves. In this scheme, termed thermally-launched jet model, the kinetic energy of the accreted mass is transferred to internal energy, e.g., heat or magnetic energy. The internal energy accelerates a small fraction of the accreted mass to high speeds and form jets. For example, thermal energy forms a pressure gradient that accelerates the gas. A second acceleration stage is possible wherein the primary outflow stretches magnetic field lines. The field lines then reconnect and accelerate small amount of mass to very high speeds. This double-stage acceleration process might form highly relativistic jets from black holes and neutron stars. The model predicts that detail analysis of accreting brown dwarfs that launch jets will show the mass accretion rate to beṀBD≳ 10−9− 10−8M⊙yr−1, which is higher than present claims in the literature.

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Disc formation in magnetized dense cores with turbulence and ambipolar diffusion

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz2436 ◽

2019 ◽

Vol 489 (4) ◽

pp. 5326-5347 ◽

Cited By ~ 8

Author(s):

Ka Ho Lam ◽

Zhi-Yun Li ◽

Che-Yu Chen ◽

Kengo Tomida ◽

Bo Zhao

Keyword(s):

Ambipolar Diffusion ◽

Accretion Flow ◽

The Core ◽

Dense Cores ◽

Formation And Evolution ◽

Field Lines ◽

Cloud Cores ◽

Magnetohydrodynamic Simulations ◽

Initial Turbulence ◽

Disc Formation

ABSTRACT Discs are essential to the formation of both stars and planets, but how they form in magnetized molecular cloud cores remains debated. This work focuses on how the disc formation is affected by turbulence and ambipolar diffusion (AD), both separately and in combination, with an emphasis on the protostellar mass accretion phase of star formation. We find that a relatively strong, sonic turbulence on the core scale strongly warps but does not completely disrupt the well-known magnetically induced flattened pseudo-disc that dominates the inner protostellar accretion flow in the laminar case, in agreement with previous work. The turbulence enables the formation of a relatively large disc at early times with or without AD, but such a disc remains strongly magnetized and does not persist to the end of our simulation unless a relatively strong AD is also present. The AD-enabled discs in laminar simulations tend to fragment gravitationally. The disc fragmentation is suppressed by initial turbulence. The AD facilitates the disc formation and survival by reducing the field strength in the circumstellar region through magnetic flux redistribution and by making the field lines there less pinched azimuthally, especially at late times. We conclude that turbulence and AD complement each other in promoting disc formation. The discs formed in our simulations inherit a rather strong magnetic field from its parental core, with a typical plasma-β of order a few tens or smaller, which is 2–3 orders of magnitude lower than the values commonly adopted in magnetohydrodynamic simulations of protoplanetary discs. To resolve this potential tension, longer term simulations of disc formation and evolution with increasingly more realistic physics are needed.

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Magnetic field amplification by relativistic shocks in a turbulent medium

Proceedings of the International Astronomical Union ◽

10.1017/s1743921311007459 ◽

2010 ◽

Vol 6 (S274) ◽

pp. 445-448

Author(s):

Yosuke Mizuno ◽

Martin Pohl ◽

Jacek Niemiec ◽

Bing Zhang ◽

Ken-Ichi Nishikawa ◽

...

Keyword(s):

Magnetic Field ◽

Magnetic Energy ◽

Turbulent Medium ◽

Small Scale ◽

Two Dimensional ◽

Filamentary Structure ◽

Field Amplification ◽

Relativistic Shocks ◽

Field Lines ◽

Magnetohydrodynamic Simulations

AbstractWe perform two-dimensional relativistic magnetohydrodynamic simulations of a mildly relativistic shock propagating through an inhomogeneous medium. We show that the postshock region becomes turbulent owing to preshock density inhomogeneities, and the magnetic field is strongly amplified due to the stretching and folding of field lines in the turbulent velocity field. The amplified magnetic field evolves into a filamentary structure in our two-dimensional simulations. The magnetic energy spectrum is flatter than Kolmogorov and indicates that a so-called small-scale dynamo is operating in the postshock region. We also find that the amount of magnetic-field amplification depends on the direction of the mean preshock magnetic field.

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Influence of Magnetic Fields on Solar Hydrodynamics: Experimental Results

International Astronomical Union Colloquium ◽

10.1017/s025292110005329x ◽

1977 ◽

Vol 36 ◽

pp. 143-180 ◽

Cited By ~ 10

Author(s):

J.O. Stenflo

Keyword(s):

Solar Activity ◽

Energy Balance ◽

Magnetic Fields ◽

Solar Atmosphere ◽

General Problem ◽

Solar Rotation ◽

Active Regions ◽

Physical Conditions ◽

Dynamic Phenomena

It is well-known that solar activity is basically caused by the Interaction of magnetic fields with convection and solar rotation, resulting in a great variety of dynamic phenomena, like flares, surges, sunspots, prominences, etc. Many conferences have been devoted to solar activity, including the role of magnetic fields. Similar attention has not been paid to the role of magnetic fields for the overall dynamics and energy balance of the solar atmosphere, related to the general problem of chromospheric and coronal heating. To penetrate this problem we have to focus our attention more on the physical conditions in the ‘quiet’ regions than on the conspicuous phenomena in active regions.

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Exploring the Role of Interaction Effects in Visual Conjoint Analysis

Journal of Mechanical Design ◽

10.1115/1.4031054 ◽

2015 ◽

Vol 137 (9) ◽

Cited By ~ 3

Author(s):

Brian Sylcott ◽

Jeremy J. Michalek ◽

Jonathan Cagan

Keyword(s):

Conjoint Analysis ◽

Consumer Preferences ◽

Consumer Preference ◽

Interaction Effects ◽

Fractional Factorial ◽

Main Effects ◽

Full Factorial ◽

Biased Estimates ◽

Data Requirements

In conjoint analysis, interaction effects characterize how preference for the level of one product attribute is dependent on the level of another attribute. When interaction effects are negligible, a main effects fractional factorial experimental design can be used to reduce data requirements and survey cost. This is particularly important when the presence of many parameters or levels makes full factorial designs intractable. However, if interaction effects are relevant, main effects design can create biased estimates and lead to erroneous conclusions. This work investigates consumer preference interactions in the nontraditional context of visual choice-based conjoint analysis, where the conjoint attributes are parameters that define a product's shape. Although many conjoint studies assume interaction effects to be negligible, they may play a larger role for shape parameters. The role of interaction effects is explored in two visual conjoint case studies. The results suggest that interactions can be either negligible or dominant in visual conjoint, depending on consumer preferences. Generally, we suggest using randomized designs to avoid any bias resulting from the presence of interaction effects.

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