scholarly journals Temporal evolution of small-scale internetwork magnetic fields in the solar photosphere

2021 ◽  
Vol 647 ◽  
pp. A182
Author(s):  
R. J. Campbell ◽  
M. Mathioudakis ◽  
M. Collados ◽  
P. H. Keys ◽  
A. Asensio Ramos ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Linear Polarization ◽  
Temporal Evolution ◽  
Vertical Component ◽  
Stray Light ◽  
Small Scale ◽  
Line Pair ◽  
Solar Photosphere ◽  
Magnetic Features ◽  
Transverse Fields

Context. While the longitudinal field that dominates in photospheric network regions has been studied extensively, small-scale transverse fields have recently been found to be ubiquitous in the quiet internetwork photosphere and this merits further study. Furthermore, few observations have been able to capture how this field evolves. Aims. We aim to statistically characterize the magnetic vector in a quiet Sun internetwork region and observe the temporal evolution of specific small-scale magnetic features. Methods. We present two high spatio-temporal resolution observations that reveal the dynamics of two disk-centre internetwork regions taken by the new GREGOR Infrared Spectrograph Integral Field Unit with the highly magnetically sensitive photospheric Fe I line pair at 15648.52 Å and 15652.87 Å. We record the full Stokes vector and apply inversions with the Stokes inversions based on response functions code to retrieve the parameters characterizing the atmosphere. We consider two inversion schemes: scheme 1 (S1), where a magnetic atmosphere is embedded in a field free medium, and scheme 2 (S2), with two magnetic models and a fixed 30% stray light component. Results. The magnetic properties produced from S1 inversions returned a median magnetic field strength of 200 and 240 G for the two datasets, respectively. We consider the median transverse (horizontal) component, among pixels with Stokes Q or U, and the median unsigned longitudinal (vertical) component, among pixels with Stokes V, above a noise threshold. We determined the former to be 263 G and 267 G, and the latter to be 131 G and 145 G, for the two datasets, respectively. Finally, we present three regions of interest, tracking the dynamics of small-scale magnetic features. We apply S1 and S2 inversions to specific profiles of interest and find that the latter produces better approximations when there is evidence of mixed polarities. We find patches of linear polarization with magnetic flux density of the order of 130−150 G and find that linear polarization appears preferentially at granule-intergranular lane boundaries. The weak magnetic field appears to be organized in terms of complex ‘loop-like’ structures, with transverse fields often flanked by opposite polarity longitudinal fields.

scholarly journals Properties of the inner penumbral boundary and temporal evolution of a decaying sunspot

2018 ◽  
Vol 620 ◽  
pp. A191 ◽  
Author(s):  
M. Benko ◽  
S. J. González Manrique ◽  
H. Balthasar ◽  
P. Gömöry ◽  
C. Kuckein ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Flux ◽  
Temporal Evolution ◽  
Vertical Component ◽  
Field Vector ◽  
Linear Increase ◽  
Vertical Magnetic Field ◽  
Magnetic Diffusion ◽  
The Magnetic Field ◽  
Linear Decay

Context. It has been empirically determined that the umbra-penumbra boundaries of stable sunspots are characterized by a constant value of the vertical magnetic field. Aims. We analyzed the evolution of the photospheric magnetic field properties of a decaying sunspot belonging to NOAA 11277 between August 28–September 3, 2011. The observations were acquired with the spectropolarimeter on-board of the Hinode satellite. We aim to prove the validity of the constant vertical magnetic-field boundary between the umbra and penumbra in decaying sunspots. Methods. A spectral-line inversion technique was used to infer the magnetic field vector from the full-Stokes profiles. In total, eight maps were inverted and the variation of the magnetic properties in time were quantified using linear or quadratic fits. Results. We find a linear decay of the umbral vertical magnetic field, magnetic flux, and area. The penumbra showed a linear increase of the vertical magnetic field and a sharp decay of the magnetic flux. In addition, the penumbral area quadratically decayed. The vertical component of the magnetic field is weaker on the umbra-penumbra boundary of the studied decaying sunspot compared to stable sunspots. Its value seem to be steadily decreasing during the decay phase. Moreover, at any time of the sunspot decay shown, the inner penumbra boundary does not match with a constant value of the vertical magnetic field, contrary to what is seen in stable sunspots. Conclusions. During the decaying phase of the studied sunspot, the umbra does not have a sufficiently strong vertical component of the magnetic field and is thus unstable and prone to be disintegrated by convection or magnetic diffusion. No constant value of the vertical magnetic field is found for the inner penumbral boundary.

scholarly journals Using the infrared iron lines to probe solar subsurface convection

2019 ◽  
Vol 630 ◽  
pp. A133 ◽  
Author(s):  
I. Milić ◽  
H. N. Smitha ◽  
A. Lagg
Keyword(s):  
Three Dimensional ◽  
Spectral Lines ◽  
Stray Light ◽  
Line Pair ◽  
Solar Photosphere ◽  
Solar Convection ◽  
Diagnostic Potential ◽  
Optimal Node ◽  
Zero Response ◽  
Magnetohydrodynamic Simulation

Context. Studying the properties of solar convection using high-resolution spectropolarimetry began in the early 1990s with the focus on observations in the visible wavelength regions. Its extension to the infrared (IR) remains largely unexplored. Aims. The IR iron lines around 15 600 Å, most commonly known for their high magnetic sensitivity, also have a non-zero response to line-of-sight (LOS) velocity below log(τ) = 0.0. In this paper we explore the possibility of using these lines to measure subsurface convective velocities. Methods. By assuming a snapshot of a three-dimensional magnetohydrodynamic simulation to represent the quiet Sun, we investigate how well the iron IR lines can reproduce the LOS velocity in the cube and to what depth. We use the recently developed spectropolarimetric inversion code SNAPI and discuss the optimal node placements for the retrieval of reliable results from these spectral lines. Results. We find that the IR iron lines can measure the convective velocities down to log(τ) = 0.5, below the photosphere, not only at the original resolution of the cube, but also when degraded with a reasonable spectral and spatial PSF and stray light. Instead, the commonly used Fe I 6300 Å line pair performs significantly worse. Conclusions. Our investigation reveals that the IR iron lines can probe the subsurface convection in the solar photosphere. This paper is a first step towards exploiting this diagnostic potential.

scholarly journals Observations of Magnetic Features with the German Solar Telescopes at the Observatorio del Teide/Tenerife

1990 ◽  
Vol 142 ◽  
pp. 113-117
Author(s):  
F. Kneer ◽  
D. Soltau ◽  
E. Wiehr
Keyword(s):  
Magnetic Field ◽  
Fine Structure ◽  
Spatial Variation ◽  
Velocity Fluctuation ◽  
Small Scale ◽  
Field Variation ◽  
Magnetic Field Variation ◽  
Quiet Sun ◽  
Magnetic Features ◽  
Solar Telescopes

The German solar facilities at the Obsrvatorio del Teide are described first. Then, a few examples of recent results from magnetic features are given: spatial variation and velocity fluctuation of small-scale magnetic fluxtubes in the quiet Sun, Evershed flow and magnetic field in connection with penumbral fine structure, and magnetic field variation in sunspot umbrae.

scholarly journals Photospheric Sources of Magnetic Field Aligned Currents

1983 ◽  
Vol 71 ◽  
pp. 601-603
Author(s):  
Ake Nordlund
Keyword(s):  
Magnetic Field ◽  
Momentum Transfer ◽  
Coronal Magnetic Field ◽  
Small Scale ◽  
Solar Photosphere ◽  
Electron Component ◽  
Neutral Gas ◽  
Electrons And Ions ◽  
Density Of Electrons ◽  
Gas Component

Possible (small-scale) photospheric sources of coronal magnetic field aligned currents are discussed. Such currents are equivalent to local (small-scale) twists of the coronal magnetic field, and may cause field topologies that are (MHD or resistively) unstable, and thus contribute to the (small-scale) coronal activity.One electro-motive force associated with photospheric magnetic fields is due to the asymmetry between ions and electrons as agents of conductivity and as agents of momentum transfer to the (dominant) neutral gas component. In the solar photosphere, where only some of the easily ionized heavier elements (Mg, Si, Fe, ...) are significantly ionized, the ratio of number density of electrons and ions to neutrals is very small, of the order of the total abundance of these elements, which is of the order 10-4, by number. Due to the larger electron than ion mobility, electric currents are mainly carried by the electron component of the plasma whereas, because of the ions greater momentum transfer to the neutrals in collisions, the friction between the charged and the neutral components of the plasma is mainly due to the ions. Thus, the Lorenz force i x B acts mainly on the electron component of the plasma, whereas the balancing gas pressure gradient and gravity terms act mainly on the neutral component.

Magnetic fields in the solar photosphere

2008 ◽  
Vol 366 (1884) ◽  
pp. 4465-4476 ◽  
Author(s):  
Paul J Bushby
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Active Regions ◽  
Theoretical Models ◽  
Solar Photosphere ◽  
Complex Field ◽  
Theoretical Understanding ◽  
Magnetic Features ◽  
Localized Magnetic Field ◽  
Made In

Recent high-resolution observations of the surface of the Sun have revealed the fine structure of a vast array of complex photospheric magnetic features. Observations of these magnetic field structures have already greatly enhanced our theoretical understanding of the interactions between magnetic fields and turbulent convection, and future photospheric observations will inevitably present new theoretical challenges. In this review, I discuss recent progress that has been made in the modelling of photospheric magnetic fields. In particular, I focus upon the complex field structures that are observed within the umbrae and the penumbrae of sunspots. On a much smaller scale, I also discuss models of the highly localized magnetic field structures that are observed in less magnetically active regions of the photosphere. As the spatial resolution of telescopes has improved over the last few years, it has now become possible to observe these features in detail, and theoretical models can now describe much of this behaviour. In the last section of this review, I discuss some of the remaining unanswered questions.

scholarly journals P-mode induced convective collapse in vertical expanding magnetic flux tubes?

2016 ◽  
Vol 12 (S327) ◽  
pp. 86-93 ◽  
Author(s):  
D. Utz ◽  
T. Van Doorsselaere ◽  
N. Magyar ◽  
M. Bárta ◽  
J. I. Campos Rozo
Keyword(s):  
Magnetic Field ◽  
Magnetic Flux ◽  
Strong Magnetic Field ◽  
Magnetic Flux Tube ◽  
Small Scale ◽  
Solar Photosphere ◽  
Ongoing Work ◽  
Standard Scenario ◽  
Wave Guides ◽  
Collapse Process

AbstractSmall-scale kG strong magnetic field elements in the solar photosphere are often identified as so-called magnetic bright points (MBPs). In principle these MBPs represent the cross-section of a vertical, strong, magnetic flux tube which is expanding with height in the solar atmosphere. As these magnetic elements represent possible MHD wave guides, a significant interest has been already paid to them from the viewpoint of observations and simulations. In this work we would like to shed more light on a possible scenario for the creation of such strong magnetic field concentrations. The accepted standard scenario involves the convective collapse process. In this ongoing work we will show indications that this convective collapse process may become triggered by sufficiently strong pressure disturbances. However, it is highly unlikely that p-mode waves can be of such a strength.

scholarly journals Magnetic field evolution in magnetar crusts through three-dimensional simulations

2016 ◽  
Vol 113 (15) ◽  
pp. 3944-3949 ◽  
Author(s):  
Konstantinos N. Gourgouliatos ◽  
Toby S. Wood ◽  
Rainer Hollerbach
Keyword(s):  
Magnetic Field ◽  
Neutron Star ◽  
Field Strength ◽  
Ohmic Heating ◽  
High Energy ◽  
Global Scale ◽  
Small Scale ◽  
Magnetic Field Generation ◽  
Transfer Energy ◽  
Magnetic Features

Current models of magnetars require extremely strong magnetic fields to explain their observed quiescent and bursting emission, implying that the field strength within the star’s outer crust is orders of magnitude larger than the dipole component inferred from spin-down measurements. This presents a serious challenge to theories of magnetic field generation in a proto-neutron star. Here, we present detailed modeling of the evolution of the magnetic field in the crust of a neutron star through 3D simulations. We find that, in the plausible scenario of equipartition of energy between global-scale poloidal and toroidal magnetic components, magnetic instabilities transfer energy to nonaxisymmetric, kilometer-sized magnetic features, in which the local field strength can greatly exceed that of the global-scale field. These intense small-scale magnetic features can induce high-energy bursts through local crust yielding, and the localized enhancement of Ohmic heating can power the star’s persistent emission. Thus, the observed diversity in magnetar behavior can be explained with mixed poloidal−toroidal fields of comparable energies.

scholarly journals Long quasi-periodic oscillations of the faculae and pores

2019 ◽  
Vol 627 ◽  
pp. A10 ◽  
Author(s):  
A. Riehokainen ◽  
P. Strekalova ◽  
A. Solov’ev ◽  
V. Smirnova ◽  
I. Zhivanovich ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Stable Phase ◽  
Small Scale ◽  
Solar Photosphere ◽  
Periodic Oscillations ◽  
Magnetic Structures ◽  
Long Period ◽  
Continuum Intensity ◽  
Structurally Stable ◽  
The Continuum

Aims. The main goal of this work is to analyze the structural and temporal evolution of small-scale magnetic structures (SSMSs) observed in the solar atmosphere, such as solitary faculae and pores, and reveal long quasi-periodic oscillations of these structures. Methods. The statistical method of regression analysis and the wavelet transform were used to obtain the periods of oscillations and dependences between the parameters of magnetic structures and periods of oscillations. Results. Long-period oscillations with periods in the interval of 18−260 min are found for the structurally stable phase of SSMSs at the level of the solar photosphere. These long-period oscillations were interpreted as natural oscillations of the structurally stable long-lived magnetic structures around their equilibrium position. These oscillations, which are of similar nature, are observed in the chromospheric bright formations associated with photospheric SSMSs. Dependences between the magnetic field and the continuum intensity of the facula elements were found. It is shown that the continuum intensity of a SSMS decreases when its magnetic field increases.

scholarly journals [no title]

1977 ◽  
Vol 4 (2) ◽  
pp. 223-239 ◽  
Author(s):  
J. Harvey
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Spatial Resolution ◽  
Small Scale ◽  
Solar Photosphere ◽  
The Sun ◽  
Solar Magnetic Fields ◽  
Structure And Dynamics ◽  
Physical Problems ◽  
Observational Techniques

If the Sun is observed like a star, without spatial resolution, its magnetic field seldom exceeds 1 Gauss. But with high spatial resolution the field is seen to be largely concentrated into kG structures. Observations of the structure and dynamics of solar magnetic fields can therefore provide a guide to the nature of magnetic fields of other stars which cannot be resolved. Solar activity and the structure of the chromosphere and inner corona are intimately linked with magnetism and a complete understanding of these features often depends on magnetic field details. There are unsolved physical problems involving solar magnetic fields which have challenged many physicists. For example, confinement of small-scale fields in kG structures is a problem of current interest (Parker, 1976; Piddington, 1976; Spruit, 1976). Solar observers are no less challenged since the Sun presents us with a complicated magnetic field having a range of scales from global to less than the scale of our best observations as illustrated in Figures 1, 2, and 3. This paper is a survey of observational techniques and results at the small-scale end of the spectrum of sizes in the solar photosphere. This topic has been frequently reviewed (e.g. Athay, 1976; Beckers, 1976; Deubner, 1975; Howard, 1972; Mullan, 1974; Severny, 1972; Stenflo, 1975) so that recent work is emphasized here.

scholarly journals Flux Separation in Photospheric Magnetoconvection

2001 ◽  
Vol 203 ◽  
pp. 219-221 ◽  
Author(s):  
N. O. Weiss ◽  
M. R. E. Proctor
Keyword(s):  
Magnetic Field ◽  
Magnetic Flux ◽  
Numerical Experiments ◽  
Large Scale ◽  
Initial Conditions ◽  
Three Dimensional ◽  
Small Scale ◽  
The Sun ◽  
Intermediate Regime ◽  
Magnetic Features

Numerical experiments on three-dimensional magnetoconvection in a stratified compressible layer reveal a range of different patterns, depending on the strength of the imposed magnetic field. As the field is decreased there is a transition from small-scale plumes, in the magnetically dominated regime, to large-scale vigorous plumes when the field is dominated by the motion. In the intermediate regime magnetic flux separates from the motion, so that there are almost field-free regions, with clusters of vigorous plumes, surrounded by regions where the Lorentz force is strong enough to control the dynamics. There is a range of field strengths where either small-scale plumes or flux-separated solutions can persist, depending on initial conditions for the computation. These results can be related to magnetic features at the surface of the Sun.

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