Magnetic flux transport in the photosphere of the Sun

2020 ◽  
Author(s):  
Dmitrii Baranov ◽  
Elena Vernova ◽  
Marta Tyasto ◽  
Olga Danilova
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Magnetic Flux ◽  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
Polar Field ◽  
The Sun ◽  
Time Diagram ◽  
Weak Magnetic Fields ◽  
The Magnetic Field

<p>On the basis of the synoptic maps of the photospheric magnetic field obtained by the National Solar Observatory Kitt Peak for 1978-2016, a latitude-time diagram of the magnetic field was built. When averaging intensity values over the heliolongitude, the magnetic field sign was taken into account. In order to consider the characteristics of the distribution of weak magnetic fields an upper limit of 5 G was set.</p><p>The latitude-time diagram clearly shows inclined bands corresponding to positive and negative polarity magnetic flows drifting towards the poles of the Sun. Two groups of flows are observed: 1. Relatively narrow bands, with alternating polarity, beginning near the equator and reaching almost the poles of the Sun. Along the time axis, the flow length of one polarity is on the order of 1-2 years; 2. short powerful flows, 3-4.5 years wide, propagating from the spot zone to the poles. These flows reach the poles simultaneously with the begin of the polar field reversal, apparently representing  the so-called “Rush to the Poles” phenomenon.</p><p>The pattern of magnetic field transport is significantly different for the northern and southern hemispheres. Alternating flows of positive and negative polarities most clearly appear in the southern hemisphere during periods of positive polarity of the southern polar field. For the northern hemisphere the picture is much less clear but for individual time intervals alternating flows of opposite polarities can be traced. The slopes of magnetic flux bands allow us to estimate the rate of meridional drift of magnetic fields, which was slightly different for the two hemispheres: V = (16±2) m/s for the southern hemisphere and V = (21±4) m/s for the northern hemisphere. The results obtained indicate that the distribution of weak magnetic fields over the surface of the Sun has a complex structure that is different for the two hemispheres and varies from cycle to cycle.</p>

Emergence of Twisted Magnetic Flux Related Sigmoidal Brightening

2000 ◽  
Vol 179 ◽  
pp. 263-264
Author(s):  
K. Sundara Raman ◽  
K. B. Ramesh ◽  
R. Selvendran ◽  
P. S. M. Aleem ◽  
K. M. Hiremath
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Magnetic Flux ◽  
Ultra Violet ◽  
Active Regions ◽  
Morphological Properties ◽  
Energy Storage And Conversion ◽  
The Sun ◽  
X Rays ◽  
The Magnetic Field

Extended AbstractWe have examined the morphological properties of a sigmoid associated with an SXR (soft X-ray) flare. The sigmoid is cospatial with the EUV (extreme ultra violet) images and in the optical part lies along an S-shaped Hαfilament. The photoheliogram shows flux emergence within an existingδtype sunspot which has caused the rotation of the umbrae giving rise to the sigmoidal brightening.It is now widely accepted that flares derive their energy from the magnetic fields of the active regions and coronal levels are considered to be the flare sites. But still a satisfactory understanding of the flare processes has not been achieved because of the difficulties encountered to predict and estimate the probability of flare eruptions. The convection flows and vortices below the photosphere transport and concentrate magnetic field, which subsequently appear as active regions in the photosphere (Rust & Kumar 1994 and the references therein). Successive emergence of magnetic flux, twist the field, creating flare productive magnetic shear and has been studied by many authors (Sundara Ramanet al.1998 and the references therein). Hence, it is considered that the flare is powered by the energy stored in the twisted magnetic flux tubes (Kurokawa 1996 and the references therein). Rust & Kumar (1996) named the S-shaped bright coronal loops that appear in soft X-rays as ‘Sigmoids’ and concluded that this S-shaped distortion is due to the twist developed in the magnetic field lines. These transient sigmoidal features tell a great deal about unstable coronal magnetic fields, as these regions are more likely to be eruptive (Canfieldet al.1999). As the magnetic fields of the active regions are deep rooted in the Sun, the twist developed in the subphotospheric flux tube penetrates the photosphere and extends in to the corona. Thus, it is essentially favourable for the subphotospheric twist to unwind the twist and transmit it through the photosphere to the corona. Therefore, it becomes essential to make complete observational descriptions of a flare from the magnetic field changes that are taking place in different atmospheric levels of the Sun, to pin down the energy storage and conversion process that trigger the flare phenomena.

Solar Dynamo

2020 ◽  
Author(s):  
Robert Cameron
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Magnetic Flux ◽  
Differential Rotation ◽  
Large Scale ◽  
Toroidal Field ◽  
Solar Dynamo ◽  
Small Scale ◽  
The Sun ◽  
The Magnetic Field

The solar dynamo is the action of flows inside the Sun to maintain its magnetic field against Ohmic decay. On small scales the magnetic field is seen at the solar surface as a ubiquitous “salt-and-pepper” disorganized field that may be generated directly by the turbulent convection. On large scales, the magnetic field is remarkably organized, with an 11-year activity cycle. During each cycle the field emerging in each hemisphere has a specific East–West alignment (known as Hale’s law) that alternates from cycle to cycle, and a statistical tendency for a North-South alignment (Joy’s law). The polar fields reverse sign during the period of maximum activity of each cycle. The relevant flows for the large-scale dynamo are those of convection, the bulk rotation of the Sun, and motions driven by magnetic fields, as well as flows produced by the interaction of these. Particularly important are the Sun’s large-scale differential rotation (for example, the equator rotates faster than the poles), and small-scale helical motions resulting from the Coriolis force acting on convective motions or on the motions associated with buoyantly rising magnetic flux. These two types of motions result in a magnetic cycle. In one phase of the cycle, differential rotation winds up a poloidal magnetic field to produce a toroidal field. Subsequently, helical motions are thought to bend the toroidal field to create new poloidal magnetic flux that reverses and replaces the poloidal field that was present at the start of the cycle. It is now clear that both small- and large-scale dynamo action are in principle possible, and the challenge is to understand which combination of flows and driving mechanisms are responsible for the time-dependent magnetic fields seen on the Sun.

FINITE ENERGY ONE-HALF MONOPOLE SOLUTIONS

2012 ◽  
Vol 27 (40) ◽  
pp. 1250233 ◽  
Author(s):  
ROSY TEH ◽  
BAN-LOONG NG ◽  
KHAI-MING WONG
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Magnetic Flux ◽  
Topological Charge ◽  
Magnetic Monopole ◽  
Magnetic Charge ◽  
Finite Energy ◽  
Spatial Infinity ◽  
Yang Mills ◽  
The Magnetic Field

We present finite energy SU(2) Yang–Mills–Higgs particles of one-half topological charge. The magnetic fields of these solutions at spatial infinity correspond to the magnetic field of a positive one-half magnetic monopole at the origin and a semi-infinite Dirac string on one-half of the z-axis carrying a magnetic flux of [Formula: see text] going into the origin. Hence the net magnetic charge is zero. The gauge potentials are singular along one-half of the z-axis, elsewhere they are regular.

scholarly journals Magnetic Fields in OH Maser Clouds

1974 ◽  
Vol 60 ◽  
pp. 275-292 ◽  
Author(s):  
R. D. Davies
Keyword(s):  
Magnetic Field ◽  
Angular Momentum ◽  
Magnetic Fields ◽  
Magnetic Flux ◽  
Field Data ◽  
Zeeman Splitting ◽  
Galactic Rotation ◽  
Magnetic Field Data ◽  
The Magnetic Field ◽  
Maser Sources

Observations of Class I OH maser sources show a range of features which are predicted on the basis of Zeeman splitting in a source magnetic field. Magnetic field strengths of 2 to 7 mG are derived for eight OH maser sources. The fields in all the clouds are directed in the sense of galactic rotation. A model of W3 OH is proposed which incorporates the magnetic field data. It is shown that no large amount of magnetic flux or angular momentum has been lost since the condensation from the interstellar medium began.

scholarly journals Solar and stellar magnetic flux tubes

1996 ◽  
Vol 176 ◽  
pp. 201-216
Author(s):  
Sami K. Solanki
Keyword(s):  
Magnetic Field ◽  
Magnetic Properties ◽  
Magnetic Flux ◽  
Large Range ◽  
The Sun ◽  
Flux Tubes ◽  
Magnetic Elements ◽  
Turbulent Pressure ◽  
Magnetic Flux Tubes ◽  
The Magnetic Field

The magnetic field of the Sun is mainly concentrated into intense magnetic flux tubes having field strengths of the order of 1 kG. In this paper an overview is given of the thermal and magnetic properties of these flux tubes, which are known to exhibit a large range in size, from the smallest magnetic elements to sunspots. Differences and similarities between the largest and smallest features are stressed. Some thoughts are also presented on how the properties of magnetic flux tubes are expected to scale from the solar case to that of solar-like stars. For example, it is pointed out that on giants and supergiants turbulent pressure may dominate over gas pressure as the main confining agent of the magnetic field. Arguments are also presented in favour of a highly complex magnetic geometry on very active stars. Thus the very large starspots seen in Doppler images probably are conglomerates of smaller (but possibly still sizable) spots.

scholarly journals Discovery of weak magnetic fields in four DZ white dwarfs in the local 20 pc volume

2019 ◽  
Vol 630 ◽  
pp. A65 ◽  
Author(s):  
S. Bagnulo ◽  
J. D. Landstreet
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
White Dwarfs ◽  
Field Measurements ◽  
Weak Magnetic Fields ◽  
Polluted Atmosphere ◽  
Highly Sensitive ◽  
Cool White Dwarfs ◽  
The Magnetic Field ◽  
Made In

We report the discovery of weak magnetic fields in three white dwarfs within the local 20 pc volume (WD 0816−310, WD 1009−184, and WD 1532+129), and we confirm the magnetic nature of a fourth star (WD 2138−332) in which we had previously detected a field at a 3σ level. The spectra of all these white dwarfs are characterised by the presence of metal lines and lack of H and He lines, that is, they belong to the spectral class DZ. The polarisation signal of the Ca II H+K lines of WD 1009−184 is particularly spectacular, with an amplitude of 20% that is due to the presence of a magnetic field with an average line-of-sight component of 40 kG. We have thus established that at least 40% of the known DZ white dwarfs with an He-rich atmosphere contained in the 20 pc volume have a magnetic field, while further observations are needed to establish whether the remaining DZ white dwarfs in the same volume are magnetic or not. Metal lines in the spectra of DZ white dwarfs are thought to have originated by accretion from rocky debris, and it might be argued that a link exists between metal accretion and higher occurrence of magnetism. However, we are not able to distinguish whether the magnetic field and the presence of a polluted atmosphere have a common origin, or if it is the presence of metal lines that allows us to detect a higher frequency of magnetic fields in cool white dwarfs, which would otherwise have featureless spectra. We argue that the new highly sensitive longitudinal field measurements that we have made in recent years are consistent with the idea that the magnetic field appears more frequently in older than in younger white dwarfs.

scholarly journals Evolution of quasi-bound states in the circular n–p junction of bilayer graphene under magnetic field

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Haijiao Ji ◽  
Yueting Pan ◽  
Haiwen Liu
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Bound States ◽  
Local Density ◽  
Energy Levels ◽  
Bilayer Graphene ◽  
Scanning Tunneling ◽  
Tunneling Microscopy ◽  
Weak Magnetic Fields ◽  
The Magnetic Field

Abstract Electron in gapless bilayer graphene can form quasi-bound states when a circular symmetric potential is created in bilayer graphene. These quasi-bound states can be adjusted by tuning the radius and strength of the potential barrier. We investigate the evolution of quasi-bound states spectra in the circular n–p junction of bilayer graphene under the magnetic field numerically. The energy levels of opposite angular momentum split and the splitting increases with the magnetic field. Moreover, weak magnetic fields can slightly shift the energy levels of quasi-bound states. While strong magnetic fields induce additional resonances in the local density states, which originates from Landau levels. We demonstrate that these numerical results are consistent with the semiclassical analysis based on Wentzel–Kramers–Brillouin approximation. Our results can be verified experimentally via scanning tunneling microscopy measurements.

scholarly journals Solar and Stellar Magnetic Fields and Atmospheric Structures: Theory

1989 ◽  
Vol 104 (1) ◽  
pp. 271-288
Author(s):  
E. N. Parker
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Dynamical Behavior ◽  
Convective Zone ◽  
Coronal Heating ◽  
The Sun ◽  
Current Sheets ◽  
Spontaneous Formation ◽  
Stellar Magnetic Fields ◽  
The Magnetic Field

AbstractThis presentation reviews selected ideas on the origin of the magnetic field of the Sun, the dynamical behavior of the azimuthal field in the convective zone, the fibril state of the field at the photosphere, the formation of sunspots, prominences, the spontaneous formation of current sheets in the bipolar field above the surface of the Sun, coronal heating, and flares.

Analytical Solution of the Perturbed Magnetic Fields of Plates Under Tensile Stress

2008 ◽  
Vol 75 (3) ◽  
Author(s):  
Fei Qin ◽  
Dongmei Yan
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Analytic Solutions ◽  
Round Hole ◽  
Governing Equations ◽  
Displacement Gradient ◽  
Weak Magnetic Fields ◽  
Testing Technology ◽  
Perturbed Magnetic Field ◽  
The Magnetic Field

Development of magnetism based nondestructive testing technology and the Microelectronic mechanical system require accurate computation of perturbed magnetic fields generated by mechanical stress. In this paper, based on the linearized magnetoelastic theory, the governing equations and continuity conditions to determine the perturbed magnetic fields were formulated for the case of weak external magnetic fields such as the earth’s magnetic field. Under those weak magnetic fields, the effect of the magnetic fields on mechanical deformation was neglected. As a result, the interaction between the deformation and the magnetic field was simplified. The effect of deformation on the perturbed magnetic field was taken into account by introducing the displacement gradient into the boundary conditions that the perturbed field should satisfy. As examples, analytic solutions of the perturbed magnetic field of infinite plates with and without a round hole, which are subjected to tensile stresses and weak external magnetic fields, were obtained by the approach presented. The results show that the perturbed magnetic fields induced by stress are three orders less in magnitude of intensity than that of magnetic fields without stress, and some prominent local features such as that has more peaks and decays more rapidly in the radial direction than the case of stress free that are predicted by the solutions.

scholarly journals Dynamically dominant magnetic fields in the diffuse interstellar medium

2008 ◽  
Vol 4 (S259) ◽  
pp. 87-88 ◽  
Author(s):  
Andrew Fletcher ◽  
M. Korpi ◽  
A. Shukurov
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Magnetic Flux ◽  
Interstellar Medium ◽  
Numerical Simulations ◽  
Hydrodynamic Model ◽  
Mass Conservation ◽  
Unstable Flow ◽  
Gas Density ◽  
The Magnetic Field

AbstractObservations show that magnetic fields in the interstellar medium (ISM) often do not respond to increases in gas density as would be naively expected for a frozen-in field. This may suggest that the magnetic field in the diffuse gas becomes detached from dense clouds as they form. We have investigated this possibility using theoretical estimates, a simple magneto-hydrodynamic model of a flow without mass conservation and numerical simulations of a thermally unstable flow. Our results show that significant magnetic flux can be shed from dense clouds as they form in the diffuse ISM, leaving behind a magnetically dominated diffuse gas.

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