scholarly journals Oscillatory convection in strong magnetic fields and origin of active regions

1968 ◽  
Vol 35 ◽  
pp. 127-130 ◽  
Author(s):  
S. I. Syrovatsky ◽  
Y. D. Zhugzhda
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Active Regions ◽  
Oscillatory Convection ◽  
Strong Magnetic Fields ◽  
Various Boundary Conditions ◽  
Convective Cells ◽  
The Magnetic Field ◽  
Polytropic Atmosphere

The convection in a compressible inhomogeneous conducting fluid in the presence of a vertical uniform magnetic field has been studied. It is shown that a new mode of oscillatory convection occurs, which exists in arbitrarily strong magnetic fields. The convective cells are stretched along the magnetic field, their horizontal dimensions are determined by radiative cooling. Criteria for convective instability in a polytropic atmosphere are obtained for various boundary conditions in the case when the Alfvén velocity is higher compared with the velocity of sound.The role of oscillatory convection in the origin of sunspots and active regions is discussed.

The Effect of a Magnetic Field on Individual Convective Cells

1974 ◽  
Vol 2 (5) ◽  
pp. 267-269
Author(s):  
J. O. Murphy
Keyword(s):  
Magnetic Field ◽  
Close Association ◽  
Cell Structure ◽  
Longitudinal Field ◽  
Strong Magnetic Fields ◽  
Convective Processes ◽  
Granulation Pattern ◽  
Convective Cells ◽  
The Magnetic Field

The darkness of sunspots has been attributed by many authors (Biermann 1941; Danielson 1961) to the inhibition of the normal solar convective processes by the presence of strong magnetic fields. Observations of the solar photospheric granulation pattern have also shown that a weak longitudinal field exists outside the activity regions. Although these observations have not revealed any close association between the magnetic field and individual granules, nor the exact reasons for the darker cell boundaries, it must be accepted that, overall, the role of the magnetic field must be such as to influence the cell structure and reduce the normal heat transfer by convection.

scholarly journals Strong magnetic fields in bipolar outflows

1991 ◽  
Vol 147 ◽  
pp. 373-376
Author(s):  
M. D. Smith ◽  
P. W. J. L. Brand ◽  
A. Moorhouse
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Molecular Hydrogen ◽  
Active Regions ◽  
Young Star ◽  
Molecular Gas ◽  
Bipolar Outflows ◽  
Strong Magnetic Fields ◽  
Bow Shocks ◽  
The Magnetic Field

A supersonic wind from a young star will produce regions of strong magnetic field in the stellar environment. The associated shocks compress the molecular gas, increasing the density n, pressure p, and field B. Crucially, the Alfvén speed, vA∝ B/n1/2, is also increased since the total shock compression is approximately of the form B ∝ n. But is there any evidence for such high vA- or ‘active cloud’ - regions within bipolar outflows? We indicate below one implication which has important observable consequences: fast shocks of low Alfvén number (v/vA) now arise. With a low ionization level, the C-shock structure is qualitatively different from the high Alfvén number flows which are common to ‘quiescent cloud’ conditions. The magnetic-field cushioning now allows molecular hydrogen to survive very fast shocks and broad H2 lines are feasible. We display results which show that the resolved broad lines and line ratio properties in the OMC-1 outflow can be explained with fast bow shocks moving through such active regions.

scholarly journals Strong magnetic fields in bipolar outflows

1991 ◽  
Vol 147 ◽  
pp. 373-376
Author(s):  
M. D. Smith ◽  
P. W. J. L. Brand ◽  
A. Moorhouse
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Molecular Hydrogen ◽  
Active Regions ◽  
Young Star ◽  
Molecular Gas ◽  
Bipolar Outflows ◽  
Strong Magnetic Fields ◽  
Bow Shocks ◽  
The Magnetic Field

A supersonic wind from a young star will produce regions of strong magnetic field in the stellar environment. The associated shocks compress the molecular gas, increasing the density n, pressure p, and field B. Crucially, the Alfvén speed, vA∝ B/n1/2, is also increased since the total shock compression is approximately of the form B ∝ n. But is there any evidence for such high vA- or ‘active cloud’ - regions within bipolar outflows? We indicate below one implication which has important observable consequences: fast shocks of low Alfvén number (v/vA) now arise. With a low ionization level, the C-shock structure is qualitatively different from the high Alfvén number flows which are common to ‘quiescent cloud’ conditions. The magnetic-field cushioning now allows molecular hydrogen to survive very fast shocks and broad H2 lines are feasible. We display results which show that the resolved broad lines and line ratio properties in the OMC-1 outflow can be explained with fast bow shocks moving through such active regions.

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.

scholarly journals Nonlinear force-free modeling of magnetic fields in flare-productive active regions

2015 ◽  
Vol 11 (S320) ◽  
pp. 167-174
Author(s):  
M. S. Wheatland ◽  
S. A. Gilchrist
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Boundary Data ◽  
Numerical Solutions ◽  
Free Field ◽  
Active Regions ◽  
Coronal Magnetic Field ◽  
Nonlinear Force ◽  
The Magnetic Field ◽  
Force Free Field

AbstractWe review nonlinear force-free field (NLFFF) modeling of magnetic fields in active regions. The NLFFF model (in which the electric current density is parallel to the magnetic field) is often adopted to describe the coronal magnetic field, and numerical solutions to the model are constructed based on photospheric vector magnetogram boundary data. Comparative tests of NLFFF codes on sets of boundary data have revealed significant problems, in particular associated with the inconsistency of the model and the data. Nevertheless NLFFF modeling is often applied, in particular to flare-productive active regions. We examine the results, and discuss their reliability.

Magnetic Fields and Disks in Star-forming Regions

1993 ◽  
Vol 10 (3) ◽  
pp. 247-249 ◽  
Author(s):  
C.M. Wright ◽  
D.K. Aitken ◽  
C.H. Smith ◽  
P.F. Roche
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Transverse Component ◽  
Young Stellar Objects ◽  
Stellar Objects ◽  
Star Forming ◽  
Star Forming Regions ◽  
Molecular Outflow ◽  
The Magnetic Field

AbstractThe star-formation process is an outstanding and largely unsolved problem in astrophysics. The role of magnetic fields is unclear but is widely considered to be important at all stages of protostellar evolution, from cloud collapse to ZAMS. For example, in some hydromagnetic models, the field may assist in removing angular momentum, thereby driving accretion and perhaps bipolar outflows.Spectropolarimetry between 8 and 13μm provides information on the direction of the transverse component of a magnetic field through the alignment of dust grains. We present results of 8–13μm spectropolarimetric observations of a number of bipolar molecular outflow sources, and compare the field directions observed with the axes of the outflows and putative disk-like structures observed to be associated with some of the objects. There is a strong correlation, though so far with limited statistics, between the magnetic field and disk orientations. We compare our results with magnetic field configurations predicted by current models for hydromagnetically driven winds from the disks around Young Stellar Objects (YSOs). Our results appear to argue against the Pudritz and Norman model and instead seem to support the Uchida and Shibata model.

Solar flare forecasting model using 3D magnetic field data

2020 ◽  
Author(s):  
Xin Huang
Keyword(s):  
Magnetic Field ◽  
Deep Learning ◽  
Solar Flare ◽  
Solar Flares ◽  
Field Data ◽  
Active Regions ◽  
Forecasting Model ◽  
Magnetic Field Data ◽  
The Magnetic Field

<p>Solar flares originate from the release of the energy stored in the magnetic field of solar active regions. Generally, the photospheric magnetograms of active regions are used as the input of the solar flare forecasting model. However, solar flares are considered to occur in the low corona. Therefore, the role of 3D magnetic field of active regions in the solar flare forecast should be explored. We extrapolate the 3D magnetic field using the potential model for all the active regions during 2010 to 2017, and then the deep learning method is applied to extract the precursors of solar flares in the 3D magnetic field data. We find that the 3D magnetic field of active regions is helpful to build a deep learning based forecasting model.</p>

Cyclotron Lines in the Spectra of Solar Flares and Solar Active Regions

1989 ◽  
Vol 104 (1) ◽  
pp. 449-456
Author(s):  
V. V. Zheleznyakov ◽  
E. Ya. Zlotnik
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Cross Section ◽  
Active Regions ◽  
Kinetic Temperature ◽  
Magnetic Tube ◽  
Tube Cross Section ◽  
Solar Active Regions ◽  
Electron Gyrofrequency ◽  
The Magnetic Field

AbstractIt was shown by Zheleznyakov and Zlotnik (1980a, b) that in complex configurations of solar magnetic fields (in hot loops above the active centres, in neutral current sheets in the preflare phase, in hot X-ray kernels in the initial flare phase) a system of cyclotron lines in the spectrum of microwave radiation is likely to be formed. Such a line was obtained by Willson (1985) in the VLA observations at harmonics of the electron gyrofrequency. This communication interprets these observations on the basis of an active region model in which thermal cyclotron radiation is produced by hot plasma filling the magnetic tube in the corona above a group of spots. In this model the frequency of the recorded 1658 MHz line corresponds to the third harmonic of electron gyrofrequency, which yields the magnetic field (196 + 4) G along the magnetic tube axis. The linewidth Af/f ∼ 0.1 is determined by the 10% inhomogeneity of the magnetic field over the cross-section of the tube; the line profile indicates the kinetic temperature distribution of electrons over the tube cross-section with the maximum value 4 x 106 K. Analysis shows that study of cyclotron lines can serve as an efficient tool for diagnostics of magnetic fields and plasma in the solar active regions and flares.

scholarly journals Open charm and charmonium states in strong magnetic fields

2021 ◽  
pp. 2150064
Author(s):  
Amruta Mishra ◽  
S. P. Misra
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Constituent Quark ◽  
Open Charm ◽  
Charm Mesons ◽  
Strong Magnetic Fields ◽  
Decay Widths ◽  
State Formula ◽  
The Masses ◽  
The Magnetic Field

The mass modifications of the open charm ([Formula: see text] and [Formula: see text]) mesons, and their effects on the decay widths [Formula: see text] as well as of the charmonium state, [Formula: see text] to open charm mesons ([Formula: see text]), are investigated in the presence of strong magnetic fields. These are studied accounting for the mixing of the pseudoscalar ([Formula: see text]) and vector ([Formula: see text]) mesons ([Formula: see text], [Formula: see text] mixings), with the mixing parameter, [Formula: see text] of a phenomenological three-point ([Formula: see text]) vertex interaction determined from the observed radiative decay width of [Formula: see text]. For charged [Formula: see text] mixing, this parameter is dependent on the magnetic field, because of the Landau level contributions to the vacuum masses of these mesons. The masses of the charged [Formula: see text] and [Formula: see text] mesons modified due to [Formula: see text] mixing, in addition, have contributions from the lowest Landau levels in the presence of a strong magnetic field. The effects of the magnetic field on the decay widths are studied using a field theoretical model of composite hadrons with quark (and antiquark) constituents. The matrix elements for these decays are evaluated using the light quark–antiquark pair creation term of the free Dirac Hamiltonian for the constituent quark field, with explicit constructions for the charmonium state [Formula: see text], the open charm ([Formula: see text], [Formula: see text], [Formula: see text]) mesons and the pion states in terms of the constituent quark fields. The parameter for the charged [Formula: see text] mixing is observed to increase appreciably with increase in the magnetic field. This leads to dominant modifications to their masses, and hence the decay widths of charged [Formula: see text] as well as [Formula: see text] at large values of the magnetic field. The modifications of the masses and decay widths of the open and hidden charm mesons in the presence of strong magnetic fields should have observable consequences on the production of the open charm ([Formula: see text] and [Formula: see text]) mesons as well as of the charmonium states resulting from noncentral ultra-relativistic heavy ion collision experiments.

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