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1.
The availability of vector-magnetogram sequences with sufficient accuracy and cadence to estimate the temporal derivative
of the magnetic field allows us to use Faraday’s law to find an approximate solution for the electric field in the photosphere,
using a Poloidal–Toroidal Decomposition (PTD) of the magnetic field and its partial time derivative. Without additional information,
however, the electric field found from this technique is under-determined – Faraday’s law provides no information about the
electric field that can be derived from the gradient of a scalar potential. Here, we show how additional information in the
form of line-of-sight Doppler-flow measurements, and motions transverse to the line-of-sight determined with ad-hoc methods such as local correlation tracking, can be combined with the PTD solutions to provide much more accurate solutions
for the solar electric field, and therefore the Poynting flux of electromagnetic energy in the solar photosphere. Reliable,
accurate maps of the Poynting flux are essential for quantitative studies of the buildup of magnetic energy before flares
and coronal mass ejections. 相似文献
2.
Kenneth H. Schatten 《Solar physics》2009,255(1):3-38
Photospheric ephemeral regions (EPRs) cover the Sun like a magnetic carpet. From this, we update the Babcock – Leighton solar
dynamo. Rather than sunspot fields appearing in the photosphere de novo from eruptions originating in the deep interior, we consider that sunspots form directly in the photosphere by a rapid accumulation
of like-sign field from EPRs. This would only occur during special circumstances: locations and times when the temperature
structure is highly superadiabatic and contains a large subsurface horizontal magnetic field (only present in the Sun’s lower
latitudes). When these conditions are met, superadiabatic percolation occurs, wherein an inflow and downflow of gas scours
the surface of EPRs to form active regions. When these conditions are not met, magnetic elements undergo normal percolation,
wherein magnetic elements move about the photosphere in Brownian-type motions. Cellular automata (CA) models are developed
that allow these processes to be calculated and thereby both small-scale and large-scale models of magnetic motions can be
obtained. The small-scale model is compared with active region development and Hinode observations. The large-scale CA model offers a solar dynamo, which suggests that fields from decaying bipolar magnetic regions
(BMRs) drift on the photosphere driven by subsurface magnetic forces. These models are related to observations and are shown
to support Waldmeier’s findings of an inverse relationship between solar cycle length and cycle size. Evidence for significant
amounts of deep magnetic activity could disprove the model presented here, but recent helioseismic observations of “butterfly
patterns” at depth are likely just a reflection of surface activity. Their existence seems to support the contention made
here that the field and flow separate, allowing cool, relatively field-free downdrafts to descend with little field into the
nether worlds of the solar interior. There they heat by compression to form a hot solar-type Santa Ana wind deep below active
regions. 相似文献
3.
4.
By using a topological model for the potential magnetic field above the photosphere, the appearance and development of the separator as a result of vortex plasma flows in the locality of the photospheric neutral line is considered. The possible relation of such vortex flows with a flare activity is revealed. The arrangement and shape of the flare ribbons in the chromosphere, the formation of X-ray intersecting loops, the early appearance of bright knots on flare ribbon edges are naturally explained by the model provided a reconnecting current sheet arises along the separator in the coronal magnetic field of active regions as a result of the evolution of the magnetic field sources in the photosphere. 相似文献
5.
Thomas R. Metcalf Marc L. DeRosa Carolus J. Schrijver Graham Barnes Adriaan A. van Ballegooijen Thomas Wiegelmann Michael S. Wheatland Gherardo Valori James M. McTtiernan 《Solar physics》2008,247(2):269-299
We compare a variety of nonlinear force-free field (NLFFF) extrapolation algorithms, including optimization, magneto-frictional,
and Grad – Rubin-like codes, applied to a solar-like reference model. The model used to test the algorithms includes realistic
photospheric Lorentz forces and a complex field including a weakly twisted, right helical flux bundle. The codes were applied
to both forced “photospheric” and more force-free “chromospheric” vector magnetic field boundary data derived from the model.
When applied to the chromospheric boundary data, the codes are able to recover the presence of the flux bundle and the field’s
free energy, though some details of the field connectivity are lost. When the codes are applied to the forced photospheric
boundary data, the reference model field is not well recovered, indicating that the combination of Lorentz forces and small
spatial scale structure at the photosphere severely impact the extrapolation of the field. Preprocessing of the forced photospheric
boundary does improve the extrapolations considerably for the layers above the chromosphere, but the extrapolations are sensitive
to the details of the numerical codes and neither the field connectivity nor the free magnetic energy in the full volume are
well recovered. The magnetic virial theorem gives a rapid measure of the total magnetic energy without extrapolation though,
like the NLFFF codes, it is sensitive to the Lorentz forces in the coronal volume. Both the magnetic virial theorem and the
Wiegelmann extrapolation, when applied to the preprocessed photospheric boundary, give a magnetic energy which is nearly equivalent
to the value derived from the chromospheric boundary, but both underestimate the free energy above the photosphere by at least
a factor of two. We discuss the interpretation of the preprocessed field in this context. When applying the NLFFF codes to
solar data, the problems associated with Lorentz forces present in the low solar atmosphere must be recognized: the various
codes will not necessarily converge to the correct, or even the same, solution.
On 07/07/2007, the NLFFF team was saddened by the news that Tom Metcalf had died as the result of an accident. We remain grateful
for having had the opportunity to benefit from his unwavering dedication to the problems encountered in attempting to understand
the Sun’s magnetic field; Tom had completed this paper several months before his death, leading the team through the many
steps described above. 相似文献
6.
In this paper we consider a random motion of magnetic bright points (MBP) associated with magnetic fields at the solar photosphere.
The MBP transport in the short time range [0–20 minutes] has a subdiffusive character as the magnetic flux tends to accumulate
at sinks of the flow field. Such a behavior can be rigorously described in the framework of a continuous time random walk
leading to the fractional Fokker-Planck dynamics. This formalism, applied for the analysis of the solar subdiffusion of magnetic
fields, generalizes the Leighton’s model.
相似文献
7.
Equilibrium configuration of the magnetosphere of a star loaded by the gravitationally accreted plasma having its own magnetic
field is investigated. Axisymmetry around the star’s magnetic axis is assumed for simplicity. It is seen that two distinct
configurations appear for the cases of parallel and antiparallel magnetic field of the accreted plasma with respect to the
star’s magnetic moment. If the external field is antiparallel to the star’s magnetic moment, the stellar magnetosphere is
confined within a spherical region surrounded by the external field with a separatric surface between them. This is an extension
of the case of the spherical accretion of non-magnetic plasma dealt with thus far in connection with the mass accretion by
the degenerate stars in X-ray binaries. It is noticed that the mass slides down along the field lines to the point closest
to the star and is stratified hydrostatically in equilibrium to form a disk in the equatorial plane. The mass loading compresses
the sphere as a whole in this case. If, on the other hand, the external field is parallel to the star’s magnetic moment, there
appears a ring of magnetic neutral point in the equatorial plane. Polar field is open and extends to infinity while the low-latitude
field is closed and faces the external field of opposite polarity across the neutral point. The increase of the loaded mass
in this case causes a shrink of the closed field region, and the open polar flux is increased. Therefore, the transition between
equilibria with small and large amount of the loaded mass requires the reconnection of magnetic lines of force, and the reconnection
of the flux through the magnetic neutral ring is proposed as the mechanism of the steady or the intermittent mass leakage
like the ones postulated for some X-ray bursters.
Visiting Scientist supported by the Japan Society for the Promotion of Sciences. 相似文献
8.
The first aim of the present work is to compute a more accurate and recent model for the Earth’s magnetic field. The second
aim is to determine the effects of the Earth’s magnetic field on the motion of a charged artificial satellite to evaluate
the variations of the orbital elements of the satellite due to these effects. The magnetic field and its variation with time
have been studied at different heights, longitudes and latitudes. The geomagnetic field is considered as a multiple potential
field and the electrical charge of the satellite is assumed to be constant. A new computer code has been constructed to follow
the components of the magnetic field in spherical harmonic models. The Gauss equations are solved numerically. The results
concentrate on the computation of the numerical values of orbital perturbation for the case of a low Earth satellite. RS-1
satellite and space craft gravity probe B (GPB) are chosen as cases of studies for a detailed numerical analysis. 相似文献
9.
Working with a magnetic field periodic along Oz and decaying in time, we deal with the Dirac-type equation characterizing the fermions evolving in magnetar’s crust. For ultra-relativistic particles, one can employ the perturbative approach, to compute the conserved current density components. If the magnetic field is frozen and the magnetar is treated as a stationary object, the fermion’s wave function is expressed in terms of the Heun’s Confluent functions. Finally, we are extending some previous investigations on the linearly independent fermionic modes solutions to the Mathieu’s equation and we discuss the energy spectrum and the Mathieu Characteristic Exponent. 相似文献
10.
V. G. Fainshtein N. N. Stepanian Z. S. Akhtemov G. V. Rudenko E. V. Silakova 《Bulletin of the Crimean Astrophysical Observatory》2011,107(1):51-59
The radial component Br of magnetic field was calculated in the potential approximation and the synoptic maps of Br for several
heights in the Solar atmosphere were constructed based on observations of the photospheric magnetic field made on the old
magnetograph at the US Kitt Peak National Observatory and on the new SOLIS magnetograph at the US National Solar Observatory
for cycle 23 (the years 1997–2009). Parameters of large-scale structures of magnetic field with positive and negative polarities
were determined at seven heights in the Sun’s atmosphere—from the photosphere (H = Ro) to H = 2.5 Ro (Ro is the Solar radius). The processes of polar reversal for polar fields and changing of the sector structure
of the field at middle latitudes were observed. Characteristic lifespans and rotations were ascertained. The general picture
of variations of the large-scale solar magnetic field during cycle 23 was put forward. Two types of boundaries of large magnetic
structures at various heights were identified. 相似文献
11.
T. Wiegelmann 《Solar physics》2007,240(2):227-239
We describe a newly developed code for the extrapolation of nonlinear force-free coronal magnetic fields in spherical coordinates.
The program uses measured vector magnetograms on the solar photosphere as input and solves the force-free equations in the
solar corona. The method is based on an optimization principle and the heritage of the newly developed code is a corresponding
method in Cartesian geometry. We test the newly developed code with the help of a semi-analytic solution and rate the quality
of our reconstruction qualitatively by magnetic field line plots and quantitatively with a number of comparison metrics. We
find that we can reconstruct the original test field with high accuracy. The method is fast if the computation is limited
to low co-latitudes (say 30°≤θ≤150°), but it becomes significantly slower if the polar regions are included. 相似文献
12.
The aim of the present paper is to explore the mechanism of fast Sweet–Parker’s magnetic reconnection with the Cowling’s conductivity.
Cowling derived the resistivity of plasma with three components: electrons, ions and neutral particles in magnetic field theoretically
after Spitzer. The resistivity is much larger than the Spitzer’s. According to the idea of partially ionized plasmas ejected
into the corona as the trigger of flares, we adopt Cowling’s Conductivity to Sweet–Parker’s reconnection model in this paper.
The result shows that the reconnection rate can be improved a lot in solar corona and approaches the timescale of solar flare
in the absence of anomalous resistivity. 相似文献
13.
It is important to understand the complex topology of the magnetic field in the solar corona in order to be able to comprehend
the mechanisms which give rise to phenomena such as coronal loop structures and x-ray bright points. A key feature of the
magnetic topology is a separator. A magnetic separator is a field line which connects two magnetic null points, places where
the magnetic field becomes zero. A stable magnetic separator is important as it is the intersection of two separatrix surfaces.
These surfaces divide the magnetic field lines into regions of different connectivity, so a separator usually borders four
regions of field-line connectivity. This work examines the topological behaviour of separators that appear in a magnetic field
produced by a system of magnetic sources lying in a plane (the photosphere). The questions of how separators arise and are
destroyed, the topological conditions for which they exist, how they interact and their relevance to the coronal magnetic
field are addressed. 相似文献
14.
We present a series of numerical simulations of the quiet-Sun plasma threaded by magnetic fields that extend from the upper
convection zone into the low corona. We discuss an efficient, simplified approximation to the physics of optically thick radiative
transport through the surface layers, and investigate the effects of convective turbulence on the magnetic structure of the
Sun’s atmosphere in an initially unipolar (open field) region. We find that the net Poynting flux below the surface is on
average directed toward the interior, while in the photosphere and chromosphere the net flow of electromagnetic energy is
outward into the solar corona. Overturning convective motions between these layers driven by rapid radiative cooling appears
to be the source of energy for the oppositely directed fluxes of electromagnetic energy. 相似文献
15.
Observational conditions for the formation and maintenance of filaments are reviewed since 1989 in the light of recent findings
on their structure, chirality, inferred magnetic topology, and mass flows. Recent observations confirm the necessary conditions
previously cited: (1) their location at a boundary between opposite-polarity magnetic fields (2) a system of overlying coronal
loops, (3) a magnetically-defined channel beneath, (4) the convergence of the opposite-polarity network magnetic fields towards
their common boundary within the channel and (5) cancellation of magnetic flux at the common polarity boundary. Evidence is
put forth for three additional conditions associated with fully developed filaments: (A) field-aligned mass flows parallel
with their fine structure (B) a multi-polar background source of small-scale magnetic fields necessary for the formation of
the filament barbs and (C) a handedness property known as chirality which requires them to be either of two types, dextral
or sinistral. One-to-one relationships have been established between the chirality of filaments and the chirality of their
filament channels and overlying coronal arcades. These findings reinforce earlier evidence that every filament magnetic field
is separate from the magnetic field of the overlying arcade but both are parts of a larger magnetic field system. The larger
system has at least quadrupolar footprints in the photosphere and includes the filament channel and subphotospheric magnetic
fields, This ‘systems’ view of filaments and their environment enables new perspectives on why arcades and channels are invariable
conditions for their existence.
Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1005026814076 相似文献
16.
Fletcher Lyndsay López Fuentes Marcelo C. Mandrini Cristina H. Schmieder Brigitte Démoulin Pascal Mason Helen E. Young Peter R. Nitta Nariaki 《Solar physics》2001,203(2):255-287
We present multi-instrument observations of active region (AR) 8048, made between 3 June and 5 June 1997, as part of the SOHO
Joint Observing Program 33. This AR has a sigmoid-like global shape and undergoes transient brightenings in both soft X-rays
and transition region (TR) lines. We compute a magneto-hydrostatic model of the AR magnetic field, using as boundary condition
the photospheric observations of SOHO/MDI. The computed large-scale magnetic field lines show that the large-scale sigmoid
is formed by two sets of coronal loops. Shorter loops, associated with the core of the SXT emission, coincide with the loops
observed in the hotter CDS lines. These loops reveal a gradient of temperature, from 2 MK at the top to 1 MK at the ends.
The field lines most closely matching these hot loops extend along the quasi-separatrix layers (QSLs) of the computed coronal
field. The TR brightenings observed with SOHO/CDS can also be associated with the magnetic field topology, both QSL intersections
with the photosphere, and places where separatrices issuing from bald patches (sites where field lines coming from the corona
are tangent to the photosphere) intersect the photosphere. There are, furthermore, suggestions that the element abundances
measured in the TR may depend on the type of topological structure present. Typically, the TR brightenings associated with
QSLs have coronal abundances, while those associated with BP separatrices have abundances closer to photospheric values. We
suggest that this difference is due to the location and manner in which magnetic reconnection occurs in two different topological
structures.
Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1013302317042 相似文献
17.
Extrapolation codes for modelling the magnetic field in the corona in Cartesian geometry do not take the curvature of the
Sun’s surface into account and can only be applied to relatively small areas, e.g., a single active region. We apply a method for nonlinear force-free coronal magnetic field modelling of photospheric vector
magnetograms in spherical geometry which allows us to study the connectivity between multi-active regions. We use Vector Spectromagnetograph
(VSM) data from the Synoptic Optical Long-term Investigations of the Sun (SOLIS) survey to model the coronal magnetic field,
where we study three neighbouring magnetically connected active regions (ARs 10987, 10988, 10989) observed on 28, 29, and
30 March 2008, respectively. We compare the magnetic field topologies and the magnetic energy densities and study the connectivities
between the active regions. We have studied the time evolution of the magnetic field over the period of three days and found
no major changes in topologies, as there was no major eruption event. From this study we have concluded that active regions
are much more connected magnetically than the electric current. 相似文献
18.
G. Allen Gary 《Solar physics》2009,257(2):271-286
The minimum dissipative rate (MDR) method for deriving a coronal non-force-free magnetic field solution is partially evaluated.
These magnetic field solutions employ a combination of three linear (constant-α) force-free-field solutions with one being a potential field (i.e., α=0). The particular case of the solutions where the other two α’s are of equal magnitude but of opposite sign is examined. This is motivated by studying the SOLIS (Synoptic Optical Long-term
Investigation of the Sun (SOLIS), a National Solar Observatory facility) vector magnetograms of AR 10987, which show a global
α value consistent with an α=0 value as evaluated by (∇×B)
z
/B
z
over the region. Typical of the current state of the observing technology, there is no definitive twist for input into the
general MDR method. This suggests that the special α case, of two α’s with equal magnitudes and opposite signs, is appropriate given the data. Only for an extensively twisted active region
does a dominant, nonzero α normally emerge from a distribution of local values. For a special set of conditions, is it found that (i) the resulting
magnetic field is a vertically inflated magnetic field resulting from the electric currents being parallel to the photosphere,
similar to the results of Gary and Alexander (Solar Phys. 186:123, 1999), and (ii) for α≈(α
max /2), the Lorentz force per unit volume normalized by the square of the magnetic field is on the order of 1.4×10−10 cm−1. The Lorentz force (F
L) is a factor of ten higher than that of the magnetic force d(B
2/8π)/dz, a component of F
L. The calculated photospheric electric current densities are an order of magnitude smaller than the maximum observed in all
active regions. Hence both the Lorentz force density and the generated electric current density seem to be physically consistent
with possible solar dynamics. The results imply that the field could be inflated with an overpressure along the neutral line.
However, the implementation of this or any other extrapolation method using the electric current density as a lower boundary
condition must be done cautiously, with the current magnetography. 相似文献
19.
This paper presents an interpretation of the evolution of the vector magnetic field at the photosphere based on measurements of the advanced Stokes polarimeter, along with chromospheric H from the Lockheed instrument operating on La Palma and X-ray images of the corona from Yohkoh. These measurements are consistent with the emergence of a nearly closed magnetic structure from the solar interior into the corona. The highly non-potential field topology inferred from the data suggests that strong field-aligned currents exist in the emergent magnetic structure as it buoyantly rises through the photosphere. Material trapped in this closed structure is pulled upward to later condense into a prominence. By analogy of this small active region evolution with the observed properties of large quiescent prominences, we speculate that this process might also be operative on a much larger scale. A 3-dimensional magnetostatic model is presented which has many topological features in common with the observations. 相似文献
20.
Preliminary data on the magnetic field structure of the unique magnetic star HD 45583 are obtained. The observational data
are well described by a configuration of two magnetic dipoles located on opposite sides relative to the star’s center, with
their axes directed roughly in a radial direction. The positive monopoles are closer to the surface and the negative, closer
to the star’s center. For this reason, there appear to be two positive magnetic poles on the star’s surface but no negative
poles. The need for further observations of this unique object is pointed out.
Translated from Astrofizika, Vol. 52, No. 1, pp. 127–133 (February 2009). 相似文献