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1.
We consider the physical origin of the hemispheric pattern of filament chirality on the Sun. Our 3D simulations of the coronal
field evolution over a period of six months, based on photospheric magnetic measurements, were previously shown to be highly
successful at reproducing observed filament chiralities. In this paper we identify and describe the physical mechanisms responsible
for this success. The key mechanisms are found to be (1) differential rotation of north – south polarity inversion lines,
(2) the shape of bipolar active regions, and (3) evolution of skew over a period of many days. As on the real Sun, the hemispheric
pattern in our simulations holds in a statistical sense. Exceptions arise naturally for filaments in certain locations relative
to bipolar active regions or from interactions among a number of active regions. 相似文献
2.
Using data from the Transition Region and Coronal Explorer (TRACE), Solar and Heliospheric Observatory (SOHO), Ramaty High Energy Solar Spectroscopic Imager (RHESSI), and Hida Observatory (HO), we present a detailed study of an EUV jet and the associated Hα filament eruption in
a major flare in the active region NOAA 10044 on 29 July 2002. In the Hα line wings, a small filament was found to erupt out
from the magnetic neutral line of the active region during the flare. Two bright EUV loops were observed rising and expanding
with the filament eruption, and both hot and cool EUV plasma ejections were observed to form the EUV jet. The two thermal
components spatially separated from each other and lasted for about 25 minutes. In the white-light corona data, a narrow coronal
mass ejection (CME) was found to respond to this EUV jet. We cannot find obvious emerging flux in the photosphere accounting
for the filament eruption and the EUV jet. However, significant sunspot decay and magnetic-flux cancelation owing to collision
of opposite flux before the events were noticed. Based on the hard X-ray data from RHESSI, which showed evidence of magnetic
reconnection along the main magnetic neutral line, we think that all of the observed dynamical phenomena, including the EUV
jet, filament eruption, flare, and CME, should have a close relation to the flux cancelation in the low atmosphere. 相似文献
3.
This paper considers the hemispheric pattern of solar filaments using newly developed simulations of the real photospheric
and 3D coronal magnetic fields over a six-month period, on a global scale. The magnetic field direction in the simulation
is compared directly with the chirality of observed filaments, at their observed locations. In our model the coronal field
evolves through a continuous sequence of nonlinear force-free equilibria, in response to the changing photospheric boundary
conditions and the emergence of new magnetic flux. In total 119 magnetic bipoles with properties matching observed active
regions are inserted. These bipoles emerge twisted and inject magnetic helicity into the solar atmosphere. When we choose
the sign of this active-region helicity to match that observed in each hemisphere, the model produces the correct chirality
for up to 96% of filaments, including exceptions to the hemispheric pattern. If the emerging bipoles have zero helicity, or
helicity of the opposite sign, then this percentage is much reduced. In addition, the simulation produces a higher proportion
of filaments with the correct chirality after longer times. This indicates that a key element in the evolution of the coronal
field is its long-term memory, and the build-up and transport of helicity from low to high latitudes over many months. It
highlights the importance of continuous evolution of the coronal field, rather than independent extrapolations at different
times. This has significant consequences for future modelling such as that related to the origin and development of coronal
mass ejections. 相似文献
4.
We study the topology of the 3D magnetic field in a filament channel to address the following questions: Is a filament always formed in a single flux tube? How does the photospheric magnetic field lead to filament interruptions and to feet formation? What is the relation between feet-related field lines and the parasitic polarities? What can topological analyses teach us about EUV filament channels? To do so, we consider a filament observed on 6 October 2004 with THEMIS/MTR, in Hα with the full line profile simultaneously and cospatially with its photospheric vector magnetic field. The coronal magnetic field was calculated from a “linear magnetohydrostatic” extrapolation of a composite THEMIS-MDI magnetogram. Its free parameters were adjusted to get the best match possible between the distribution of modeled plasma-supporting dips and the Hα filament morphology. The model results in moderate plasma β≤1 at low altitudes in the filament, in conjunction with non-negligible departures from force-freeness measured by various metrics. The filament here is formed by a split flux tube. One part of the flux tube is rooted in the photosphere aside an observed interruption in the filament. This splitted topology is due to strong network polarities on the edge of the filament channel, not to flux concentrations closer to the filament. We focus our study to the northwest portion of the filament. The related flux tube is highly fragmented at low altitudes. This fragmentation is due to small flux concentrations of two types. First, some locally distort the tube, leading to noticeable thickness variations along the filament body. Second, parasitic polarities, associated with filament feet, result in secondary dips above the related local inversion line. These dips belong to long field lines that pass below the flux tube. Many of these field lines are not rooted near the related foot. Finally, the present model shows that the coronal void interpretation cannot be ruled out to interpret the wideness of EUV filament channels. 相似文献
5.
Statistical Assessment of Photospheric Magnetic Features in Imminent Solar Flare Predictions 总被引:1,自引:0,他引:1
Hui Song Changyi Tan Ju Jing Haimin Wang Vasyl Yurchyshyn Valentyna Abramenko 《Solar physics》2009,254(1):101-125
In this study we use the ordinal logistic regression method to establish a prediction model, which estimates the probability
for each solar active region to produce X-, M-, or C-class flares during the next 1-day time period. The three predictive
parameters are (1) the total unsigned magnetic flux T
flux, which is a measure of an active region’s size, (2) the length of the strong-gradient neutral line L
gnl, which describes the global nonpotentiality of an active region, and (3) the total magnetic dissipation E
diss, which is another proxy of an active region’s nonpotentiality. These parameters are all derived from SOHO MDI magnetograms.
The ordinal response variable is the different level of solar flare magnitude. By analyzing 174 active regions, L
gnl is proven to be the most powerful predictor, if only one predictor is chosen. Compared with the current prediction methods
used by the Solar Monitor at the Solar Data Analysis Center (SDAC) and NOAA’s Space Weather Prediction Center (SWPC), the
ordinal logistic model using L
gnl, T
flux, and E
diss as predictors demonstrated its automatic functionality, simplicity, and fairly high prediction accuracy. To our knowledge,
this is the first time the ordinal logistic regression model has been used in solar physics to predict solar flares. 相似文献
6.
利用最小二乘法拟合了1995年1月至2001年9月Wind卫星观测到的行星际磁通量绳。根据拟合所得磁通量绳的直径,分析了行星际磁通量绳在这段时间内的发生率随磁通量绳直径D变化的关系,发现磁通量绳的发生率P(D)随直径D的变化可近似以幂律形式表示为:P(D)≈64D-0.768。行星际磁通量绳的发生率相对其直径的幂律分布表明所有行星际磁通量绳很可能是同一类现象且有共同的源,即它们都是太阳上日冕物质抛射的行星际对应物,只不过小尺度的磁通量绳对应较小的日冕物质抛射。最后,对行星际磁通量绳、日冕物质抛射和太阳耀斑的可能关系做了讨论。 相似文献
7.
The occurrence of a large number of high and low amplitude anisotropic wave train events over the years 1981–1994 has been examined along with the different solar features. The results indicate that the time of maximum of diurnal variation significantly remains in the 18-h direction for majority of the high and low amplitude wave trains. The amplitude of diurnal anisotropy remains significantly high and phase shifts towards earlier hours as compared to the quite day annual average values for majority of the HAEs. The diurnal amplitude remains significantly low and phase shifts towards earlier hours as compared to the quiet day annual average values for majority of the LAEs. The occurrence of these enhanced/low amplitude events is found to be dominant during the positive polarity of the Bz component of the interplanetary magnetic field. The amplitude of the diurnal anisotropy of these events is found to increase on the days of magnetic cloud as compared to the days prior to the event and it found to decrease during the later period of the event as the cloud passes the Earth. The high-speed solar wind streams do not play any significant role in causing these types of events. The interplanetary disturbances (magnetic clouds) are also effective in producing cosmic ray decreases. 相似文献
8.
A. M. Uralov V. V. Grechnev G. V. Rudenko I. G. Rudenko H. Nakajima 《Solar physics》2008,249(2):315-335
Neutral Line associated Sources (NLSs) are quasi-stationary microwave sources projected onto vicinities of the neutral line
of the photospheric magnetic field. NLSs are often precursors of powerful flares, but their nature is unclear. We endeavor
to reveal the structure of an NLS and to analyze a physical connection between such a source with a site of energy release
in the corona above NOAA 10488 (October/November 2003). Evolution of this AR includes emergence and collision of two bipolar
magnetic structures, rise of the main magnetic separator, and the appearance of an NLS underneath. The NLS appears at a contact
site of colliding sunspots, whose relative motion goes on, resulting in a large shear along a tangent. Then the nascent NLS
becomes the main source of microwave fluctuations in the AR. The NLS emission at 17 GHz is dominated by either footpoints
or the top of a loop-like structure, an NLS loop, which connects two colliding sunspots. During a considerable amount of time,
the emission dominates over that footpoint of the NLS loop, where the magnetic field is stronger. At that time, the NLS resembles
a usual sunspot–associated radio source, whose brightness center is displaced towards the periphery of a sunspot. Microwave
emission of an X2.7 flare is mainly concentrated in an ascending flare loop, initially coinciding with the NLS loop. The top
of this loop is located at the base of a non-uniform bar-like structure visible in soft X-rays and at 34 GHz at the flare
onset. We reveal i) upward lengthening of this bar before the flare onset, ii) the motion of the top of an apparently ascending flare loop along the axis of this bar, and iii) a non-thermal microwave source, whose descent along the bar was associated with the launching of a coronal ejection. We
connect the bar with a probable position of a nearly vertical diffusion region, a site of maximal energy release inside an
extended pre-flare current sheet. The top of the NLS loop is located at the bottom of this region. A combination of the NLS
loop and diffusion region constitutes the skeleton of a quasi-stationary microwave NLS. 相似文献
9.
观测研究表明有利于磁重联的新浮磁流与日冕物质抛射(CME)有密切关系.利用数值模拟的方法,新浮磁流触发CME的物理模型对观测结果进行了物理解释.基于这种模型,不考虑重力和热传导, 2.5维的数值模拟的理论结果显示:是否能够触发暗条爆发及CME,取决于新浮磁流磁通量的大小、浮现的位置以及其磁极走向,并给出了能够触发暗条爆发与不能触发爆发的参数空间.利用2002年和2003年的15个暗条爆发事例以及2002年的44个非爆发事例,对新浮磁流磁通量的大小、浮现的位置以及磁极走向进行了统计研究.结果表明并非所有的新浮磁流都能够使暗条失去平衡,形成CME.统计结果基本上支持了数值模拟的理论结果.这个结果可为空间天气预报研究提供有用的参考信息. 相似文献
10.
V. E. Abramov-Maksimov G. F. Vyalshin G. B. Gelfreikh V. I. Shatilov 《Solar physics》1996,164(1-2):333-343
In the present paper we present the results of measurement of magnetic fields in some sunspots at different heights in the solar atmosphere, based on simultaneous optical and radio measurements. The optical measurements were made by traditional photographic spectral observations of Zeeman splitting in a number of spectral lines originating at different heights in the solar photosphere and chromosphere. Radio observations of the spectra and polarization of the sunspot - associated sources were made in the wavelength range of 2–4 cm using large reflector-type radio telescope RATAN-600. The magnetic field penetrating the hot regions of the solar atmosphere were found from the shortest wavelength of generation of thermal cyclotron emission (presumably in the third harmonic of electron gyrofrequency). For all the eight cases under consideration we have found that magnetic field first drops with height, increases from the photosphere to lower chromosphere, and then decreases again as we proceed to higher chromosphere and chromosphere-corona transition region. Radio measurements were found to be well correlated with optical measurements of magnetic fields for the same sunspot. An alternative interpretation implies that different lines used for magnetic field measurements refer to different locations on the solar surface. If this is the case, then the inversion in vertical gradients of magnetic fields may not exist above the sunspots. Possible sources of systematic and random errors are also discussed. 相似文献
11.
M. L. Demidov E. M. Golubeva H. Balthasar J. Staude V. M. Grigoryev 《Solar physics》2008,250(2):279-301
In this paper we analyze the distribution of magnetic strength ratios (MSR) across the solar disk using magnetograms in different
spectral lines from the same observatory (Mount Wilson Observatory (MWO) and Sayan Observatory (SO)), magnetograms in the
same line from different observatories (MWO, SO, Wilcox Solar Observatory (WSO)), and in different spectral lines from different
observatories (the three observatories mentioned above, the National Solar Observatory/Kitt Peak (KP) and Michelson Doppler
Imager (MDI) on board Solar and Heliospheric Observatory (SoHO)). We find peculiarities in some combinations of data sets.
Besides the expected MSR center-to-limb variations, there is an equator-to-pole asymmetry, especially in the near-limb areas.
Therefore, it is generally necessary to use 2D matrices of correction coefficients to reduce one kind of observation into
another one. 相似文献
12.
The evolution of the current sheet in the electric current direction (in the guiding magnetic field direction) is studied
numerically in the 3-D particle-in-cell model with two current sheets and periodic boundary conditions. In the regime with
(where v
D and
are the electric current drift and electron thermal velocities, respectively) the current sheets are unstable owing to the
Buneman and kink instabilities and become strongly fragmented. During their evolution, in addition to an increase of the energy
of the electric field component in the guiding magnetic field direction, the energies of the electric field components in
the perpendicular direction are even more enhanced. In the current sheet the anomalous resistivity (η
anom/η
C∼7×105, where η
C is the classical resistivity) is generated and thus the magnetic field dissipates. Most of the dissipated magnetic energy
is transformed into the electron kinetic energy in the direction of the electric current. The associated electric field accelerates
the electrons from the tail of the distribution function. 相似文献
13.
The non-axisymmetric, non-dipolar magnetic fields of Uranus and Neptune are markedly different from the axially-dipolar dominated fields of the other planets in our Solar System with active dynamos. Stanley and Bloxham [Stanley, S., Bloxham, J., 2004. Nature 428, 151-153] used numerical modeling to demonstrate that Uranus' and Neptune's unusual fields could be the result of a different convective region geometry in these planets. They found that a numerical dynamo operating in a thin shell surrounding a stably-stratified fluid interior produces magnetic field morphologies similar to those of Uranus and Neptune. This geometry for the convective region was initially proposed by Hubbard et al. [Hubbard, W.B., Podolak, M., Stevenson, D.J., 1995. In: Cruickshank, D. (Ed.), Neptune and Triton. Univ. of Arizona Press, Tucson, pp. 109-138] to explain both the magnetic field morphology as well as the low intrinsic heat flows from these planets. Here we examine the influence of varying the stable layer radius in numerical models and compare the results to thin shell models surrounding solid inner cores. We find that a limited range of stable-layer shell thicknesses exist in which Uranus/Neptune-like field morphologies result. This allows us to put constraints on the size of the convective layers in Uranus and Neptune. 相似文献
14.
In this study we present a review of low-temperature magnetic properties of alabandite (Fe, Mn)S, daubreelite FeCr2S4, pyrrhotite Fe1−xS and troilite FeS updated with new experimental data. The results indicate that besides FeNi alloys mainly daubreelite with its Curie temperature TC ∼ 150 K and strong induced and remanent magnetizations may be a significant magnetic mineral in cold environments and may complement that of FeNi or even dominate magnetic properties of sulfide rich bodies at temperatures below TC.Comets are known to contain iron-bearing sulfides within dusty fraction and their surfaces are subject to temperature variations in the range of 100-200 K down to the depth of several meters while the cometary interior is thermally stable at several tens of Kelvin which is within the temperature range where alabandite, daubreelite or troilite are “magnetic”. Thus not only FeNi alloys, but also sulfides have to be considered in the interpretation of magnetic data from cometary objects such as will be delivered by Rosetta mission. Modeling indicates that magnetic interactions between cometary nucleus containing iron-bearing sulfides and interplanetary magnetic field would be difficult, but not impossible, to detect from orbit. Rosetta’s Philae lander present on the surface would provide more reliable signal. 相似文献
15.
A substantial part of Mercury's iron core may be stably stratified because the temperature gradient is subadiabatic. A dynamo would operate only in a deep sublayer. We show that such a situation arises for a wide range of values for the heat flow and the sulfur content in the core. In Saturn the upper part of the metallic hydrogen core could be stably stratified because of helium depletion. The magnetic field is unusually weak in the case of Mercury and unusually axisymmetric at Saturn. We study numerical dynamo models in rotating spherical shells with a stable outer region. The control parameters are chosen such that the magnetic Reynolds number is in the range of expected Mercury values. Because of its slow rotation, Mercury may be in a regime where the dipole contribution to the internal magnetic field is weak. Most of our models are in this regime, where the dynamo field consists mainly of rapidly varying higher multipole components. They can hardly pass the stable conducting layer because of the skin effect. The weak low-degree components vary more slowly and control the structure of the field outside the core, whose strength matches the observed field strength at Mercury. In some models the axial dipole dominates at the planet's surface and in others the axial quadrupole is dominant. Differential rotation in the stable layer, representing a thermal wind, is important for attenuating non-axisymmetric components in the exterior field. In some models that we relate to Saturn the axial dipole is intrinsically strong inside the dynamo. The surface field strength is much larger than in the other cases, but the stable layer eliminates non-axisymmetric modes. The Messenger and Bepi Colombo space missions can test our predictions that Mercury's field is large-scaled, fairly axisymmetric, and shows no secular variations on the decadal time scale. 相似文献
16.
M. S. Wheatland 《Solar physics》2007,245(2):251-262
Improvements to an existing method for calculating nonlinear force-free magnetic fields (Wheatland, Solar Phys. 238, 29, 2006) are described. In particular a solution of the 3-D Poisson equation using 2-D Fourier transforms is presented. The improved
nonlinear force-free method is demonstrated in application to linear force-free test cases with localized nonzero values of
the normal component of the field in the boundary. These fields provide suitable test cases for nonlinear force-free calculations
because the boundary conditions involve localized nonzero values of the normal components of the field and of the current
density, and because (being linear force-free fields) they have more direct numerical solutions. Despite their simplicity,
fields of this kind have not been recognized as test cases for nonlinear methods before. The examples illustrate the treatment
of the boundary conditions on current in the nonlinear force-free method, and in particular the limitations imposed by field
lines that connect outside of the boundary region. 相似文献
17.
Observations of the strength and spatial distribution of vector magnetic fields in active regions have revealed several fundamental
properties of the twist of their magnetic fields. First, the handedness of this twist obeys a hemispheric rule: left-handed
in the northern hemisphere, right-handed in the southern. Second, the rule is weak; active regions often disobey it. It is
statistically valid only in a large ensemble. Third, the rule itself, and the amplitude of the scatter about the rule, are
quantitatively consistent with twisting of fields by turbulence as flux tubes buoy up through the convection zone. Fourth,
there is considerable spatial variation of twist within active regions. However, relaxation to a linear force-free state,
which has been documented amply in laboratory plasmas, is not observed. 相似文献
18.
Eric G. Blackman 《Astrophysics and Space Science》2007,307(1-3):7-10
The absence of other viable momentum sources for collimated flows leads to the likelihood that magnetic fields play a fundamental
role in jet launch and/or collimation in astrophysical jets. To best understand the physics of jets, it is useful to distinguish
between the launch region where the jet is accelerated and the larger scales where the jet propagates as a collimated structure.
Observations presently resolve jet propagation, but not the launch region. Simulations typically probe the launch and propagation
regions separately, but not both together. Here, I IDentify some of the physics of jet launch vs. propagation and what laboratory
jet experiments to date have probed. Reproducing an astrophysical jet in the lab is unrealistic, so maximizing the benefit
of the experiments requires clarifying the astrophysical connection. 相似文献
19.
. Nordlund S. B. F. Dorch R. F. Stein 《Journal of Astrophysics and Astronomy》2000,21(3-4):307-313
We review current understanding of the interaction of magnetic fields with convective motions in stellar convection zones.
Among the most exciting recent results is the discovery that magnetic fields need not primarily be confined to the stable
layer below the convection zone; numerical simulations have shown that surprisingly, strong magnetic fields can be maintained
in the interior of the convection zone. 相似文献
20.
The atmospheres of Jupiter and Saturn exhibit strong and stable zonal winds. How deep the winds penetrate unabated into each planet is unknown. Our investigation favors shallow winds. It consists of two parts. The first part makes use of an Ohmic constraint; Ohmic dissipation associated with the planet's magnetic field cannot exceed the planet's net luminosity. Application to Jupiter (J) and Saturn (S) shows that the observed zonal winds cannot penetrate below a depth at which the electrical conductivity is about six orders of magnitude smaller than its value at the molecular-metallic transition. Measured values of the electrical conductivity of molecular hydrogen yield radii of maximum penetration of 0.96RJ and 0.86RS, with uncertainties of a few percent of R. At these radii, the magnetic Reynolds number based on the zonal wind velocity and the scale height of the magnetic diffusivity is of order unity. These limits are insensitive to difficulties in modeling turbulent convection. They permit complete penetration along cylinders of the equatorial jets observed in the atmospheres of Jupiter and Saturn. The second part investigates how deep the observed zonal winds actually do penetrate. As it applies heuristic models of turbulent convection, its conclusions must be regarded as tentative. Truncation of the winds in the planet's convective envelope would involve breaking the Taylor-Proudman constraint on cylindrical flow. This would require a suitable nonpotential acceleration which none of the obvious candidates appears able to provide. Accelerations arising from entropy gradients, magnetic stresses, and Reynolds stresses appear to be much too weak. These considerations suggest that strong zonal winds are confined to shallow, stably stratified layers, with equatorial jets being the possible exception. 相似文献