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1.
The formation of the penumbra of the leading spot of the active region NOAA 11117 has been studied using data fromthe Solar DynamicObservatory (SDO). HMI data on longitudinal magnetic fields, line-of-sight velocities, and continuum images were used. The appearance of localized upflows between the umbra and undisturbed photosphere precedes the penumbra formation. The sizes of them reach 1.5″–2″ and the velocity increases to 1 km/s over several minutes. These localized upflows change themselves to a region of material flowing horizontally from the penumbra (the Evershed effect). The formation of individual spine namely fine radial element of the penumbra magnetic field with higher strength and lower inclination than in the surrounding is traced for the first time. The formation of the spine manifests itself as appearance of region of 2″–3″ in size with enhanced upflow near the sunspot umbra, protrusion in longitudinal-field contours on one side of the upwelling center, and the subsequent appearance of magnetic pole of opposite polarity on the other side of the upwelling. This process is accompanied by a bending of the contour marking the boundary of the undisturbed photosphere, which puts the upwelling center in a zone of higher brightness. One possible explanation for this is the emergence of hot magnetic tube. The appearance and growth of the sunspot spines results in the formation of the penumbra. 相似文献
2.
A. V. Getling 《Astronomy Reports》2001,45(7):569-576
The well-known model that attributes the formation of a bipolar sunspot group to the emergence of a flux tube disagrees sharply with the usual observed pattern of phenomena. At the same time, the observed patterns can be accounted for quite convincingly in terms of local magnetic-field amplification due to cellular convective motions of the solar plasma. In this study, magnetoconvection in a plane horizontal fluid layer is simulated numerically in the framework of the fully nonlinear, three-dimensional problem. A weak horizontal magnetic field and weak cellular flow are assumed to be present initially. Convection is shown to be capable of producing bipolar magnetic configurations of the strongly amplified magnetic field. Indications of magnetic freezing of the flow in the cell are found. The action of the amplification mechanism under study may be controlled by the large-scale toroidal magnetic field of the Sun. 相似文献
3.
The rare phenomenon of the coalescence of two rotating sunspots of the same magnetic polarity during the emergence of the active region NOAA 11117 is investigated using data from the SDO space observatory. The coalescing spots rotated in opposite directions. The leading spot which formed from this process rotated counterclockwise with an angular velocity of 4°/h. A possible explanation is presented, based on a model of the emerging, twisted magnetic Ω flux tube that interacts with convective flows as it crosses the convective zone. 相似文献
4.
The evolution of photospheric velocities from the first minutes after the emergence of fresh magnetic flux and the formation
of the first pores in active region NOAA 10488 is studied with a time resolution of 1 min and spatial resolution of 4″. The
emerging magnetic flux of a major active region is initially a bundle of magnetic-flux loops. Some of these loops erupt through
the system of supergranular cells with speeds of up to 1 km/s within 15–25 min and form pores and small spots. It is suggested
that the development of a pore represents the emergence of a horizontal magnetic field, which is converted into elements with
a strong vertical magnetic field. The region of ascending plasma initially coincides with the zero line of a bipolar magnetic
pair. Downflow and upflow regions are related to and appear with the development of pores. During the first hours of their
evolution, the trailing-polarity pores exhibit downflows with mean speeds of ∼500 m/s, while upflows with speeds of ∼250 m/s
dominate near the leading-polarity pores. It is concluded that a matter flow from the leading to the trailing end is present
in the rising loop of a magnetic flux tube, in agreement with well-known numerical-simulation results. The flow that develops
in the magnetic-flux tube erupting through the convection zone persists when pores and small spots emerge in the photosphere,
at least during the first hours of their evolution. 相似文献
5.
The emergence of photospheric magnetic fields and the dynamics of the associated pattern of vertical motions in a developing active region are studied based on SOHO/MDI data. Objects were selected for which complete time series of data were available, so as to make it possible to determine the onset time of the magnetic-field emergence at the surface and tracing the formation of the first pores. The active regions studied originated near the central meridian. The total area of sunspots in these regions exceeded 100 millionths of the hemisphere at the maximum of active region evolution. A generalized evolutionary scenario is constructed for the magnetic field and vertical motions in the emerging active region. An asymmetry in the Doppler velocities is noted at an early stage of the active-region development, which corresponds to a matter flow from the leading to the trailing end of the emerging Ω-shaped tube. A direct relationship is found between the matter-downflow velocity in the area of the pore development and the growth in the strength of the longitudinal magnetic field. 相似文献
6.
Local helioseismology techniques yielding the temperature and flow-velocity distributions under a sunspot indicate an unambiguous sign for the horizontal gas-pressure difference between the spot and ambient medium at depths of 4 Mm and more. In the Parker sunspot model, the transverse equilibrium condition cannot be satisfied in these layers: a cluster of vertical, strongly compressed magnetic flux tubes in a plasma that is hotter than the ambient medium with flows that diverge sidewise cannot be in equilibrium. Equilibrium can be satisfied in the hot zone under the spot only if the magnetic flux tube expands sharply with depth, so that the mean magnetic-field strength decreases dramatically at depths exceeding 4 Mm. This corresponds to the “shallow” sunspot model that has been used to interpret long-period sunspot oscillations. 相似文献
7.
M. A. Livshits I. Yu. Grigoryeva I. I. Myshyakov G. V. Rudenko 《Astronomy Reports》2016,60(10):939-948
Multi-wavelength observations and magnetic-field data for the solar flare of May 10, 2012 (04: 18 UT) are analyzed. A sign change in the line-of-sight magnetic field in the umbra of a small spot has been detected. This is at least partly associated with the emergence of a new magnetic field. A hard X-ray flare was recorded at almost the same time, and a “sunquake” was generated by the impact of the disturbance in the range of energy release on the photosphere. A sigmoid flare was recorded at the beginning of the event, but did not spread, as it usually does, along the polarity inversion (neutral) line. SDO/HMI full vectormagnetic-fieldmeasurements are used to extrapolate the magnetic field of AR 11476 into the corona, and to derive the distribution of vertical currents jz in the photosphere. The relationship between the distribution of currents in the active region and the occurrence of flares is quite complex. The expected “ideal” behavior of the current system before and after the flare (e.g., described by Sharykin and Kosovichev) is observed only in the sigmoid region. The results obtained are compared with observations of two other flares recorded in this active region on the same day, one similar to the discussed flare and the other different. The results confirm that the formation and eruption of large-scale magnetic flux ropes in sigmoid flares is associated with shear motions in the photosphere, the emergence of twisted magnetic tubes, and the subsequent development of the torus instability. 相似文献
8.
A mechanism for the acceleration of electrons in the ionosphere of Io due to the moon's motion through the Jovian magnetic field and the presence of Io's ionosphere is considered. Attention is drawn to the important role of the anisotropic conductivity of the ionosphere, which results in the formation of a longitudinal (with respect to the planetary magnetic field) component of the charge-separation electric field. Owing to this anisotropy, the electric field induced by the motion of Io, Ei, produces in Io's ionosphere not only a Pedersen electrical current along Ei but also a Hall current that is approximately perpendicular to the moon's surface in the “upstream” and “downstream” parts of the ionosphere. However, this current cannot be closed through the surface, leading to the formation of a powerful charge-separation field in Io's ionosphere. This field has a component parallel to the magnetic field, with an amplitude comparable to that of the induced electric field. Electron runaway along the magnetic field is also considered, and the occurrence of “active longitudes” and preferred locations for the sources of decametric radio emission in the northern hemisphere of Jupiter are interpreted. The characteristic energies and fluxes of the accelerated electrons injected into Io's flux tube are estimated. The energy of these electron fluxes is sufficient to produce the electromagnetic radiation observed from Io's magnetic tube. 相似文献
9.
We have carried out 3D MHD modeling of the solar corona above the active region AR 0365 before a series of flares observed on May 26–27, 2003. Maps of the evolving photospheric magnetic fields preceding the flares were used as boundary conditions. An emergence of new flux equal to ～1.5 × 1022 Maxwell preceded the observed series of X-ray flares. Modeling a large region 4 × 1010 cm in size demonstrates the formation of several current sheets in the vicinities of coronal Xlines, both already existing in the initial potential field and arising due to the emergence of the new magnetic flux. Each current sheet could be responsible for an elementary flare. 相似文献
10.
A scenario for the production of a current sheet above an active region during the emergence of new magnetic flux is considered. The formation of a current sheet is demonstrated via a numerical solution of a system of MHD equations with dissipative terms. The flare energy is stored in the magnetic field of the current sheet. The decay of the current sheet can account for a number of solar-flare phenomena, including the observed divergence of H α ribbons. 相似文献
11.
The complex active region NOAA 9672 is studied when it was near the central meridian, from October 21–26, 2001. At that time, there was an emergence of new magnetic flux, with the ongoing formation of a filament. The dynamics of the magnetic field are studied in order to search for their possible manifestations in the filament structure, using SOHO MDI magnetograms, SOHO EIT and TRACE filtergrams in the 171 Å line, and Hα filtergrams available via the Internet. Our earlier conclusion that filaments form at the boundaries of supergranules near polarity-inversion lines is confirmed. The conclusion of Chae that sinistral filaments have positive magnetic helicity is also confirmed. New information about magnetic-field decay processes is obtained. The direction of motion of the magnetic poles and their relative positions suggest that the axial field of a filament forms as a result of either reconnection of cancelling magnetic poles, or emergence of horizontal magnetic-flux tubes. 相似文献
12.
I. Yu. Grigor’eva M. A. Livshits G. V. Rudenko I. I. Mysh’yakov 《Astronomy Reports》2013,57(8):611-621
Data on small active regions on the Sun collected over three years (2007–2009) are analyzed. Under very quiescent conditions (a low X-ray background level), the shapes of the coronal loops of some active regions correspond fairly well to the shapes of magnetic-field lines calculated in a potential approximation. This is true of several active regions (e.g., the group AR 10999 in June 2008) in which no flares more powerful than B3 were observed. The radio emission of this active region detected by the RATAN-600 telescope was very weak and virtually no polarization was detected. Subflares were observed in most groups. It is demonstrated using AR 10933 (January 2007) as an example that a growth in the soft X-ray emission by up to factors of ten simultaneous with an increase in the radio flux is characteristic for such active regions. A source with the opposite polarization developed to the Northwest of the main spot in AR 10933. A series of SOHO/MDI (and also Hinode) magnetograms shows the emergence of new magnetic flux before the development of this polarized source, which continued for several hours on January 8, 2007. The current density at surfaces located at various heights is estimated based on observations of the total vector magnetic field (Hinode data) and a non-linear, force-free magnetic-field extrapolation. The height-integrated current becomes appreciably stronger at two nodes above a field neutral line, near the location of the main emerging flux. This supports the idea that the emergence of new magnetic flux is a key factor in the evolution of active regions at all stages of their existence. The development of this picture could help in elucidating the inter-relationship between current enhancements, plasma heating, and particle acceleration, in both weak active regions and strong activity complexes. 相似文献
13.
Results of a study of the corona above a large sunspot in the active region NOAA 10105 with a penumbra size of ～70″ observed in September 2002 are reported. Maps of the active region and emission spectra were constructed using observational data from the NoRH, SSRT, and RATAN-600 telescopes. The sizes and brightness temperatures of the microwave emission above the sunspot are determined. SOHO/MDI and Kitt Peak magnetograms, as well as CaII K line images obtained at the Meudon Observatory, are compared. The derived characteristics are interpreted as cyclotron emission of thermal plasma, assuming a dipole structure for themagnetic field. A stable darkening at the sunspot center observed at short wavelengths and only in the ordinary emission mode was detected. A jump-like change was observed in the structure of the sunspot source in the ordinary emission mode, due to an increase in the size and spectral flux density. These results demand a fundamental correction of model concepts about cyclotron emission sources above sunspots, since they are at variance with the initial assumptions. It is suggested that, at the top of the transition region, the cyclotron emission source may be represented only by the third gyrolevel, but is observed in the extraordinary and ordinary emission modes (in contrast to the generally accepted model, which has a combination of the second and third gyrolevels). Taking into account the new observational data may allow us to refine model distributions of the main parameters of the coronal plasma above sunspots (the electron temperature and density) and information about the character of the magnetic field. 相似文献
14.
A topological method for detecting the new emergence of magnetic flux using SOHO/MDI magnetograms of the full solar disk is
proposed. This method uses the number of pixels in the image that can be distinguished from a specified value to within a
predetermined threshold (the number of disconnected components). We study more than ten very powerful active regions (ARs)
with very high flare activity and show that the number of disconnected components increases directly before the development
of a series of M and X flares, or accompanies this process. This behaviour is evident not only when there is an explicit emergence
of a new flux and a series of fast flares, such as in AR 9236 (November 2000), but also in groups with many non-stationary
processes developing along a neutral line of the large-scale magnetic field. We also discuss the possibility of using the
obtained results for flare prediction. 相似文献
15.
I. Yu. Grigor’eva A. N. Shakhovskaya M. A. Livshits I. S. Knyazeva 《Astronomy Reports》2012,56(11):887-894
Solar filtergrams obtained at the Crimean Astrophysical Observatory at the center and wings of the H?? line are used to study variations in filaments, in particular, in arch filament systems (AFSs). These are considered as an indicator of emerging new magnetic flux, providing information about the spatial locations of magnetic-field elements. Magnetic-field maps for the active region NOAA 10030 are analyzed as an example. A method developed earlier for detecting elements of emerging flux using SOHO/MDI magnetograms indicates a close link between the increase in flare activity in theNOAA 10030 group during July 14?C18, 2002 and variations in the topological disconnectedness of the magnetograms. Moreover, variations in the flare activity one day before a flare event are correlated with variations in the topological complexity of the field (the Euler characteristic) in regions with high field strengths (more than 700 G). Analysis of multi-wavelength polarization observations on the RATAN-600 radio telescope during July 13?C17, 2002 indicate dominance of the radio emission above the central spot associated with the increase in flare activity. In addition to the flare site near the large spot in the group, numerous weak flares developed along an extended local neutral line, far from the central line of the large-scale field. The statistical characteristics of the magnetic-field maps analyzed were determined, and show flare activity of both types, i.e., localized in spot penumbras and above the neutral line of the field. 相似文献
16.
The evolution of large solar activity centers is studied, and the conditions resulting in powerful nonstationary processes are clarified. In addition to the factors that are usually considered (changes in sunspot area, the structure of magnetic fields, the character of motions), we examine to what extent observations of nonstationary processes (flares and associated coronal mass ejections) can be used to predict the development of such processes in the subsequent evolution of the activity center. We considered the example of a powerful group in October 2003, which could be observed before its appearance at the eastern limb using a spacecraft in near-Mars orbit. We plotted for events occurring in 2003 images of flares in various spectral ranges and analyzed high-energy processes in group 486, which was isolated at the beginning of its development, and then in the interrelated groups 486 and 484. The analysis of the peculiar early development of group 486 suggested that an intensification of the activity could be expected due to the emergence of new magnetic flux (and satellite groups), as well as the interaction and synchronization of two and then three large groups of the end of October 2003. In other words, in this case, extremely powerful nonstationary processes are associated with a relatively higher contribution of large-scale magnetic fields. We compare our results to analyses of motions and magnetic fields in this activity center throughout its transit across the disk from October 23 to November 5, 2003. 相似文献
17.
This paper presents a statistical study of various integrated parameters of solar active regions, such as the distance between the polarity centroids, the inclination of the magnetic axis, the flux imbalance between the polarities, and the interosculation parameter of the magnetic fluxes of opposite polarities. The study is based on observations of the longitudinal photospheric magnetic field. We analyze ten active regions for which an appreciable volume of data with good spatial resolution are available. The distributions of the above parameters with field strength are very different for quiet and flare-productive active regions and for quiet and flare-active evolutionary phases of the same active region. Some distributions exhibit substantial and characteristic variations during the development of certain flare processes. The first moments of the distributions reflect specific features in the configuration of the photospheric magnetic fields and are correlated with the level of eruptive processes in the active regions. 相似文献
18.
Regularities have been searched for in the dynamics of characteristics of flare solar radiation during the development of the active region NOAA 0069 in the interval of August 14–24, 2002. The SONG (Solar Neutrons and Gamma rays) instrument onboard the Russian CORONAS-F Solar Observatory recorded hard X-ray and gamma-ray radiation in nine of the 30 flares of class above C5 in this active region within the indicated time interval. It was obtained that, in accordance with the development of the active region, the X- and gamma-ray flux tended to increase at the flare maxima while the hard X-ray spectral index tended to decrease; flares with a harder radiation spectrum occurred in the sunspot umbra, i.e., in the region with the strongest magnetic fields. 相似文献
19.
The correlation between the magnetic flux in an active solar region and associated powerful solar flares is studied. The behavior
of the active regions AR 10486 and AR 10365 is considered. These regions produced a series of class X flares as they crossed
the solar disk. The flares appeared when the magnetic flux exceeded 1022 Mx. The magnetic flux remained constant during all the flares except for one. During this flare, the flux decreased by about
10%; this impulsive decrease of the flux was also recorded in the absence of flares. No energy flux from the photosphere to
the corona at the time of the flare was observed. The behavior of the photospheric field in AR 10486 and AR 10365 is consistent
with a slow accumulation of energy in the corona and the explosive release of energy stored in the magnetic field of a current
sheet above an active region during the flare. 相似文献
20.
Structural magnetic elements observed in sunspot penumbrae are employed as indicators of motions occurring in and around penumbrae. The analysis presented here is base on SDO/HMI continuum images and magnetograms of the line-of-sight field obtained for the active region NOAA 11117. In a first approximation, the penumbral magnetic fields can be considered alternating spines and interspine filaments. In the plane of the sky, spines are thin radial elements with higher field strengths and lower magnetic-field inclinations compared with those in surrounding areas. It is confirmed that spines first appear as protrusions of the umbra magnetic fields visible in magnetograms, and then develop simultaneously with the growth of the penumbra. The departure of magnetic elements from penumbrae as a result of the detachment of the ends of spines begin 1–1.5 h after the spine formation. Inmature penumbrae, magnetic elements emerge fairly often, and the departure of groups of field elements sometimes generates structures resembling moving ribbons. The velocities of magnetic elements that have separated from spines are a factor of two to three lower than those of elements that have separated from inter-spine filaments. The results obtained agree well with an “uncombed” model for the penumbral magnetic fields. 相似文献