Structures of chromospheric magnetic fields in the solar flare producing active region 5747

In this paper, the formation and the measurement of the H line in chromospheric magnetic fields are discussed. The evolution of the chromospheric magnetic structures and the relation with the photospheric vector magnetic fields and chromospheric velocity fields in the flare producing active region AR 5747 are also demonstrated.The chromospheric magnetic gulfs and islands of opposite polarity relative to the photospheric field are found in the flare-producing region. This probably reflects the complication of the magnetic force lines above the photosphere in the active region. The evolution of the chromospheric magnetic structures in the active region is caused by the emergence of magnetic flux from the sub-atmosphere or the shear motion of photospheric magnetic fields. The filaments separate the opposite polarities of the chromospheric magnetic field, but only roughly those of the photospheric field. The filaments also mark the inversion lines of the chromospheric Doppler velocity field which are caused by the relative motion of the main magnetic poles of opposite polarities in the active region under discussion.     

Fine structures of chromospheric magnetic field and material flow in a solar active region

In this paper, we analyze the relations between photospheric vector magnetic fields, chromospheric longitudinal magnetic fields and velocity fields in a solar active region. Agreements between the photospheric and chromospheric magnetograms can be found in large-scale structures or in the stronger magnetic structures, but differences also can be found in the fine structures or in other places, which reflect the variation of the magnetic force lines from the photosphere to the chromosphere. The chromospheric superpenumbral magnetic field, measured by the Hline, presents a spoke-like structure. It consists of thick magnetic fibrils which are different from photospheric penumbral magnetic fibrils. The outer superpenumbral magnetic field is almost horizontal. The direction of the chromospheric magnetic fibrils is generally parallel to the transverse components of the photospheric vector magnetic fields. The chromospheric material flow is coupled with the magnetic field structure. The structures of the H chromospheric magnetic fibrils in the network are similar to H dark fibrils, and the feet of the magnetic fibrils are located at the photospheric magnetic elements.     

Configuration of the chromospheric magnetic field in a unipolar sunspot region

A set of H chromospheric magnetograms at various wavelengths near the line center, chromospheric Dopplergrams, and photospheric vector magnetograms of a unipolar sunspot region near the solar limb were obtained with the vector video magnetograph at the Huairou Solar Observing Station. The superpenumbral chromospheric magnetic field is almost parallel to the surface at the outside of the sunspot penumbra, where the magnetic lines of force are mainly concentrated in the superpenumbral filaments. In the gaps between the filaments the chromospheric horizontal field is weak.     

Reversed-polarity structures of chromospheric magnetic field

Reversed-polarity structures of chromospheric magnetic fields are magnetic gulfs and islands of opposite polarity relative to the underlying photospheric fields. In this paper data measured with the Solar Magnetic Field Telescope of the Huairou Solar Observing Station in Beijing were analyzed. From more than 300 pairs of photospheric magnetograms (in FeI λ5324.19 Å) and relevant chromospheric magnetograms (Hβ λ4861.34 Å), the reality of the reversed-polarity structures is demonstrated. According to an analysis of the fine structure of the magnetic field in the two layers of active regions, we found that there are probably four different types as follows: Type A: magnetic islands of opposite polarity corresponding to photospheric fields appear in the chromospheric magnetogram. Type B: magnetic gulfs of opposite polarity corresponding to photospheric fields appear in the chromospheric magnetogram. Type C is the reverse of type B. That is, a magnetic gulf of opposite polarity corresponding to the chromospheric field appears in the photospheric magnetogram. Type D is the reverse of type A.     

White-light enhancements and small-scale chromospheric activities in an active region

A microflare or a group of Ellerman bombs was found to be associated with several points of white-light enhancements. These points had similar sizes as facular points (d 0.3 arc sec). Temporal evolution of these activities is described. Origins of these activities are discussed to be deeply seated excess heating in chromospheric and photospheric levels.     

Influence of a solar active region on the interplanetary magnetic field

The interplanetary magnetic field has been mapped between 0.4 and 1.2 AU in the ecliptic plane, extrapolating from satellite measurements at 1 AU. The structure within sectors and the evolution of sectors are discussed. The development of a solar active region appears to produce magnetic loops in the interplanetary medium that result in the formation of a new sector.     

On the relation between chromospheric and photospheric fine structure in an active region

A comparative study was done on the bright fine structure in the upper photosphere and in the lower chromosphere of an active region. The results are shown in the following: (a) The bright points in the H wing are cospatial to the facular points, which confirms the result of Wilson (1981). (b) Some points bright in the H wing are associated with the facular granules which have larger sizes than the facular points, (c) The brightness enhancement in the Ha wing is positively correlated to the enhancement in the blue continuum. However, the correlation is not so strong. (d) The moustache points are also cospatial to the facular features. (e) The geometrical shape of a moustache point is like a funnel and diverging upward in the upper photospheric and the lower chromospheric levels.Some discussions are given on the nature of the heating mechanism of the fine structure based upon these results.On leave from Kyoto University and Hida Observatory, Japan.     

Influence of a chromospheric magnetic field on solar acoustic modes

This paper studies the effect of a magnetic atmosphere on the global solar acoustic oscillations in a simple Cartesian model. First, the influence of the ratio of the coronal and the photospheric temperature τ and the strength of the magnetic field at the base of the corona B_c on the oscillation modes is studied for a convection zone-corona model with a true discontinuity. The ratio τ seems to be an important parameter. Subsequently, the discontinuity is replaced by an intermediate chromospheric layer of thickness L and the effect of the thickness on the frequencies of the acoustic waves is studied. In addition, nonuniformity in the magnetic field, plasma density and temperature in the transition layer gives rise to continuous Alfvén and slow spectra. Modes with characteristic frequencies lying within the range of the continuum may resonantly couple to Alfvén and/or slow waves.     

Dual chromospheric flows in the vicinity of a solar pore

Chromospheric line-of-sight velocities are investigated in a small pore and its vicinity on the part of the active region NOAA 11024 with a size of 5″. We used H_α spectra of the active region and undisturbed atmosphere obtained with the French–Italian solar telescope THEMIS (Tenerife, Spain). Significant line-of-sight velocity time variations are found. At the beginning of the observations, the investigated region consisted of two areas of oppositely directed flows. The first area had a bright point in the vicinity of the pore and the second area covered the pore. There were upflows in the former and downflows in the latter. Oppositely directed flows appeared in both areas 2.7 min after the start of observations. In the part of the active region with a length of 2Mm, two oppositely directed flows within the same resolution elements, the so-called dual flows, were observed. The size of the area occupied by the dual flows varied quickly. The area shifted toward the pore. The velocity of upflows and downflows reached 25 km/s. The downflows in the first area lasted only for approximately 1 min. Upflows in the second area gradually covered the pore and lasted for 2 min. The resulting velocity field distribution can be due to a new small-scale magnetic flux emergence.     

A note on chromospheric fine structure at active region polarity boundaries

High resolution H filtergrams from Big Bear Solar Observatory reveal that some filamentary features in active regions have fine structure and hence magnetic field transverse to the gross structure and the zero longitudinal field line. These features are distinct from the usual active region filament, in which fine structure, magnetic field and filament are all parallel to the zero longitudinal field line. The latter occur on boundaries between regions of weaker fields while the former occur at boundaries between regions of stronger field.     

Modeling the distribution of magnetic fluxes in field concentrations in a solar active region

Much of the magnetic field in solar and stellar photospheres is arranged into clusters of ‘flux tubes’, i.e., clustered into compact areas in which the intrinsic field strength is approximately a kilogauss. The flux concentrations are constantly evolving as they merge with or annihilate against other concentrations, or fragment into smaller concentrations. These processes result in the formation of concentrations containing widely different fluxes. Schrijver et al. (1997, Paper I) developed a statistical model for this distribution of fluxes, and tested it on data for the quiet Sun. In this paper we apply that model to a magnetic plage with an average absolute flux density that is 25 times higher than that of the quiet network studied in Paper I. The model result matches the observed distribution for the plage region quite accurately. The model parameter that determines the functional form of the distribution is the ratio of the fragmentation and collision parameters. We conclude that this ratio is the same in the magnetic plage and in quiet network. We discuss the implications of this for (near-)surface convection, and the applicability of the model to stars other than the Sun and as input to the study of coronal heating.     

The formation of spicules in the course of the chromospheric network magnetic field reconnection

We investigate the physical processes occurring in the supergranule boundary cylinder layer (SBCL). Taking into account the Coriolis force, we obtain an expression for the component of the magnetic field and velocity in the SBCL. Within the framework of linear MHD, we consider the formation and coalescence of magnetic tubes, i.e. spicules, in the course of the reconnection of the SBCL magnetic field. The estimated number of spicules appearing on each supergranule cell is in agreement with observations. This number depends on the solar latitude : (1) if the normal component of the magnetic fieldB _z is assumed to be independent of , then the maximum number of spicules should be at = 71°; (2) ifB _z is assumed to be the component of the dipolar fieldB _z sin , then the maximum number should be at the pole: = 90°. The timescale of the formation and the coalescence of the magnetic tubes is 10–20 min, which is of the order of the observed lifetime of the spicules.     

Large-scale photospheric magnetic field: The diffusion of active region fields

The large-scale photospheric magnetic field has been computed by allowing observed active region fields to diffuse and to be sheared by differential rotation in accordance with the Leighton (1969) magnetokinematic model of the solar cycle. The differential rotation of the computed field patterns as determined by autocorrelation curves is similar to that of the observed photospheric field, and poleward of 20° latitude both are significantly different from the differential rotation of the long-lived sunspots (Newton and Nunn, 1951) used as an input into the computations.Now at Department of Physics, Victoria University of Wellington, Wellington, New Zealand.     

Orientation of the galactic magnetic field in the vicinity of the solar system

It is found from analysis of the position angles of the plane of polarization of about 3000 stars (¦b¦ 5° andP 0.5%) that the angle between the magnetic field and the equatorial plane of the galaxy is approximately 0–5°. The distance within which the local magnetic fields of the galaxy have a greater effect on the position angles of the plane of polarization than the galactic magnetic field is estimated to be about 500 pc. The effect of the galactic magnetic field becomes dominant for distancesr 1000 pc.Translated fromAstrofizika, Vol. 39, No. 4, pp. 553–559, November, 1996.     

On the low-temperature region of chromospheric flares

Solar Physics - Most of the energy of particles accelerated in a flare is used for the creation of a high-temperature flare region, the structure of which is determined by the heat conduction...     

A statistical study on property of spatial magnetic field for solar active region

Magnetic fields dominate most solar activities, there exist direct relations between solar flare and the distributions of magnetic field, and also its corresponding magnetic energy. In this paper, the statistical results about the relationships between the spatial magnetic field and solar flare are given basing on vector magnetic field observed by the Solar Magnetic Field Telescope (SMFT) at Huairou Solar Observing Station (HSOS). The spatial magnetic fields are obtained by extrapolated photosphere vector magnetic field observed by SMFT. There are 23 active regions with flare eruption are chosen as data samples, which were observed from 1997 to 2007. The results are as follows: 1. Magnetic field lines become lower after flare for 16 (69 %) active regions; 2. The free energy are decreased after flare for 17 (74 %) active regions. It can conclude that for most active regions the changes of magnetic field after solar flare re coincident with the previous observations and studies.     

On the chromospheric velocity field in sunspot regions

The wavelength shifts of approximately 8000 absorption elements in the H-line from spectra of 66 different sunspot regions have been measured.The average velocity field in the chromosphere close to sunspots is determined. Inside 15000 km from the spot's penumbral rim the average velocity vector is directed towards the spot and downwards in the chromosphere; the angle with the horizontal direction is on the average equal to 20°. The magnitude of the average velocity vector shows a maximum of 6.8 ± 1.2 km/sec just outside the penumbral rim and decreases quickly with increasing distance from the spot. Outside 15000 km from the penumbral rim the average velocity vector is small (-0.7 km/sec) and directed nearly vertically outwards from the sun. No significant tangential component of the average velocity field is found.The deviations of the individual elements from the average velocity field are on the average larger than the value of the average velocity. The total rms deviation in the line of sight velocity is equal to 6.8 km/sec. Thus, a large number of elements, as used in this investigation, is required to give significant values of the average velocity vector.We have also observed velocities in the penumbra. The average velocity vector is here probably small and its direction uncertain. The rms deviation in the line of sight velocities observed in the penumbra is equal to 7.5 km/sec.     

Local solar magnetic and velocity field development and related photospheric and chromospheric activity

We have compiled the results of our long-term studies of the local magnetic field and its activity development, derived from investigating sunspot group evolution, photoelectrically measured longitudinal magnetic and velocity fields, and measurements of sunspot proper motions. We estimate certain regularities according to which the magnetic and velocity fields, and photospheric, as well as chromospheric activities develop. We speculate about the physical background of such processes.Dedicated to Cornelis de Jager     

Flare-associated magnetic changes in an active region

We report an instance of localized chromospheric polarity reversal in a rapidly-formed sunspot which appears to be part of new emerging flux. The chromospheric polarity reversal is preceded by extraordinarily fast growth of the transverse magnetic field and an increase in the line-of-sight magnetic flux of the newly formed sunspot in the photosphere. The strength of this reversal is more than 350 G at maximum, in contrast to approximately - 1300 G for the line-of-sight field and 400 G for the transverse field in the photosphere. Continued flare activity takes place around the site of the reversal with progressively increasing flare size and extent. It is suggested that a kinked or knotted flux loop, or a self-closed flux system developed above the fast-forming sunspot. So far, this phenomenon has been revealed in several active regions.     

Magnetic field topology of an active region

The global 3-dimensional topology of the magnetic field of the weakly flaring active region AR 5420 in the early phase has been estimated using a series of photospheric longitudinal and vector magnetogams together with Hα filtergrams and white-light images. As a physical model for this task, we have used the assumption ofa force-free magnetic field character. An arcade-like structure of the magnetic field has been identified in the preflare phase with an apparent sheared configuration already present in the current-free field case. This system might have been an important source of generation of a field-aligned current system for the eruptions that followed. That was, in particular, suggeted by a significant extension of the active region area in the observation period from June 22 to 25, 1984, that resulted in a stronger shear of the detected arcade-like system. The atmospheric electric currents generated in such a way and the transition triggered by a large-amplitude perturbation generated by new flux emergences on June 23 at this place together might be the reason of the sequence of flares observed. Despite the changes in the Hα structure, the global force-free character of the field did not change significantly over the time of observations. The invariance (in the first order) of the force-free (nearly current-free) character of the magnetic field is consistent with the occurrence of relatively small flares only.