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1.
We investigate the reliability with which magnetograph observations of the large-scale polar fields establish the zero-flux contour by comparing magnetic maps from various sources with one another and with the locations of filament structures seen on the disk in H filtergrams. The daily MWO and NSOKP magnetograms smoothed over 120 arc sec provide consistent large-scale zero-flux contours which align with the filaments out to heliocentric angles of about 75°. Synoptic maps match in regions where the locations of the zero-flux contour and of the filaments are maintained for several days. Attention is drawn to regions at the tips of unipolar `plumes' and the polar crown gap where the contours are variable from day to day; these are tentatively identified as regions of active reorganization of large-scale flux. 相似文献
2.
Three examples of the unusual development of high-latitude large-scale features during cycle 23 are described. These features are found in synoptic plots constructed using data obtained at both the NSOKP and the MWO Observatories. Several properties of these features cannot be reproduced in direct simulations using a modified form of the flux-transport equation appropriate for synoptic fields and it is inferred that their evolution is not due solely to the advection and diffusion of decaying active region fields. The analysis shows that one feature may be related to a high-latitude bipolar region which emerged in an earlier rotation. By imposing the locations of H filaments on enlargements of the NSOKP daily magnetograms, we can identify the location of the other features and study their structure at high resolution. This suggests that they are related to the emergence of small magnetic knots at high latitudes. By repeating the simulations including overlays of non-random patterns of bipoles emerging at appropriate times during the simulations, it is possible to study the effects of different patterns and to reproduce some of the qualitative properties of these features not present in the direct simulations. These results support Stenflo's contention that `quite minute deviations from a random distribution (in the emergence of small-scale fields) would suffice for these fields to have global effects'. 相似文献
3.
We present high-resolution studies of the solar polar magnetic fields near sunspot maximum in 1989 and towards sunspot minimum in 1995. We show that, in 1989, the polar latitudes were covered by several unipolar regions of both polarities. In 1995, however, after the polar field reversal was complete, each pole exhibited only one dominant polarity region.Each unipolar region contains magnetic knots of both polarities but the number count of the knots of the dominant polarity exceeds that of the opposite polarity by a ratio of order 4:1, and it is rare to find opposite polarity pairs, i.e., magnetic bipoles.These knots have lifetimes greater than 7 hours but less than 24 hours. We interpret the longitudinal displacement of the knots over a 7-hour period as a measure of the local rotation rate. This rotation rate is found to be generally consistent with Snodgrass' (1983) magnetic rotation law.In an attempt to obtain some insight into the operation of the solar dynamo, sketches of postulated subsurface field configurations corresponding to the observed surface fields at these two epochs of the solar cycle are presented. 相似文献
4.
A spatiotemporal analysis of long-term measurements of the Sun’s magnetic field was carried out to study changes in its zonal structure and reversals of the polar fields in Cycles 21?–?24. A causal relationship between activity complexes, their remnant magnetic fields, and high-latitude magnetic fields has been demonstrated in the current cycle. The appearance of unipolar magnetic regions near the poles is largely determined by the decay of long-lived activity complexes. The nonuniform distribution of sunspot activity and its north–south asymmetry result in the asymmetry of remnant fields that are transported poleward due to meridional circulation. The asymmetry of high-latitude magnetic fields leads to an asynchrony of polar-field reversals in both hemispheres. The interaction of high-latitude unipolar magnetic regions with the polar fields affects the embedded coronal holes. The evolution of large-scale magnetic fields was also studied in a time–latitude aspect. It is shown that regular reversals of the Sun’s polar fields resulted from cyclic changes in high-latitude magnetic fields. A triple polarity reversal of the polar fields in Cycle 21 and short-term polarity alternations at the poles were interpreted taking into account the interaction of the remnant fields with the Sun’s polar fields. 相似文献
5.
We define for observational study two subsets of all polar zone filaments, which we call polemost filaments and polar filament bands. The behavior of the mean latitude of both the polemost filaments and the polar filament bands is examined and compared with the evolution of the polar magnetic field over an activity cycle as recently distilled by Howard and LaBonte (1981) from the past 13 years of Mt. Wilson full-disk magnetograms. The magnetic data reveal that the polar magnetic fields are built up and maintained by the episodic arrival of discrete f-polarity regions that originate in active region latitudes and subsequently drift to the poles. After leaving the active-region latitudes, these unipolar f-polarity regions do not spread equatorward even though there is less net flux equatorward; this indicates that the f-polarity regions are carried poleward by a meridional flow, rather than by diffusion. The polar zone filaments are an independent tracer which confirms both the episodic polar field formation and the meridional flow. We find:
- The mean latitude of the polemost filaments tracks the boundary of the polar field cap and undergoes an equatorward dip during each arrival of additional polar field.
- Polar filament bands track the boundary latitudes of the unipolar regions, drifting poleward with the regions at about 10 m s-1.
- The Mt. Wilson magnetic data, combined with a simple model calculation, show that the filament drift expected from diffusion alone would be slower than observed, and in some cases would be equatorward rather than poleward.
- The observation that filaments drift poleward along with the magnetic regions shows that fields of both polarities are carried by the meridional flow, as would be expected, rather than only the f-polarity flux which dominates the strength. This leads to the prediction that in the mid-latitudes during intervals between the passage of f-polarity regions, both polarities are present in nearly equal amounts. This prediction is confirmed by the magnetic data.
6.
The observational set-up for a detailed study of the velocity, intensity and magnetic-field fine structure in and around a sunspot is described. On highly resolved spectra we detected in the vicinity of a sunspot a large number of points with strong magnetic fields (magnetic knots). The magnetic field in these knots causes a striking decrease of the line depth (or a line gap after Sheeley, 1967). The properties of the magnetic knots are: (1) magnetic fields up to 1400 gauss; (2) diameter 1100 km; (3) coincidence with dark intergranular spaces; (4) generally downward material motion; (5) lifetime>30min; (6) estimated total number around an unipolar spot 2000; (7) combined magnetic flux comparable to the sunspot flux; (8) coincidence with Ca+ plages.For the smallest sunspots (pores) we obtained magnetic fields >1500 gauss. Hence a magnetic field of about 1400–1500 gauss appears to be a rather critical level for pore and spot formation.We found a large number of small areas producing line gaps without measurable magnetic field. These non-magnetic gap-regions coincide with bright continuum structures.Some aspects arising from the occurrence of hundreds of magnetic knots in an active region are discussed in the last section.Presently guest investigator at the Göttingen Observatory.Previously member of the High Altitude Observatory solar project at Sacramento Peak (Contract Nr. AF (628) - 4078). 相似文献
7.
The peculiar development of solar activity in the current cycle resulted in an asynchronous reversal of the Sun’s polar fields. The asymmetry is also observed in the formation of polar coronal holes. A stable coronal hole was first formed at the South Pole, despite the later polar-field reversal there. The aim of this study is to understand the processes making this situation possible. Synoptic magnetic maps from the Global Oscillation Network Group and corresponding coronal-hole maps from the Extreme ultraviolet Imaging Telescope onboard the Solar and Heliospheric Observatory and the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory are analyzed here to study the causal relationship between the decay of activity complexes, evolution of large-scale magnetic fields, and formation of coronal holes. Ensembles of coronal holes associated with decaying active regions and activity complexes are presented. These ensembles take part in global rearrangements of the Sun’s open magnetic flux. In particular, the south polar coronal hole was formed from an ensemble of coronal holes that came into existence after the decay of multiple activity complexes observed during 2014. 相似文献
8.
The Mount Wilson synoptic magnetic data for the period September 1987 through March 1996 are completely revised and used to provide polar plots of the solar magnetic fields for both hemispheres. This period, from Carrington rotations 1793 to 1906, covers the reversals of the polar magnetic fields in cycle 22. Comparison of our plots with the presently available H filtergrams for this period shows that the polarity boundaries are consistent in these two data sets where they overlap. The Mount Wilson plots show that the polar field reversals involve a complex sequence of events. Although the details differ slightly, the basic patterns are similar in each hemisphere. First the old polarity becomes isolated at the pole, then shortly thereafter, the isolation is broken, and the polar field includes unipolar regions of both polarities. The old polarity then reclaims the polar region, but when the isolation of this field is established for a second time, it declines in both area and strength. We take the reversal to be complete when the old polarity field is no longer observed in the Mount Wilson plots. With this criterion we find that the polar field reversal is completed in the north by CR 1836, i.e., by December 1990, and in the south by CR 1853, i.e., March 1992. 相似文献
9.
The solar magnetic fields observed in active regions and their residues are thought to be parts of toroidal field systems renewed every 11-yr cycle from a poloidal field. The latter may be either a reversing (dynamo) field or a non-reversing, primordial field. The latter view was held for some 70 yr, but the apparent reversals of the polar-cap fields in 1957–8 and the development of dynamo theory brought wide acceptance of the former. Here we consider evidence for and against each model, with these conclusions. (i) Several errors combine so that the non-spot measurements of gross magnetic fluxes are too low by factors of 10 or more. A permanent field of 2 G or more might remain unobserved. (ii) Measurements of average magnetic field strength are subject to various large errors. In particular, the reported reversals of the polar-cap fields are better explained in terms of tilts of toroidal field residues. (iii) Observations of new-cycle magnetic fields among old-cycle fields, of the gradual fading away of large unipolar regions, and the ubiquitous jumble of very small magnetic loop structures appear explicable only in terms of a primordial field. (iv) More positive evidence of a primordial field is found in the extreme order, symmetry and long-term stability of the polar cap streamers or rays. During one eclipse (1954) the primordial field was seen in the absence of all toroidal field residues. (v) A form of reversal of the interplanetary magnetic field is re-interpreted and shown to be consistent with a primordial, but not a dynamo, field. (vi) A test for a primordial field is that the fields below coronal holes should tend to be positive (outwards) in the northern hemisphere and negative in the southern hemisphere. (vii) Further evidence may be available by studying various plasma structures below coronal holes. An urgent requirement is a study of fibrils, faculae, macrospicules and rays in these regions. 相似文献
10.
Auto-correlation analysis was performed using digitized synoptic charts of photospheric magnetic fields for the past three solar activity cycles (1965–1994). The obtained correlograms were used to study the rotation and the zonal-sector structure of large-scale solar magnetic fields all over the observable region of heliolatitudes in various phases of solar activity. It is shown that the large-scale system of solar magnetic fields is rather complex and comprises at least three different systems. One is a global rigidly rotating system. It determines the cyclic variation of magnetic fields and is probably responsible for the behavior of magnetic fields in the polar zones. Another is a rigidly rotating 4-sector structure in the central (equatorial and mid-latitude) zone. The third is a differentially rotating system that determines the behavior of the LSSMF structure elements with a size of 30–60° and less. This one is the most noticeable in the central zone and absent in the polar zones. Various cyclic and rotation parameters of the three field structures are discussed. 相似文献
11.
Taking into account magneto-optical effects, we have obtained numerical solutions of the transfer equations for the Stokes parameters, calculated the linearly polarized intensity (U) and constructed its monochromatic images of unipolar sunspots. By comparison with the observational material of the vector magnetograph of the Marshall Space Flight Center, Huntsville (Alabama), we have found that the model of radial magnetic fields may give rise to U monochromatic images close to those observed. The same conclusion has been obtained previously by Landi Degl'Innocenti (1979), although his analysis was performed with the Milne-Eddington approximation instead of a detailed sunspot model. Moreover, we have shown that the model of spiral magnetic fields leads to results in contrast with observations. 相似文献
12.
R. K. Zhigalkin G. V. Rudenko N. N. Stepanian V. G. Fainshtein N. I. Shtertser 《Bulletin of the Crimean Astrophysical Observatory》2008,104(1):67-78
Based on the developed method of jointly using data on the magnetic fields and brightness of filaments and coronal holes (CHs) at various heights in the solar atmosphere as well as on the velocities in the photosphere, we have obtained the following results: The upward motion of matter is typical of filament channels in the form of bright stripes that often surround the filaments when observed in the HeI 1083 nm line. The filament channels observed simultaneously in Hα and HeI 1083 nm differ in size, emission characteristics, and other parameters. We conclude that by simultaneously investigating the filament channels in two spectral ranges, we can make progress in understanding the physics of their formation and evolution. Most of the filaments observed in the HeI 1083 nm line consist of dark knots with different velocity distributions in them. A possible interpretation of these knots is offered. The height of the small-scale magnetic field distribution near the individual dark knots of filaments in the solar atmosphere varies between 3000 and 20000 km. The zero surface separating the large-scale magnetic field structures in the corona and calculated in the potential approximation changes the inclination to the solar surface with height and is displaced in one or two days. The observed formation of a filament in a CH was accompanied by a significant magnetic field variation in the CH region at heights from 0 to 30000 km up to the change of the predominant field sign over the entire CH area. We assume that this occurs at the stage of CH disappearance. 相似文献
13.
V. M. Grigorjev 《Solar physics》1969,6(1):67-71
Observations of longitudinal and transversal fields and of radial velocities in the magnetic ‘knots’ close to a sunspot were made with the help of Sayan Observatory magnetograph with spatial resolution 1″.2 x 1″.8. The analysis led to following conclusions:
- The magnetic field in the knots is mainly vertical. The mean inclination of the magnetic-field vector to the vertical direction is equal to 26°.
- The phenomenon of darkening is connected with essentially vertical fields and brightening in the faculae with the horizontal fields on the sun.
- An inverse relation between the value of darkening and the inclination of the field vector to the vertical direction and a direct relation on the longitudinal magnetic-field strength exist for the magnetic knots.
- The magnetic knots in the active region are located in the Hα flocculi near the line where the radial velocity is changing sign in the photosphere.
14.
A. G. Tlatov 《Solar physics》2009,260(2):465-477
This paper considers the indices characterizing the minimum activity epoch, according to the data of large-scale magnetic fields and polar activity. Such indices include: dipole–octopole index, area and average latitude of the field with dominant polarity in each hemisphere, polar activity seen in polar faculae and Ca?ii K line bright points, coronal emission line intensity (5303?Å) and others. We studied the correlation between these indices and the amplitude of the following sunspot cycle, and the relation between the duration of the cycle of large-scale magnetic fields and the duration of the sunspot cycle. The obtained relationships allow us to presume that the polar field is formed from the sources of both preceding and the current activity cycles during the decay phase and at the activity minimum. The balance in these sources would therefore determine the features of the following sunspot cycle. The prediction for the 24th activity cycle using these results leads to W=102±13. 相似文献
15.
J. H. Piddington 《Solar physics》1973,33(2):363-373
The solar atmosphere is heated by a flux of mechanical waves propagating in one or more of the modes: acoustic, Alfvén and gravitational.The acoustic theory is compared with observational data and found inadequate. First, the theory is based quantitatively on the Böhm-Vitense convection zone model, and large-scale convective motions (supergranulation) and magnetic fields (unipolar regions) show that convection has another form. On the other hand, when granular motions are invoked the energy flux is too small. Second, atmospheric heating is localized in faculae, and enhanced acoustic flux beneath these regions is no longer explicable. Finally, the short periods of 10–30 s invoked recently appear inexplicable. Objections to the gravitational wave heating process are given briefly.Previous objections to Alfvén waves as an energy source followed from the belief that fields were generally uniform and of strength 50 G, now known to be incorrect. Models of Alfvén wave generation are based on (i) granule eddy motions, (ii) overstable oscillations in subsurface flux tubes and sunspot flux ropes, and (iii) supergranule motions, both horizontal and vertical.The first provides waves which propagate along thin flux tubes oscillating as taut wires in a compressible fluid; they may explain mottles, fibrils and other small emission features. The second may explain the enormous dissipation in spot groups, including flares. The third has been invoked earlier to explain spicules, and may have effects in the solar wind. 相似文献
16.
Observations of the first large-scale patterns of magnetic fields near the sunspot minimum of 1986 (the start of cycle 22) are presented using synoptic magnetic data provided by the National Solar Observatory and contour maps constructed from data provided by the Mount Wilson Solar Observatory. The latter are compared with simulated contour maps derived from numerical solutions of the flux transport equation using data from particular Carrington rotations as initial conditions.The simulated evolutions of the large-scale magnetic fields are qualitatively consistent with observed evolutions, but differ in several significant respects. Some of the differences can be removed by varying the diffusivity and the parameters of the large-scale velocity fields. The remaining differences include: (i) the complexity of fine structure, (ii) the response to differential rotation, (iii) the evolution of decaying active regions, and (iv) the emergence of new elements in the weak, large-scale fields independent of the evolution of the observed active regions.It is concluded that the patterns of weak magnetic fields which comprise the large-scale features cannot be formed entirely by the diffusive decay of active regions. There must be a significant contribution to these patterns by non-random flux eruptions within the network structure, independent of active regions. 相似文献
17.
He i 10830 Å images show that early in sunspot cycles 21 and 22, large bipolar magnetic regions strongly affected the boundaries of the nearby polar coronal holes. East of each eruption, the hole boundary immediately contracted poleward, leaving a band of enhanced helium network. West of the eruption, the boundary remained diffuse and gradually expanded equatorward into the leading, like-polarity part of the bipolar magnetic region. Comparisons between these observations and simulations based on a current-free coronal model suggest that:
- The Sun's polar magnetic fields are confined to relatively small caps of high average field strength, apparently by a poleward meridional flow.
- The enhanced helium network at high latitude marks the location of relatively strong polar fields that have become linked to the newly erupted bipolar region in that hemisphere.
- The distortion of the polar-hole boundary is accompanied by a corresponding distortion of the equatorial neutral sheet in the outer corona, in which the amount of warping depends on the magnitude of the erupted flux relative to the strength of the Sun's polar magnetic fields.
18.
Polar Coronal Holes During Cycles 22 and 23 总被引：3，自引：0，他引：3
The National Solar Observatory/Kitt Peak synoptic rotation maps of the magnetic field and of the equivalent width of the He i 1083 nm line are used to identify and measure polar coronal holes from September 1989 to the present. This period covers the entire lifetime of the northern and southern polar holes present during cycles 22 and 23 and includes the disappearance of the previous southern polar coronal hole in 1990 and and formation of the new northern polar hole in 2001. From this sample of polar hole observations, we found that polar coronal holes evolve from high-latitude (60° ) isolated holes. The isolated pre-polar holes form in the follower of the remnants of old active region fields just before the polar magnetic fields complete their reversal during the maximum phase of a cycle, and expand to cover the poles within 3 solar rotations after the reversal of the polar fields. During the initial 1.2–1.4 years, the polar holes are asymmetric about the pole and frequently have lobes extending into the active region latitudes. During this period, the area and magnetic flux of the polar holes increase rapidly. The surface areas, and in one case the net magnetic flux, reach an initial brief maximum within a few months. Following this initial phase, the areas (and in one case magnetic flux) decrease and then increase more slowly reaching their maxima during the cycle minimum. Over much of the lifetime of the measured polar holes, the area of the southern polar hole was smaller than the northern hole and had a significantly higher magnetic flux density. Both polar holes had essentially the same amount of magnetic flux at the time of cycle minimum. The decline in area and magnetic flux begins with the first new cycle regions with the holes disappearing about 1.1–1.8 years before the polar fields complete their reversal. The lifetime of the two polar coronal holes observed in their entirety during cycles 22 and 23 was 8.7 years for the northern polar hole and 8.3 years for the southern polar hole. 相似文献
19.
Extreme ultraviolet observations of coronal holes 总被引：2，自引：0，他引：2
Extreme-ultraviolet Skylab and ground-based solar magnetic field data have been combined to study the origin and evolution of coronal holes. It is shown that holes exist only within the large-scale unipolar magnetic cells into which the solar surface is divided at any given time. A well-defined boundary zone usually exists between the edge of a hole and the neutral line which marks the edge of its magnetic cell. This boundary zone is the region across which a cell is connected by magnetic arcades with adjacent cells of opposite polarity. Three pieces of observational evidence are offered to support the hypothesis that the magnetic lines of force from a hole are open. Kitt Peak magnetograms are used to show that, at least on a relative scale, the average field strengths within holes are quite variable, but indistinguishable from the field strengths in other quiet parts of the Sun's surface.Finally it is shown that the large, equatorial holes characteristic of the declining phase of the last solar cycle during Skylab (1973–74) were all formed as a result of the mergence of bipolar magnetic regions (BMR's), confirming an earlier hypothesis by Timothy et al. (1975). Systematic application of this model to the different aspects of the solar cycle correctly predicts the occurrence of both large, equatorial coronal holes (the M-regions which cause recurrent geomagnetic storms) and the polar cap holes. 相似文献
20.
Difficulties in relating magnetograph measurements to the actual solar magnetic field are discussed. After a brief review both of problems inherent in the nature of the measurements and of sources of instrumental error, we show that field measurements taken within the photosphere can map out large-scale regions of a single magnetic polarity even though these regions contain no footpoints of large-scale magnetic structures, but instead only aggregates of small, unresolved bipoles. This may occur wherever the density of unresolved bipoles has a preferred orientation and a spatial variation along the direction of that orientation. We call these regionsvirtual unipolar regions, as they are not connected to regions of opposite polarity by field loops or lines passing through the corona. Investigation of these regions shows that they can arise at widely separated locations, and that they may evolve into real unipolar magnetic regions which are connected to the chromospheric and coronal fields. These results can explain a number of puzzling aspects of magnetograph observations of the solar background magnetic field. 相似文献