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1.
Surface magnetic fields during the solar activity cycle 总被引：1，自引：0，他引：1
We examine magnetic field measurements from Mount Wilson that cover the solar surface over a 13 1/2 year interval, from 1967 to mid-1980. Seen in long-term averages, the sunspot latitudes are characterized by fields of preceding polarity, while the polar fields are built up by a few discrete flows of following polarity fields. These drift speeds average about 10 m s-1 in latitude - slower early in the cycle and faster later in the cycle - and result from a large-scale poleward displacement of field lines, not diffusion. Weak field plots show essentially the same pattern as the stronger fields, and both data indicate that the large-scale field patterns result only from fields emerging at active region latitudes. The total magnetic flux over the solar surface varies only by a factor of about 3 from minimum to a very strong maximum (1979). Magnetic flux is highly concentrated toward the solar equator; only about 1% of the flux is at the poles. Magnetic flux appears at the solar surface at a rate which is sufficient to create all the flux that is seen at the solar surface within a period of only 10 days. Flux can spread relatively rapidly over the solar surface from outbreaks of activity. This is presumably caused by diffusion. In general, magnetic field lines at the photospheric level are nearly radial.Proceedings of the 14th ESLAB Symposium on Physics of Solar Variations, 16–19 September 1980, Scheveningen, The Netherlands. 相似文献
2.
The structure and variations of open field regions (OFRs) are analyzed against the solar cycle for the time interval of 1970–1996. The cycle of the large-scale magnetic field (LSMF) begins in the vicinity of maximum Wolf numbers, i.e. during the polar field reversal. At the beginning of the LSMF cycle, the polar and mid-latitude magnetic field systems are connected by a narrow bridge, but later they evolve independently. The polar field at the latitudes above 60° has a completely open configuration and fills the whole area of the polar caps near the cycle minimum of local fields. At this time, essentially all of the open solar flux is from the polar caps. The mid-latitude open field regions (OFRs) occur at a latitude of 30–40° away from solar minimum and drift slowly towards the equator to form a typical 'butterfly diagram' at the periphery of the local field zone. This supports the concept of a single complex – 'large-scale magnetic field – active region – coronal hole'. The rotation characteristics of OFRs have been analyzed to reveal a near solid-body rotation, much more rigid than in the case of sunspots. The rotation characteristics are shown to depend on the phase of the solar cycle. 相似文献
3.
Large-scale solar activity is considered as a manifestation of 3 types of magnetic field activity which is demonstrated in the 22-year cycle (a) of small-scale flux emergence (polar faculae at latitudes > 40°), (b) of somewhat larger scale flux emergence (sunspots at latitudes < 40°), and (c) of the global magnetic neutral lines at all latitudes. The migration (poleward or equatorward) of the place of birth and/or of the phenomena themselves of these three types of manifestation of magnetic field is discussed. The poleward migration of the global field is explained in a phenomenological way. 相似文献
4.
S. Latushko 《Solar physics》1994,149(2):231-241
A method of two-dimensional correlation functions has been applied to a sequence of synoptic maps of the large-scale magnetic field to obtain the meridional drift pattern of field structures. The meridional drift profile obtained is antisymmetric about the equator. The meridional drift is directed from the equator to the poles at latitudes below 45°. A maximum drift velocity of 11–13 m s–1 is attained in the latitude range 30°. A picture of the space-time distribution of meridional drift is also obtained, which may be interpreted as resulting from the effect of azimuthal convective rolls (3 rolls per hemisphere) on the large-scale magnetic field. Rolls originate at high latitudes following the cycle maximum, and migrate equatorwards until the minimum of the next cycle. The picture in the equatorial region can correspond to convective rolls with lifetimes of about two years, or to the process of interaction of rolls from two hemispheres. 相似文献
5.
S. Latushko 《Solar physics》1996,166(2):261-266
A study is made of the rotation of large-scale magnetic fields using the synoptic maps from the Kitt Peak National Observatory for the time interval 1976–1985. The auto-correlation method and the mass-centers method of magnetic structures was applied to infer mean differential rotation profiles and rotation profiles separately for each magnetic field polarity. It has been found that in both hemispheres the leading polarity rotates faster than the following polarity at all latitudes by about 0.04° day–1. The maximum rotation rate of the leading polarity is reached at about 6° latitude. In the mean profile for both polarities, this brings about two angular velocity maxima at 6° latitudes in both hemispheres. Such a profile appears as to have a dimple on the equator. 相似文献
6.
We cross-correlate pairs of Mt. Wilson magnetograms spaced at intervals of 24–38 days to investigate the meridional motions of small magnetic features in the photosphere. Our study spans the 26-yr period July 1967–August 1993, and the correlations determine longitude averages of these motions, as functions of latitude and time. The time-average of our results over the entire 26-yr period is, as expected, antisymmetric about the equator. It is poleward between 10° and 60°, with a maximum rate of 13 m s–1, but for latitudes below ±10° it is markedly equatorward, and it is weakly equatorward for latitudes above 60°. A running 1-yr average shows that this complex latitude dependence of the long-term time average comes from a pattern of motions that changes dramatically during the course of the activity cycle. At low latitudes the motion is equatorward during the active phase of the cycle. It tends to increase as the zones of activity move toward the equator, but it reverses briefly to become poleward at solar minimum. On the poleward sides of the activity zones the motion is most strongly poleward when the activity is greatest. At high latitudes, where the results are more uncertain, the motion seems to be equatorward except around the times of polar field reversal. The difference-from-average meridional motions pattern is remarkably similar to the pattern of the magnetic rotation torsional oscillations. The correspondence is such that the zones in which the difference-from-average motion is poleward are the zones where the magnetic rotation is slower than average, and the zones in which it is equatorward are the zones where the rotation is faster.Our results suggest the following characterization: there is a constant and generally prevailing motion which is perhaps everywhere poleward and varies smoothly with latitude. On this is superimposed a cycle-dependent pattern of similar amplitude in which the meridional motions of the small magnetic features are directed away from regions of magnetic flux concentration. This is suggestive of simple diffusion, and of the models of Leighton (1964) and Sheeley, Nash, and Wang (1987). The correspondence between the meridional motions pattern and the torsional oscillations pattern in the magnetic rotation suggests that the latter may be an artifact of the combination of meridional motion and differential rotation. 相似文献
7.
Ronald L. Rosenberg 《Solar physics》1970,15(1):72-78
A simple model is used to present a unified picture of the polarity pattern of the interplanetary magnetic field observed during the solar cycle. Emphasis in this paper is on the field near solar maximum. The heliographic latitude dependence of the dominant polarity of the interplanetary magnetic field is explained in terms of weak poloidal (dipolar) field sources in the sun's photosphere. Unlike the Babcock theory, the author hypothesizes that the dipolar field exists at equatorial latitudes (0–20°), too, (as well as in polar regions) and that the major source of the interplanetary magnetic field observed near the ecliptic plane is the dipolar field from equatorial latitudes. The polarity of the interplanetary field data taken in 1968 and in the first half of 1969 near solar maximum may possibly be explained in terms of a depression of the dipolar field boundary in space. The effect on the solar wind of the greater activity in the northern hemisphere of the sun that existed in 1968 and in the first half of 1969 is believed responsible for this hypothesized depression, especially near solar maximum, of the plane separating the + and - dipolar polarity below the solar equatorial plane in space. Predictions are made concerning the interplanetary field to be observed near the ecliptic plane in each portion of the next solar cycle. 相似文献
8.
Sixteen years of WSO magnetogram data have been studied to determine the solar cycle variation and latitude dependence of the east-west inclination of photospheric magnetic field lines. East-west inclination is here defined as the angle between a field line and its local radial vector, as projected onto the plane of the latitude and line of sight. Inclination is determined by a least-squares fit of observed magnetic fields to a simple projection model, and is found to depend on polarity and to change with the solar cycle. Leading and following polarities are tipped towards each by about 9° and have an overall net tilt in the direction of rotation (to the west) of 0.6°. New cycles are seen to begin at high latitudes and to grow through the lower latitudes over approximately 5 years, providing evidence for an extended cycle length of 16–18 years. 相似文献
9.
An asymptotic solution of generation equations for the solar mean magnetic field is given and studied. The variation of rotational angular velocity with depth is taken from helioseismological data. Average helicity is prescribed according to the mixing length theory. It is shown that three dynamo waves of the magnetic field are excited. The first wave is generated at the surface layer and concentrates at latitudes of about 60°. Its activity becomes apparent in the poleward migration of the zone of polar faculae formation. The second more powerful wave of the field is excited in the center of the convection zone and its activity shows up in a sunspot cycle. The third wave which is similar to the first wave, is generated at the bottom of the convection zone and attenuates towards the surface. Its activity may appear as a three-fold reversal of the polar magnetic field. 相似文献
10.
It is known for over two decades now that the rotation of the photospheric magnetic fields determined by two different methods
of correlation analysis leads to two vastly differing rotation laws - one the differential and the other rigid rotation. Snodgrass
and Smith (2001) reexamining this puzzle show that the averaging of the correlation amplitudes can tilt the final profile
in favour of rigid rotation whenever the contribution of the rigidly rotating large-scale magnetic structures (the plumes)
to the correlation dominates over that of the differentially rotating small-scale and mesoscale features. We present arguments
to show that the large-scale unipolar structures in latitudes >40 deg, which also show rigid rotation (Stenflo, 1989), are
formed mainly from the intranetwork magnetic elements (abbreviated as IN elements). We then estimate the anchor depths of
the various surface magnetic elements as locations of the Sun's internal plasma layers that rotate at the same rate as the
flux elements, using the rotation rates of the internal plasma layers given by helioseismology. We infer that the anchor depths
of the flux broken off from the decay of sunspot active regions (the small-scale and mesoscale features that constitute the
plumes) are located in the shallow layers close to the solar surface. From a similar comparison with helioseismic rotation
rates we infer that the rigid rotation of the large-scale unipolar regions in high latitudes could only be coming from plasma
layers at a radial distance of about 0.66–0.68 R
⊙ from the Sun's centre. Using Stenflo's (1991) ‘balloon man’ analogy, we interpret these layers as the source of the magnetic
flux of the IN elements. If so, the IN flux elements seem to constitute a fundamental component of solar magnetism. 相似文献
11.
High-resolution magnetograms of the solar polar region were used for the study of the polar magnetic field. In contrast to low-resolution magnetograph observations which measure the polar magnetic field averaged over a large area, we focused our efforts on the properties of the small magnetic elements in the polar region. Evolution of the filling factor - the ratio of the area occupied by the magnetic elements to the total area - of these magnetic elements, as well as the average magnetic field strength, were studied during the maximum and declining phase of solar cycle 22, from early 1991 to mid-1993.We found that during the sunspot maximum period, the polar regions were occupied by about equal numbers of positive and negative magnetic elements, with equal average field strength. As the solar cycle progresses toward sunspot minimum, the magnetic field elements in the polar region become predominantly of one polarity. The average magnetic field of the dominant polarity elements also increases with the filling factor. In the meanwhile, both the filling factor and the average field strength of the non-dominant polarity elements decrease. The combined effects of the changing filling factors and average field strength produce the observed evolution of the integrated polar flux over the solar cycle.We compared the evolutionary histories of both filling factor and average field strength, for regions of high (70°–80°) and low (60°–70°) latitudes. For the south pole, we found no significant evidence of difference in the time of reversal. However, the low-latitude region of the north pole did reverse polarity much earlier than the high-latitude region. It later showed an oscillatory behavior. We suggest this may be caused by the poleward migration of flux from a large active region in 1989 with highly imbalanced flux. 相似文献
12.
E. E. Benevolenskaya 《Solar physics》1995,161(1):1-8
The source of the poloidal magnetic field was fixed using a uniform series of surface low-resolution magnetic field observations begun at Wilcox Solar Observatory at Stanford. The results obtained confirm the idea that low-frequency dynamo waves with a period approximately equal to 22 years and a high-frequency wave of a quasi-two-year period can coexist. It seems that an interaction between these components in the convection zone takes place on the Sun. Surface large-scale solar magnetic fields are analyzed using a two-dimensional Fourier method technique to study the poloidal field distribution. The first harmonic approximately equals the period of the magnetic cycle, appears at all latitudes, and reaches its the maximum value in the polar regions. Moreover, spectral analyses of axisymmetric magnetic field derivative in time found that the second important harmonic of a period approximately equal to two years appears at all latitudes. This second high-frequency harmonic dominates the polar latitude regions at the same time as the low-frequency one. 相似文献
13.
We calculate analytical and numerical solutions to the magnetic flux transport equation in the absence of new bipolar sources of flux, for several meridional flow profiles and a range of peak flow speeds. We find that a poleward flow with a broad profile and a nominal 10 m s–1 maximum speed concentrates the large-scale field into very small caps of less than 15° half-angle, with average field strengths of several tens of gauss, contrary to observations. A flow which reaches its peak speed at a relatively low latitude and then decreases rapidly to zero at higher latitudes leads to a large-scale field pattern which is consistent with observations. For such a flow, only lower latitude sunspot groups can contribute to interhemispheric flux annihilation and the resulting decay and reversal of the polar magnetic fields. 相似文献
14.
In the present work, the phase relation between activities of solar active prominences respectively at low and high latitudes in the period 1957–1998 has been studied. We found that from the solar equator to the solar poles, the activity of the solar active prominences occurs earlier at higher latitudes, and that the cycle of the solar active prominences at high latitudes (larger than 50°) leads by 4 years both the sunspot cycle and the corresponding cycle of the solar active prominences at low latitudes (less than 40°). 相似文献
15.
We have studied the variations of the height of polar crown prominences according to daily observations of the Sun at the Kodaikanal Observatory (India) during 1905–1975. Polar ring filaments at latitudes 60°–80° are related to the polar magnetic field reversal. A double decrease of the height of polar ring filaments was found in the course of their migration from 40°to the poles. We estimated the limiting height of the equilibrium of polar ring filaments from the stability condition of a strong electric current. We found that the transition from large-scale to small-scale ring filaments reduces the critical height of the stability for the prominences. A model of an inverse-polarity filament was used. 相似文献
16.
The structure of the large-scale background magnetic field evolves in time and space. The large-scale horizontal transport
velocity field of the magnetic flux patterns was inferred over the whole solar photosphere in the course of two solar activity
cycles from year 1976 to 1999. The method of velocity determination and the testing procedures of the velocity accuracy are
presented. The non-axially symmetric component of the horizontal velocity was found and both zonal and meridional velocity
regions were described. The horizontal large-scale transport velocity regions vary in shape and the intensity during different
phases of the 11-year solar activity cycle. The total horizontal transport velocity is characterized by the presence of variable
amounts of the vector field vortices with symmetric orientation relative to the solar equator. The zonal velocity regions,
distributed inside of the zonal belt limited by latitudes ± 35°, are persistent for about 4 Carrington rotations. Recurrent
structures of similar velocity distributions are not coherent over the whole solar photosphere. 相似文献
17.
P. C. Hedgecock 《Solar physics》1975,44(1):205-224
Data from the two HEOS satellites obtained during the period December 1968 to August 1974 are used to investigate the large-scale properties of the interplanetary magnetic field.The sector structure has been deduced from the observed times of sector boundary crossings which are tabulated. A two-sector pattern existed throughout most of the period with occasional intervals of 2–3 months duration in which four sectors appeared. The variation of the dominant sector polarity with heliographic latitude showed a reversal in sense during 1971 at the time of the reported reversal in the Sun's polar field. A statistical analysis of the change in polarity distribution with latitude suggests that at Earth's orbit the sector boundaries are inclined to the solar equator on average at an angle of 12 deg.No evidence was found in the HEOS measurements of the north-south field component to confirm the systematic latitude-dependent deviation of the plasma flow away from the solar equatorial plane suggested by several analyses of data from previous spacecraft. The mean field magnitude and the average amplitude of the directional fluctuations appeared to be independent of heliographic latitude within the ±7.3° range explored. 相似文献
18.
L. A. Plyusnina 《Solar physics》1985,102(1-2):191-201
For the period 1969–1975, a study has been made of the dependence of the interplanetary magnetic field structure on the distribution and evolutionary properties of solar magnetic fields. By direct comparison of a sequence of synoptic charts of the photospheric magnetic field with the interplanetary magnetic field, and by applying the method of correlation analysis, it is shown that to areas with an unstable polarity of the interplanetary magnetic field there correspond regions with a complicated inverse polarity line that forms either narrow gulfs and islands against a background of the dominant polarity, or bipolar magnetic regions and their clusters. At the time of reconstruction of the photospheric magnetic field the correlation between the photospheric and interplanetary magnetic field element distributions worsens. An asymmetry of the correlation between the interplanetary and photospheric magnetic field structures of different hemispheres is found. During the period of study, the interplanetary field structure shows a better correlation with the distribution of the photospheric magnetic field at middle and lower latitudes (0°–40°) of the southern hemisphere. 相似文献
19.
Poleward migration of the magnetic neutral line on the Sun has been calculated for the periods 1945–1950 and 1955–1981 using synoptic charts based on H observations. Epochs of sign reversal of the solar magnetic field at latitudes 50° to 90° have been determined for these periods. During the cycles 19 and 20 a threefold sign reversal took place in the northern hemisphere. During all the above cycles both the solar poles were of one polarity for a period ranging from 0.5 to 1 year. The poleward drift velocity of the magnetic neutral line varies from 6 to 29 m s–1 and seems to depend on the strength of the cycle. 相似文献
20.
We derive the poleward migration trajectory diagram of the filament bands for the years 1915–1982 from the H-alpha synoptic charts. We find that the global solar activity commences soon after the polar field reversal in the form of two components in each hemisphere. The first component we identify with the polar faculae that appear at latitudes 40–70° and migrate polewards. The second and the more powerful component representing the sunspots shows up at 40° latitudes 5–6 years later and drifts equatorward giving rise to the butterfly diagram. Thus the global solar activity is described by the faculae and the sunspots that occur at different latitude belts and displaced in time by 5–6 years. This gives rise to the prolonged duration for the global solar activity lasting for 16–18 years as against the 11 years which has come about based only on the spots. The two components match with the pattern of the coronal emission in 5303 Å line. Finally, we show that the two components of activity also match with the pattern of excess shear associated with the torsional oscillations on the Sun and this provides a link between the torsional oscillations and the magnetic activity. 相似文献