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1.
Analysis of long-term measurements of solar magnetic fields and the flux of UV radiation from the Sun indicates a cause-effect relationship between activity complexs, their residual magnetic fields, and coronal holes. A comparison of the background magnetic fields of the Sun and the evolution of former activity complexes reveals unipolar magnetic regions that form after the decay of these complexes. The latitude and time evolution of unipolar magnetic regions in solar cycles 21–24 is studied. A North-South asymmetry in solar activity is manifest in the distribution of unipolar regions migrating toward higher latitudes. It is shown that, when residual magnetic fields of the opposite polarity reach the polar regions, this leads to a sign change of the polar magnetic field and a decrease in the area of polar coronal holes, or even their complete disappearance. These interactions can explain the triple sign change of the polar magnetic field of the Sun in cycle 21 and the short-term polarity reversals observed in 2010 and 2011. 相似文献
2.
A catalog of observations of polar faculae by the Mountain Astronomical Station of the Pulkovo Observatory (Kislovodsk) for the 21st polar-activity cycle of the Sun (1972–1976) has been compiled. The mean annual and semiannual longitude distributions of the facular surface density have been constructed for latitude bands from 35 to 85° with steps of 10° in latitude and 30° in longitude in polar (the “wind roses”) and cylindrical projections, using a Bartels coordinate-grid rotation system. Coherent spatial structures in these distributions, which are characteristically elongated in two mutually perpendicular directions (i.e., they have an “X”-like appearance), can be identified. The high-latitude activity in the northern and southern hemispheres tends to be in spatial antiphase. This behavior corresponds to a four-sector global polar-activity structure. This indicates the presence of a magnetic-field source that is not associated with the differential rotation of the sun and modulates the evolution of local magnetic fields. 相似文献
3.
Variations in the positions of the intersection points of tangents to ray structures in the polar corona of the Sun during the solar cycle are considered. At first glance, the decrease in the distance q between the tangent intersection point and the center of the solar disk during activity maximum contradicts harmonic analyses that indicate that the relative weight of higher harmonics in the global field increases during this period. Indeed, the higher the harmonic number in an axisymmetric field, the closer the intersection point of the field-line tangents (the magnetic focus) to the solar surface. It is shown that q for a field composed of two harmonics with opposite polarities at the poles can be smaller than q for either of them taken alone. A simple model representing the global field using the third and seventh harmonics is analyzed; this model can reproduce quite satisfactorily the observed dynamics of magnetic foci of the polar field. 相似文献
4.
The latitudes of the zonal boundaries of the global magnetic field of the Sun are determined from the magnetic neutral lines on synoptic Hα maps obtained during 1878–1999. The area of the polar zone occupied by magnetic field of a single polarity at solar minima has doubled over the last 120 years. This provides an explanation for the secular increase in heliospheric characteristics, which differs from the two-fold increase of the magnetic field strength predicted for this period. The temporal variations of the magnetic flux from the polar regions and their role in global changes of the Earth’s climate are discussed in connection with secular variations in the structure of the internal magnetic field of the Sun. 相似文献
5.
A new concept of “Global Complexes of Activity” on the Sun is presented, which brings together objects associated with both global and local fields in a single framework. Activity complexes have traditionally been identified purely from observations of active regions. We show here that a global complex also includes coronal holes and active regions. Our analysis is based on a large dataset on magnetic fields on various scales, SOHO/MDI observations of active regions and magnetic fields, and UV observations of coronal holes. It is shown that the evolution of coronal holes and active regions are parts of a single process. The relationships between the fields on different scales during the generation of the cycle is discussed. 相似文献
6.
A new representation for the database created by J. Sykora on the 5303 Å Fe XIV line emission observed from 1939 to 2001 is proposed. Observations of the corona at an altitude of 60″ above the limb reduced to a uniform photometric scale provide estimates of the emission of the entire visible solar surface. It is proposed to use the resulting series of daily measurements as a new index of the solar activity, GLSun (The Green-Line Sun). This index is purely observational and is free of the model-dependent limitations imposed on other indices of coronal activity. GLSun describeswell both the cyclic activity and the rotational modulation of the brightness of the corona of the Sun as a star. The GLSun series was subject to a wavelet analysis similar to that applied to long-term variability in the chromospheric emission of late-type active stars. We obtain that the brightness inhomogeneities in the solar corona rotate more slowly during epochs of high activity than their average rotational rate over the entire time observations. The time interval of slower rotation of the inhomogeneities is close to the epoch when the Sun’s field represents a horizontal magnetic dipole in each activity cycle, but is somewhat longer than the duration of the polarity reversal in both hemispheres. The difference between the periods for the slower and mean rotation exceeds three days, as is typical for some stars with higher but less regular activity than solar one. The importance of these findings for dynamo theory for the origin and evolution of the magnetic fields of the Sun and other late-type stars is briefly discussed. 相似文献
7.
The distributions of dominant magnetic polarities in synoptic maps of photospheric magnetic fields and their extrapolations to the corona based on Stanford Observatory data are studied. Both dipolar and quadrupolar magnetic patterns are detected in the distributions of dominant polarities in the near-equatorial region of the photosphere for activity cycles 21, 22, and 23. The field in these patterns often has opposite signs on opposite sides of the equator, with this sign changing from cycle to cycle. A longitude-time analysis of variations of the mean solar magnetic field shows that the contribution of the large-scale magnetic patterns to the total field does not exceed 20 µT. The most stable magnetic structures at a quasi-source surface in the solar corona are separated by approximately 180° in heliographic longitude and are close to dipolar. The nature and behavior of these large-scale magnetic patterns are interpreted as a superposition of cyclic dynamo modes and the nonaxially symmetric relic field of the Sun. The contribution of the relic field to the mean solar magnetic field appears as a weak but stable rotational modulation whose amplitude does not exceed 8 µT. 相似文献
8.
Basic scenarios and mechanisms for the formation and decay of small-scale magnetic elements and their manifestation in synthesized Stokes profiles of the Fe I 15648.5 Å infrared line are considered in the context of two-dimensional modeling of nonstationary magnetogranulation on the Sun. The stage of convective collapse is characterized by large redshifts in the V profiles accompanied by complete Zeeman splitting of the I profiles. This is due to intense downward flows of material, which facilitates the concentration of longitudinal field with an amplitude of about several kG in the tube. The dissipation of strong magnetic structures is characterized by blueshifts in their profiles, which result from upward fluxes that decrease the magnetic field in the tube. Typical signatures during key stages in the evolution of compact magnetic elements should be detectable via observations with sufficiently high spatial and temporal resolution. 相似文献
9.
A model for the nonradial motion of an eruptive prominence in the solar corona is proposed. Such motions, which can sometimes be inaccessible to observation, result in an apparent break in the causal link between eruptive prominences and coronal mass ejections. The global magnetic field of the Sun governs coronal plasma motions. The complex structure of this field can form prominence trajectories that differ considerably from a simple vertical rise (i.e., radial motion). A solar filament is modeled as a current-carrying ring or twisted toroidal magnetic rope in equilibrium with the coronal magnetic field. The global field is described using two spherical harmonics. A catastrophic violation of the filament equilibrium followed by its rapid acceleration—eruption—is possible in this nonlinear system. The numerical solution of the equations of motion corresponds well to the eruption pattern observed on December 14, 1997. 相似文献
10.
A. V. Mordvinov 《Astronomy Reports》2006,50(11):936-943
The asymmetry of the magnetic field of the Sun and its manifestation in the interplanetary magnetic field (IMF) are studied. The dominant magnetic polarity of the radial component of the IMF alternates from cycle to cycle, but with an overall systematic dominance of polarity directed toward the Sun. The global asymmetry is also manifest in the component of the IMF perpendicular to the plane of the solar equator. The dominance of positive values of B z together with an appreciable linear trend in the cumulative sum of this quantity is interpreted as a manifestation of a relic solar magnetic field. The strength of this relic magnetic field near the Earth is estimated to be 0.048 ± 0.015 nT, based on the growth of the linear component of the cumulative sum of B z . Time intervals, in which negative values of the B z component of the IMF dominate and enhanced geomagnetic activity is observed, are identified. Our analysis of solar and heliospheric magnetic fields in an integrated representation has enabled us to compare various types of measurements and estimate their stability. 相似文献
11.
Evidence that the distribution of the abundances of admixtures with low first-ionization potentials (FIP < 10 eV) in the lower solar corona could be associated with the typology of the largescale magnetic field is presented. Solar observations show an enhancement in the abundances of elements with low FIPs compared to elements with high FIPs (>10 eV) in active regions and closed magnetic configurations in the lower corona. Observations with the ULYSSES spacecraft and at the Stanford Solar Observatory have revealed strong correlations between the manifestation of the FIP effect in the solar wind, the strength of the open magnetic flux (without regard to sign), and the ratio of the large-scale toroidal and poloidal magnetic fields at the solar surface. Analyses of observations of the Sun as a star show that the enhancement of the abundances of admixtures with low FIPs in the corona compared to their abundances in the photosphere (the FIP effect) is closely related to the solar-activity cycle and also with variations in the topology of the large-scale magnetic field. A possible mechanism for the relationship between the FIP effect and the spectral type of a star is discussed in the framework of solar–stellar analogies. 相似文献
12.
The large-scale stream structure of the solar wind near the Sun and its evolution during the 11-year solar activity cycle are investigated. The study is based on observations of scattering of the radiation from compact natural radio sources at radial distances R≤14R S (R S is the solar radius). Regular observations were conducted in 1981–1998 on the RT-22 and DKR-1000 radio telescopes of the Russian Academy of Sciences at Pushchino, at λ=1.35 cm and 2.7 m, respectively. The radial dependences of the interplanetary scintillations m(R) and the scattering angle 2?(R) are considered together with the structure of large-scale magnetic fields in the solar corona at R=2.5R S. The entire range of variations in the level of scattering and the associated heliolatitude flow structures in the subsonic solar wind forms over the 11-year solar cycle, as a direct result of the large-scale structure of the evolving magnetic fields at the source of the solar-wind streamlines. 相似文献
13.
Latitude-time (butterfly) diagrams of the large-scale solar magnetic field differ appreciably from the butterfly diagrams
for sunspots. Tilted features corresponding to waves propagating from the middle latitudes to the equator are virtually absent
from the diagrams for the large-scale magnetic field. The latitude-time diagram of the 22-year solar cycle based on data for
the large-scale surface field appears as a checkerboard pattern rather than a traveling wave. Solutions describing similar
behavior for the poloidal magnetic field are found for Parker’s solar-dynamo equations. These solutions agree with observations
especially well if meridional circulation is added to the two sources generating the magnetic-field in this dynamo-differential
rotation and mirror-asymmetric convection. 相似文献
14.
Data on the global magnetic field (GMF) of the Sun as a star for 1968–1999 are used to determine the correlation of the GMF with the radial component of the interplanetary magnetic field (IMF) |B r|; all data were averaged over a half year. The time variations in the GMF |H| are better correlated with variations in |B r|; than the results of extrapolating the field from the “source surface” to the Earth’s orbit in a potential model based on magnetic synoptic maps of the photosphere. Possible origins for the higher correlation between the GMF and IMF are discussed. For both the GMF and IMF, the source surface actually corresponds to the quiet photosphere—i.e., background fields and coronal holes—rather than to a spherical surface artificially placed ≈2.5 R ⊙ from the center of the Sun, as assumed in potential models (R ⊙ is the solar radius). The mean effective strength of the photospheric field is about 1.9 G. There is a nearly linear dependence between |H| and |B r|. The strong correlation between variations in |H| and |B r| casts doubt on the validity of correcting solar magnetic fields using the so-called “saturation” factor δ?1 (for magnetograph measurements in the λ 525.0 nm FeI line). 相似文献
15.
We present the results of radio sounding observations probing the inner solar wind near the minimum of the solar-activity cycle, using polarized pulses from PSR B0525+21 and PSR B0531+21 received when the lines of sight toward these pulsars were close to the Sun. The observations were obtained in June 2005 and June 2007 on the Large Phased Array of the Lebedev Physical Institute at 111 MHz. An upper limit for the scattering of giant pulses from PSR B0531+21 due to their passage through the turbulent solar-wind plasma is determined. The arrival-time delays for pulses from PSR B0531+21 are used to derive the radial dependence of the mean density of the circumsolar plasma. The resulting density distribution indicates that the acceleration of fast, high-latitude solar-wind outflows continues to heliocentric distances of 5–10R ⊙, where R ⊙ is the solar radius. The mean plasma density at heliocentric distances of about 5R ⊙ is 1.4 × 104 cm?3, substantially lower than at the solar-activity maximum. This is associated with the presence of polar coronal holes. The Faraday rotation measure at heliocentric distances of 6–7R ⊙ is estimated. Deviations of the spatial distribution of the magnetic field from spherical symmetry are comparatively modest in the studied range of heliocentric distances. 相似文献
16.
We have performed three-dimensional magnetohydrodynamical calculations of stream accretion in cataclysmic variable stars for
which the white dwarf primary possesses a strong, complex magnetic field. These calculations were motivated by observations
of polars: cataclysmic variables containing white dwarfs with magnetic fields sufficiently strong to prevent the formation
of an accretion disk. In this case, an accretion stream flows from the L1 point and impacts directly onto one or more spots on the surface of the white dwarf. Observations indicate that the white
dwarfs in some binaries possess complex (non-dipolar) magnetic fields. We performed simulations of ten polars, with the only
variable being the azimuthal angle of the secondary with respect to the white dwarf. These calculations are also applicable
to asynchronous polars, where the spin period of the white dwarf differs by a few percent from the orbital period. Our results
are equivalent to calculating the structure of one asynchronous polar at ten different spin-orbit beat phases. Our models
have an aligned dipolar plus quadrupolar magnetic field centered on the whitedwarf primary. We find that, with a sufficiently
strong quadrupolar component, an accretion spot arises near the magnetic equator for slightly less than half our simulations,
while a polar accretion zone is active for most of the remaining simulations. For two configurations, accretion at a dominant
polar region and in an equatorial zone occurs simultaneously. Most polar studies assume that the magnetic field is dipolar,
especially for single-pole accretors. We demonstrate that, with the orbital parameters and magnetic-field strengths typical
of polars, the accretion flow patterns can vary widely in the case of a complex magnetic field. This may make it difficult
formany polars to determine observationally whether the field is pure dipolar or is more complex, but there shoulid be indications
for some systems. In particular, a complex magnetic field should be suspected if there is an accretion zone near the white
dwarf’s equator (assumed to be in the orbital plane) or if there are two or more accretion regions that cannot be fitted by
dipolar magnetic field. Magnetic-field constraints are expected to be substantially stronger for asynchronous polars, with
clearer signs of complex field geometry due to changes in the accretion flow structure as a function of azimuthal angle. These
indications become clearer in asynchronous polars because each azimuthal angle corresponds to a different spin-orbit beat
phase. 相似文献
17.
Quasi-biennial oscillations (QBOs) can clearly be distinguished in uniform series of data on the solar magnetic-field polarity derived from Hα observations in 1915–1999. These have been proven to represent oscillations of the global magnetic field of the Sun. This is verified by spectral analyses executed using various methods: the QBOs are clearly visible in low harmonics (l=1–3), but abruptly disappear for l=4 and higher. First and foremost, the QBOs are displayed in variations of the sector structure of the large-scale magnetic field, demonstrating that they correspond to variations of the horizontal multipoles. 相似文献
18.
Observations of the large-scale solar magnetic field (synoptic maps) and measurements of the magnetic field of the Sun as a star (the total magnetic field) are used to determine the dipole magnetic moment and direction of the dipole field for three successive solar cycles. Both the magnetic moment and its vertical and horizontal components vary regularly during the cycle, but never disappear completely. A wavelet analysis of the total magnetic field shows that the amplitude of the 27-day variations of this field is very closely related to the magnetic moment of the horizontal dipole. The reversal of the global dipole field corresponds to a change in the inclination of its axis and occurs in a series of steps lasting one to two years rather than continuously. Before the onset of the reversal, the dipole axis precesses relative to the solar rotational axis, then shifts in a meridianal plane, reaching very low latitudes, where a substantial shift in longitude then begins. These results are discussed in connection with helioseismological data indicating the existence of oscillations with a period of about 1.3 yr and properties of dynamo processes for the case of an inclined rotator. 相似文献
19.
We consider the influence of a non-dipolar magnetic field on the gamma-ray emission from the polar regions of a radio pulsar. The pulsar is treated in a Goldreich-Julian model with a free flow of charge from the surface of the neutron star. When finding the intensity of the gamma-ray radiation of the pulsar tube, both curvature gamma-ray radiation from the primary electrons and non-resonance inverse Compton scattering of thermal photons from the polar cap on primary electrons are taken into account. When finding the height of the upper plate of the pulsar diode, we included only positrons created by the curvature radiation of primary electrons. We assumed that the polar cap is heated by the return positron current. The influence on the gamma-ray emission of variations in both the radius of curvature of the magnetic force lines and in the electric field due to the non-dipolarity of the magnetic field were taken into account. The presence of even weak non-dipolarity of the magnetic field leads to a sharp decrease in the intensity of the gamma-ray emission from the pulsar tube at energies 1–100 MeV, while the intensity of the inverse Compton radiation (at energies 1–100 GeV) varies only relatively weakly. 相似文献
20.
The global component of the large-scale magnetic field is identified using two methods applied to Stanford Observatory data on the photospheric magnetic field obtained in 1976–2000. Two significantly different phases are observed in the evolution of the global magnetic field detected during the 11-year cycle. Phase I includes the cycle growth and maximum, while Phase II includes the cycle decay and minimum. During Phases I and II of the 11-year cycle, two different processes dominate both the magnetic-field generation and the solar activity as a whole. At lower latitudes, Phase I demonstrates a longitudinal splitting of the magnetic field, which takes the form of stripes of opposite polarities located parallel to the equator. The long dimensions of these stripes are grouped near 90° and 180°. The global magnetic field rotates as a rigid body with a period that is appreciably shorter than the Carrington-rotation period and reaches about 27.225 days. During reversals of the polarity of the global magnetic field, the field displays opposite signs in antipodal longitude intervals with lengths of about 135°. Thus, the equatorial dipolar field is clearly manifest during Phase I. Transitional longitude intervals with widths of 45° located between 135° intervals correspond to the positions of active longitudes of sunspots, indicating a close relationship between the global and local magnetic fields. 相似文献