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1.
Astronomy Reports - The effect of large-scale magnetic fields generated by the solar dynamo on the irradiance of the Sun and stratification of the solar convection zone is studied using a numerical... 相似文献
2.
V. V. Pipin 《Astronomy Reports》2007,51(5):411-420
We consider a solar dynamo mechanism that generates large-scale magnetic fields due to the combined action of cyclonic flows (the α effect), differential rotation (the Θ effect), and the non-uniformity of large-scale magnetic fields (the Θ × J effect). Our results are based on numerical model which takes into account currently available data on the differential rotation of the convection zone and the intensity of convective flows in the solar interior. A reasonable choice of parameters characterizing the intensity of magnetic-field generation by the α and Θ × J mechanisms can account for an oscillatory dynamo regime with properties similar to the 22-year magnetic-activity cycle of the Sun. We analyze the nonlinear saturation of the generation effects in the large-scale magnetic field, due to either magnetic stresses or the conservation of magnetic helicity. Allowance for the helicity of the small-scale magnetic fields is of crucial importance in limiting the energy of the generated large-scale magnetic field. 相似文献
3.
Large-scale solar magnetic fields in the latitude range 50° S–50° N are analyzed in detail for a long time interval (1915–1990). We are primarily concerned with the two types of large-scale fields forming the two-and four-sector patterns on the Sun. The rotation parameters of these structures are obtained for all latitudes considered. The contribution of the two-sector structure grows and that of the four-sector structure decreases toward high latitudes. The magnetic field is activated simultaneously over a wide latitude range. Since both magnetic-field systems exhibit quasi-rigid rotation, their current systems must either be concentrated in a narrow latitude range or be situated beneath the convection zone, where rotation is only weakly differential. A period of about three years is manifest in the difference between the rotation periods for the two types of magnetic field. Physically, this may imply that these oscillations are external with respect to any level, and there is some phase delay due to their propagation from one level to another. We can conclude with a fair degree of certainty that as the activity level rises, the rotation speed decreases, and vice versa. 相似文献
4.
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
5.
It is shown that a hypothetical relict magnetic field in the solar radiative-transport zone that penetrates into the convective
zone would affect the solar dynamo, resulting in radical changes in the butterfly diagrams. This would transform the traveling
waves of activity into standing waves. A comparison of our results with the well-known butterfly diagrams for the Sun gives
an upper limit of the order of some tens G for the value of relict magnetic field penetrating into the solar convective zone.
At the same time, it is not ruled out that such relict magnetic fields in other solar-type stars are strong enough to make
the activity waves become standing waves. 相似文献
6.
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
7.
V. N. Krivodubskii 《Astronomy Reports》2001,45(9):738-745
A mixing-length approximation is used to calculate Kλ for a Parker dynamo wave excited by the dynamo mechanism near the base of the solar convection zone (K is the wave number of the dynamo wave and λ the extent of the dynamo region). In a turbulent-dynamo model, this number characterizes the modes of the global magnetic field generated by a mechanism based on the joint action of the mean helical turbulence and solar differential rotation. Estimates are obtained for the helicity and radial angular-velocity gradient using the most recent helioseismological measurements at the growth phase of solar cycle 23. These estimates indicate that the dynamo mechanism most efficiently excites the fundamental antisymmetric (odd), dipole, mode of the poloidal field (Kλ≈?7) at low latitudes, while the conditions at latitudes above 50° are more favorable for the excitation of the lowest symmetric (even), quadrupole, mode (Kλ≈+8). The resulting north-south asymmetry of the poloidal field can explain the magnetic anomaly (“monopole” structure) of the polar fields observed near solar-cycle maxima. The effect of α quenching increases the calculated period of the dynamo-wave propagation from middle latitudes to the equator to about seven years, in rough agreement with the observed duration of the solar cycle. 相似文献
8.
Magnetic Hα synoptic maps of the Sun for 1915–1999 are analyzed and the intensities of spherical harmonics of the large-scale solar magnetic field computed. The possibility of using these Hα maps as a database for investigations of long-term variations of solar activity is demonstrated. As an example, the magnetic-field polarity distribution for the Hα maps and the analogous polarity distribution for the magnetographic maps of the Stanford observatory for 1975–1999 are compared. An activity index A(t) is introduced for the large-scale magnetic field, which is the sum of the magnetic-moment intensities for the dipole and octupole components. The 11-year cycle of the large-scale solar magnetic field leads the 11-year sunspot cycle by, on average, 5.5 years. It is concluded that the observed weak large-scale solar magnetic field is not the product of the decay of strong active-region fields. Based on the new data, the level of the current (23rd) solar-activity cycle and some aspects of solar-cycle theory are discussed. 相似文献
9.
The sector structure and variations in the large-scale magnetic field of the Sun are studied in detail using solar magnetic-field data taken over a long time interval (1915–1990). The two-sector and four-sector structures are independent entities (i.e., their cross correlation is very small), and they are manifest in different ways during the main phases of the 11-year cycle. The contribution of the two-sector structure increases toward the cycle minimum, whereas that of the four-sector structure is larger near the maximum. The magnetic-field sources determining the two-sector structure are localized near the bottom of the convection zone. The well-known 2–3-year quasi-periodic oscillations are primarily associated with the four-sector structure. The variations in the rotational characteristics of these structures have a period of 55–60 years. The results obtained are compared with the latest helioseismology data. 相似文献
10.
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
11.
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
12.
L. L. Kitchatinov 《Astronomy Reports》2004,48(2):153-160
Although the theory of differential rotation is in satisfactory agreement with helioseismological data for the deep convection zone, there are considerable discrepancies near the solar surface. This disagreement can be eliminated if the anisotropy of turbulent convection is taken into account together with the effects of nonuniformity of the medium, on which the most recent models for differential rotation are based. The model for the differential rotation of the convection envelope is supplemented by computations for the transition layer between nonuniform and rigid-body rotation in the upper layers of the solar radiative zone. These are the first computations of differential rotation for the entire volume of the Sun. 相似文献
13.
An experimental study of the source and formation of large-scale streams in the solar wind is presented. Radio-astronomical data from 1998 are compared with optical SOHO observations and solar coronal magnetic fields calculated from Zeeman data obtained at the Wilcox Observatory. A correlation between the geometry of the solar-wind transition region and the strength of coronal magnetic fields is revealed. For the moderate heliolatitudes studied, this correlation divides into three branches corresponding to three types of coronal magnetic-field structures: open structures with field lines escaping into interplanetary space, closed structures with loop-like field lines, and intermediate structures including both open and closed configurations. High-speed streams of solar wind originate in regions with open magnetic structures. These structures are connected with the lateral lobes of streamers at moderate heliolatitudes. Low-speed flows originate above closed magnetic structures, typical of the main bodies of streamers. The lowest-speed solar-wind flows are not associated with coronal streamer structures, and originate in coronal regions with intermediate magnetic configurations simultaneously containing open and closed field lines. In these regions, the white-light corona becomes an extended and amorphous area with high luminosity, which stratifies into a radial structure with narrow stripes at higher resolution. 相似文献
14.
M. Yu. Reshetnyak 《Astronomy Reports》2016,60(2):294-305
The dependences of the magnetic-field strength, variations of the magnetic field, and the multipole level on the amplitudes of the α and ω effects are considered using a two-dimensional model for a Parker dynamo in a spherical layer. Calculations have been carried out for both traditional spatial distributions of α and ω and geostrophic regimes obtained from three-dimensional modeling of thermal convection. Two-dimensional distributions of the dynamo-wave velocities in the zone where magnetic field is generated are presented. Comparisons with the solar and planetary dynamos are considered. 相似文献
15.
Variations in the mean solar magnetic field (MSMF) are studied in both the frequency-time and longitude-time domains. A wavelet analysis of the MSMF clearly demonstrates that variations in the mean field are not stationary. Combined with longitude-time diagrams for the background solar magnetic field (BSMF), the analysis reveals the emergence of the background field, which occurs discretely at intervals of 1.5–2 years. Based on an analysis of the fine structure in MSMF variations, we develop a numerical technique to study timedependent heliographic-longitude distribution of the large-scale magnetic field. A detailed picture of the rotation of the large-scale magnetic field is derived for activity cycles 20–23. Coherent structures are detected in longitude-time diagrams obtained by deconvolving the MSMF series. These structures are related to discrete rigid-rotation modes of the large-scale magnetic fields. Various rotational modes coexist and replace one another. During the phase of activity growth, modes with periods of 27.8–28.5 days dominate, whereas a mode with a rotational period of about 27 days dominates during the decline phase. Occasionally, modes with periods of 29–30 days appear. Most structures in the longitude-time MSMF distribution correspond to similar structures in the BSMF distribution for the northern or southern hemisphere. Chronologically, the emergence of the BSMF has frequently been accompanied by changes in the solar rotational regime and has been correlated with variations in the polarity asymmetry in the course of the 11-year activity cycle. 相似文献
16.
L. L. Kitchatinov 《Astronomy Reports》2008,52(3):247-255
The stability of a toroidal magnetic field in the rotating radiation zone of a star is analyzed to estimate the maximum possible magnitude of relic fields. Equations for small perturbations are obtained taking into account the finite diffusivity and the stabilizing effect of the subadiabatic stratification. The numerical solution of the eigenvalue problem indicates that the threshold field strength for the onset of instability in the radiation zone of the Sun is about 600 G. This figure sets an upper bound for the strength of the relic field. The assumption that magnetic instabilities are present in the solar radiation zone disagrees with the observed abundance of lithium. Our analysis of joint stability of toroidal field and nonuniform rotation shows that two-dimensional MHD solutions for the solar tachocline are stable against three-dimensional perturbations. 相似文献
17.
18.
SOHO-MDI daily magnetic field synoptic data (a 14-year series of daily maps of the solar magnetic field intensity B available at the site ) have been used to analyze the dynamics of the photospheric magnetic field in the vicinity of the solar equator. The standard
deviation s
B
of the field B calculated over areas of tens of square degrees on the solar disk was taken as a basic index. An 11-year variation similar
to that observed at higher latitudes is observed in the vicinity of the equator, and is similar for weak and strong fields;
i.e., the solar cycle exists in the sunspot-free zone. New qualitative data support the idea that the weak background magnetic
field increases toward the solar limb. This angular dependence suggests the existence of a transverse component of the background
field. The magnetic fields in the vicinity of the equator were significantly different in the initial phases of Cycles 23
and 24. Annual variations of s
B
were observed near the center of the solar disk. These variations are due to two factors: the annual variation of the distance
from the equator to the disk center and the increase of s
B
with with distance from the equator. Reliable detection of these variations is an evidence of high accuracy of the s
B
estimates. 相似文献
19.
It is shown that, when all components of the large-scale solar magnetic field are longitudinally averaged, the N polarity and the eastward transverse component of the B φ field associated with both local and large-scale fields over the Northern hemisphere are somewhat stronger and occupy a smaller area during odd cycles than does the field of opposite polarity. This behavior is reversed for even cycles or the Southern hemisphere. The regular Hale law is a particular form of the above rule. The nature of this asymmetry seems to be rooted in the dynamo mechanism itself, and should be important for fields on any scale. 相似文献
20.
L. L. Kitchatinov 《Astronomy Reports》2010,54(1):1-5
The difference in rotation laws between top and bottom of the solar convection zone as revealed by helioseismology may result
from an instability switched on near the bottom. The conclusion results from the analysis of the differential rotation stability.
The instability is sensitive to both differential rotation magnitude and details of the latitudinal profile of the angular
velocity. It can be active in subadiabatically stratified fluids only. The instability does not develop in the bulk of convection
zone but may switch-on in the region of penetrative convection near its base. The growth rates and symmetry types of most
rapidly growing disturbances in dependence on the differential rotation parameters are computed. 相似文献