共查询到20条相似文献，搜索用时 31 毫秒
1.
We summarize studies of helical properties of solar magnetic fields such as current helicity and twist of magnetic fields in solar active regions (ARs), that are observational tracers of the alpha-effect in the solar convective zone (SCZ). Information on their spatial distribution is obtained by analysis of systematic mag-netographic observations of active regions taken at Huairou Solar Observing Station of National Astronomical Observatories of Chinese Academy of Sciences. The main property is that the tracers of the alpha-effect are antisymmetric about the solar equator. Identifying longitudinal migration of active regions with their individual rotation rates and taking into account the internal differential rotation law within the SCZ known from helioseismology, we deduce the distribution of the effect over depth. We have found evidence that the alpha-effect changes its value and sign near the bottom of the SCZ, and this is in accord with the theoretical studies and numerical simulations. We discuss 相似文献
2.
R. Brajša H. Wöhl D. Ruždjak B. Vršnak G. Verbanac L. Svalgaard J.-F. Hochedez 《Astronomische Nachrichten》2007,328(10):1013-1015
The interaction between differential rotation and magnetic fields in the solar convection zone was recently modelled by Brun (2004). One consequence of that model is that the Maxwell stresses can oppose the Reynolds stresses, and thus contribute to the transport of the angular momentum towards the solar poles, leading to a reduced differential rotation. So, when magnetic fields are weaker, a more pronounced differential rotation can be expected, yielding a higher rotation velocity at low latitudes taken on the average. This hypothesis is consistent with the behaviour of the solar rotation during the Maunder minimum. In this work we search for similar signatures of the relationship between the solar activity and rotation determined tracing sunspot groups and coronal bright points. We use the extended Greenwich data set (1878–1981) and a series of full-disc solar images taken at 28.4 nm with the EIT instrument on the SOHO spacecraft (1998–2000). We investigate the dependence of the solar rotation on the solar activity (described by the relative sunspot number) and the interplanetary magnetic field (calculated from the interdiurnal variability index). Possible rotational signatures of two weak solar activity cycles at the beginning of the 20th century (Gleissberg minimum) are discussed. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
3.
J. O. Stenflo 《Solar physics》1974,36(2):495-515
The differential rotation and sector structure of solar magnetic fields has been studied using digitized data on photospheric magnetic fields recorded at the Mount Wilson Observatory during the period August 1959–May 1970. The power spectra show considerable power in high-frequency peaks, corresponding to harmonic components with wavelengths less than 1/10 solar rotation. Calculations for a series of shorter time intervals show how the distribution of power over the various harmonic components in the sector pattern varies strongly with the solar cycle. The equatorial rotation rate of solar magnetic fields is about 0.1 km s-1 faster than that of the photospheric plasma determined from Doppler shifts. It is shown that the Doppler measurements mainly refer to the non-network regions. The differential flow of 0.1 km s-1 forms streamlines around the magnetic fine structures. The different rotation rates of various solar features can be explained in terms of the rotation rates of magnetic and non-magnetic regions. The rotation rates of the magnetic fields in active and quiet regions agree at the equator. At higher latitudes, however, the background fields deviate less from solid-body rotation, indicating that their source is below the deepest layers to which the sunspot magnetic fields penetrate. This suggests that turbulent diffusion of the field in old active regions may not be the main source for the background magnetic field, but that the source is located close to a rigidly rotating solar core with a synodic rotation period of 26.87 days. 相似文献
4.
5.
Allan Sacha Brun 《Solar physics》2004,220(2):333-345
We have performed 3-D numerical simulations of compressible convection under the influence of rotation and magnetic fields
in spherical shells. They aim at understanding the subtle coupling between convection, rotation and magnetic fields in the
solar convection zone. We show that as the magnetic Reynolds number is increased in the simulations, the magnetic energy saturates
via nonlinear dynamo action, to a value smaller but comparable to the kinetic energy contained in the shell, leading to increasingly
strong Maxwell stresses that tend to weaken the differential rotation driven by the convection. These simulations also indicate
that the mean toroidal and poloidal magnetic fields are small compared to their fluctuating counterparts, most of the magnetic
energy being contained in the non-axisymmetric fields. The intermittent nature of the magnetic fields generated by such a
turbulent convective dynamo confirms that in the Sun the large-scale ordered dynamo responsible for the 22-year cycle of activity
can hardly be located in the solar convective envelope. 相似文献
6.
A. A. Ruzmaikin 《Solar physics》1985,100(1-2):125-140
The basic features of the solar activity mechanism are explained in terms of the dynamo theory of mean magnetic fields. The field generation sources are the differential rotation and the mean helicity of turbulent motions in the convective zone. A nonlinear effect of the magnetic field upon the mean helicity results in stabilizing the amplitude of the 22-year oscillations and forming a basic limiting cycle. When two magnetic modes (with dipole and quadrupole symmetry) are excited nonlinear beats appear, which may be related to the secular cycle modulation.The torsional waves observed may be explained as a result of the magnetic field effect upon rotation. The magnetic field evokes also meriodional flows.Adctual variations of the solar activity are nonperiodic since there are recurrent random periods of low activity of the Maunder minimum type. A regime of such a magnetic hydrodynamic chaos may be revealed even in rather simple nonlinear solar dynamo models.The solar dynamo gives rise also to three-dimensional, non-axisymmetric magnetic fields which may be related to a sector structure of the solar field. 相似文献
7.
O. A. Andryeyeva Ya. I. Zyelyk N. N. Stepanian Yu. T. Tsap 《Bulletin of the Crimean Astrophysical Observatory》2010,106(1):8-13
The cyclicity in the latitudinal distribution of the growth and decay rates of the total magnetic fluxes for weak magnetic
fields is investigated. The synoptic maps of the line-of-sight solar magnetic field strength obtained at the Kitt Peak Observatory
(USA) from January 1, 1977, to September 30, 2003, are used as the observational material. The latitudinal distributions of
the growth rates of total magnetic fluxes with various strengths constructed from them and their evolution during three solar
cycles have been compared with the analogous distribution of the total powers of rotation with various periods as well as
the relative sunspot numbers and areas. The results obtained allow a unified picture of the development of solar cycles for
weak and strong magnetic fields to be formulated. A new cycle begins with the growth of weak magnetic fields with a strength
of 0–200 G at latitudes 20°–25° in both hemispheres. This occurs one year before the activity minimum determined from sunspots.
Two years later, the growth rate of the total magnetic flux, which begins to propagate equatorward and poleward, reaches a
maximum. This process coincides with the onset of the growth of strong sunspot magnetic fields at the corresponding latitudes
and the formation of zones with a stable rotation. Subsequently, a fall-off in growth rate and then a flux decay for weak
magnetic fields correspond to the growth of the sunspot areas. In light of the dynamo theory, the results obtained suggest
that strong and weak magnetic fields are generated near the bottom of the convection zone, while the observed differences
in their behavior are determined by the interaction of emerging magnetic flux tubes of various strengths with turbulent plasma
motions inside the Sun. 相似文献
8.
V. Bumba 《Solar physics》1987,110(1):51-57
We have tried to decide whether the typical circular cellular-like features, which are striking during some intervals in the large-scale distribution of weak magnetic fields measured with low resolution, are related to large-scale convective motions. Two scales of such patterns were found and their morphological, kinematical and evolutionary behaviour was estimated. Their slower and overall rotation is also demonstrated in comparison with the rotation of highly averaged sunspot and magnetic fields. It is difficult to explain all the observed characteristics as random, or due to the method of field measurement and map construction used. We also discuss the change of their magnetic field polarities with the solar polar field reversal. 相似文献
9.
G. D. Parker 《Solar physics》1987,108(1):77-87
Long-lived brightness structures in the solar electron corona persist over many solar rotation periods and permit an observational determination of coronal magnetic tracer rotation as a function of latitude and height in the solar atmosphere. For observations over 1964–1976 spanning solar cycle 20, we compare the latitude dependence of rotation at two heights in the corona. Comparison of rotation rates from East and West limbs and from independent computational procedures is used to estimate uncertainty. Time-averaged rotation rates based on three methods of analysis demonstrate that, on average, coronal differential rotation decreases with height from 1.125 to 1.5 R
S. The observed radial variation of differential rotation implies a scale height of approximately 0.7 R
S for coronal differential rotation.Model calculations for a simple MHD loop show that magnetic connections between high and low latitudes may produce the observed radial variations of magnetic tracer rotation. If the observed tracer rotation represents the rotation of open magnetic field lines as well as that of closed loops, the small scale height for differential rotation suggests that the rotation of solar magnetic fields at the base of the solar wind may be only weakly latitude dependent. If, instead, closed loops account completely for the radial gradients of rotation, outward extrapolation of electron coronal rotation may not describe magnetic field rotation at the solar wind source. Inward extrapolations of observed rotation rates suggest that magnetic field and plasma are coupled a few hundredths of a solar radius beneath the photosphere. 相似文献
10.
Mordvinov A.V. Salakhutdinova I.I. Plyusnina L.A. Makarenko N.G. Karimova L.M. 《Solar physics》2002,211(1-2):241-253
We investigate the topological properties and evolution of background magnetic fields on synoptic maps from Wilcox Solar Observatory using mathematical morphology methods in terms of the Minkowski functionals. The total length of the neutral line, the total areas occupied by positive and negative polarities, and the Euler characteristics of background magnetic fields vary over an eleven-year cycle. Changes in the length of the neutral line that separates the polarities of the background magnetic field correlate well with flare activity. A time–longitude analysis of solar flare activity revealed a complicated organization and rotation of the entire flare ensemble. On the time–longitude diagram, flare activity is organized into the patterns which follow the rearrangements in background magnetic field and exhibit coexisting and alternating modes of rigid rotation. The character of rotation of the entire flare ensemble is similar to the rotation of background magnetic fields. The emergence of background magnetic fields and changes in their topology and rotation are often accompanied by enhancements in flare activity. A comparative analysis of the topological changes in background magnetic fields and flare activity reveals their causal relation. 相似文献
11.
G. W. Pneuman 《Solar physics》1971,19(1):16-31
Eclipse photographs indicate that large regions of the inner solar corona are confined in various types of closed magnetic configurations and, as a result, do not participate in the general solar wind expansion. In this paper, the rotation of initially poloidal loop configurations of this type, as influenced by differential rotation of the footpoints, is investigated. The analysis is restricted to axially symmetric fields and it is assumed that the toroidal magnetic field induced by differential rotation is small as compared to the initial poloidal field. This restricts the validity of the analysis to times less than about one month.The most interesting physical situation is that of flux tubes existing in one solar hemisphere only, one end of the tube being fixed in the photosphere at a higher latitude than the other. As a consequence, the lower end of the tube rotates at a faster rate than the upper end. Solution of the pertinent equations reveals that the angular velocity measured along a field line increases monotonically from its value at the poleward footpoint to that at the lower footpoint. The variation of angular velocity along the field depends upon the field geometry only and is not directly related to the variation of angular velocity along the solar surface between the footpoints. Depending upon the field configuration, both outward radial increases and decreases are possible. Using the Newton and Nunn model for the surface differential rotation rate, the angular velocity distribution on two particularly simple types of closed magnetic loop systems is determined analytically. It is shown that the angular velocity increases outward in the polar regions but decreases outward near the equator - leading to a decrease in differential rotation with height.The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
12.
S. V. Berdyugina 《Solar physics》2004,224(1-2):123-131
The modulation of solar activity closely follows the solar rotation period suggesting the existence of long-lived active regions
at preferred longitudes. For instance, two preferred active longitudes in both southern and northern hemispheres are found
to be persistent at the century time scale. These regions migrate with differential rotation and periodically alternate their
activity levels showing a flip-flop cycle. The pattern and behaviour of active longitudes on the Sun is similar to that on
cool, rapidly rotating stars with outer convective envelopes. This suggests that the magnetic dynamo, including non-axisymmetric
magnetic fields and flip-flop cycles, is also similar in these stars. This allows us to overview the phenomenon of stellar
magnetic activity and to study it in detail on the Sun. 相似文献
13.
O. A. Andreyeva Ya. I. Zyelyk N. N. Stepanian 《Bulletin of the Crimean Astrophysical Observatory》2008,104(1):1-6
The connection of the differential rotation of solar magnetic fields with the field sign and strength is studied. The synoptic maps of magnetic fields over the last three solar cycles taken at the Kitt Peak Observatory served as input data for the study. The algorithm of magnetic field filtering over 14 chosen strengt intervals and successive 5-degree latitude zones was applied to these data. The Fourier transform of the time series obtained was then used. Analysis of the power spectra led to the conclusion that there are two types of magnetic fields. These differ in strength (0–50 and 50–700 G) and rotation characteristics. The rotation differentiality for strong magnetic field is almost twice as large as that for weak magnetic fields. 相似文献
14.
We examine the effects of rotation about a vertical axis on thermal convection with a simple model in which an inviscid, incompressible fluid of zero thermal conductivity and electrical resistivity is contained in a thin annulus of rectangular cross-section. The initial steady state assumed is one of no motion relative to the rotating frame with constant (unstable) vertical temperature gradient and uniform toroidal magnetic field. Small periodic disturbances are then introduced and the linearized perturbation equations solved. We also determine the second-order mean circulations and magnetic fields that are forced by non-zero Reynolds and thermal stresses and magnetic field transports.The solutions have several properties which are relevant to large-scale solar phenomena if giant long-lived convection cells exist on the sun. In particular, the convective cells are tilted in latitude in the same sense as bipolar magnetic regions, and induce vertical magnetic fields with the same tilt. They transport momentum across latitude circles through Reynolds stresses and induced meridional circulations thus setting up a differential rotation. Cells which grow slowly compared to the rotation rate and have comparable dimensions in latitude and longitude transport momentum toward the equator. The cells also form a poloidal magnetic field from initial toroidal field, in a manner similar to that put forth by Parker.The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
15.
In this paper we study the longitudinal distribution of solar magnetic regions, using the synoptic magnetic maps from Kitt Peak National Observatory, the active region data from Solar Geophysical Data and the Hobservations from Prairie View Solar Observatory. The clusters of activity were identified by comparing the positions of sunspot groups between successive Carrington rotations. We have found that a large percentage of active regions was involved in the clustering process (40–50%, if we only take into account clusters with a minimum lifetime of 4 rotations). The nests followed the differential rotation of the solar surface, within an intrinsic spread. A remarkable feature of sunspot nests detected in our study is their high degree of complexity, with a large number of nests being organized in diverging, converging, or parallel structures. Of the flares which occurred during the time interval of interest, the great majority originated from the sunspot nests; the distribution of the flares between these nests was not uniform, revealing active and quiet nests. A high flaring rate was recorded at the intersection points of diverging or converging nests, suggesting that these points represent violent interactions of magnetic fluxes. The complexes were in continuous interaction, which impacts their properties and future evolution. The behavior of the nests indicate that they are maintained by repeated injection of magnetic flux rather than by the evolution of the surface magnetic fields. 相似文献
16.
M. A. Raadu 《Solar physics》1972,22(2):443-449
It is argued that differential rotation of the photospheric magnetic fields will induce currents in the corona. The work done against surface magnetic stresses will increase the energy content of the coronal magnetic field. The electrical conductivities are high and the foot points of field lines move with the differential rotation. The force-free field equations are solved with this constraint to obtain a minimum estimate of the energy increase for a quadrupole field. During a solar rotation the magnetic energy increases by 25%. Local release of this energy in the corona would have a significant effect. The expansion of field lines as a result of the differential rotation should increase the amount of flux and the field strength in the solar wind region.The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
17.
A. G. Tlatov 《Astronomy Letters》2007,33(11):771-779
We have performed a comparative analysis of the results of our study of the 22-year rotation variations obtained from data on large-scale magnetic fields in the Hα line, magnetographic observations, and spectral-corona observations. All these types of data suggest that the rotation rate at low latitudes slows down at an epoch close to the maximum of odd activity cycles. The 22-year waves of rotation-rate deviation from the mean values drift from high latitudes toward the equator in a time comparable to the magnetic-cycle duration. We discuss the possibility of the generation of a solar magnetic cycle by the interaction of 22-year torsional oscillations with the slowly changing or relic magnetic field. We consider the generation mechanisms of the high-latitude magnetic field through a superposition of the magnetic fields produced by the decay and dissipation of bipolar groups and the relic or slowly changing magnetic field and a superposition of the activity wave from the next activity cycle at high latitudes. 相似文献
18.
太阳活动，除了涵盖太阳表面磁场驱动的活动现象外，还包括光度、自转和对称性等物理因素的长期演化。研究它们变化的周期对深入理解其产生机制有着重要的指导意义。从1984年Rieger等人首次发现耀斑的产生率存在约154d周期始，人们在很多现象中都找到了它的踪影，150余d的周期成了继11yr太阳活动周和27d太阳自转周后最引人注目的新周期。重点综述了在耀斑、黑子等活动领域内对150d周期现象研究的现状，介绍了有关它成因的研究进展，指出了尚待解决的问题及进一步努力的方向。 相似文献
19.
Solar synoptic charts are normally displayed using Carrington Coordinates with each Carrington rotation being centered at a Carrington longitude of 180^° and with a full 360^° of solar surface properties included. For the case of reproducing solar magnetic fields in the corona and heliosphere, these maps are wrapped onto the solar surface to provide the boundary conditions for a solution to a set of modeling equations such as the potential field theory equations. Due to differential rotation, the full solar surface cannot be reproduced in this fashion since different parts of the solar surface are observed at different times. We describe here the proper technique for combining observations of the solar magnetic or velocity fields made at different times into a representation of the whole solar surface at a particular specified time that we refer to as a “snapshot heliographic map“. 相似文献
20.
Ke-Ke Zhang Xin-Hao LiaoSchool of Mathematical Sciences University of Exeter EX QE UK kzhang@ex.ac.ukShanghai Astronomical Observatory Shanghai xhliao@center.shao.ac.cn 《中国天文和天体物理学报》2003,3(1):12-33
Generation of the Sun‘s magnetic fields by self-inductive processes in the solar electrically conducting interior, the solar dynamo theory, is a fundamentally important subject in astrophysics. The kinematic dynamo theory concerns how the magnetic fields are produced by kinematically possible flows without being constrained by the dynamic equation. We review a number of basic aspects of the kinematic dynamo theory, including the magnetohydrodynamic approximation for the dynamo equation, the impossibility of dynamo action with the solar differential rotation, the Cowling‘s anti-dynamo theorem in the solar context, the turbulent alpha effect and recently constructed three-dimensional interface dynamos controlled by the solar tachocline at the base of the convection zone. 相似文献