Cyclic Variations,Magnetic Morphology,and Complexity of Active Regions in Solar Cycles 23 and 24     

Zhukova  A. V.  Sokoloff  D. D.  Abramenko  V. I.  Khlystova  A. I. 《Geomagnetism and Aeronomy》2020,60(6):673-683

Geomagnetism and Aeronomy - In this paper, 2046 active regions of solar cycle 23 and 1507 active regions of solar cycle 24 observed during the period from May 1996 to December 2018 have been...  相似文献   

The Maunder Minimum and the Solar Dynamo     

D. Sokoloff 《Solar physics》2004,224(1-2):145-152

Based on archival observations of solar activity, we suggest a scenario for the Maunder minimum, and compare to what extent this is reproduced by dynamo models of Grand minima. In particular, we argue that the transition into the Maunder minimum was very abrupt, while the end of Maunder minimum was gradual, however, rather rapid as well.  相似文献   

Star formation rate and magnetic fields in spiral galaxies     

E. A. Mikhailov  D. D. Sokoloff  Yu. N. Efremov 《Astronomy Letters》2012,38(9):543-548

We have constructed a dynamo model for the magnetic field in spiral galaxies that takes into account the differences in star formation rates in different galaxies. The difficulty in constructing the model is that the star formation rate does not enter directly into the equations of magnetohydrodynamics, which include only the root-mean-square velocity of the interstellar gas, its density, and the half-thickness of the ionized gas disk. We propose a parametrization of these quantities that relates them to the star formation rate and investigate our model in terms of the so-called no-z approximation, which neglects the details of the magnetic field structure in a direction perpendicular to the galactic disk. The influence of the star formation rate on the galactic dynamo is a threshold one. This influence is small at moderate star formation rates and significant only at very high star formation rates. If the starburst intensity reaches some critical level (exceeding that in the Milky Way by an order of magnitude), then the large-scale magnetic field is destroyed and it is restored only after completion of the starburst. We provide a list of galaxies that exhibit a fairly high star formation rate and that can be interesting to study their magnetic fields.  相似文献   

What can we hope to know about the symmetry properties of stellar magnetic fields?     

David Moss  Steven H. Saar  Dmitry Sokoloff 《Monthly notices of the Royal Astronomical Society》2008,388(1):416-420

We summarize evidence that neither dynamo theory nor the observational data give strong support to the idea that stellar magnetic fields must have dipolar rather than quadrupolar symmetry with respect to the stellar equator. We demonstrate that even the most basic model for magnetic stellar activity, i.e. the Parker migratory dynamo, provides many possibilities for the excitation of large-scale stellar magnetic fields of non-dipolar symmetry. We demonstrate the spontaneous transition of the dynamo-excited magnetic field from one symmetry type to another. We explore observational tests to distinguish between the two types of magnetic field symmetry, and thus detect the presence of quadrupolar magnetic symmetry in stars. Complete absence of quadrupolar symmetry would present a distinct challenge for contemporary stellar dynamo theory. We revisit some observations which, depending on further clarification, may already be revealing some properties of the quadrupolar component of the magnetic fields generated by stellar dynamos.  相似文献   

Current Helicity and Twist as Two Indicators of the Mirror Asymmetry of Solar Magnetic Fields     

D. Sokoloff  H. Zhang  K. M. Kuzanyan  V. N. Obridko  D. N. Tomin  V. N. Tutubalin 《Solar physics》2008,248(1):17-28

A comparison between the two tracers of magnetic field mirror asymmetry in solar active regions – twist and current helicity – is presented. It is shown that for individual active regions these tracers do not possess visible similarity but averaging by time over the solar cycle, or by latitude, reveals similarities in their behavior. The main property of the data set is antisymmetry over the solar equator. Considering the evolution of helical properties over the solar cycle we find signatures of a possible sign change at the beginning of the cycle, though more systematic observational data are required for a definite confirmation. We discuss the role of both tracers in the context of solar dynamo theory.  相似文献   

Turbulent generation of magnetic fields in astrophysical jets     

V. V. Gvaramadze  J. G. Lominadze  A. A. Ruzmaikin  D. d. Sokoloff  A. M. Shukurov 《Astrophysics and Space Science》1988,140(1):165-174

We consider evolution of the regular magnetic field in turbulent astrophysical jets. The observed lateral expansion of a jet is approximately described by a linear in coordinates regular velocity field (the Hubble flow). It is shown that in expanding turbulent jets with non-vanishing mean helicity of the turbulence temporal amplification and effective realignment of the regular magnetic field occurs with the field changing orientation from the transverse to the longitudinal one along the jet axis. The distance at which the realiggment occurs depends on parameters of the jet, in particular, on the power of the central source. Estimates for the jet in a weak source 3C 31 favourably agree with observations.  相似文献   

Asymptotic Properties of a Nonlinear αΩ-Dynamo     

Sokoloff  D.  Soward  A.M. 《Studia Geophysica et Geodaetica》1998,42(3):309-313

We discuss various asymptotic regimes of kinematic nonlinear -dynamos in a thin differentially rotating shell as well as conditions for the applicability of the corresponding asymptotic solutions.  相似文献   

Depolarization and Faraday effects in galaxies     

D. D. Sokoloff  A. A. Bykov  A. Shukurov  E. M. Berkhuijsen  R. Beck  & A. D. Poezd 《Monthly notices of the Royal Astronomical Society》1998,299(1):189-206

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Light propagation in a universe with spatial inhomogeneities     

Victor?LamburtEmail author  Dmitry?Sokoloff  Valery?Tutubalin 《Astrophysics and Space Science》2005,298(3):409-418

A light propagation in a universe which is homogeneous only in average systematically differs from a light propagation in a strictly homogeneous Universe. We demonstrate a link between this effect and the general theory of transport phenomenon in random media. The effective spatial curvature of a universe which is homogeneous only in average is introduced. This curvature is governing a light propagation in such universe. We show that the effective spatial curvature is lower than the average curvature. It implies that a universe with critical mean density looks like a space with negative curvature.  相似文献   

Activity cycle periods in late-type stars     

N. I. Kleeorin  A. A. Ruzmaikin  D. D. Sokoloff 《Astrophysics and Space Science》1983,95(1):131-136

Period of magnetic activity versus the stellar angular velocity for stars of given spectral type having extended convective shells is estimated within the framework of mean field dynamo theory. The dependence appears to be not monotonous, and can be checked by observations.  相似文献