Journal articles on the topic 'Solar magnetic field'
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Korotchenkov, O. O. "Magnetic field-stimulated change of photovoltage in solar silicon crystals." Semiconductor Physics Quantum Electronics and Optoelectronics 16, no. 1 (February 28, 2013): 72–75. http://dx.doi.org/10.15407/spqeo16.01.072.
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Benevolenskaya, E. E. "Solar polar magnetic field." Geomagnetism and Aeronomy 53, no. 7 (November 26, 2013): 891–95. http://dx.doi.org/10.1134/s0016793213070037.
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Solanki, Sami K., Bernd Inhester, and Manfred Schüssler. "The solar magnetic field." Reports on Progress in Physics 69, no. 3 (February 7, 2006): 563–668. http://dx.doi.org/10.1088/0034-4885/69/3/r02.
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Nordlund, Å., and R. F. Stein. "Solar Magnetoconvection." Symposium - International Astronomical Union 138 (1990): 191–211. http://dx.doi.org/10.1017/s0074180900044144.
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As a prelude to discussing the interaction of magnetic fields with convection, we first review some general properties of convection in a stratified medium. Granulation, which is the surface manifestation of the major energy carrying convection scales, is a shallow phenomenon. Below the surface, the topology changes to one of filamentary cool downdrafts, immersed in a gently ascending isentropic background. The granular downflows merge into more widely separated downdrafts, on scales of mesogranulation and super-granulation.The local topology and time evolution of the small scale, kilo Gauss, network and facular magnetic field elements are controlled by convection on the scale of granulation. The topology and time evolution of larger scale magnetic field concentrations are controlled by the hierarchical structure of the horizontal components of the large scale velocity field. In sunspots, the small scale magnetic field structure determines the energy balance, the systematic flows and the waves. Below the surface, the small scale structure of the magnetic field may change drastically, with little observable effect at the surface. We discuss results of some recent numerical simulations of sunspot magnetic fields, and some mechanisms that may be relevant in determining the topology of the sub-surface magnetic field. Finally, we discuss the role of active region magnetic fields in the global solar dynamo.
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Hildebrandt, J., B. Kliem, and A. Krüger. "Solar Coronal Magnetic Fields." Symposium - International Astronomical Union 157 (1993): 59–61. http://dx.doi.org/10.1017/s0074180900173875.
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A short compilation of various radio methods of the determination of magnetic fields in the solar corona is given which, completed by observations in other spectral ranges (e.g. the optical and X-ray ranges), results in a complex picture of the magnetic field. Some topics of interest are the following: (1)Comparison with a standard reference magnetic field in the solar corona,(2)Possible evidence of substantial small-scale fluctuations of the magnetic field (e.g. in active regions),(3)Indication of magnetic fields substantially in excess of the standard distribution (e.g. in limb flare events).
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CHAUHAN, B. C., U. C. PANDEY, and S. DEV. "RSFP PREDICTIONS FOR TRANSVERSE SOLAR MAGNETIC FIELD DISTRIBUTION FROM SOLAR NEUTRINO DATA." Modern Physics Letters A 13, no. 15 (May 20, 1998): 1163–70. http://dx.doi.org/10.1142/s0217732398001236.
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Even though the standard solar model (SSM) has been very successful in predicting the thermal and nuclear evolution of the Sun, it does not throw enough light on solar magnetic activity. In the absence of a generally accepted theory of solar dynamo, various general arguments have been put forth to constrain solar magnetic fields. In the absence of reliable knowledge of solar magnetic fields from available astrophysical data, it may be worthwhile to constrain the solar magnetic fields from solar neutrino observations assuming Resonant Spin-Flavor Precession (RSFP) to be responsible for the solar neutrino deficit. The configuration of solar magnetic field derived in this work is in reasonably good agreement with the magnetic field distribution proposed by Akhmedov et al. (Sov. Phys. JETP68, 250 (1989)). However, the magnetic field distribution in the radiation zone used by Pulido (Phys. Rep.211, 167 (1992)) is ruled out. The magnitude of the magnetic field in the radiation and convective zones of the Sun are very sensitive to the value chosen for the neutrino magnetic moment. However, any change in the value of neutrino magnetic moment does not affect the magnetic field distribution as it only scales the magnetic field strength at different points by the same amount.
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Candelaresi, S., D. I. Pontin, and G. Hornig. "Magnetic field line braiding in the solar atmosphere." Proceedings of the International Astronomical Union 12, S327 (October 2016): 77–81. http://dx.doi.org/10.1017/s1743921317001818.
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AbstractUsing a magnetic carpet as model for the near surface solar magnetic field we study its effects on the propagation of energy injectected by photospheric footpoint motions. Such a magnetic carpet structure is topologically highly non-trivial and with its magnetic nulls exhibits qualitatively different behavior than simpler magnetic fields. We show that the presence of magnetic fields connecting back to the photosphere inhibits the propagation of energy into higher layers of the solar atmosphere, like the solar corona. By applying certain types of footpoint motions the magnetic field topology is is greatly reduced through magnetic field reconnection which facilitates the propagation of energy and disturbances from the photosphere.
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Tobias, Steven, and Niget Weiss. "Solar magnetic field poses problems." Physics World 12, no. 12 (December 1999): 56. http://dx.doi.org/10.1088/2058-7058/12/12/18.
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Демидов, Михаил, and Mikhail Demidov. "Possibilities and problems of solar magnetic field observations for space weather forecast." Solar-Terrestrial Physics 3, no. 1 (May 5, 2017): 26–39. http://dx.doi.org/10.12737/article_58f96ef99d4cd9.20657784.
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An essential part of the space weather problem, important in the last decades, is the forecast of near-Earth space parameters, ionospheric and geomagnetic conditions on the basis of observations of various phenomena on the Sun. Of particular importance are measurements of magnetic fields as they determine the spatial structure of outer layers of the solar atmosphere and, to a large extent, solar wind parameters. Due to lack of opportunities to observe magnetic fields directly in the corona, the almost only source of various models for quantitative calculation of heliospheric parameters are daily magnetograms measured in photospheric lines and synoptic maps derived from these magnetograms. It turns out that results of the forecast, in particular of the solar wind velocity in Earth’s orbit and the position of the heliospheric current sheet, greatly depend not only on the chosen calculation model, but also on the original material because magnetograms from different instruments (and often observations in different lines at the same), although being morphologically similar, may differ significantly in a detailed quantitative analysis. A considerable part of this paper focuses on a detailed analysis of this particular aspect of the problem of space weather forecast.
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Мордвинов, Александр, Aleksandr Mordvinov, Алексей Певцов, Aleksey Pevtsov, Лука Бертелло, Luka Bertello, Гордон Петри, and Gordon Petri. "The reversal of the Sun’s magnetic field in cycle 24." Solar-Terrestrial Physics 2, no. 1 (June 1, 2016): 3–18. http://dx.doi.org/10.12737/19856.
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Analysis of synoptic data from the Vector Spectromagnetograph (VSM) of the Synoptic Optical Long-term Investigations of the Sun (SOLIS) and the NASA/NSO Spectromagnetograph (SPM) at the NSO/Kitt Peak Vacuum Telescope facility shows that the reversals of solar polar magnetic fields exhibit elements of a stochastic process, which may include the development of specific patterns of emerging magnetic flux, and the asymmetry in activity between Northern and Southern hemispheres. The presence of such irregularities makes the modeling and prediction of polar field reversals extremely hard if possible. In a classical model of solar activity cycle, the unipolar magnetic regions (UMRs) of predominantly following polarity fields are transported polewards due to meridional flows and diffusion. The UMRs gradually cancel out the polar magnetic field of the previous cycle, and rebuild the polar field of opposite polarity setting the stage for the next cycle. We show, however, that this deterministic picture can be easily altered by the developing of a strong center of activity, or by the emergence of an extremely large active region, or by a ‘strategically placed’ coronal hole. We demonstrate that the activity occurring during the current cycle 24 may be the result of this randomness in the evolution of the solar surface magnetic field.
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Yoshida, Minami, Toshifumi Shimizu, and Shin Toriumi. "Which Component of Solar Magnetic Field Drives the Evolution of Interplanetary Magnetic Field over the Solar Cycle?" Astrophysical Journal 950, no. 2 (June 1, 2023): 156. http://dx.doi.org/10.3847/1538-4357/acd053.
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Abstract The solar magnetic structure changes over the solar cycle. It has a dipole structure during solar minimum, where the open flux extends mainly from the polar regions into the interplanetary space. During maximum, a complex structure is formed with low-latitude active regions and weakened polar fields, resulting in spread open field regions. However, the components of the solar magnetic field that are responsible for long-term variations in the interplanetary magnetic field (IMF) are not clear, and the IMF strength estimated based on the solar magnetic field is known to be underestimated by a factor of 3–4 against the actual in situ observations (the open flux problem). To this end, we decomposed the coronal magnetic field into the components of the spherical harmonic function of degree and order (ℓ, m) using the potential field source surface model with synoptic maps from SDO/HMI for 2010–2021. As a result, we found that the IMF rapidly increased in 2014 December (7 months after the solar maximum), which coincided with the increase in the equatorial dipole, (ℓ, m) = (1, ±1), corresponding to the diffusion of active regions toward the poles and in the longitudinal direction. The IMF gradually decreased until 2019 December (solar minimum) and its variation corresponded to that of the nondipole component ℓ ≥ 2. Our results suggest that the understanding of the open flux problem may be improved by focusing on the equatorial dipole and the nondipole component and that the influence of the polar magnetic field is less significant.
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Schmieder, Brigitte. "Extreme solar storms based on solar magnetic field." Journal of Atmospheric and Solar-Terrestrial Physics 180 (November 2018): 46–51. http://dx.doi.org/10.1016/j.jastp.2017.07.018.
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Virtanen, I. O. I., I. I. Virtanen, A. A. Pevtsov, L. Bertello, A. Yeates, and K. Mursula. "Reconstructing solar magnetic fields from historical observations." Astronomy & Astrophysics 627 (June 25, 2019): A11. http://dx.doi.org/10.1051/0004-6361/201935606.
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Aims. The evolution of the photospheric magnetic field has only been regularly observed since the 1970s. The absence of earlier observations severely limits our ability to understand the long-term evolution of solar magnetic fields, especially the polar fields that are important drivers of space weather. Here, we test the possibility to reconstruct the large-scale solar magnetic fields from Ca II K line observations and sunspot magnetic field observations, and to create synoptic maps of the photospheric magnetic field for times before modern-time magnetographic observations. Methods. We reconstructed active regions from Ca II K line synoptic maps and assigned them magnetic polarities using sunspot magnetic field observations. We used the reconstructed active regions as input in a surface flux transport simulation to produce synoptic maps of the photospheric magnetic field. We compared the simulated field with the observed field in 1975−1985 in order to test and validate our method. Results. The reconstruction very accurately reproduces the long-term evolution of the large-scale field, including the poleward flux surges and the strength of polar fields. The reconstruction has slightly less emerging flux because a few weak active regions are missing, but it includes the large active regions that are the most important for the large-scale evolution of the field. Although our reconstruction method is very robust, individual reconstructed active regions may be slightly inaccurate in terms of area, total flux, or polarity, which leads to some uncertainty in the simulation. However, due to the randomness of these inaccuracies and the lack of long-term memory in the simulation, these problems do not significantly affect the long-term evolution of the large-scale field.
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Rice, Oliver E. K., and Anthony R. Yeates. "Global Coronal Equilibria with Solar Wind Outflow." Astrophysical Journal 923, no. 1 (December 1, 2021): 57. http://dx.doi.org/10.3847/1538-4357/ac2c71.
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Abstract Given a known radial magnetic field distribution on the Sun’s photospheric surface, there exist well-established methods for computing a potential magnetic field in the corona above. Such potential fields are routinely used as input to solar wind models, and to initialize magneto-frictional or full magnetohydrodynamic simulations of the coronal and heliospheric magnetic fields. We describe an improved magnetic field model that calculates a magneto-frictional equilibrium with an imposed solar wind profile (which can be Parker’s solar wind solution, or any reasonable equivalent). These “outflow fields” appear to approximate the real coronal magnetic field more closely than a potential field, take a similar time to compute, and avoid the need to impose an artificial source surface. Thus they provide a practical alternative to the potential field model for initializing time-evolving simulations or modeling the heliospheric magnetic field. We give an open-source Python implementation in spherical coordinates and apply the model to data from solar cycle 24. The outflow tends to increase the open magnetic flux compared to the potential field model, reducing the well-known discrepancy with in situ observations.
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Stein, Robert F., and Åke Nordlund. "Solar Surface Magnetoconvection." Symposium - International Astronomical Union 210 (2003): 169–80. http://dx.doi.org/10.1017/s0074180900133340.
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Magnetoconvection simulations on meso-granule and granule scales near the solar surface are used to study small scale dynamo activity, the emergence and disappearance of magnetic flux tubes, and the formation and evolution of micropores.From weak seed fields, convective motions produce highly intermittent magnetic fields in the intergranular lanes which collect over the boundaries of the underlying meso-granular scale cells. Instances of both emerging magnetic flux loops and magnetic flux disappearing from the surface occur in the simulations. We show an example of a flux tube collapsing to kG field strength and discuss how the nature of flux disappearance can be investigated. Observed Stokes profiles of small magnetic structures are severely distorted by telescope diffraction and seeing.Because of the strong stratification, there is little recycling of plasma and field in the surface layers. Recycling instead occurs by exchange with the deep layers of the convection zone. Plasma and field from the surface descend through the convection zone and rise again toward the surface. Because only a tiny fraction of plasma rising up from deep in the convection zone reaches the surface due to mass conservation, little of the magnetic energy resides in the near surface layers. Thus the dynamo acting on weak incoherent fields is global, rather than a local surface dynamo.
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Zhang, Hongqi. "Helicity of solar magnetic field from observations." Proceedings of the International Astronomical Union 5, S264 (August 2009): 181–90. http://dx.doi.org/10.1017/s1743921309992602.
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AbstractThe helicity is an important quantity to present the basic topological configuration of magnetic field transferred form the solar subatmosphere into the interplanetary space. In this paper, we present the observational solar magnetic field and the relationship with the magnetic helicity.
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Tiwari, Sanjiv Kumar. "Helicity of the solar magnetic field." Proceedings of the International Astronomical Union 6, S273 (August 2010): 21–27. http://dx.doi.org/10.1017/s1743921311014955.
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AbstractHelicity measures complexity in the field. Magnetic helicity is given by a volume integral over the scalar product of magnetic field B and its vector potential A. A direct computation of magnetic helicity in the solar atmosphere is not possible due to unavailability of the observations at different heights and also due to non-uniqueness of A. The force-free parameter α has been used as a proxy of magnetic helicity for a long time. We have clarified the physical meaning of α and its relationship with the magnetic helicity. We have studied the effect of polarimetric noise on estimation of various magnetic parameters. Fine structures of sunspots in terms of vertical current (Jz) and α have been examined. We have introduced the concept of signed shear angle (SSA) for sunspots and established its importance for non force-free fields. We find that there is no net current in sunspots even in presence of a significant twist, showing consistency with their fibril-bundle nature. The finding of existence of a lower limit of SASSA for a given class of X-ray flare will be very useful for space weather forecasting. A good correlation is found between the sign of helicity in the sunspots and the chirality of the associated chromospheric and coronal features. We find that a large number of sunspots observed in the declining phase of solar cycle 23 do not follow the hemispheric helicity rule whereas most of the sunspots observed in the beginning of new solar cycle 24 do follow. This indicates a long term behaviour of the hemispheric helicity patterns in the Sun. The above sums up my PhD thesis.
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Zhang, Hongqi. "Observations of magnetic and kinetic helicity proxies." Proceedings of the International Astronomical Union 8, S294 (August 2012): 13–24. http://dx.doi.org/10.1017/s1743921313002160.
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AbstractThe helicity is important to present the basic topological configuration of magnetic field in solar atmosphere. The distribution of magnetic helicity in solar atmosphere is presented by means of the observational (vector) magnetograms. As the kinetic helicity in the solar subatmosphere can be inferred from the velocity field based on the technique of the helioseismology and used to compare with the magnetic helicity in the solar atmosphere, the observational helicities provide the important chance for the confirmation on the generation of magnetic fields in the subatmosphere and solar dynamo models also. In this paper, we present the observational magnetic and kinetic helicity in solar active regions and corresponding questions, except the relationship with solar eruptive phenomena.
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Prasad, A., R. Bhattacharyya, Q. Hu, S. S. Nayak, and Sanjay Kumar. "Study of magnetic field topology of active region 12192 using an extrapolated non-force-free magnetic field." Proceedings of the International Astronomical Union 13, S340 (February 2018): 81–82. http://dx.doi.org/10.1017/s1743921318001151.
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AbstractThe solar active region (AR) 12192 was one of the most flare productive region of solar cycle 24, which produced many X-class flares; the most energetic being an X3.1 flare on October 24, 2014 at 21:10 UT. Customarily, such events are believed to be triggered by magnetic reconnection in coronal magnetic fields. Here we use the vector magnetograms from solar photosphere, obtained from Heliospheric Magnetic Imager (HMI) to investigate the magnetic field topology prior to the X3.1 event, and ascertain the conditions that might have caused the flare. To infer the coronal magnetic field, a novel non-force-free field (NFFF) extrapolation technique of the photospheric field is used, which suitably mimics the Lorentz forces present in the photospheric plasma. We also highlight the presence of magnetic null points and quasi-separatrix layers (QSLs) in the magnetic field topology, which are preferred sites for magnetic reconnections and discuss the probable reconnection scenarios.
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Mackay, Duncan H. "The Sun's global magnetic field." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 370, no. 1970 (July 13, 2012): 3151–68. http://dx.doi.org/10.1098/rsta.2011.0536.
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Our present-day understanding of solar and stellar magnetic fields is discussed from both an observational and theoretical viewpoint. To begin with, observations of the Sun's large-scale magnetic field are described, along with recent advances in measuring the spatial distribution of magnetic fields on other stars. Following this, magnetic flux transport models used to simulate photospheric magnetic fields and the wide variety of techniques used to deduce global coronal magnetic fields are considered. The application and comparison of these models to the Sun's open flux, hemispheric pattern of solar filaments and coronal mass ejections are then discussed. Finally, recent developments in the construction of steady-state global magnetohydrodynamic models are considered, along with key areas of future research.
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Tlatov, Andrey G., and Ivan Berezin. "Modeling the Magnetic Field of the Inner Corona in a Radially Expanding Solar Wind." Physics 5, no. 1 (January 29, 2023): 161–67. http://dx.doi.org/10.3390/physics5010012.
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The magnetic field in the interplanetary medium is formed by the action of magnetic field sources on the photosphere of the Sun and currents in the expanding atmosphere of the Sun and the solar wind. In turn, the high-speed plasma flow changes the configuration of the magnetic field lines. The problem of determining the parameters of the magnetic field near the Sun is thus a three-dimensional problem of the interaction of the magnetic field and the plasma of the solar wind. We present analytical expressions for calculating the total magnetic field vector B→(r, θ, ϕ) (in spherical coordinates) for a radially expanding solar wind flow of finite conductivity. The parameters of the solar wind are given in the form of a dimensionless magnetic Reynolds number given as an arbitrary function of the radius, r: Rm = rσμv=ξ(r), where σ, μ, and v denote, respectively, the conductivity, magnetic permeability, and velocity of the solar wind. The solution for the magnetic field components is obtained in the form of a decomposition in spherical functions and a radial part depending on the distance from the Sun. Examples of calculations of the configuration of magnetic fields and structures of the solar corona for the solar eclipse of 21 August 2017 are given.
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Virtanen, Ilpo, and Kalevi Mursula. "Photospheric and coronal magnetic fields in six magnetographs." Astronomy & Astrophysics 626 (June 2019): A67. http://dx.doi.org/10.1051/0004-6361/201935713.
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Context. Solar photospheric magnetic fields have been observed since the 1950s and calibrated digital data are available from the 1970s onwards. Synoptic maps of the photospheric magnetic field are widely used in solar research, especially in the modeling of the solar corona and solar wind, and in studies of space weather and space climate. Magnetic flux density of the solar corona is a key parameter for heliospheric physics. Aims. The observed photospheric magnetic flux depends on the instrument and data processing used, which is a major problem for long-term studies. Here we scale the different observations of the photospheric field to the same absolute level and form a uniform record of coronal magnetic flux since the 1970s. Methods. We use a recently suggested method of harmonic scaling, which scales any pair of synoptic observations of any resolution to the same level. After scaling, we use the Potential Field Source Surface (PFSS) model to calculate the scaled magnetic field at various altitudes from photosphere to coronal source surface. Results. Harmonic scaling gives effective, latitudinally dependent scaling factors, which vary over the solar cycle. When scaling low-resolution data to high-resolution data, effective scaling factors are typically largest at low latitudes in the ascending phase of solar cycle and smallest for unipolar polar fields around solar minima. The harmonic scaling method used here allows for the observations of the different data sets to be scaled to the same level and the scaled unsigned coronal flux densities agree very well with each other. We also find that scaled coronal magnetic fields show a slightly different solar cycle variation from that of the nonscaled fields.
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Jiang, J., R. H. Cameron, D. Schmitt, and M. Schüssler. "The solar magnetic field since 1700." Astronomy & Astrophysics 528 (March 4, 2011): A82. http://dx.doi.org/10.1051/0004-6361/201016167.
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Jiang, J., R. H. Cameron, D. Schmitt, and M. Schüssler. "The solar magnetic field since 1700." Astronomy & Astrophysics 528 (March 4, 2011): A83. http://dx.doi.org/10.1051/0004-6361/201016168.
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Ulrich, Roger K., and John E. Boyden. "The Solar Surface Toroidal Magnetic Field." Astrophysical Journal 620, no. 2 (January 21, 2005): L123—L127. http://dx.doi.org/10.1086/428724.
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Antiochos, S. K., R. B. Dahlburg, and J. A. Klimchuk. "The magnetic field of solar prominences." Astrophysical Journal 420 (January 1994): L41. http://dx.doi.org/10.1086/187158.
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Kotov, V. A., and I. V. Kotova. "Does the solar magnetic field increase?" Astronomy Letters 27, no. 4 (April 2001): 260–66. http://dx.doi.org/10.1134/1.1358384.
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Erofeev, D. V. "Solar magnetic quadrupole and interplanetary field." Proceedings of the International Astronomical Union 2004, IAUS223 (June 2004): 99–100. http://dx.doi.org/10.1017/s174392130400523x.
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Vats, Hari Om. "Interplanetary magnetic field and solar rotation." Planetary and Space Science 63-64 (April 2012): 158–63. http://dx.doi.org/10.1016/j.pss.2011.06.008.
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Zhang, Hongqi. "Diagnosis of solar chromospheric magnetic field." Science in China Series A: Mathematics 45, S1 (October 2002): 19–24. http://dx.doi.org/10.1007/bf02889679.
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Vidotto, A. A. "How to make the Sun look less like the Sun and more like a star?" Proceedings of the International Astronomical Union 12, S328 (October 2016): 237–39. http://dx.doi.org/10.1017/s1743921317003908.
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AbstractSynoptic maps of the vector magnetic field have routinely been made available from stellar observations and recently have started to be obtained for the solar photospheric field. Although solar magnetic maps show a multitude of details, stellar maps are limited to imaging large-scale fields only. In spite of their lower resolution, magnetic field imaging of solar-type stars allow us to put the Sun in a much more general context. However, direct comparison between stellar and solar magnetic maps are hampered by their dramatic differences in resolution. Here, I present the results of a method to filter out the small-scale component of vector fields, in such a way that comparison between solar and stellar (large-scale) magnetic field vector maps can be directly made. This approach extends the technique widely used to decompose the radial component of the solar magnetic field to the azimuthal and meridional components as well, and is entirely consistent with the description adopted in several stellar studies. This method can also be used to confront synoptic maps synthesised in numerical simulations of dynamo and magnetic flux transport studies to those derived from stellar observations.
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Hayashi, Keiji, Chin-Chun Wu, and Kan Liou. "An Electric-field-driven Global Coronal Magnetohydrodynamics Simulation Model Using Helioseismic and Magnetic Imager Vector-magnetic-field Synoptic Map Data." Astrophysical Journal 930, no. 1 (May 1, 2022): 60. http://dx.doi.org/10.3847/1538-4357/ac6173.
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Abstract We present the simulation methodology and results of our new data-driven global coronal magnetohydrodynamics (MHD) simulation model. In this model, the solar-surface electric field is first calculated such that the curl will satisfy both the induction equation and the given temporal variations of the solar-surface magnetic field. We use the synoptic maps of the Helioseismic and Magnetic Imager three-component vector-magnetic-field data to specify the solar-surface magnetic-field vector for a period from Carrington Rotations (CRs) 2106 to 2110. A set of whole-Sun three-component electric-field maps are obtained for each CR transition interval of about 27.3 days. Using the inverted electric field as the driving variable, our new global coronal MHD model, with the angular resolution of π/64, can trace the evolution of the three-dimensional coronal magnetic field that matches the specified time-dependent solar-surface magnetic-field maps and simultaneously satisfies the divergence-free condition. A set of additional boundary treatments are introduced to control the contribution of the horizontal components of the magnetic field at the weak-field regions. The strength of the solar-surface magnetic field is limited to 20 Gauss for the sake of computational stability in this study. With these numerical treatments, the nonpotential coronal features, such as twisted loop structures, and their eruptive outward motions are obtained. This present model, capable of introducing three-component solar-surface magnetic-field observation data to coronal MHD simulations, is our first step toward a better model framework for the solar corona and hence solar wind.
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Hoeksema, J. Todd. "The Evolution of the Solar Magnetic Field." Proceedings of the International Astronomical Union 10, H16 (August 2012): 86–89. http://dx.doi.org/10.1017/s1743921314004670.
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AbstractThe almost stately evolution of the global heliospheric magnetic field pattern during most of the solar cycle belies the intense dynamic interplay of photospheric and coronal flux concentrations on scales both large and small. The statistical characteristics of emerging bipoles and active regions lead to development of systematic magnetic patterns. Diffusion and flows impel features to interact constructively and destructively, and on longer time scales they may help drive the creation of new flux. Peculiar properties of the components in each solar cycle determine the specific details and provide additional clues about their sources. The interactions of complex developing features with the existing global magnetic environment drive impulsive events on all scales. Predominantly new-polarity surges originating in active regions at low latitudes can reach the poles in a year or two. Coronal holes and polar caps composed of short-lived, small-scale magnetic elements can persist for months and years. Advanced models coupled with comprehensive measurements of the visible solar surface, as well as the interior, corona, and heliosphere promise to revolutionize our understanding of the hierarchy we call the solar magnetic field.
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Virtanen, Ilpo I., Alexei A. Pevtsov, and Kalevi Mursula. "Structure and evolution of the photospheric magnetic field in 2010–2017: comparison of SOLIS/VSM vector field and BLOS potential field." Astronomy & Astrophysics 624 (April 2019): A73. http://dx.doi.org/10.1051/0004-6361/201834895.
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Context. The line-of-sight (LOS) component of the large-scale photospheric magnetic field has been observed since the 1950s, but the daily full-disk observations of the full vector magnetic field started only in 2010 using the SOLIS Vector Stokes Magnetograph (VSM) and the SDO helioseismic and magnetic imager (HMI). Traditionally, potential field extrapolations are based on the assumption that the magnetic field in the photosphere is approximately radial. The validity of this assumption has not been tested yet. Aims. We investigate here the structure and evolution of the three components of the solar large-scale magnetic field in 2010–2017, covering the ascending to mid-declining phase of solar cycle 24, using SOLIS/VSM vector synoptic maps of the photospheric magnetic field. Methods. We compare the observed VSM vector magnetic field to the potential vector field derived using the VSM LOS magnetic field observations as an input. The new vector field data allow us to derive the meridional inclination and the azimuth angle of the magnetic field and to investigate their solar cycle evolution and latitudinal profile of these quantities. Results. SOLIS/VSM vector data show that the photospheric magnetic field is in general fairly non-radial. In the meridional plane the field is inclined toward the equator, reflecting the dipolar structure of the solar magnetic field. Rotationally averaged meridional inclination does not have significant solar cycle variation. While the vector radial component Br and the potential radial component BPFSSr are fairly similar, the meridional and zonal components do not agree very well. We find that SOLIS/VSM vector observations are noisy at high latitudes and suffer from the vantage point effect more than LOS observations. This is due to different noise properties in the LOS and transverse components of the magnetic field, which needs to be addressed in future studies.
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Петухова, Анастасия, Anastasia Petukhova, Станислав Петухов, and Stanislav Petukhov. "Toroidal models of magnetic field with twisted structure." Solar-Terrestrial Physics 5, no. 2 (June 28, 2019): 69–75. http://dx.doi.org/10.12737/stp-52201910.
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We present and discuss properties of the following magnetic field models in a magnetic cloud: Miller and Turner solution, modified Miller–Turner solution, Romashets–Vandas toroidal and integral models, and Krittinatham–Ruffolo model. Helicity of the magnetic field in all the models is the main feature of magnetic clouds. The first three models describe the magnetic field inside an ideal torus. In the integral model, parameters of a generating torus ambiguously determine the volume and form of the magnetic field region. In the Krittinatham–Ruffolo model, the cross-section radius of the torus is variable, thereby it corresponds more closely to the real form of magnetic clouds in the inner heliosphere. These models can be used to interpret in-situ observations of the magnetic flux rope, to study a Forbush decrease in magnetic clouds and transport effects of solar energetic particles injected into a coronal mass ejection.
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Bushby, Paul J. "Magnetic fields in the solar photosphere." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 366, no. 1884 (September 23, 2008): 4465–76. http://dx.doi.org/10.1098/rsta.2008.0158.
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Recent high-resolution observations of the surface of the Sun have revealed the fine structure of a vast array of complex photospheric magnetic features. Observations of these magnetic field structures have already greatly enhanced our theoretical understanding of the interactions between magnetic fields and turbulent convection, and future photospheric observations will inevitably present new theoretical challenges. In this review, I discuss recent progress that has been made in the modelling of photospheric magnetic fields. In particular, I focus upon the complex field structures that are observed within the umbrae and the penumbrae of sunspots. On a much smaller scale, I also discuss models of the highly localized magnetic field structures that are observed in less magnetically active regions of the photosphere. As the spatial resolution of telescopes has improved over the last few years, it has now become possible to observe these features in detail, and theoretical models can now describe much of this behaviour. In the last section of this review, I discuss some of the remaining unanswered questions.
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Benevolenskaya, E. E. "A Topological Model of the Solar Magnetic Field Reversals." International Astronomical Union Colloquium 130 (1991): 234–36. http://dx.doi.org/10.1017/s0252921100079677.
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The phenomenon of a three-fold reversal of the solar polar magnetic field in both hemispheres has not been observed during the last 115 years. Such three-fold reversals took place in the southern hemisphere alone in the even cycles Nos 12 (1885.8), 14 (1908.4) and in the northern hemisphere alone in solar cycles Nos 16 (1928.5), 18 (1949.0), 20 (1970.6). The single reversal took place in the odd cycles, the only exception is the solar cycle No 19 (Fig. 1).There are periods of 1.7-2.5 years in the variation of background magnetic fields (Makarov et al., 1985). It determines the quasi-period of the high-frequency component and corresponds to a time interval between the zones of alternating polarity of the magnetic field. This enables us to show topologically that single and three-fold polarity reversals of the solar magnetic fields can result from interaction of two types of magnetic fields: a low-frequency component with period of the order of 20 years and a high frequency component with period of order of 1.7-2.5 years (Benevolenskaya and Makarov, 1990).
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Tlatov, Andrey G., and Vladimir N. Obridko. "Global magnetic fields: variation of solar minima." Proceedings of the International Astronomical Union 7, S286 (October 2011): 113–22. http://dx.doi.org/10.1017/s1743921312004723.
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AbstractThe topology of the large-scale magnetic field of the Sun and its role in the development of magnetic activity were investigated using Hα charts of the Sun in the period 1887-2011. We have considered the indices characterizing the minimum activity epoch, according to the data of large-scale magnetic fields. Such indices include: dipole-octopole index, area and average latitude of the field with dominant polarity in each hemisphere and others. We studied the correlation between these indices and the amplitude of the following sunspot cycle, and the relation between the duration of the cycle of large-scale magnetic fields and the duration of the sunspot cycle.The comparative analysis of the solar corona during the minimum epochs in activity cycles 12 to 24 shows that the large-scale magnetic field has been slow and steadily changing during the past 130 years. The reasons for the variations in the solar coronal structure and its relation with long-term variations in the geomagnetic indices, solar wind and Gleissberg cycle are discussed.We also discuss the origin of the large-scale magnetic field. Perhaps the large-scale field leads to the generation of small-scale bipolar ephemeral regions, which in turn support the large-scale field. The existence of two dynamos: a dynamo of sunspots and a surface dynamo can explain phenomena such as long periods of sunspot minima, permanent dynamo in stars and the geomagnetic field.
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Foullon, C. "Playing Music with Magnetic Fields." International Astronomical Union Colloquium 185 (2002): 482–83. http://dx.doi.org/10.1017/s0252921100016882.
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AbstractThrough an increase in magnetic field strength, solar magnetic fields in the atmosphere or subsurface of the Sun can explain the frequency shifts observed on the time scale of the solar activity cycle. A separate study of the contribution of internal magnetic layers clarifies the relative importance of these effects. However, at the base of the convection zone, the cyclical change of orientation of magnetic field lines has a larger effect on global mode frequencies than an increase in field strength alone.
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Brandenburg, Axel. "Simulating the Solar Dynamo." Symposium - International Astronomical Union 157 (1993): 111–21. http://dx.doi.org/10.1017/s0074180900173966.
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Mean-field and direct simulations of the hydrodynamics and hydromagnetics of the solar convection zone are discussed with the ultimate aim to understand the generation of differential rotation and magnetic fields. Various arguments constraining the values of the various turbulent diffusion coefficients are presented. It is suggested that the turbulent magnetic diffusivity is much smaller than the eddy viscosity which, in turn, is by up to a factor of ten smaller than the eddy conductivity. The magnetic field obtained from direct simulations is highly intermittent, and there is no clear systematic orientation of bipolar regions emerging from the convection zone. Various mechanisms that might cause such a field orientation are considered. Finally, the application of direct simulations to the determination of mean-field transport coefficients is emphasised.
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Schatten, Kenneth H. "Solar Field Mapping and Dynamo Behavior." Advances in Astronomy 2012 (2012): 1–28. http://dx.doi.org/10.1155/2012/923578.
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We discuss the importance of the Sun’s large-scale magnetic field to the Sun-Planetary environment. This paper narrows its focus down to the motion and evolution of the photospheric large-scale magnetic field which affects many environments throughout this region. For this purpose we utilize a newly developed Netlogo cellular automata model. The domain of this algorithmic model is the Sun’s photosphere. Within this computational space are placed two types of entities or agents; one may refer to them as bluebirds and cardinals; the former carries outward magnetic flux and the latter carries out inward magnetic flux. One may simply call them blue and red agents. The agents provide a granularity with discrete changes not present in smooth MHD models; they undergo three processes: birth, motion, and death within the photospheric domain. We discuss these processes, as well as how we are able to develop a model that restricts its domain to the photosphere and allows the deeper layers to be considered only through boundary conditions. We show the model’s ability to mimic a number of photospheric magnetic phenomena: the solar cycle (11-year) oscillations, the Waldmeier effect, unipolar magnetic regions (e.g. sectors and coronal holes), Maunder minima, and the march/rush to the poles involving the geometry of magnetic field reversals. We also discuss why the Sun sometimes appears as a magnetic monopole, which of course requires no alteration of Maxwell’s equations.
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Di Campli, R., R. Ramelli, M. Bianda, I. Furno, S. Kumar Dhara, and L. Belluzzi. "Imaging spectropolarimetry for magnetic field diagnostics in solar prominences." Astronomy & Astrophysics 644 (December 2020): A89. http://dx.doi.org/10.1051/0004-6361/202037931.
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Context. Narrowband imaging spectropolarimetry is one of the most powerful tools available to infer information about the intensity and topology of the magnetic fields present in extended plasma structures in the solar atmosphere. Aims. We describe the instrumental set-up and the observing procedure that we have developed and optimized at the Istituto Ricerche Solari Locarno in order to perform imaging spectropolarimetry. A measurement that highlights the potential of the ensuing observations for magnetic field diagnostics in solar prominences is presented. Methods. Monochromatic images of solar prominences were obtained by combining a tunable narrowband filter, based on two Fabry-Perot etalons, with a Czerny-Turner spectrograph. Linear and circular polarization were measured at every pixel of the monochromatic image with the Zurich Imaging Polarimeter, ZIMPOL. A wavelength scan was performed across the profile of the considered spectral line. The HAZEL inversion code was applied to the observed Stokes profiles to infer a series of physical properties of the observed structure. Results. We carried out a spectropolarimetric observation of a prominence, consisting of a set of quasi-monochromatic images across the He I D3 line at 5876 Å in the four Stokes parameters. The map of observed Stokes profiles was inverted with HAZEL, finding magnetic fields with intensities between 15 and 30 G and directed along the spine of the prominence, which is in agreement with the results of previous works.
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Zirin, Harold. "Evolution of Weak Solar Magnetic Fields." Australian Journal of Physics 38, no. 6 (1985): 961. http://dx.doi.org/10.1071/ph850961.
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We review studies of the evolution of weak solar magnetic fields with the Big Bear videomagnetograph. To all detectable limits, the field is clumped in small elements. The size of the smallest detectable intranetwork elements is probably 3x 1015 Mx (==3x 107 Wb) and the field strength in these elements probably less than 10 G (1 G == 10--4 T). The general weak network fields are the remnants of ephemeral regions, which also playa role in field diffusion as proposed by Marsh. The intranetwork elements show a shorter lifetime and much more rapid motion than the network elements. In some cases they stream into existing network elements and may merge to form new elements, but many show no preferential motion to the network edges. Consonant with X-ray bright point counts, there appear to be fewer ephemeral regions in magnetically active areas.
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Benevolenskaya, Elena E. "Polar magnetic field reversals on the Sun." Proceedings of the International Astronomical Union 2, no. 14 (August 2006): 273–74. http://dx.doi.org/10.1017/s1743921307010551.
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AbstractThe polar magnetic fields on the Sun have been an attractive subject for solar researches since Babcock measured them in solar cycle 19. One of the remarkable features of the polar magnetic fields is their reversal during the maxima of 11-year sunspot cycles. I have present results of the investigations of the polar magnetic field using SOHO-mdi data. It is found, that the polar magnetic field reversal is detected with mdi data for polar region within 78°–88°. The North Pole has changed polarity in CR1975 (April 2001). The South reversed later in CR1980 (September 2001). The total unsigned magnetic flux does not show the dramatic decreasing during the polar reversals due to omnipresent bi-polar small-scale magnetic elements. The observational and theoretical aspects of the polar magnetic field reversals are discussed.
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Jones, G. H., and A. Balogh. "The global heliospheric magnetic field polarity distribution as seen at Ulysses." Annales Geophysicae 21, no. 6 (June 30, 2003): 1377–82. http://dx.doi.org/10.5194/angeo-21-1377-2003.
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Abstract. The Ulysses spacecraft is in a near-polar solar orbit with a period of 6.2 years. The heliospheric magnetic field polarity detected by Ulysses from its 1992 Jupiter encounter to the current time is presented, following ballistic mapping of the polarity information to the solar wind source surface, at approximately 2.5 solar radii. The spacecraft’s first foray to polar latitudes and first rapid heliolatitude scan occurred in 1994–1995, near a minimum in solar activity. The heliospheric current sheet during this period was confined to low heliolatitudes. In 2000–2001, Ulysses returned in situ data from the same region of its orbit as in 1994–1995, but near to the maximum in solar activity. Unlike at solar minimum, heliospheric current sheet crossings were detected at the spacecraft over a wide heliolatitude range, which is consistent with the reversal of the solar magnetic dipole occurring during solar maximum. Despite complexity in the solar wind parameters during the latest fast latitude scan (McComas et al., 2002), the underlying magnetic field structure appears consistent with a simple dipole inclined at a large angle to the solar rotational axis. The most recent data show the heliospheric current sheet returning to lower heliolatitudes, indicating that the dipole and rotational axes are realigning, with the Sun’s magnetic polarity having reversed.Key words. Interplanetary physics (interplanetary magnetic fields; sources of the solar wind) – Solar physics, astrophysics and astronomy (magnetic fields)
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Liu, Yang, Kefei Song, Xiaodong Wang, Bo Chen, Junlin Ma, and Zhenwei Han. "Displacement Analysis of Solar Magnetic Field Images in EUV Wavelengths of Space Solar Telescope." International Journal of Pattern Recognition and Artificial Intelligence 33, no. 03 (February 19, 2019): 1950005. http://dx.doi.org/10.1142/s0218001419500058.
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In this paper, the combination of nonlinear gradient iteration and crossing method is presented in order to analyze high precision remote sensing images of solar magnetic field in extreme ultraviolet (EUV) wavelengths which are usually affected by solar magnetic evolution, satellite attitude changes and random satellite jitter, and to reduce structural complexity the complicated correlation tracker is normally adopted. Using crossing method which better approached the inefficiency by computing full-scale solar magnetic field images, nine point areas are uniformly selected in full-scale solar magnetic field images which solves the problem of low-computing efficiency. Meanwhile, nonlinear gradient iteration algorithm through numerical simulation experiments is adopted to analyze displacement of solar magnetic field images in EUV wavelengths, which reduces the errors due to the solar intensity changing and tiny deformation of solar magnetic field compared to traditional algorithms. The results clearly indicate that the precision of mean error field and square deviation field for deformed displacement are both less than 5% of pixel by solar magnetic field images of Solar Dynamics Observatory (SDO).
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Flyer, N., B. Fornberg, S. Thomas, and B. C. Low. "Magnetic Field Confinement in the Solar Corona. I. Force‐free Magnetic Fields." Astrophysical Journal 606, no. 2 (May 10, 2004): 1210–22. http://dx.doi.org/10.1086/383025.
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Hamouda, Samir Ahmed, Nada Eaz-Alden Emgau, Rabab Muftah Bohagar, and Aisha Mohammed Eissa. "STUDY OF PLANETARY MAGNETIC FIELDS." International Journal of Research -GRANTHAALAYAH 5, no. 3 (March 31, 2017): 29–44. http://dx.doi.org/10.29121/granthaalayah.v5.i3.2017.1752.
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Magnetic fields are an important phenomenon in the solar system and beyond. Their causes are complex and have a variety of effects on their surroundings; they have become a critical tool for the exploration of solar system bodies. Magnetic fields play a very important role in the Sun. From sunspots to coronal heating, from solar ares to coronal mass ejections all these apparently diverse phenomena have magnetic fields as their ultimate cause. The study of the terrestrial dynamo is a difficult problem made more so by the inability to construct planetary-scale dynamos for laboratory study. However, understanding the nature of the matter comprising the Solar System is crucial for understanding the mechanism that generates Earth’s geomagnetic field and the magnetic fields of other planets and satellites planetary dynamo models. In this study, in this study, classifications of planets are introduced. Development of planetary magnetism model is discussed. General concepts of the magnetic dynamo theory are introduced. Properties of planetary magnetic fields are presented and Earth crustal magnetic field is briefly discussed.
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Schmitt, D. "The Solar Dynamo." Symposium - International Astronomical Union 157 (1993): 1–12. http://dx.doi.org/10.1017/s0074180900173784.
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The generation of the solar magnetic field is generally ascribed to dynamo processes in the convection zone. The dynamo effects, differential rotation (ω–effect) and helical turbulence (α–effect) are explained, and the basic properties of the mean–field dynamo equations are discussed in close comparison with the observed solar cycle.Especially the question of the seat of the dynamo is addressed. Problems of a dynamo in the convection zone proper could be magnetic buoyancy, the nearly strict observance of the polarity rules and the migration pattern of the magnetic fields which are difficult to understand in the light of recent studies of the field structure in the convection zone and by observations of the solar acoustic oscillations. To overcome some of these problems it has been suggested that the solar dynamo operates in the thin overshoot region at the base of the convection zone instead. Some aspects of such an interface dynamo are discussed. As an alternative to the turbulent α–effect a dynamic α-effect based on magnetostrophic waves driven by a magnetic buoyancy instability of a magnetic flux layer is introduced. Model calculations for both pictures, a convection zone and an interface dynamo, are presented which use the internal rotation of the sun as deduced from helioseismology. Solutions with solar cycle behaviour are only obtained if the magnetic flux is bounded in the lower convection zone and the α–effect is concentrated near the equator.Another aspect briefly addressed is the nonlinear saturation of the magnetic field. The necessity of the dynamic nature of the dynamo processes is emphasized, and different processes, e.g. magnetic buoyancy and α-quenching, are mentioned.
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Huaning, Wang, and Lin Yuanzhang. "A Synthesized Method for Solving the 180° Ambiguity of Solar Transverse Magnetic Field." International Astronomical Union Colloquium 141 (1993): 461–64. http://dx.doi.org/10.1017/s0252921100029638.
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The 180° ambiguity of the transverse magnetic field measured by a heliomagnetograph is an intrinsic problem due to the linear polarization in Zeeman effect(Harvey, 1969). Thus we have to make use of some criteria for calibrating the transverse magnetic fields in vector magnetograms. Up to now, a few criteria have been suggested by some solar physicists (Harvey, 1969; Krall et al., 1982; Sakurai et al., 1985; Aly, 1989; Wu and Ai, 1990; Canfield et al., 1991. The existing criteria could be classified as observational criteria and mathematical criteria. The former is based on the observation facts, such as the fibrils and the filaments in solar filtergrams, and the latter is derived from the mathematical model of solar magnetic field, such as divergence equation (∆. B = 0), potential field model and force-free field model. These criteria, however, are not applicable to all solar active regions, especially to those with complicated magnetic fields. For this reason, we suggest a synthesized method for calibrating the transverse magnetic fields in solar vector magnetograms.