scholarly journals Long-Term Coherent Periodicities in the Mean Magnetic Field of the Sun

1983 ◽  
Vol 102 ◽  
pp. 23-27
Author(s):  
V.A. Kotov ◽  
L.S. Levitsky

To investigate periodic variations of the magnetic field of the Sun as a star (SMMF; see Severny, 1969) we have used the mean field measurements made in Crimea, Mt. Wilson, and Stanford observatories; in total N = 5783 daily values were available for the time interval 1968–1981. In essence, these data offer a unique possibility to study the Sun as a variable magnetic star (Scherrer et al., 1977).

2000 ◽  
Vol 179 ◽  
pp. 209-212
Author(s):  
M. L. Demidov

AbstractA comparison is made of observational data on the mean magnetic field of the Sun from several observatories (a selection of published information and new measurements). Results of correlation and regression analyses of observations of background magnetic fields at the STOP telescope of the Sayan solar observatory in different spectral lines are also presented. Results obtained furnish an opportunity to obtain more unbiased information about large-scale magnetic fields of the Sun and, in particular, about manifestations of strong (kilogauss) magnetic fields in them.


2020 ◽  
Vol 636 ◽  
pp. A6 ◽  
Author(s):  
G. Mathys ◽  
V. Khalack ◽  
J. D. Landstreet

How magnetic fields contribute to the differentiation of the rotation rates of the Ap stars and affect the occurrence of non-radial pulsation in some of them are important open questions. Valuable insight can be gained into these questions by studying some of the most extreme examples of the processes at play. The super-slowly rotating rapidly oscillating Ap (roAp) star HD 166473 is such an example. We performed the first accurate determination of its rotation period, Prot = (3836 ± 30) d, from the analysis of 56 measurements of the mean magnetic field modulus ⟨B⟩ based on high-resolution spectra acquired between 1992 and 2019 at various observatories and with various instrumental configurations. We complemented this analysis with the consideration of an inhomogeneous set of 21 determinations of the mean longitudinal magnetic field ⟨Bz⟩ spanning the same time interval. This makes HD 166473 one of only four Ap stars with a period longer than 10 years for which magnetic field measurements have been obtained over more than a full cycle. The variation curves of ⟨B⟩ and of ⟨Bz⟩ are well approximated by cosine waves. The magnetic field of HD 166473 only seems to deviate slightly from axisymmetry, but it definitely involves a considerable non-dipolar component. Among the stars with rotation periods longer than 1000 d for which magnetic field measurements with full phase coverage are available, HD 166473 has the strongest field. Its magnetic field is also one of the strongest known among roAp stars. Overall, the magnetic properties of HD 166473 do not seem fundamentally distinct from those of the faster-rotating Ap stars. However, considering as a group the eight Ap stars that have accurately determined periods longer than 1000 d and whose magnetic variations have been characterised over a full cycle suggests that the angles between their magnetic and rotation axes tend to be systematically large.


Author(s):  
Alexei Pevtsov ◽  
Luca Bertello ◽  
Yuri Nagovitsyn ◽  
Andrey Tlatov ◽  
Valery Pipin

We briefly review the history of observations of magnetic fields on the Sun, and  describe early magnetograps for full disk measurements. Changes in instruments and detectors, the cohort of observers, the knowledge base etc may result in non-uniformity of the long-term synoptic datasets. Still, such data are critical for detecting and understanding the long-term trends in solar activity. We demonstrate the value of historical data using studies of active region tilt (Joy's law) and the evolution of polar field and its reversal. Using the longest dataset of sunspot field strength measurements from Mount Wilson Observatory (1917-present) supplemented by shorter datasets from Pulkovo (1956--1997) and Crimean (1956--present) observatories we demonstrate that the magnetic properties of sunspots did not change over the last hundred years. We also show that the relationship between the sunspot area and its magnetic flux can be used to extend the studies of magnetic field in sunspots to periods with no direct magnetic field measurements. Finally, we show how more recent full disk observations of the vector magnetic field can be used to study the long-term (solar cycle) variations in  magnetic helicity on the Sun.


1998 ◽  
Vol 11 (2) ◽  
pp. 679-681
Author(s):  
M. Landolfi

The observational quantities commonly used to study the magnetic field of CP stars – the mean field modulus and the mean longitudinal field, as well as the ‘mean asymmetry of the longitudinal field’ and the ‘mean quadratic field’ recently introduced by Mathys (1995a,b) – are based either on the Stokes parameter / or on the Stokes parameter V. However, a complete description of polarized radiation requires the knowledge of the full Stokes vector: in other words, we should expect that useful information is also contained in linear polarization (the Stokes parameters Q and U); or rather we should expect the information contained in (Q, U) and in V to be complementary, since linear and circular polarization are basically related to the transverse and the longitudinal component of the magnetic field, respectively.


1973 ◽  
Vol 26 (5) ◽  
pp. 617 ◽  
Author(s):  
R Van der Borght ◽  
JO Murphy

The combined effect of an imposed rotation and magnetic field on convective transfer in a horizontal Boussinesq layer of fluid heated from below is studied in the mean field approximation. The basic equations are derived by a variational technique and their solutions are then found over a wide range of conditions, in the case of free boundaries, by numerical and analytic techniques, in particular by asymptotic and perturbation methods. The results obtained by the different techniques are shown to be in excellent agreement. As for the linear theory, the calculations predict that the simultaneous presence' of a magnetic field and rotation may produce conflicting tendencies.


Solar Physics ◽  
1977 ◽  
Vol 54 (2) ◽  
pp. 353-361 ◽  
Author(s):  
Philip H. Scherrer ◽  
John M. Wilcox ◽  
Leif Svalgaard ◽  
Thomas L. Duvall ◽  
Phil H. Dittmer ◽  
...  
Keyword(s):  
The Sun ◽  

1761 ◽  
Vol 52 ◽  
pp. 182-183

Having measured the diameter of Venus, on the sun, three times, with the object-glass micrometer, the mean was found to be 58 seconds; and but 6/10 of a second, the difference of the extremes.


2020 ◽  
Vol 240 ◽  
pp. 07011
Author(s):  
Kushagra Shrivastava ◽  
Keith Wen Kai Chia ◽  
Kang Jun Wong ◽  
Alfred Yong Liang Tan ◽  
Hwee Tiang Ning

Solar activity research provides insight into the Sun’s past, future (Science Daily, 2018). The solar activity includes observations of large numbers of intense sunspots, flares, and other phenomena; and demands a wide range of techniques and measurements on the observations. This research needs long term data collection before critical analyses can occur, to generate meaningful learning and knowledge. In this project, we will use solar imaging to make observations of solar activity, and take our baby steps to make contributions in citizen science. Observations will be made in 3 wavelengths to gain a more thorough analysis by looking at different perspectives of the Sun, namely H-Alpha, Calcium-K, and white light.


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