No abstract

Comparisons of solar magnetic-field measurements made in different spectral lines are very important, especially in those lines in which observations have a long history or (and) specific diagnostic significance. The spectral lines Fe I 523.3 nm and Fe I 525.0 nm belong to this class. Therefore, this study is devoted to a comprehensive analysis using new high-precision Stokes-meter full-disk observations. The disk-averaged magnetic-field strength ratio R = B(523.3)/B(525.0) equals 1.97 ± 0.02. The center-to-limb variation (CLV) is R = 1.74 − 2.43μ + 3.43μ 2 , where μ is the cosine of the center-to-limb angle. For the disk center, we find R = 2.74, and for near-limb areas with μ = 0.3, R equals 1.32. There is only a small dependence of R on the spatial resolution. Our results are rather close to those published three decades ago, but differ significantly from recent magnetographic observations. An application of our results to the important SOHO/MDI magnetic data calibration issue is discussed. We conclude that the revision of the SOHO/MDI data, based only on the comparison of magnetic-field measurements in the line pair Fe I 523.3 nm and Fe I 525.0 nm (increasing by a factor of 1.7 or 1.6 on average according to recent publications) is not obvious and new investigations are urgently needed.

In this paper we analyze the distribution of magnetic strength ratios (MSR) across the solar disk using magnetograms in different spectral lines from the same observatory (Mount Wilson Observatory (MWO) and Sayan Observatory (SO)), magnetograms in the same line from different observatories (MWO, SO, Wilcox Solar Observatory (WSO)), and in different spectral lines from different observatories (the three observatories mentioned above, the National Solar Observatory/Kitt Peak (KP) and Michelson Doppler Imager (MDI) on board Solar and Heliospheric Observatory (SoHO)). We find peculiarities in some combinations of data sets. Besides the expected MSR center-to-limb variations, there is an equatorto-pole asymmetry, especially in the near-limb areas. Therefore, it is generally necessary to use 2D matrices of correction coefficients to reduce one kind of observation into another one.

This paper presents some results of observations of the mean magnetic field of the Sun as a star (SMMF) at the Sayan Observatory during 1982-1984. A description of the instrument is given, as well as some major points in the technique of data acquisition and treatment such as calibration, zero-level control, etc. The comparison of a new SMMF series with observations from the Wilcox Solar Observatory showed a high correlation between the two series (p = 0.88) but with a rather great difference in amplitudes. We discuss time variations of SMMF, both long-term caused by the magnetic field evolution with the activity cycle and those of shorter time-scales caused by solar rotation.

Spectral inversion codes are powerful tools to analyze spectropolarimetric observations, and they provide important diagnostics of solar magnetic fields. Inversion codes differ by numerical procedures, approximations of the atmospheric model, and description of radiative transfer. Stokes Inversion based on Response functions (SIR) is an implementation widely used by the solar physics community. It allows to work with different atmospheric components, where gradients of different physical parameters are possible, e.g., magnetic field strength and velocities. The spectropolarimetric full-disk observations were carried out with the Stokesmeter of the Solar Telescope for Operative Predictions (STOP) at the Sayan Observatory on 3 February 2009, when neither an active region nor any other extended flux concentration was present on the Sun. In this study of quiet Sun magnetic fields, we apply the SIR code simultaneously to 15 spectral lines. A tendency is found that weaker magnetic field strengths occur closer to the limb. We explain this finding by the fact that close to the limb, we are more sensitive to higher altitudes in an expanding flux tube, where the field strength should be smaller since the magnetic flux is conserved with height. Typically, the inversions deliver two populations of magnetic elements: (1) high magnetic field strengths (1500-2000 G) and high temperatures (5500-6500 K) and (2) weak magnetic fields (50-150 G) and low temperatures (5000-5300 K).