Two peculiarities of the magnetic splitting of a line in sunspot spectra have been investigated. The one is that in a rather small region of the penumbra near the umbra-penumbra boundary the π-component is absent in one circular polarization spectrum while both σ-components are present. In the spectrum of opposite circular polarization the σ-components are absent but the π-component is present. The second peculiarity consists of the anomalous splitting of the π-component of Zeeman triplets which are of the same and opposite signs in comparison with splitting of the σ-components. The nature of these effects is discussed.

The present paper describes the results of a preliminary investigation of the effects on the absorption, emission, and scattering of polarized light caused by collisions between the atoms of interest and surrounding perturbers under physical conditions typical of solar magnetic regions. The description of these effects in terms of atomic level polarization is reviewed and the processes which can lead to atomic level polarization in solar magnetic regions and those which tend to reduce it are summarized. The effects associated with collisional relaxation of atomic level polarization are discussed and a method for estimating relaxation rates is described. Estimates of collisional relaxation rates are used to calculate upper limits on the degree of polarization of the levels involved in the formation of five magnetically-sensitive FeI absorption lines. The implications of the results for the form of radiative transfer equations used to describe the formation of these lines are discussed.

Until now, analytic solutions for the problem of line formation in magnetic fields have been given only under special assumptions concerning either the magnetic field or the atmospheric model. Conditions are given for which the system of differential equations can be solved analytically. For the general case a method is given to solve the system in approximation and analytically. LTE is generally assumed which means that we use the system given by Unno (1956) or that given by Beckers (1969) including the Faraday rotation.

This review is restricted to a few topics of the extensive problem under discussion; it refers to the literature since 1967 only. The literature prior to 1967 is reviewed in Zwaan, 1968; Howard, 1967; Lüst, 1965; Kiepenheuer, 1968; Jäger, 1964; and Bray and Loughead, 1964.

We study the local variations of η0 and ξ (Milne-Eddington model) which are necessary in order to bring in agreement three independent determinations of the total field H, obtained from simultaneous observations of the two lines λ 5250,2 Fe I and λ 5225,5 Fe I. The distribution of the broadening as a function of field direction is consistent with the motions induced by hydromagnetic waves.

Photoelectric polarization measurements in a stable sunspot (type H) with a particularly dark umbra, where ‘umbral dots’ were virtually lacking, have been carried out with the Capri magnetograph. The measurements were evaluated in terms of Unno's theory to give the value and direction of the magnetic field vector. The parameters η0 = 5, β0 = 2.5 and ΔλD = 40mÅ have been adopted for the Fe I 5250 line. Taking the configuration of the sunspot into account as well as simple conditions of steadiness of the distributions to be obtained, it is possible to derive the magnetic vector field from two-dimensional records of circular and linear polarization without ambiguities.

The longitudinal component of the magnetic field, B∥, has been recorded in about 135 quiescent prominences observed at Climax during the period 1968–1969. The measurements were obtained with the magnetograph which records the Zeeman effect on hydrogen, helium and metal lines. The following lines were used, Hα; He I, D3, He I, 4471 Å; Na I, D1 and D2, and the observed magnetic field component in these prominences was independent of the line. The overall mean value of the field B∥ for all the prominences was 7.3G. As a rule, the magnetic field enters the prominence on one side and exits on the other, but in traversing the prominence material, the field tends to run along the long axis of the prominence.

Some comments are given concerning the fine structures in the umbra and penumbra of sunspots and their changes on the basis of high resolution photographs.

This talk deals with the spatial distribution of the total magnetic vector H and of electric currents in the big unipolar sunspot of October 17, 1966.

Profiles of various lines in the spectra of umbrae are discussed, emphasizing the use of purely umbral lines. In the dark core of a large umbra the field strengths measured from various lines are the same, yielding 3080 ± 50G. In regions with umbral dots the field strengths do depend on the spectral line; the strengths are lower than in the dark core. Some conclusions are discussed.

The strengths of the longitudinal magnetic fields recorded at different depths of active regions with a double magnetograph of the Crimean Astrophysical Observatory are compared.

The recordings of the magnetic fields were made in the lines Fe Iλ5250Å, Ca Iλ6103Å, Na I D1, BIIλ4554Å, Mg Iλ5184Å, Hα, Hγ, Hδ.

It is shown, that there is a close correlation between the longitudinal magnetic field at different levels.

Inhomogeneity of magnetic field structure, ‘granulation’ in sunspot umbrae and fine structure of the Evershed motions lead to the conclusion that the sunspot umbra is composed of magnetic ropes (or plaits) with dimensions near the limit of resolution. Progress in the study of these ropes is closely connected with the possibility of obtaining extensive spectroscopic information about some selected regions on the solar disc. It is extremely interesting to obtain a picture of short-time-scale variations of the magnetic field strength and the radial velocity field in connection with the transfer of energy from the photosphere to the upper layers of the solar atmosphere (chromosphere, corona).

Advantages of ‘circular polarimetry’ (determination of the Stokes parameter V) in active regions as compared to ‘elliptical polarimetry’ (determination of all Stokes parameters) are discussed:

1. (1) Complicated and doubtful reduction procedures by means of line formation theory generally are needed for ‘elliptical polarimetry’. This is not the case for ‘circular polarimetry’.

2. (2) Even if the difficulties (1) could be removed, ‘elliptical polarimetry’ would not help to determine the total magnetic vector outside the disc center. This is due to the fact that the azimuth φ of the linear polarization is only defined for 0° ⩽ φ < 180°. When converting the measured inclination Ψ to the line-of-sight into the true inclination γ to the solar surface normal for active regions outside the disc center, the ambiguity of φ always yields an ambiguity of γ. The normal field component and thus the flux can therefore not be determined without making an important assumption on the unknown field structure (see Wiehr, 1970a).

3. (3) For active regions near the disc center, however, where the difficulty (2) disappears, ‘circular polarimetry’ is sufficient for the determination of the normal field component and flux. It furthermore avoids the difficulty (1).

We show how to determine the magnetic field structure in active regions from the Hα morphology. We also show the role of the EFR (emerging flux region) as a bipolar region of velocity downflow. Finally, we point out that since all new magnetic flux emerges in strictly bipolar form, complex spot groups must result from surface interaction, hence most of the solar surface field may be produced on the surface.

Described and discussed is the evolution of the magnetic field configuration in an Active Region from observations made with high time resolution.

The Kitt Peak multi-channel magnetograph was used to make raster scans of the supergranulation at the center of the disk. The scan pattern was arranged to largely cancel out the effects of the 5 min oscillations and the granulation and to enhance visible effects of the supergranulation.

The results show vertical supergranular motions. These motions consist of relatively isolated ‘patches’ of downward flowing material, or ‘downdrafts’, with an average speed of 0.1 km/s. These downdrafts coincide with patches of magnetic field, and the speed of the downdraft is linearly proportional to the magnetic field strength (50 to 100 G). These downdrafts are also regions of increased brightness in the chromosphere and photosphere.

The value of high resolution photo-electric observations of plage fields and their photospheric effects is demonstrated, with especial regard to obtaining an empirical model of a weakly active region.

Simultaneous observations of the magnetic fields, the line-of-sight velocities and brightness were made in active and quiet regions with the Crimean double-magnetograph in the following lines: Hα, K3 Ca II, Hβ, Hγ, Hδ, MgI λ 5184 Å, CaI λ 4227 Å, D1 NaI, BaII λ 4554 Å, CaI λ 6103 Å, FeI λ 5250 Å.

It is shown, that in the active regions the horizontal velocity is larger than the vertical one.

The mean velocities in the quiet solar photosphere have an isotropic distribution (Gopasyuk and Kalman, 1971).

The mean vertical velocities increase exponentially with height in active and quiet regions.

The correlation between velocities at different levels in active and quiet regions decreases with the distance between the levels of the formation of spectral lines, and it disappears for the velocities recorded in λ 6103 Å and Hβ, for λ 5184 and Hα lines in active regions and for the velocities recorded in λ 5250 Å and Hα lines in quiet regions.

The position of the maximal field strength within a magnetic hill coincides statistically with the zero line of the line-of-sight velocities for active as well as for quiet regions.