Series of high resolution spectrograms taken simultaneously in three spectral regions were recorded with a lambda meter and subjected to a statistical analysis of the fluctuations of Doppler shift and brightness.

Some properties of velocity fields in the solar photosphere

Turbulence in stellar atmospheres

Photoelectric measurements of Doppler shifts of various Fraunhofer lines obtained with the Capri magnetograph were analysed. The height dependence of the supergranular and oscillatory motions, as well as the two dimensional structure of these velocity fields is investigated.The most interesting results are the following:(1)The oscillatory and supergranular motions are still clearly present in very deep photospheric layers as detected e.g. by means of the Ci line at 5380.3 Å.(2)Whereas the vertical motions (both of oscillation and supergranulation) increase with height, the horizontal component of the supergranular flow is found to be decreasing slightly.(3)Aperiodic horizontal motions are observed in the photospheric layers, which are probably connected with the process of excitation of the oscillatory field.(4)There is no simple way of describing the oscillatory field in terms of independently oscillating ‘cells’, since the two-dimensional pattern changes its appearance drastically already in a fraction of one oscillation period.(5)The correlation obtained by previous observers between vertical stationary motions, the chromospheric network and magnetic fields in particular is confirmed.

Some properties of velocity fields in the solar photosphere. iii. oscillatory and supergranular motions as a function of height.

Continuum brightness and Doppler velocity fluctuations in the lines λ 6301.5 and λ 6302.5 A of Fei, measured in two selected spectrograms, are analysed by standard statistical (power- and coherence spectrum) methods. It is shown qualitatively that the oscillatory component of the velocity fluctuations (at spatial wavelengths > 4″) decreases, while the supposedly ‘granular’ component (at spatial wavelengths < 4″) as well as the coherence between brightness and velocity fluctuations increases with optical depth.

Studies of granular velocities. IV. Statistical analysis of granular Doppler-shifts

A very high quality wiggly-line spectrogram was analyzed by making high-resolution spectral scans of numerous small solar features. An attempt from the line profiles to detect a magnetic field difference between the granular and intergranular regions, resulted in a field increase of 20 ± 15 G in the darker regions of the granular field. Line width increases apparently due to small-scale turbulent velocities are seen in the darker regions. It is postulated that in general darker regions show increased turbulent velocities. Conspicuous asymmetries in line profiles are seen in dark intergranular regions. It is suggested that these are the result of velocity gradients in the downward flow of material. An ionized Cr line showed a conspicuous increase in equivalent width in the darker regions of the granular field, thus indicating a decrease in electron pressure in these areas.

On the Spectrum of Granular and Intergranular Regions

A solar granulation spectrogram

Following a technique developed by Saito, the positions and orientations of the polar rays visible in a photograph of the total solar eclipse of 12 November 1966 were examined to infer the length of an equivalent bar magnet representing the Sun's external magnetic field and the true distribution of polar rays from the two-dimensional projection seen in the photograph. In spite of the strong asymmetry in solar activity between the northern and southern solar hemispheres at the time of the eclipse, it was found that the magnetic field as delineated by the polar rays could be well represented by an extended dipole whose poles were each 0.43 R
⊙ from the center of the Sun and on the axis of rotation. The polar rays are distributed mainly in a circular zone 9° away from the pole and about 8° wide, with this zone bounded by empty regions at the pole and 15° to 20° away from it, beyond which there are again some rays, but not so many. These results are in good accord with expectation from Saito's analysis.

J. G. Kirk

Papers

A solar granulation spectrogram

Curvature and surface distribution of the polar rays in the solar corona on 12 November 1966