Reply to ‘The relations between chromospheric features and photospheric magnetic fields’ by E. N. Frazier
✍ Scribed by Peter Foukal; Harold Zirin
- Publisher
- Springer
- Year
- 1972
- Tongue
- English
- Weight
- 210 KB
- Volume
- 26
- Category
- Article
- ISSN
- 0038-0938
No coin nor oath required. For personal study only.
✦ Synopsis
Frazier (1972)
has criticized the conclusions of Zirin (1971Zirin ( , 1972)), Veeder and Zirin (1970), and those of Foukal (1971a, b, c) on the relation between He structure and magnetic fields. We wish to reply to these criticisms. Some of the points Frazier mentions refer to statements made by Veeder and Zirin (1970) based on low resolution magnetograms and medium resolution He pictures. These statements were based on the best magnetograms available at the time and have already been corrected in a more recent paper to which Dr Frazier has access (Zirin, 1972). Dr Frazier actually has a similar difficulty in that his He pictures do not have sufficient resolution to derive full information from his magnetograms.
Our remarks on the general relation between He brightness and longitudinal field strength (Zirin, 1972) are based on comparison with photoelectric magnetograms from Mt Wilson (fine scans) and Kitt Peak. Presumably these are better calibrated than photographic systems such as used by Frazier or video systems such as used by Jansens (1972), and they in fact show a dependence of He brightness on longitudinal field strength. Of course, as finer details are uncovered, deviations will appear, as He intensity also depends somewhat on rate of change of the field. Also, near active regions, some regions of enhanced field are covered by dark fibrils in centerline He and only appear in off-band or K-line pictures. K-line pictures are very sensitive to longitudinal B but do not show transverse fibrils very well. However, in general all regions of longitudinal field above 25 G produce a discernible effect in He, usually a brightening in centerline and a darkening in the wing.
Frazier's statement that the correspondence between fibrils and field breaks down in active regions is not borne out by his picture. In the strong field region the fibrils which outline the rim of the plage correspond quite closely to the magnetic field in his magnetogram. They seem packed together only on his relatively low resolution He picture. Good Big Bear Solar Observatory pictures show the individual structure of each such AR fibril with little ambiguity. The example given of a 'missing plage' seems to contain a small spot or pore-it should be examined further off-band to tell for sure.
We feel that Frazier's examples, even using He pictures that are not state of the art,