Observations of magnetic fields and motions for sunspot umbrae
Open Access
- 1 May 1983
- journal article
- Published by Oxford University Press (OUP) in Monthly Notices of the Royal Astronomical Society
- Vol. 203 (1) , 9-18
- https://doi.org/10.1093/mnras/203.1.9
Abstract
Observations of two very large sunspots (1966, 1969) are used to investigate the motion of the plasma of the umbral column with respect both to the magnetic structure and the general solar photosphere. Sight-line velocities are obtained spectroscopically for 12 (11) positions of the spots on the solar disc from lines formed at four depths in the sunspot umbra. Analysis of the measures shows a downflow of 0.8 km s−1 at the highest level (Fe Iλ 5250.2 Å) but only 0.1 km s−1 deeper down (Fe Iλ 6302.5 Å). Solar rotation is obtained from spot disc positions as well as spectroscopically. The results are interpreted as showing that, higher than some 100 km above the umbral continuum level, the plasma of the umbral column rotates at the same rate as the photospheric plasma while the magnetic structure slips through the solar photosphere rotating some 0.1 km s−1 faster.Keywords
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