Astronomy and Astrophysics – Astrophysics
Scientific paper
Jan 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995a%26a...293..252r&link_type=abstract
Astronomy and Astrophysics 293, 252-262 (1995)
Astronomy and Astrophysics
Astrophysics
45
Sun: Magnetic Fields, Sunspots, Chromosphere, Techniques: Polarimetric
Scientific paper
The need for a simple but quantitative diagnostic of upper chromospheric magnetic fields is keenly felt. We develop the HeI 10830A line as such a diagnostic. An application to observations of an active region allows us to compare the magnetic field in the upper chromosphere with the field in the underlying photosphere. In general, the magnetic field in the chromosphere is found to be significantly more homogeneous. We find that dB/dz in the umbra of a large sunspot (0.4-0.6G/km) is similar to other determinations of this quantity over an equivalent height range. Also, dB/dz decreases outwards in the spot. Thus, in the outer penumbra it has dropped to 0.1-0.3 G/km. A comparison of these values with the results of dB/dz measurements in the photosphere suggests that dB/dz decreases with height. We also find evidence for magnetic canopies near sunspots and for the conservation of magnetic flux with height in solar plages when averaged horizontally over a few arc s. Observations of complex Stokes V profiles at the neutral line in a sunspot penumbra (crossover effect) suggest that the upper chromospheric penumbral magnetic field is not fluted to the same extent as the photospheric field. The large line broadening of He I (up to 10km/s) is found to be due to motions which are largely field aligned.
Livingston William Charles
Rueedi I.
Solanki Sami K.
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