Speaker
Jayant Joshi
(ISP Stockholm)
Description
We studied magnetic field structure of a sunspot penumbra in
the upper chromosphere
and compared it to that in the photosphere. High spatial
resolution
spectropolarimetric observations were recorded with the
1.5-meter GREGOR telescope
using the GREGOR Infrared Spectrograph (GRIS). The observed
spectral domain includes
the upper chromospheric He I triplet at 10830 Å and the
photospheric Si I 10827.1 Å
and Ca I 10833.4 Å lines. The upper chromospheric magnetic
field is obtained by
inversions applied to the He i triplet assuming a
Milne-Eddington type atmosphere.
The height dependent photospheric magnetic field is
retrieved by inversions applied
to the Si I 10827.1 Å and Ca I 10833.4 Å lines. We find that
the magnetic field
strength of the observed penumbra does not show variations
on small spatial scales in
the upper chromosphere, whereas the inclination of the
magnetic field shows
variations in the azimuthal direction, resembling the well
known spine-interspine
structure in the photospheric layers of penumbrae. The
variations in the magnetic
field inclination in the upper chromosphere remarkably
coincide with the variations
in the inclination of the photospheric field. The typical
peak to peak variation in
the inclination of the magnetic field in the upper
chromosphere is found to be
10°-15°, compared to 20°-25° in the photosphere.
Primary author
Jayant Joshi
(ISP Stockholm)
