  The magnetic field of a sunspot guides magnetohydrodynamic waves toward
higher atmospheric layers. In the upper photosphere and lower chromosphere,
wave modes with periods longer than the acoustic cut-off period become
evanescent. The cut-off period essentially changes due to the atmospheric
properties, e.g., increases for larger zenith inclinations of the magnetic
field. In this work, we aim at introducing a novel technique of reconstructing
the magnetic field inclination on the basis of the dominating wave periods in
the sunspot chromosphere and upper photosphere. On 2013 August 21st, we
observed an isolated, circular sunspot (NOAA11823) for 58 min in a purely
spectroscopic multi-wavelength mode with the Interferometric Bidimensional
Spectro-polarimeter (IBIS) at the Dunn Solar Telescope. By means of a wavelet
power analysis, we retrieved the dominating wave periods and reconstructed the
zenith inclinations in the chromosphere and upper photosphere. The results are
in good agreement with the lower photospheric HMI magnetograms. The sunspot's
magnetic field in the chromosphere inclines from almost vertical (0$^{\circ}$)
in the umbra to around 60$^{\circ}$ in the outer penumbra. With increasing
altitude in the sunspot atmosphere, the magnetic field of the penumbra becomes
less inclined. We conclude that the reconstruction of the magnetic field
topology on the basis of sunspot oscillations yields consistent and conclusive
results. The technique opens up a new possibility to infer the magnetic field
inclination in the solar chromosphere.
