Abstract:
We study intensity oscillations in the solar chromosphere and corona, above a quiet-Sun magnetic network.
Methods. We analyse the time series of He II 256.32 Å, Fe XI 188.23 Å and Fe XII 195.12 Å spectral lines, observed close to the
south pole, by the EUV Imaging Spectrometer (EIS), onboard Hinode. We use a standard wavelet tool, to produce power spectra of
intensity oscillations above the magnetic network.
Results. For all spectral lines, we detect intensity oscillations of period of approximately seven minutes; and for the He II 256.32 Å
line only, we detect an intensity oscillation of period of thirteen minutes, with a probability of approximately 96−98%, which provides
the most likely signature of magneto-acoustic wave propagation above the network.
Conclusions. We propose that field-free cavity areas under bipolar magnetic canopies, in the vicinity of a magnetic network, are
likely to serve as resonators for the magneto-acoustic waves. The cavities with photospheric sound-speed, and granular dimensions,
can produce waves with observed periods. These waves may propagate upwards in the transition region/corona and cause observed
intensity oscillations.
