Letter to the Editor
Intensity oscillations observed with Hinode near the south pole of the Sun: leakage of low frequency magneto-acoustic waves into the solar corona
Armagh Observatory, College Hill, Armagh BT61 9DG, N. Ireland e-mail: firstname.lastname@example.org
2 Abastumani Astrophysical Observatory at I. Chavchavadze State University, Al Kazbegi ave. 2a, 0160 Tbilisi, Georgia e-mail: [dato;temury]@genao.org
3 Department of Applied Physics, Institute of Technology, Banaras Hindu University, Varanasi-221005, India e-mail: email@example.com
Accepted: 21 February 2008
Aims. 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.
Key words: Sun: corona / magnetohydrodynamics (MHD) / waves
© ESO, 2008