Physical conditions and velocity fields in coronal holes. i. radial velocity oscillations in and out of coronal holes

Abstract

Abstract Power spectra of radial velocity in and out coronal holes were studied. Thirteen of spectra with temporal resolution 17–20 s were used for this investigation. The duration of each set varied from 1.5–2 h. We analysed two spectral lines: Si I 10827A (photosphere) and He I 10830A (chromosphere). The following conclusions have been draw. (1) All power spectra in the frequency range 0.001–0.05 Hz have confident peaks in the range 0.002–0.010 Hz. (2) The power of oscillations (the sum of squares of amplitudes in a power spectrum) in the frequency range 0.02–0.010 Hz increases from the photosphere to higher levels of the chromosphere. (3) The power of oscillations in the chromosphere is higher inside coronal holes than out side. (4) There are four peaks in the chromosphere power spectrum of a coronal hole and two in the spectrum of a quiet region. Peak frequencies for coronal holes differ from those for quiet regions. We did not find confident peaks in photosphere power spectra of coronal holes. There ...