Properties of Magnetohydrodynamic Waves in the Solar Photosphere Obtained with Hinode

Abstract

We report the observations of the magnetohydrodynamic (MHD) waves propagating along magnetic flux tubes in the solar photosphere. We identified 20 isolated strong peaks (8 peaks for pores and 12 peaks for intergranular magnetic structure) in the power spectra of the line-of-sight (LOS) magnetic flux, the LOS velocity, and the intensity for 14 different magnetic concentrations. The observation is performed with the spectro-polarimeter of the Solar Optical Telescope aboard the Hinode satellite. The oscillation periods are located in 3-6 minutes for the pores and in 4-9 minutes for the intergranular magnetic elements. These peaks correspond to the magnetic, the velocity, and the intensity fluctuation in time domain with root-mean-square amplitudes of 4-17 G (0.3%-1.2%), 0.03-0.12 km s^-1, and 0.1%-1%, respectively. Phase differences between the LOS magnetic flux (phi _B ), the LOS velocity (phi _v ), the intensities of the line core (phi _I,core), and the continuum intensity (phi _I,cont) have striking concentrations at around -90° for phi _B - phi _v and phi _v - phi _I,core, around 180° for phi _I,core - phi _B , and around 10° for phi _I,core - phi _I,cont. Here, for example, phi _B - phi _v ~ -90° means that the velocity leads the magnetic field by a quarter of cycle. The observed phase relation between the magnetic and the photometric intensity fluctuations would not be consistent with that caused by the opacity effect, if the magnetic field strength decreases with height along the oblique LOS. We suggest that the observed fluctuations are due to longitudinal (sausage-mode) and/or transverse (kink-mode) MHD waves. The observed phase relation between the fluctuations in the magnetic flux and the velocity is consistent with the superposition of the ascending wave and the descending wave reflected at chromosphere/corona boundary (standing wave). Even with such reflected waves, the residual upward Poynting flux is estimated to be 2.7 × 10⁶ erg cm^-2 s^-1 for a case of the kink wave. Seismology of the magnetic flux tubes is possible to obtain various physical parameters from the observed period and amplitude of the oscillations.