Magnetohydrodynamic (MHD) waves, especially Alfven waves, are believed to have an important role for coronal heating. Although there are many observational studies about Alfven waves, most of the studies do not discuss the excitation, propagation and dissipation of Alfven waves. Further, there are few studies dealing with magnetic field quantitatively, because these previous studies are not done by means of spectropolarimetric data. We focused on a previous study (Fujimura & Tsuneta 2009), which studied about photospheric MHD waves driven by the p-mode oscillation with Hinode Solar Optical Telescope (SOT)’s repeated sequence of SP spectropolarimetric data for a very narrow field of view. We expand the previous study as follows.
1) We increased the temporal resolution to 21 sec, which is about three times higher than that of the previous study (67 sec), and the increased cadence is more suitable for investigating details of the temporal waveform. Phase relation between the magnetic flux and the Intensity is important for identifying Alfven waves precisely. 2) We performed a set of the high-cadence observations coordinated between Hinode and IRIS for studying propagating processes of MHD waves.
We analyzed data observed in a plage region, which is not located near the solar disk center. Oscillated signals in the line-of-sight (LOS) velocity, the Intensity and the LOS magnetic flux (only Hinode/SOT can obtain) were identified at both the photosphere and the upper atmosphere. In the IRIS spectra such as Mg II and Si IV, the LOS velocity oscillations show larger amplitude and sawtooth patterns compared with the photospheric oscillation, indicating the shock forming as the waves propagate upward. The phase relation between the photospheric LOS magnetic flux and the photospheric Intensity implies that the magnetic flux oscillation does not caused by Alfven waves but a consequence of the opacity effect. The opacity effect means that there region where the spectral line profiles are sensitive to magnetic fields moves upward and downward. This result is not consistent to the previous study. This discrepancy might come from the technique based on the Fourier transform used in the previous study.