Astronomy & Astrophysics

Table 1: Observing parameters corresponding to the four studied pore regions. $\alpha$ denotes the direction to disk center (see Fig. 1; counterclockwise from the x-axis); $\cos\theta$ is the off-center position; $\lambda _{1/2}$ is the FWHM of the FPI; $N_{\lambda }$ and $\Delta \lambda$ give the number of spectral positions in one scan and the distance between two subsequent spectral positions; $t_{\rm ex}$ denotes the exposure times; $N_{\rm scan}$ is the number of scans in the time series and $\Delta t$ gives the time intervals between two subsequent scans, respectively.