Multi-height Diagnosis of MHD Wave Periods and their Propagation in Solar Plages Using IRIS Observations
This work aims to investigate magnetohydrodynamic (MHD) waves in solar plages at five distinct heights, spanning from photosphere to the upper chromosphere, using spectroscopic observations provided by Interface Region Imaging Spectrograph (IRIS). The dominant period is found to not change within the plages, while, in pores, the dominant period decreases linearly from 4.20 to 3.20 minutes from the photosphere to the upper chromosphere. Furthermore, in the solar plages, cross-wavelet analysis reveals that periods from 2.0 to 6.0 minutes propagate till the upper chromosphere from the photosphere. The periods beyond 6 minutes have a zero/constant phase difference in the photosphere and in the middle chromosphere. Thus, the 6.0-minute period would be considered the cutoff period at these heights. Next, the propagation speeds of MHD waves above solar plages are estimated in the photosphere and chromosphere. Within the limit of uncertainties, the propagation speed in solar plage is close to the sound speed; hence, the waves are slow magnetoacoustic in nature. Lastly, with the help of phase difference analysis, we found that formation heights of Mg ii k2r and Mg ii k3 are underestimated in solar plage, while the formation height of Mn i is overestimated. In case of pores, the formation heights of Mg ii k2r, Mg ii k3, and Mn i are overestimated. Interestingly, in the quiet-Sun (QS), the formation heights of Mn i and Fe i are nearly the same, and also the formation height of Mg ii k3 is similar to the formation height of Mg ii k2r. In conclusion, some important findings are reported in this work, namely, (1) dominant periods at five different heights between the photosphere and chromosphere, (2) estimation of cutoff periods in the photosphere, middle chromosphere, and the upper chromosphere in the plages, and (3) variations in the formation heights of these spectral lines in pore, plage, and QS.