| Authors : | Kartika Sangal1, A.K. Srivastava1, P. Kayshap2
1 Department of Physics, Indian Institute of Technology (BHU), Varanasi-221005, India
2 Vellore Institute of Technology, Kotri Kalan, Ashta, Near, Indore Road, Bhopal, Madhya Pradesh, 466114 |
| Abstract : | We use IRIS sit-and-stare observations of the quiet sun, which allow us to study the propagation of the waves above quiet-Sun atmosphere. In order to investigate the propagation of waves, we have analyzed a number of IRIS spectral lines, including those in the photospheric region (Fe I 2799.972 Å, Mn I 2801.907 Å), the chromospheric region (Mg II h 2802.704 Å), and the transition region (Si IV 1393.755 Å). Wavelet tools (power, cross-power, coherence, and phase difference) are used along with a generic noise model (power-law + constant) to derive the statistically dominant periods at different atmospheric heights, and in determining the cut-off. A study of the Doppler velocity oscillations in the network region of the photosphere, chromosphere, and transitions is presented. For each region, we compute the histogram distribution of significant periods at different locations and find the dominant period. These dominant oscillatory periods are likely associated with field-aligned magnetoacoustic waves. In the photosphere, the 5 min period wave dominates, while in the chromosphere, the 3 min wave dominates,. In the transition region, we find a range of periodicities with the mean period at 7 min. The cut-off frequency is further computed by estimating the phase difference between velocity signals at two different heights. We show the variation of the phase difference with respect to the periods. The observed patch of the quiet-Sun behaves like an ideal magnetic portal where 5 minute magnetoacoustic waves were dominant upto the top of the photopshere, however, only the wave power related to 3.0 min dominant oscillation period only reaches upto the chromospheric heights. Transition region does not stamp the signature of these two waves (5 and 3 minutes) which were dominant at lower heights rather it shows the generation of some longer period oscillations generated in situ there.
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