Power halo and magnetic shadow in a solar quiet region observed in the Hαline

Abstract

Context. We investigate the oscillatory behavior of the quiet solar chromosphere and its discrete components in terms of oscillation properties, i.e. network and internetwork. For this purpose, we use a time series of high resolution filtergrams at five wavelengths along the Hα profile, obtained by the Dutch Open Telescope. Aims. We aim to gain insight on the distribution of power in different period bands and its variation between network and internetwork. Our spectral resolution provides information on the vertical distribution of power, since the Hα line has both photospheric and chromospheric components. We investigate the effect of Hα mottles on chromospheric oscillations, since they are the most prominent feature of the Hα chromosphere and outline inclined magnetic fields. Methods. We use wavelet and phase difference analyses of Hα intensities and Doppler signals. Two-dimensional power maps in the 3, 5 and 7 min period bands as well as coherence and phase difference maps were constructed. Results. At photospheric heights, where the Hα ± 0.7 Å wing is formed, the 3 and 5 min power is enhanced around the network, and forms power halos. Higher in the chromosphere these areas are replaced by magnetic shadows, i.e. places of power suppression. Interestingly, the power maps show a filamentary structure in the network which correlates very well with mottles. These areas show positive phase differences at the 3 min period band. At the 5 min and 7 min period bands both positive and negative phase differences are obtained with an increased number of pixels with high coherence, indicating the existence of both upward and downward propagating waves. Conclusions. We attribute our findings to the interaction between acoustic oscillations and the magnetic fields that constitute the magnetic network. The network flux tubes diverge at chromospheric levels and obtain a significant horizontal component, which is betrayed by the presence of mottles. The variation of power reveals the discrete role of the magnetic field at different heights, which guides or suppresses the oscillations, depending on its inclination. Spectral resolution in Hα provides useful information on the coupling between the acoustic sub-canopy atmosphere and the magnetized chromosphere.

The Effects of Transients on Photospheric and Chromospheric Power Distributions

“…2001; McIntosh et al 2003;Moretti et al 2007;Vecchio et al 2007;Kontogiannis et al 2010bKontogiannis et al , 2014. Using Dutch Open Telescope Hα observations with a cadence of 30 s, Kontogiannis et al (2010aKontogiannis et al ( , 2010b pointed out that there is a strong possibility that power at longer time periods (∼7 minutes) may be enhanced as a result of the lifetimes of the mottles. Furthermore, Kontogiannis et al (2010a) also highlighted that the observed power enhancements, at both photospheric and chromospheric heights, may be closely related to the temporal dynamics of such transients and their lifetimes.…”

“…Imaging data from a passband centered at 0.7 Å from the Hα line core was used to produce the power maps where quiet-Sun "power halos" were positively identified (Kontogiannis et al 2010a(Kontogiannis et al , 2010b(Kontogiannis et al , 2014. This is closer to the Hα line core when compared to the predominantly photospheric bandpass at +0.9 Å.…”

“…Figure 2 reveals that power is suppressed in rosettes over the network in the 3 minute band at the lower chromosphere (Hα+0.543 and Hα+0.362 Å) and enhanced close to the photosphere (Hα+0.906 Å) in all bands. These phenomena are known as magnetic shadows (Judge et al 2001;McIntosh et al 2003;Moretti et al 2007;Vecchio et al 2007;Kontogiannis et al 2010bKontogiannis et al , 2014 and power halos (Kontogiannis et al 2010a), respectively.…”

“…The longer periods generally do not propagate to greater heights and are, instead, evanescent. There is substantial observational evidence for the presence of long period oscillations (Vecchio et al 2007; Kontogiannis et al 2010aKontogiannis et al , 2014Bostancı et al 2014) in the chromosphere around network magnetic elements. It appears that the presence of a strong network magnetic field changes the scenario (Rosenthal et al 2002;Bogdan et al 2003).…”

The Frequency-dependent Damping of Slow Magnetoacoustic Waves in a Sunspot Umbral Atmosphere

“…With the advent of highresolution observations from ground-and space-based instruments, both standing and propagating SMAWs have been discovered in a multitude of structures in the solar atmosphere including magnetic pores (Morton et al 2011;Dorotovič et al 2014;Moreels et al 2015;Freij et al 2016), chromospheric network (Vecchio et al 2007; Kontogiannis et al 2010Kontogiannis et al , 2014, coronal loops (Wang et al 2015;Jess et al 2016), and polar plumes (Krishna Prasad et al 2011;Su 2014). Recent multiwavelength observations of sunspots reveal that umbral flashes (Beckers & Tallant 1969;Rouppe van der Voort et al 2003) and running penumbral waves (Giovanelli 1972;Bloomfield et al 2007;Freij et al 2014) observed in the chromosphere, and quasi-periodic propagating disturbances observed in the coronal loops (Berghmans & Clette 1999;De Moortel et al 2000;De Moortel 2009), are just different manifestations of the SMAWs that propagate from the photosphere through to the corona (Jess et al 2012a;Krishna Prasad et al 2015;Zhao et al 2016).…”