Hinode and Iris Observations of the Magnetohydrodynamic Waves Propagating From the Photosphere to the Chromosphere in a Sunspot

Abstract

Magnetohydrodynamic (MHD) waves have been considered as energy sources for heating the solar chromosphere and the corona. Although MHD waves have been observed in the solar atmosphere, there are a lack of quantitative estimates on the energy transfer and dissipation in the atmosphere. We performed simultaneous Hinode and IRIS observations of a sunspot umbra to derive the upward energy fluxes at two different atmospheric layers (photosphere and lower transition region) and estimate the energy dissipation. The observations revealed some properties of the observed periodic oscillations in physical quantities, such as their phase relations, temporal behaviors, and power spectra, making a conclusion that standing slow-mode waves are dominant at the photosphere with their high-frequency leakage, which is observed as upward waves at the chromosphere and the lower transition region. Our estimates of upward energy fluxes are 2.0 × 10 7 erg cm −2 s −1 at the photospheric level and 8.3 × 10 4 erg cm −2 s −1 at the lower transition region level. The difference between the energy fluxes is larger than the energy required to maintain the chromosphere in the sunspot umbrae, suggesting that the observed waves can make a crucial contribution to the heating of the chromosphere in the sunspot umbrae. In contrast, the upward energy flux derived at the lower transition region level is smaller than the energy flux required for heating the corona, implying that we may need another heating mechanism. We should, however, note a possibility that the energy dissipated at the chromosphere might be overestimated because of the opacity effect.

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

“…The latter value would be 765± 57erg cm −2 s −1 if the alternative height (1500 km), inferred from the phase difference spectra, is assumed for the IRIS1330 Å channel. In either case, these values indicate significant damping in agreement with Kanoh et al (2016). Of course, it is not trivial to state whether or not the entire missing wave energy directly resulted in the thermalization of the local plasma.…”

“…Felipe et al (2011) found an energy flux of the order of 10 6 erg cm −2 s −1 at photospheric heights, and concluded that the energy flux available from acoustic oscillations is insufficient to balance the radiative losses in chromospheric umbrae. Recently, using simultaneous observations of a sunspot umbra with Hinode (Kosugi et al 2007) and IRIS, Kanoh et al (2016) estimated the energy fluxes for 6-10 mHz SMAWs at the photospheric and lower transition region levels as 2×10 7 erg cm −2 s −1 and 8.3×10 4 erg cm −2 s −1 , respectively. These results, in contrast to Felipe et al (2011), demonstrate the potential for SMAWs to contribute significantly to the heating of the umbral chromosphere.…”

“…This value is on the same order of that obtained by Felipe et al (2011) near the photosphere. On the contrary, based on the observational data of a sunspot umbra, Kanoh et al (2016) erg cm −2 s −1 at the lower transition region level in the 6-10 mHz frequency band, implying a dissipation of sufficient energy to maintain the umbral chromosphere. The authors, however, add a caveat that the energies could be overestimated due to opacity effects.…”

High-frequency Spicule Oscillations Generated via Mode Conversion

“…We set δv and f 0 to 0.4 km s −1 and 5 mHz, respectively. Furthermore, f 0 is set close to the most dominant frequency of the chromospheric longitudinal waves (Tian et al 2014;Kanoh et al 2016).…”

Propagating wave in active region-loops, located over the solar disk observed by the Interface Region Imaging Spectrograph

“…Although there have been many studies of MHD waves in the last few decades, observations about the propagating wave taken by the IRIS are rarely reported (Okamoto et al 2015). Over the solar disk, there are only a few published results of chromospheric waves from the IRIS data (Bryans et al 2016;Kanoh et al 2016). One important reason is that there are so many fine structures in the chromosphere, thus making it difficult to detect the wave signal in a particular chromospheric structure among the abundant features.…”