13.1.2.1 Naphthosemiquinones derived from 1,2-dihydroxynaphthalenes

Ulmschneider, K. B.; Stegmann, H. B.

doi:10.1007/10201292_53

Cited by 3 publications

(4 citation statements)

References 23 publications

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“…Out of this region we have imposed adiabatic propagation. Our approach at layers deeper than z = 200 km is similar to that employed by Ulmschneider (1971), who assumed a completely optically thick medium (adiabatic propagation) below z ∼ 140 km. At the chromosphere, the effect of the radiative dissipation on wave propagation is negligible (Schmieder 1977).…”

Section: Impact Of Radiative Losses On the Cutoffmentioning

confidence: 99%

Numerical determination of the cutoff frequency in solar models

Felipe,

Sangeetha

2020

Preprint

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Context. In stratified atmospheres, acoustic waves can only propagate if their frequency is above the cutoff value. The determination of the cutoff frequency is fundamental for several topics in solar physics, such as evaluating the contribution of those waves to the chromospheric heating or the application of seismic techniques. However, different theories provide different cutoff values. Aims. We developed an alternative method to derive the cutoff frequency in several standard solar models, including various quiet-Sun and umbral atmospheres. The effects of magnetic field and radiative losses on the cutoff are examined. Methods. We performed numerical simulations of wave propagation in the solar atmosphere using the code MANCHA. The cutoff frequency is determined from the inspection of phase difference spectra computed between the velocity signal at two atmospheric heights. The process is performed by choosing pairs of heights across all the layers between the photosphere and the chromosphere, to derive the vertical stratification of the cutoff in the solar models.Results. The cutoff frequency predicted by the theoretical calculations departs significantly from the measurements obtained from the numerical simulations. In quiet-Sun atmospheres, the cutoff shows a strong dependence on the magnetic field for adiabatic wave propagation. When radiative losses are taken into account, the cutoff frequency is greatly reduced and the variation of the cutoff with the strength of the magnetic field is lower. The effect of the radiative losses in the cutoff is necessary to understand recent quiet-Sun and sunspot observations. In the presence of inclined magnetic fields, our numerical calculations confirm the reduction of the cutoff frequency due to the reduced gravity experienced by waves propagating along field lines. An additional reduction is also found in regions with significant changes in the temperature, due to the lower temperature gradient along the path of field-guided waves. Conclusions. Our results show solid evidences of the stratification of the cutoff frequency in the solar atmosphere. The cutoff values are not correctly captured by theoretical estimates. In addition, most of the widely-used analytical cutoff formulae neglect the impact of magnetic fields and radiative losses, whose role is critical to determine the evanescent or propagating nature of the waves.

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Section: Impact Of Radiative Losses On the Cutoffmentioning

confidence: 99%

Numerical determination of the cutoff frequency in solar models

Felipe,

Sangeetha

2020

Preprint

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“…Below z = 0.2 Mm, Spiegel's formula exhibits unrealistic low values for the radiative cooling time due to the optically thin treatment. We have followed the same approach from Ulmschneider (1971), assuming a completely optically thick atmosphere below a certain arbitrary height. Ulmschneider (1971) chose a height between z = 0.11 and z = 0.14 Mm as the lower limit of applicability of Eq.…”

Section: Chromospheric Cavity With Radiative Losses and Magnetic Fieldmentioning

confidence: 99%

“…We have followed the same approach from Ulmschneider (1971), assuming a completely optically thick atmosphere below a certain arbitrary height. Ulmschneider (1971) chose a height between z = 0.11 and z = 0.14 Mm as the lower limit of applicability of Eq. 22.…”

Section: Chromospheric Cavity With Radiative Losses and Magnetic Fieldmentioning

confidence: 99%

Origin of the chromospheric three-minute oscillations in sunspot umbrae

Felipe

2019

A&A

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Context. Sunspot umbrae show a change in the dominant period of their oscillations from five minutes (3.3 mHz) in the photosphere to three minutes (5.5 mHz) in the chromosphere. Aims. In this paper, we explore the two most popular models proposed to explain the three-minute oscillations: the chromospheric acoustic resonator and the propagation of waves with frequency above the cutoff value directly from lower layers. Methods. We employ numerical simulations of wave propagation from the solar interior to the corona. Waves are driven by a piston at the bottom boundary. We have performed a parametric study of the measured chromospheric power spectra in a large number of numerical simulations with differences in the driving method, the height of the transition region (or absence of transition region), the strength of the vertical magnetic field, and the value of the radiative cooling time.Results. We find that both mechanisms require the presence of waves with period in the three-minute band at the photosphere. These waves propagate upward and their amplitude increases due to the drop of the density. Their amplification is stronger than that of evanescent low-frequency waves. This effect is enough to explain the dominant period observed in chromospheric spectral lines. However, waves are partially trapped between the photosphere and the transition region, forming an acoustic resonator. This chromospheric resonant cavity strongly enhances the power in the three-minute band. Conclusions. The chromospheric acoustic resonator model and the propagation of waves in the three-minute band directly from the photosphere can explain the observed chromospheric three-minute oscillations. They are both important in different scenarios. Resonances are produced by waves trapped between the temperature minimum and the transition region. Strong magnetic fields and radiative losses remove energy from the waves inside the cavity, resulting in weaker amplitude resonances.

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“…There are also a number of numerical studies of the acoustic wave propagation in the solar atmosphere (e.g., Ulmschneider 1971;Ulmschneider et al 1978;Carlsson et al 1997;Cuntz et al 1998;Fazwy et al 2002) in which the authors tried to determine the role played -4by acoustic waves of different frequencies in the atmospheric heating. Typically propagating acoustic waves were considered, which means that the authors did not have to dwell upon the concept of the acoustic cutoff frequency.…”

Section: Introductionmentioning

confidence: 99%

Variation of Acoustic Cutoff Period With Height in the Solar Atmosphere: Theory Versus Observations

Murawski

Musielak

Konkol

et al. 2016

ApJ

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Recently Wiśniewska et al. demonstrated observationally how the acoustic cutoff frequency varies with height in the solar atmosphere including the upper photosphere and the lower and middle chromosphere, and showed that the observational results cannot be accounted for by the existing theoretical formulas for the acoustic cutoff. In order to reproduce the observed variation of the cutoff with atmospheric height, numerical simulations of impulsively generated acoustic waves in the solar atmosphere are performed, and the spectral analysis of temporal wave profiles is used to compute numerically changes of the acoustic cutoff with height. Comparison of the numerical results with the observational data shows good agreement, which clearly indicates that the obtained results may be used to determine the structure of the background solar atmosphere.

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13.1.2.1 Naphthosemiquinones derived from 1,2-dihydroxynaphthalenes

Cited by 3 publications

References 23 publications

Numerical determination of the cutoff frequency in solar models

Numerical determination of the cutoff frequency in solar models

Origin of the chromospheric three-minute oscillations in sunspot umbrae

Variation of Acoustic Cutoff Period With Height in the Solar Atmosphere: Theory Versus Observations

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