Helioseismic Holography of Simulated Sunspots: Magnetic and Thermal Contributions to Travel Times

Felipe, T.; Braun, D. C.; Crouch, A. D.; Birch, A. C.

doi:10.3847/0004-637x/829/2/67

Cited by 15 publications

(22 citation statements)

References 58 publications

(104 reference statements)

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“…where τ 0 = 0.5ωt − π and A is the amplitude. This driver excites a broadband wave spectrum with its central peak at frequency ω, which was chosen to correspond to a period P = 300 s. Drivers with this temporal evolution have been shown to excite a wave spectrum which resembles the solar observations (e.g., Parchevsky et al 2008;Felipe et al 2016).…”

Section: Numerical Simulationsmentioning

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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Section: Numerical Simulationsmentioning

confidence: 99%

Origin of the chromospheric three-minute oscillations in sunspot umbrae

Felipe

2019

A&A

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“…The shape and temporal variation of each source is described by Parchevsky et al (2008). This driver generates a wave field that resembles the solar spectrum (e.g., Parchevsky et al 2008;Felipe et al 2016). We have performed several independent numerical experiments which differ in the amount and location of the sources.…”

Section: Numerical Simulationsmentioning

confidence: 99%

Dependence of sunspot photospheric waves on the depth of the source of solarp-modes

Felipe

Khomenko

2017

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Photospheric waves in sunspots moving radially outward at speeds faster than the characteristic wave velocities have been recently detected. It has been suggested that they are the visual pattern of p-modes excited around 5 Mm beneath the sunspot's surface. Using numerical simulations, we performed a parametric study of the waves observed at the photosphere and higher layers that were produced by sources located at different depths beneath the sunspot's surface. The observational measurements are consistent with waves driven between approximately 1 Mm and 5 Mm below the sunspot's surface.

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“…The first is that the thermal rather than magnetic structure of the spot is primarily responsible for the two-skip travel time delays. This is testable within linear wave simulations since the magnetic field may simply be turned off with the thermal structure left unchanged (Cally 2009;Lindsey et al 2010;Felipe et al 2016Felipe et al , 2017.…”

Section: Discussionmentioning

confidence: 99%

Probing sunspots with two-skip time–distance helioseismology

Duvall

Cally

Przybylski

et al. 2018

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Context. Previous helioseismology of sunspots has been sensitive to both the structural and magnetic aspects of sunspot structure. Aims. We aim to develop a technique that is insensitive to the magnetic component so the two aspects can be more readily separated. Methods. We study waves reflected almost vertically from the underside of a sunspot. Time-distance helioseismology was used to measure travel times for the waves. Ray theory and a detailed sunspot model were used to calculate travel times for comparison. Results. It is shown that these large distance waves are insensitive to the magnetic field in the sunspot. The largest travel time differences for any solar phenomena are observed. Conclusions. With sufficient modeling effort, these should lead to better understanding of sunspot structure.

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Helioseismic Holography of Simulated Sunspots: Magnetic and Thermal Contributions to Travel Times

Cited by 15 publications

References 58 publications

Origin of the chromospheric three-minute oscillations in sunspot umbrae

Origin of the chromospheric three-minute oscillations in sunspot umbrae

Dependence of sunspot photospheric waves on the depth of the source of solarp-modes

Probing sunspots with two-skip time–distance helioseismology

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