Three-Minute Oscillations Above Sunspot Umbra Observed With the Solar Dynamics Observatory/Atmospheric Imaging Assembly and Nobeyama Radioheliograph

Reznikova, Veronika; Shibasaki, Κ.; Сыч, Р. А.; Nakariakov, V. M.

doi:10.1088/0004-637x/746/2/119

Cited by 74 publications

(70 citation statements)

References 33 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…An exception is the power around 5.5mHz in the Ca II K, Hα, and IRIS2796 Å channels, where the power/distance behavior appears to be reversed, i.e., the power near the umbral center is higher than that at the outer radii. This is perhaps similar to the findings of Reznikova et al (2012), where the authors show that oscillations with relatively higher frequencies are more pronounced near the umbral center than at the peripheral regions. Raja Bayanna et al (2014) reported similar observations suggesting larger power at high frequencies in a sunspot umbra compared to that at the umbra-penumbra boundary at chromospheric heights.…”

Section: Radial Variationsupporting

confidence: 89%

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

Prasad

Jess

Doorsselaere

et al. 2017

ApJ

View full text Add to dashboard Cite

High spatial and temporal resolution images of a sunspot, obtained simultaneously in multiple optical and UV wavelengths, are employed to study the propagation and damping characteristics of slow magnetoacoustic waves up to transition region heights. Power spectra are generated from intensity oscillations in sunspot umbra, across multiple atmospheric heights, for frequencies up to a few hundred mHz. It is observed that the power spectra display a power-law dependence over the entire frequency range, with a significant enhancement around 5.5 mHz found for the chromospheric channels. The phase difference spectra reveal a cutoff frequency near 3 mHz, up to which the oscillations are evanescent, while those with higher frequencies propagate upward. The power-law index appears to increase with atmospheric height. Also, shorter damping lengths are observed for oscillations with higher frequencies suggesting frequency-dependent damping. Using the relative amplitudes of the 5.5 mHz (3 minute) oscillations, we estimate the energy flux at different heights, which seems to decay gradually from the photosphere, in agreement with recent numerical simulations. Furthermore, a comparison of power spectra across the umbral radius highlights an enhancement of high-frequency waves near the umbral center, which does not seem to be related to magnetic field inclination angle effects.

show abstract

Section: Radial Variationsupporting

confidence: 89%

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

Prasad

Jess

Doorsselaere

et al. 2017

ApJ

View full text Add to dashboard Cite

show abstract

“…For investigating statistical properties of the intensity variations in different channels, we selected two square regions of interest (ROI 1 and 2) shown in Φ = −3.98 • ). This sunspot showed well pronounced 3-min oscillations which were previously detected with SDO/AIA (Reznikova et al 2012;Yuan et al 2014;Deres & Anfinogentov 2015).…”

Section: Noise-testing Of Sdo/aia Datasupporting

confidence: 75%

“…In particular, the analysed sunspot showed clear 3-min oscillations A153, page 8 of 9 of a non-regular deep-modulated wave-train profile shape (see, e.g., Fig. 4 in Reznikova et al 2012). Due to its adaptive nature, EMD was chosen as the most suitable method for processing such sort of signals.…”

Section: Discussionmentioning

confidence: 96%

Empirical mode decomposition analysis of random processes in the solar atmosphere

Kolotkov

Anfinogentov

Nakariakov

2016

A&A

Self Cite

View full text Add to dashboard Cite

Context. Coloured noisy components with a power law spectral energy distribution are often shown to appear in solar signals of various types. Such a frequency-dependent noise may indicate the operation of various randomly distributed dynamical processes in the solar atmosphere. Aims. We develop a recipe for the correct usage of the empirical mode decomposition (EMD) technique in the presence of coloured noise, allowing for clear distinguishing between quasi-periodic oscillatory phenomena in the solar atmosphere and superimposed random background processes. For illustration, we statistically investigate extreme ultraviolet (EUV) emission intensity variations observed with SDO/AIA in the coronal (171 Å), chromospheric (304 Å), and upper photospheric (1600 Å) layers of the solar atmosphere, from a quiet sun and a sunspot umbrae region. Methods. EMD has been used for analysis because of its adaptive nature and essential applicability to the processing non-stationary and amplitude-modulated time series. For the comparison of the results obtained with EMD, we use the Fourier transform technique as an etalon. Results. We empirically revealed statistical properties of synthetic coloured noises in EMD, and suggested a scheme that allows for the detection of noisy components among the intrinsic modes obtained with EMD in real signals. Application of the method to the solar EUV signals showed that they indeed behave randomly and could be represented as a combination of different coloured noises characterised by a specific value of the power law indices in their spectral energy distributions. On the other hand, 3-min oscillations in the analysed sunspot were detected to have energies significantly above the corresponding noise level. Conclusions. The correct accounting for the background frequency-dependent random processes is essential when using EMD for analysis of oscillations in the solar atmosphere. For the quiet sun region the power law index was found to increase with height above the photosphere, indicating that the higher frequency processes are trapped deeper in the quiet sun atmosphere. In contrast, lower levels of the sunspot umbrae were found to be characterised by higher values of the power law index, meaning the domination of lower frequencies deep inside the sunspot atmosphere. Comparison of the EMD results with those obtained with the Fourier transform showed good consistency, justifying the applicability of EMD.

show abstract

“…Thomas et al (1987) observed multiple peaks in the threeminute band (4.5-10 mHz) from both space and ground instruments. A similar excited range of frequencies is present in Reznikova et al (2012). A recent overview of magnetohydrodynamic waves and coronal seismology can be found in De Moortel & Nakariakov (2012).…”

Section: Introductionmentioning

confidence: 56%

“…Furthermore, many observations show a harmonic wave structure (Yuan et al 2011;Reznikova et al 2012;Sych et al 2011) as opposed to the saw-tooth signal required for the shock wave model. As such, the chromospheric resonator model is a promising explanation for the three-minute oscillations.…”

Section: Introductionmentioning

confidence: 99%

Chromospheric seismology above sunspot umbrae

Snow

Botha

Régnier

2015

A&A

View full text Add to dashboard Cite

Context. The acoustic resonator is an important model for explaining the three-minute oscillations in the chromosphere above sunspot umbrae. The steep temperature gradients at the photosphere and transition region provide the cavity for the acoustic resonator, which allows waves to be both partially transmitted and partially reflected. Aims. In this paper, a new method of estimating the size and temperature profile of the chromospheric cavity above a sunspot umbra is developed. Methods. The magnetic field above umbrae is modelled numerically in 1.5D with slow magnetoacoustic wave trains travelling along magnetic fieldlines. Resonances are driven by applying the random noise of three different colours-white, pink and brown-as small velocity perturbations to the upper convection zone. Energy escapes the resonating cavity and generates wave trains moving into the corona. Line of sight (LOS) integration is also performed to determine the observable spectra through SDO/AIA. Results. The numerical results show that the gradient of the coronal spectra is directly correlated with the chromosperic temperature configuration. As the chromospheric cavity size increases, the spectral gradient becomes shallower. When LOS integrations is performed, the resulting spectra demonstrate a broadband of excited frequencies that is correlated with the chromospheric cavity size. The broadband of excited frequencies becomes narrower as the chromospheric cavity size increases. Conclusions. These two results provide a potentially useful diagnostic for the chromospheric temperature profile by considering coronal velocity oscillations.

show abstract

Three-Minute Oscillations Above Sunspot Umbra Observed With the Solar Dynamics Observatory/Atmospheric Imaging Assembly and Nobeyama Radioheliograph

Cited by 74 publications

References 33 publications

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

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

Empirical mode decomposition analysis of random processes in the solar atmosphere

Chromospheric seismology above sunspot umbrae

Contact Info

Product

Resources

About