Oscillations in a Sunspot With Light Bridges

Yuan, Ding; Nakariakov, V. M.; Huang, Zhaoqin; Li, Bo; Su, Jiangtao; Yan, Yihua; Tan, Baolin

doi:10.1088/0004-637x/792/1/41

Cited by 38 publications

(39 citation statements)

References 53 publications

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“…Five-minute oscillations (3−5 min) are significant in all bandpasses considered (Fig. 2); this phenomenon was reported earlier at chromospheric heights by Yuan et al (2014a) and Su et al (2016). Another significant spectral component is detected at 0.5−1 min (sub-minute oscillations), but only in the 211 Å channel.…”

Section: Resultssupporting

confidence: 76%

“…An isolated sunspot could be assumed to have an expanding axisymmetric magnetic field; inhomogeneities, such as light bridges, umbral dots, are normally observed at a variety of scales (see a review by Borrero & Ichimoto 2011). These inhomogeneities could modify the distribution of the oscillation frequency (Jess et al 2012) and even even cause abnormal frequency changes (Yuan et al 2014a;Su et al 2016). Therefore, they are excellent objects to test the feasibility and robustness of the presumed theory and to explore the induced extra dynamics, for example reconnections, heating, flows, and convections.…”

Section: Introductionmentioning

confidence: 99%

“…This implies that the magnetic field of a light bridge may be twisted along its length and the field may only shape a magnetic null point at one flank. Yuan et al (2014a) reported the first detection of five-minute oscillation at a light bridge observed at the chromospheric height. Su et al (2016) suggested that the inference counterstream three-minute umbral wave might be the source of the five-minute oscillations at light bridge.…”

Section: Introductionmentioning

confidence: 99%

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Abnormal oscillation modes in a waning light bridge

Yuan

Walsh

2016

A&A

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Context. A sunspot acts as a waveguide in response to the dynamics of the solar interior; the trapped waves and oscillations could reveal its thermal and magnetic structures. Aims. We study the oscillations in a sunspot intruded by a light bridge, and the details of these oscillations could reveal the fine structure of the magnetic topology. Methods. We used the Solar Dynamics Observatory/Atmospheric Imaging Assembly data to analyse the oscillations in the emission intensity of light bridge plasma at different temperatures, and we investigated their spatial distributions. Results. The extreme ultraviolet emission intensity exhibits two persistent oscillations at five-minute and sub-minute ranges. The spatial distribution of the five-minute oscillation follows the spine of the bridge, whereas the sub-minute oscillations overlap with two flanks of the bridge. Moreover, the sub-minute oscillations are highly correlated in spatial domain, however, the oscillations at the eastern and western flanks are asymmetric with regard to the lag time. In the meantime, jet-like activities are only found at the eastern flank. Conclusions. Asymmetries in the form of oscillatory pattern and jet-like activities are found between two flanks of a granular light bridge. Based on our study and recent findings, we propose a new model of twisted magnetic field for a light bridge and its dynamic interactions with the magnetic field of a sunspot.

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Section: Resultssupporting

confidence: 76%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Abnormal oscillation modes in a waning light bridge

Yuan

Walsh

2016

A&A

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“…MHD seismology was successfully applied in estimating the coronal magnetic field (Nakariakov & Ofman 2001), transverse loop structuring (Aschwanden et al 2003), Alfvén transit times (Arregui et al 2007), polytropic index (Van Doorsselaere et al 2011b), thermal conduction coefficient (Van Doorsselaere et al 2011b), the magnetic topology of sunspots (Jess et al 2013;Yuan et al 2014aYuan et al , 2014b, and the magnetic structure of large-scale streamers (Chen et al 2010(Chen et al , 2011. It could also be used to determine the coronal density scale height (Andries et al 2005), to quantify the expansion factor of the coronal loops (Verth et al 2008), and to probe the characteristic spatial scale of randomly structured plasmas (Yuan et al 2015).…”

Section: Introductionmentioning

confidence: 99%

Forward Modeling of Standing Slow Modes in Flaring Coronal Loops

Yuan

Doorsselaere

Banerjee

et al. 2015

ApJ

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Standing slow-mode waves in hot flaring loops are exclusively observed in spectrometers and are used to diagnose the magnetic field strength and temperature of the loop structure. Owing to the lack of spatial information, the longitudinal mode cannot be effectively identified. In this study, we simulate standing slow-mode waves in flaring loops and compare the synthesized line emission properties with Solar Ultraviolet Measurements of Emitted Radiation spectrographic and Solar Dynamics Observatory/Atmospheric Imaging Assembly imaging observations. We find that the emission intensity and line width oscillations are a quarter period out of phase with Doppler shift velocity in both time and spatial domain, which can be used to identify a standing slow-mode wave from spectroscopic observations. However, the longitudinal overtones could only be measured with the assistance of imagers. We find emission intensity asymmetry in the positive and negative modulations;this is because the contribution function pertaining to the atomic emission process responds differently to positive and negative temperature variations. One may detect half periodicity close to the loop apex, where emission intensity modulation is relatively small. The line-of-sight projection affects the observation of Doppler shift significantly. A more accurate estimate of the amplitude of velocity perturbation is obtained by de-projecting the Doppler shift by a factor of 1-2θ/π rather than the traditionally used cos q. If a loop is heated to the hotter wing, the intensity modulation could be overwhelmed by background emission, while the Doppler shift velocity could still be detected to a certain extent.

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“…They were first observed by Beckers & Tallant (1969) as sudden brightenings in Ca ii H and K lines known as umbral flashes (UFs). UFs were found to have periods of around three minutes in chromospheric lines and are now understood to be the chromosphere's response to forcing from photospheric p-mode oscillations (Kneer et al 1981; Thomas et al 1982;Thomas 1985;Lites 1992;Yuan et al 2014). Early theories suggested that UFs were a chromospheric resonant standing wave in the sunspot umbra, but observations of highly nonlinear three-minute oscillations in the transition region and corona suggested they are likely propagating waves (Brynildsen et al 1999a(Brynildsen et al , 1999b(Brynildsen et al , 2002(Brynildsen et al , 2004Maltby et al 1999;O'Shea et al 2002;De Moortel et al 2002;Tian et al 2014).…”

Section: Introductionmentioning

confidence: 99%

Observations of Umbral Flashes and Running Sunspot Waves With the Interface Region Imaging Spectrograph

Madsen

Tian

DeLuca

2015

ApJ

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We present simultaneous, high-resolution, multi-temperature observations of running waves and umbral flashes in a sunspot with the Interface Region Imaging Spectrograph. We analyze intensity variations in slit-jaw images to investigate the relationship between running waves in the 1400 Å (Si iv/transition region) passband and umbral flashes in the 2796 Å (Mg ii/chromosphere) passband. Using global wavelet analysis, we find that the dominant wave periods increase from approximately 150 s near the sunspot center to about 300 s in the penumbra in both passbands. This coincides extremely well with the radially increasing inclination of magnetic field lines observed with Solar Dynamics Observatory/Helioseismic and Magnetic Imager, suggesting that the waves are propagating vertically along the inclined field lines. Furthermore, apparent horizontal velocities for running waves decrease from about 12 km s −1 in the umbra to about 4 km s −1 in the penumbra which is predicted by the same inclined field geometry. Finally, we find that umbral flashes lead running waves in both the spatial and temporal domains. The former result is attributable to the inclined field geometry; however, the geometry does not predict the radially increasing time lag which is likely due to the opacity difference between the emission lines that dominate the two passbands. These results suggest that running waves and umbral flashes both originate from photospheric p-mode oscillations and are manifestations of upward-propagating slow magnetoacoustic modes at different altitudes and temperatures. The apparent trans-sunspot propagation of running waves is not real but rather an image of these upward-propagating modes traveling along field lines of radially increasing inclination.

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Oscillations in a Sunspot With Light Bridges

Cited by 38 publications

References 53 publications

Abnormal oscillation modes in a waning light bridge

Abnormal oscillation modes in a waning light bridge

Forward Modeling of Standing Slow Modes in Flaring Coronal Loops

Observations of Umbral Flashes and Running Sunspot Waves With the Interface Region Imaging Spectrograph

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