Traveling waves in the sunspot chromosphere: Problems and puzzles of experiments

Кобанов, Н. И.; Kolobov, D. Yu.; Chupin, S. A.

doi:10.1134/s1063773708020060

Cited by 16 publications

(13 citation statements)

References 19 publications

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“…The umbral apparent velocity is largely consistent with previous observations of RWs (e.g., Tziotziou et al 2006Tziotziou et al , 2007; however, the penumbral estimate is atypically low. It should also be noted that much higher apparent velocities reaching average values of 55 km s −1 in the umbra and 50 km s −1 in the penumbra have also been observed (Kobanov et al 2008). East of the sunspot center, the slope smoothly decreases with the exception of an area of low signal-to-noise near Solar X = 98 arcsec where it is difficult to determine the shape of the enhancement.…”

Section: Apparent Velocitymentioning

confidence: 96%

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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Section: Apparent Velocitymentioning

confidence: 96%

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

Madsen

Tian

DeLuca

2015

ApJ

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“…It was also found that the instant oscillation period varies with the amplitude . High-precision spectral measurements revealed the effect of 3 min oscillation height inversion: in the umbral 3 min oscillations are more suppressed than in the neighbouring regions, whereas the chromospheric oscillations are enhanced (Kobanov et al 2008. The propagation channel guiding 3 min oscillations from the photospheric levels to the corona was traced in Jess et al (2012) and Su et al (2013).…”

Section: Introductionmentioning

confidence: 99%

Wave dynamics in a sunspot umbra

Сыч

Nakariakov

2014

A&A

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Context. Sunspot oscillations are one of the most frequently studied wave phenomena in the solar atmosphere. Understanding the basic physical processes responsible for sunspot oscillations requires detailed information about their fine structure. Aims. We aim to reveal the relationship between the fine horizontal and vertical structure, time evolution, and the fine spectral structure of oscillations in a sunspot umbra. Methods. The high spatial and time resolution data obtained with SDO/AIA for the sunspot in active region NOAA 11131 on 08 December 2010 were analysed with the time-distance plot technique and the pixelised wavelet filtering method. Different levels of the sunspot atmosphere were studied from the temperature minimum to the corona. Results. Oscillations in the 3 min band dominate in the umbra. The integrated spectrum of umbral oscillations contains distinct narrowband peaks at 1.9 min, 2.3 min, and 2.8 min. The power significantly varies in time, forming distinct 12-20 min oscillation trains. The oscillation power distribution over the sunspot in the horizontal plane reveals that the enhancements of the oscillation amplitude, or wave fronts, have a distinct structure consisting of an evolving two-armed spiral and a stationary circular patch at the spiral origin, situated near the umbra centre. This structure is seen from the temperature minimum at 1700 Å to the 1.6 MK corona at 193 Å. In time, the spiral rotates anti-clockwise. The wave front spirality is most pronounced during the maximum amplitude phases of the oscillations, and in the bandpasses where umbral oscillations have the highest power, 304 Å and 171 Å. In the low-amplitude phases the spiral breaks into arc-shaped patches. The 2D cross-correlation function shows that the oscillations at higher atmospheric levels occur later than at lower layers. The phase speed is estimated to be about 100 km s −1 . The fine spectral analysis shows that the central patch corresponds to the high-frequency oscillations, while the spiral arms highlight the lower-frequency oscillations in the 3 min band. Conclusions. The vertical and horizontal radial structure of the oscillations is consistent with the model that interprets umbral oscillations as slow magnetoacoustic waves filtered by the atmospheric temperature non-uniformity in the presence of the magnetic field inclination from the vertical. The mechanism for the polar-angle structure of the oscillations, in particular the spirality of the wave fronts, needs to be revealed.

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“…Orrall 1966;Elliott 1969;Liu 1974). Fluctuations in the 3-min range are relatively weak at the photospheric level of sunspots, but they are significantly enhanced in their chromospheres (Lites 1986;Bard & Carlsson 1997;Tziotziou et al 2002;Kobanov et al 2008Kobanov et al , 2011 and in the transition region (Gurman et al 1982;Lites 1992;Bogdan 2000). Observations of the photospheric magnetic field oscillations (Norton et al 1999;Balthasar et al 1998;Bellot Rubio et al 2000) show a fine fragmentation of the magnetic field in the regions where the main power of fluctuations is localised inside sunspots.…”

Section: Introductionmentioning

confidence: 99%

Frequency drifts of 3-min oscillations in microwave and EUV emission above sunspots

Сыч

Zaqarashvili

Nakariakov

et al. 2012

A&A

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Aims. We analysed 3-min oscillations of microwave and extreme ultraviolet (EUV) emission generated at different heights of a sunspot atmosphere, studied the amplitude and frequency modulation of the oscillations, and its relationship with the variation of the spatial structure of the oscillations. Methods. High-resolution data obtained with the Nobeyama Radioheliograph, TRACE and SDO/AIA were analysed with pixelised wavelet filtering (PWF) and wavelet skeleton techniques. Results. Three-minute oscillations in sunspots appear in the form of recurring trains of 8-20 min duration (13 min in average). The typical interval between the trains is 30-50 min. The oscillation trains are transient in frequency and power. The relative amplitude of 3-min oscillations was about 3-8% and sometimes reached 17%. Recurring frequency drifts of 3-min oscillations were detected during the development of individual trains, with the period varying in the range 90-240 s. A wavelet analysis showed that there are three types of oscillation trains: with positive drifts (to high frequencies), negative drifts, and without a drift. Negative drifts, i.e., when the 3-min oscillation period gradually increases, were found to occur more often. The start and end of the drifts coincides with the start time and end of the train. Sometimes two drifts co-exist, i.e. during the end of the previous drift, a new drift appears near 160 s, when the frequency is in the low-frequency part of the 3-min spectrum, near 200 s. This behaviour is seen at all levels of the sunspot atmosphere. The speed of the drift is 4-5 mHz/h in the photosphere, 5-8 mHz/h in the chromosphere, and 11-13 mHz/h in the corona. There were also low-frequency peaks in the spectrum, corresponding to the periods of 10-20 min, and 30-60 min. The comparative study of the spatial structure of 3-min oscillations in microwave and EUV shows the appearance of new sources of the sunspot oscillations during the development of the trains. Conclusions. These structures can be interpreted as waveguides that channel upward propagating waves, which in turn are responsible for the 3-min oscillations. A possible explanation of the observed properties are two simultaneously operating factors: dispersive evolution of the upward propagating wave pulses and the non-uniformity of the oscillation power distribution over the sunspot umbra with different wave sources that correspond to different magnetic flux tubes with different physical conditions and line-of-sight angles.

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Traveling waves in the sunspot chromosphere: Problems and puzzles of experiments

Cited by 16 publications

References 19 publications

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

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

Wave dynamics in a sunspot umbra

Frequency drifts of 3-min oscillations in microwave and EUV emission above sunspots

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