Height distribution of the power of 3-min oscillations over sunspots

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

doi:10.1051/0004-6361/200913533

Cited by 25 publications

(26 citation statements)

References 40 publications

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“…According to [Balthasar and Woehl, 1983], the depression of the umbral photosphere with respect to the penumbra (the Wilson effect) is about 700 km. This difference in height can lead to the decrease in the 3-min oscillation amplitude by a factor of 2 [Lites et al, 1998] and consistent with the 3-min the line-of-sight (LOS) velocity power distribution obtained at the photospheric level [Kobanov et al, 2011]. The second mechanism connected with the topology of the sunspot magnetic field.…”

Section: Introductionsupporting

confidence: 79%

MHD Wave in Sunspots

Сыч¹

2016

Low‐Frequency Waves in Space Plasmas

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Section: Introductionsupporting

confidence: 79%

MHD Wave in Sunspots

Сыч¹

2016

Low‐Frequency Waves in Space Plasmas

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“…Such an inclination angle may explain why Kobanov et al (2008Kobanov et al ( , 2011a were unable to correlate (on a pixel-by-pixel basis) high chromospheric oscillatory power to that occurring in the underlying photosphere.…”

Section: Chromospherementioning

confidence: 99%

“…Indeed, Nagashima et al (2007) utilized Hinode/SOT image sequences to show how oscillatory power, at all frequencies, is significantly reduced in sunspot umbrae. More recently, Kobanov et al (2008Kobanov et al ( , 2011a have not only detected photospheric 3 minute oscillations, but the authors also claim that the location of maximum chromospheric power also corresponds to a co-spatial decrease in power of the photospheric oscillations. However, the spatial resolution obtained by Kobanov et al (2008Kobanov et al ( , 2011a was on the order of 1 , so precise diagnostics of the exact umbral structures displaying 3 minute periodicities was impossible.…”

Section: Introductionmentioning

confidence: 99%

The Source of 3 Minute Magnetoacoustic Oscillations in Coronal Fans

Jess

Moortel

Mathioudakis

et al. 2012

ApJ

100

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We use images of high spatial, spectral, and temporal resolution, obtained using both ground-and space-based instrumentation, to investigate the coupling between wave phenomena observed at numerous heights in the solar atmosphere. Analysis of 4170 Å continuum images reveals small-scale umbral intensity enhancements, with diameters ∼0. 6, lasting in excess of 30 minutes. Intensity oscillations of ≈3 minutes are observed to encompass these photospheric structures, with power at least three orders of magnitude higher than the surrounding umbra. Simultaneous chromospheric velocity and intensity time series reveal an 87• ± 8• out-of-phase behavior, implying the presence of standing modes created as a result of partial wave reflection at the transition region boundary. We find a maximum waveguide inclination angle of ≈40• between photospheric and chromospheric heights, combined with a radial expansion factor of <76%. An average blueshifted Doppler velocity of ≈1.5 km s −1 , in addition to a time lag between photospheric and chromospheric oscillatory phenomena, confirms the presence of upwardly propagating slow-mode waves in the lower solar atmosphere. Propagating oscillations in EUV intensity are detected in simultaneous coronal fan structures, with a periodicity of 172 ± 17 s and a propagation velocity of 45 ± 7 km s −1 . Numerical simulations reveal that the damping of the magnetoacoustic wave trains is dominated by thermal conduction. The coronal fans are seen to anchor into the photosphere in locations where large-amplitude umbral dot (UD) oscillations manifest. Derived kinetic temperature and emission measure time series display prominent outof-phase characteristics, and when combined with the previously established sub-sonic wave speeds, we conclude that the observed EUV waves are the coronal counterparts of the upwardly propagating magnetoacoustic slow modes detected in the lower solar atmosphere. Thus, for the first time, we reveal how the propagation of 3 minute magnetoacoustic waves in solar coronal structures is a direct result of amplitude enhancements occurring in photospheric UDs.

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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: 98%

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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Height distribution of the power of 3-min oscillations over sunspots

Cited by 25 publications

References 40 publications

MHD Wave in Sunspots

MHD Wave in Sunspots

The Source of 3 Minute Magnetoacoustic Oscillations in Coronal Fans

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

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