Oscillation properties in two sunspots and two facular regions are studied using Solar Dynamics Observatory (SDO) data and groundbased observations in the Si i 10827Å and He i 10830Å lines. The aim is to study different-frequency spatial distribution characteristics above sunspots and faculae and their dependence on magnetic-field features and to detect the oscillations that reach the corona from the deep photosphere most effectively. We used Fast-Fourier-Transform and frequency filtration of the intensity and Doppler-velocity variations with Morlet wavelet to trace the wave propagating from the photosphere to the chromosphere and corona. Spatial distribution of lowfrequency (1 -2 mHz) oscillations outlines well the fan-loop structures in the corona (the Fe ix 171 Å line) above sunspots and faculae. Highfrequency oscillations (5 -7 mHz) are concentrated in fragments inside the photospheric umbra boundaries and close to facular-region centers. This implies that the upper parts of most coronal loops, which transfer low-frequency oscillations from the photosphere, sit in the Fe ix 171 Å line-formation layer. We used dominant frequency vs. distance from barycenter relations to estimate magnetic-tube inclination angle in the higher layers, which poses difficulties for direct magnetic-field measurements. According to our calculations, this angle is ≈40°in the transition region around umbra borders. Phase velocities measured in the coronal loops' upper parts in the Fe ix 171 Å line-formation layer reach 100 -150 km s −1 for sunspots and 50 -100 km s −1 for faculae.
Context. An analysis of the oscillations above sunspots was carried out using simultaneous ground-based and Solar Dynamics Observatory (SDO) observations (Si 10827 Å, He 10830 Å, Fe 6173 Å, 1700 Å, He 304 Å, Fe 171 Å). Aims. Investigation of the spatial distribution of oscillation power in the frequency range 1-8 mHz for the different height levels of the solar atmosphere. Measuring the time lags between the oscillations at the different layers. Methods. We used frequency filtration of the intensity and Doppler velocity variations with Morlet wavelet to trace the wave propagation from the photosphere to the chromosphere and the corona. Results. The 15 min oscillations are concentrated near the outer penumbra in the upper photosphere (1700 Å), forming a ring that expands in the transition zone. These oscillations propagate upward and reach the corona level, where their spatial distribution resembles a fan structure. The spatial distribution of the 5 min oscillation power looks like a circle-shape structure matching the sunspot umbra border at the photospheric level. The circle expands at the higher levels (He 304 Å and Fe 171 Å). This indicates that the low-frequency oscillations propagate along the inclined magnetic tubes in the spot. We found that the inclination of the tubes reaches 50−60 degrees in the upper chromosphere and the transition zone. The main oscillation power in the 5-8 mHz range concentrates within the umbra boundaries at all the levels. The highest frequency oscillations (8 mHz) are located in the peculiar points inside the umbra. These points probably coincide with umbral dots. We deduced the propagation velocities to be 28 ± 15 km s −1 , 26 ± 15 km s −1 , and 55 ± 10 km s −1 for the Si 10827 Å-He 10830 Å, 1700 Å-He 304 Å, and He 304 Å-Fe 171 Å height levels, respectively.
We present an investigation of line-of-sight (LOS) velocity oscillations in solar faculae and sunspots. To study the phase relations between chromospheric and photospheric oscillations of the LOS velocity, we measured the time lag of the chromospheric signal relative to the photospheric one for several faculae and sunspots in a set of spectral line pairs. The measured time lags are different for different objects. The mean measured delay between the oscillations in the five-minute band in faculae is 50 s for the Si i 10 827Å -He i 10 830Å pair; for the pair Fe i 6569Å -Hα 6563Å the mean delay is 20 s; for the pair Fe i 4551Å -Ba ii 4554Å the mean delay is 7 s; for the pair Si i 8536Å -Ca ii 8542Å the mean delay is 20 s. For the oscillations in the three-minute band in sunspot umbrae the mean delay is 55 s for the Si i 10 827Å -He i 10 830Å pair; for the Fe i 6569Å -Hα 6563Å pair it was not possible to determine the delay; for the Fe i 4551Å -Ba ii 4554Å pair the mean delay is 6 s; for the Si i 8536Å -Ca ii 8542Å pair the mean delay is 21 s. Measured delays correspond to the wave propagation speed which significantly exceeds the generally adopted speed of sound in the photosphere. This raises the question of the origin of these oscillations. The possibility that we deal with slow MHD waves is not ruled out.
A small-scale flare SOL2012-09-21T02:19 (B2) occurred in a spotless active region that we observed at a groundbased telescope equipped with a spectrograph. During the flare, we registered an increase in absorption in the He i 10830Å line by 25%, while other chromospheric and coronal spectral lines demonstrated increase in brightness at the same location. This phenomenon called negative flare had rarely been observed at the Sun before. In this paper, we describe the morphology of this flare and investigate its dynamics based on our spectral observations and space imaging data. The Hα and He i 10830Å lines reach their extreme intensities 5 and 6 minutes after the 171Å line. The brightening first occurred in the 171Å and 193Å Solar Dynamics Observatory (SDO) channels followed by the 94Å, 304Å, and 1600Å signals ∼2 minutes after (for the maximum phases). However, the abrupt changes in line-of-sight (LOS) velocities in the chromospheric lines occur simultaneously with the intensity changes in the 304Å and 1600Å lines: we observed a downward motion that was followed by two upward motions. The measured horizontal speed of the perturbation propagation was close to 70 km s −1 both in the chromospheric and coronal lines.We assume that we observed the photoionization-recombination process caused by UV radiation from the transition region during the coronal flare. With this, we point out the difficulties in interpreting the time lag between the emission maximum in the SDO UV channels and the second absorption maximum in the He i 10830Å line.
In this work, we studied oscillation parameters in faculae above magnetic knots and in the adjacent to them areas. Using SDO data we analysed oscillations in magnetic strength, Doppler velocity, and intensity signals for the lower photosphere, and in intensity for the higher levels. We found that in the magnetic field strength oscillation spectra in magnetic knots, peaks at a frequency of about 4.8 mHz appear, while there are no such frequencies in the adjacent facular patches of a moderate field strength. On the contrary, Doppler velocity photospheric oscillation spectra are similar for these types of regions: in both cases, the significant peaks are in the 2.5--4.5 mHz range, though the oscillations in magnetic knots are 2--3 times weaker than those at the facular periphery. At the upper photosphere, the dominant frequencies in magnetic knots are 0.5--1 mHz higher than in the medium-field regions. The transition region oscillations above magnetic knots mainly concentrate in the 3--6 mHz range, and those above moderate-field patches concentrate below 3 mHz.Comment: 16 pages, 9 figure
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