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Oscillation Dynamics in Short-Lived Facula Regions during Their Lifetime  

Andrei Chelpanov   Submitted: 2022-02-23 23:54

We performed a multi-wave study of the oscillation dynamic in short-lived facula regions during their lifetime. We studied oscillations in five regions, three of which belonged to the beginning of the current solar activity cycle, and two of them existed at the end of the previous cycle. We found that in the facula regions of the current cycle, low-frequency 1-2 mHz oscillation dominated at the early stages of the faculae formation, while in the regions of the previous cycle, five-minute oscillations dominated at this stage. At the maximal development phase of all the facula regions, the locations of observed low frequencies are closely related to those of the coronal loops. These results support the version that the sources of the low-frequency oscillations in loops lie loops' foot points.

Authors: Andrei Chelpanov, Nikolai Kobanov
Projects: None

Publication Status: Accepted in Solar Physics
Last Modified: 2022-02-27 12:57
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Propagating Oscillations in the Lower Atmosphere Under Coronal Holes  

Andrei Chelpanov   Submitted: 2022-01-11 20:30

The subject of this study is oscillations in the lower atmosphere in coronal-hole regions, where the conditions are favorable for propagation between the atmospheric layers. Based on spectroscopic observations in photospheric and chromospheric lines, we analyzed the features of the oscillations that show signs of propagation between the layers of the solar atmosphere. Using the cross-spectrum wavelet algorithm, we found that both chromospheric and photospheric signals under coronal holes share a range of significant oscillations with periods around five minutes, while the signals outside coronal holes show no mutual oscillations in the photosphere and chromosphere. The phase shift between the layers indicates a predominantly upward propagation with partial presence of standing waves. We have also tested the assumption that the torsional Alfvén waves propagating in the corona originate in the lower atmosphere. However, the observed line-width oscillations, although similar in period to the Alfvén waves observed earlier in the corona of open-field regions, seem to be associated with other magnetohydrodynamic (MHD) modes. If we assume that the oscillations that we observed are related to Alfvén waves, then perhaps this is only through the mechanisms of the slow-MHD-wave transformation.

Authors: Andrei Chelpanov, Nikolai Kobanov, Maksim Chelpanov, Aleksandr Kiselev
Projects: None

Publication Status: Published in Solar Physics
Last Modified: 2022-01-12 13:27
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Using Flare-Induced Modulation of Three- and Five-Minute Oscillations for Studying Wave Propagation in the Solar Atmosphere  

Andrei Chelpanov   Submitted: 2022-01-11 20:28

We propose a method for diagnosing the physical conditions in the solar atmosphere using an increase in oscillation amplitudes resulting from minuscule solar flares. As an example, we consider a B2 flare, which caused a sharp short-lived increase in the amplitude of three- and five-minute oscillations in the lower layers of the solar atmosphere. Enhanced three- and five-minute oscillations propagated from the lower layers of the atmosphere into the corona. Such short oscillation trains made it possible to remove the uncertainties arising in the measurements of the phase and group lags between the layers. In addition, the amplification of the oscillations that reach the corona may add to the likelihood of a repeated flare. Studying oscillations in small flare events has the advantage of exploring the atmosphere in its quasi-quiet condition as opposed to powerful flares, which cause substantial and prolonged disturbance of the environment. In addition, small flares are much more common than powerful flares, which allows one to choose from a larger sample of observational material.

Authors: Andrei Chelpanov, Nikolai Kobanov
Projects: None

Publication Status: Published in Solar Physics
Last Modified: 2022-01-12 13:27
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Multilevel Observations of the Oscillations in the First Active Region of the New Cycle  

Andrei Chelpanov   Submitted: 2020-06-13 02:34

For the first time, a multi-wave research of oscillation dynamics in a solar facula from its birth to decay was carried out. We performed spectral observations of active region NOAA 12744 at Horizontal Solar Telescope of the Sayan Solar Observatory in the Hα, He I 10830 A, and Si I 10827 Å lines. We used Solar Dynamics Observatory (SDO) line-of-sight magnetic field data and the 1600 A, 304 Å, and 171 Å UV channels. At the early stages of the facula evolution, we observed low-frequency (1-2 mHz) oscillations concentrate in the central part of the facula. In the lower solar atmosphere, this is registered in the intensity, line-of-sight velocity, and magnetic field signals. These frequencies were also observed in the transition region and corona (304 Å and 171 Å channels). At the maximal development phase of the facula evolution, the low frequency oscillations closely reproduce the coronal loop structures forming above the active region. At the decay phase, the spatial distributions of the observed frequencies resemble those found in and above the undisturbed chromosphere network. Our results indicate a direct relation of the low frequency oscillations observed in the lower solar atmosphere with the oscillations in the coronal loops, which is probably implemented through the loop footpoints.

Authors: Andrei Chelpanov and Nikolai Kobanov
Projects: None

Publication Status: Accepted to Solar Physics
Last Modified: 2020-06-17 13:07
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Oscillations Accompanying a He I 10830 Å Negative Fare in a Solar Facula II. Response of the Transition Region and Corona  

Andrei Chelpanov   Submitted: 2019-04-25 20:47

We studied oscillations related to flare SOL2012-09-21T02:19 in the transition region and chromosphere based on Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) and Solar Dynamics Observatory (SDO) data, as well as data from a ground-based observatory. We found that 2-minute oscillations triggered by the flare first appeared in the RHESSI channels then subsequently showed up in the SDO 171 Å and 304 Å channels and after that in the chromospheric He I 10830 Å line. The delay of the chromospheric signal compared to the RHESSI signal is 7 minutes, which indicates that the wave perturbation propagated from the corona to the chromosphere. We used the sharp increase in 3- and 5-minute oscillations during the flare in the lower atmosphere to trace the propagation of the oscillation trains to the transition region and corona. The results show that the 171 Å channel signals lagged behind the photospheric and chromospheric signals by 200 s on average. We suggest that we observed slow magnetoacoustic waves both in the case of 2-minute oscillations propagating downwards from the corona and in the case of 3- and 5-minute oscillations leaking to the corona from beneath.

Authors: Nikolai Kobanov and Andrei Chelpanov
Projects: None

Publication Status: Accepted to Solar Physics
Last Modified: 2019-05-01 12:05
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Oscillations accompanying a He I 10830 Å negative flare in a solar facula  

Andrei Chelpanov   Submitted: 2018-11-07 20:07

On 21 September 21 2012, we carried out spectral observations of a solar facula in the Si I 10827 Å , He I 10830 Å, and Hα spectral lines. Later, in the process of analyzing the data, we found a small-scale flare in the middle of the time series. Due to an anomalous increase in the absorption of the He I 10830 Å line, we identified this flare as a negative flare. The aim of this article is to study the influence of the negative flare on the oscillation characteristics in the facular photosphere and chromosphere. We measured line-of-sight (LOS) velocity and intensity of all the three lines as well as the half width of the chromospheric lines. We also used Helioseismic and Magnetic Imager (HMI) magnetic field data. The flare caused a modulation of all the studied parameters. In the location of the negative flare, the amplitude of the oscillations increased four times on average. In the adjacent magnetic field local maxima, the chromospheric LOS velocity oscillations appreciably decreased during the flare. The facular region oscillated as a whole with a 5-minute period before the flare, and this synchronicity was disrupted after the flare. The flare changed the spectral composition of the LOS magnetic field oscillations, causing an increase in the low-frequency oscillation power.

Authors: Andrei Chelpanov, Nikolai Kobanov
Projects: None

Publication Status: Accepted to Solar Physics
Last Modified: 2018-11-08 11:40
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Negative flare in the He I 10830 Å line in facula  

Andrei Chelpanov   Submitted: 2018-04-23 02:19

A small-scale flare SOL2012-09-21T02:19 (B2) occurred in a spotless active region that we observed at a ground-based telescope equipped with a spectrograph. During the flare, we registered an increase in absorption in the He I 10830 Å 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 10830 Å lines reach their extreme intensities 5 and 6 minutes after the 171 Å line. The brightening first occurred in the 171 Å and 193 Å Solar Dynamics Observatory (SDO) channels followed by the 94 Å, 304 Å, and 1600 Å 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 304 Å and 1600 Å 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 10830 Å line.

Authors: Nikolai Kobanov, Andrei Chelpanov, Vasiliy Pulyaev
Projects: None

Publication Status: Accepted in Journal of Atmospheric and Solar-Terrestrial Physics
Last Modified: 2018-04-25 12:15
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Influence of the Magnetic Field on Oscillation Spectra in Solar Faculae  

Andrei Chelpanov   Submitted: 2016-07-19 21:54

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.

Authors: Andrei A. Chelpanov, Nikolai I. Kobanov, Dmitry Y. Kolobov
Projects: None

Publication Status: Accepted in Solar Physics
Last Modified: 2016-07-20 12:23
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Abstracts by Author
Oscillation Dynamics in Short-Lived Facula Regions during Their Lifetime
Propagating Oscillations in the Lower Atmosphere Under Coronal Holes
Using Flare-Induced Modulation of Three- and Five-Minute Oscillations for Studying Wave Propagation in the Solar Atmosphere
Multilevel Observations of the Oscillations in the First Active Region of the New Cycle
Oscillations Accompanying a He I 10830 ? Negative Fare in a Solar Facula II. Response of the Transition Region and Corona
Oscillations accompanying a He I 10830 ? negative flare in a solar facula
Negative flare in the He I 10830 ? line in facula
Influence of the Magnetic Field on Oscillation Spectra in Solar Faculae

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