Amplification of compressional magnetohydrodynamic waves in systems with forced entropy oscillations

Shergelashvili, B. M.; Maes, Christian; Poedts, Stefaan; Zaqarashvili, T. V.

doi:10.1103/physreve.76.046404

Cited by 15 publications

(15 citation statements)

References 34 publications

(46 reference statements)

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“…This indicates that acoustic waves may be responsible for these observed periods in the occurrence of jets (Nakariakov & Verwichte 2005). Quasi-oscillatory variations of intensity can also be the signature of MHD wave excitation processes, which are generated by very rapid dynamical changes in velocity, temperature, and other parameters manifesting the apparent non-equilibrium state of the medium in which the oscillations are sustained (Shergelashvili et al 2005(Shergelashvili et al , 2007Zaqarashvili & Roberts 2002). In 3D reconnection regions such as the QSL, a sharp velocity gradient is likely to be present.…”

Section: Discussionmentioning

confidence: 99%

Case study of multi-temperature coronal jets for emerging flux MHD models

Joshi

Chandra

Schmieder

et al. 2020

A&A

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Context. Hot coronal jets are a basic observed feature of the solar atmosphere whose physical origin is still actively debated. Aims. We study six recurrent jets that occurred in active region NOAA 12644 on April 4, 2017. They are observed in all the hot filters of AIA as well as cool surges in IRIS slit–jaw high spatial and temporal resolution images. Methods. The AIA filters allow us to study the temperature and the emission measure of the jets using the filter ratio method. We studied the pre-jet phases by analysing the intensity oscillations at the base of the jets with the wavelet technique. Results. A fine co-alignment of the AIA and IRIS data shows that the jets are initiated at the top of a canopy-like double-chambered structure with cool emission on one and hot emission on the other side. The hot jets are collimated in the hot temperature filters, have high velocities (around 250 km s−1) and are accompanied by cool surges and ejected kernels that both move at about 45 km s−1. In the pre-phase of the jets, we find quasi-periodic intensity oscillations at their base that are in phase with small ejections; they have a period of between 2 and 6 min, and are reminiscent of acoustic or magnetohydrodynamic waves. Conclusions. This series of jets and surges provides a good case study for testing the 2D and 3D magnetohydrodynamic emerging flux models. The double-chambered structure that is found in the observations corresponds to the regions with cold and hot loops that are in the models below the current sheet that contains the reconnection site. The cool surge with kernels is comparable with the cool ejection and plasmoids that naturally appears in the models.

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Section: Discussionmentioning

confidence: 99%

Case study of multi-temperature coronal jets for emerging flux MHD models

Joshi

Chandra

Schmieder

et al. 2020

A&A

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“…In turn, these wave fields may be engaged in complex conversion and dissipation processes in the solar corona in terms of processes driven by shear flows (see, e.g., Shergelashvili et al 2006), thermal variability related to wave couplings (Shergelashvili et al 2007), and a variety of parametric interactions of waves Zaqarashvili & Roberts 2002;.…”

Section: Introductionmentioning

confidence: 99%

Long-period oscillations of active region patterns: least-squares mapping on second-order curves

Dumbadze

Shergelashvili

Kukhianidze

et al. 2017

A&A

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Context. Active regions (ARs) are the main sources of variety in solar dynamic events. Automated detection and identification tools need to be developed for solar features for a deeper understanding of the solar cycle. Of particular interest here are the dynamical properties of the ARs, regardless of their internal structure and sunspot distribution. Aims. We studied the oscillatory dynamics of two ARs: NOAA 11327 and NOAA 11726 using two different methods of pattern recognition. Methods. We developed a novel method of automated AR border detection and compared it to an existing method for the proofof-concept. The first method uses least-squares fitting on the smallest ellipse enclosing the AR, while the second method applies regression on the convex hull. Results. After processing the data, we found that the axes and the inclination angle of the ellipse and the convex hull oscillate in time. These oscillations are interpreted as the second harmonic of the standing long-period kink oscillations (with the node at the apex) of the magnetic flux tube connecting the two main sunspots of the ARs. We also found that the inclination angles oscillate with characteristic periods of 4.9 h in AR 11726 and 4.6 h in AR 11327. In addition, we discovered that the lengths of the pattern axes in the ARs oscillate with similar characteristic periods and these oscillations might be ascribed to standing global flute modes. Conclusions. In both ARs we have estimated the distribution of the phase speed magnitude along the magnetic tubes (along the two main spots) by interpreting the obtained oscillation of the inclination angle as the standing second harmonic kink mode. After comparing the obtained results for fast and slow kink modes, we conclude that both of these modes are good candidates to explain the observed oscillations of the AR inclination angles, as in the high plasma β regime the phase speeds of these modes are comparable and on the order of the Alfvén speed. Based on the properties of the observed oscillations, we detected the appropriate depth of the sunspot patterns, which coincides with estimations made by helioseismic methods. The latter analysis can be used as a basis for developing a magneto-seismological tool for ARs.

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“…It is evident that, whatever nature these oscillations have, they must be energetically supported by convective motions beneath the solar surface, which represents the source of entropy production in the system through macroscopic stochastic super-granular motions of the plasma. The entropy variations can be due to microscopic transport processes as well (Shergelashvili et al, 2007). The presence of oscillations in the radial magnetic flux data may be connected with a periodic flux emergence/cancellation process.…”

Section: Discussionmentioning

confidence: 95%

Eigenspectra of solar active region long-period oscillations

Dumbadze

Shergelashvili

Poedts

et al. 2021

A&A

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Context. The low-frequency 0.5 hour −1 (long-period 2 hours) oscillations of active regions (ARs) are studied. The investigation is based on an analysis of time series built from SDO/HMI photospheric magnetograms and comprises case studies of several types of AR structures.Aims. The main goals are to investigate whether ARs can be engaged in long-period oscillations as unified oscillatory entities and, if so, to determine the spectral pattern of such oscillations.Methods. Time series of characteristic parameters of the ARs, such as, the total area, total unsigned radial magnetic flux, and tilt angle, have been measured and recorded by using the image Dumbadze et al.: Eigenspectra of active region long-period oscillations moment method. The power spectra have been built out of Gaussian apodized and zero padded datasets.Results. There are long period oscillations with periods ranging from 2 to 20 hours, similar to the characteristic lifetimes of super-granulation, determined from the datasets of the AR total area and radial magnetic flux, respectively. However, no periodicity in tilt angle data was found.Conclusions. Whatever nature these oscillations have, they must be energetically supported by convective motions beneath the solar surface. The possible interpretations can be related to different types of MHD oscillations of the multi-scale structure of the AR magnetic field, probably linked with the characteristic turnover timescales of the super-granulation cells. The presence of oscillations in the radial magnetic flux data may be connected to periodic flux emergence/cancellation processes.

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Amplification of compressional magnetohydrodynamic waves in systems with forced entropy oscillations

Cited by 15 publications

References 34 publications

Case study of multi-temperature coronal jets for emerging flux MHD models

Case study of multi-temperature coronal jets for emerging flux MHD models

Long-period oscillations of active region patterns: least-squares mapping on second-order curves

Eigenspectra of solar active region long-period oscillations

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