A 50-min coronal kink oscillation and its possible photospheric counterpart

TL;DR

The study addresses whether low-frequency photospheric motions can feed energy into the corona and drive coronal loop oscillations. Using coordinated SDO/AIA, SDO/HMI, and CHASE/HIS data, the authors apply advanced processing to extract a ~50-min decayless coronal kink oscillation in a 290 Mm loop and a concurrent ~50-min periodic variation in the LoS photospheric magnetic field near the loop footpoint, finding a strong cross-correlation (≈0.73) between the two signals. They identify a second, shorter ~4.8-min decayless kink mode consistent with a loop eigenmode, while the 50-min coronal oscillation appears to be externally driven, supporting a photosphere-to-corona energy-transport channel via low-frequency motions and potential violin/self-oscillatory coupling. The results imply that low-frequency components of the photospheric spectrum can influence coronal dynamics and contribute to the broader energy transport and dissipation processes in the solar atmosphere, though the exact transmission paths and dissipation mechanisms require further study.

Abstract

A coronal loop of 290~Mm length, observed at 171~Å with SDO/AIA on February 6th 2024 near AR 13571, is found to oscillate with two significantly different oscillation periods, $48.8 \pm 6.1$~min and $4.8\pm 0.3$~min. The oscillations occur in the time intervals without detected flares or eruptions. Simultaneously, near the Northern footpoint of the oscillating loop, we detect a $49.6 \pm 5.0$-min periodic variation of the average projected photospheric magnetic field observed with SDO/HMI. The shorter-period decayless oscillation is attributed to the eigen-mode, standing kink oscillation of the loop, while the longer-period oscillation may be the oscillatory motion caused by the periodic footpoint driver. The photospheric long-period process can also drive the short-period, eigen oscillation of the loop via the self-oscillatory, \lq\lq violin\rq\rq\, mechanism, in which a transverse oscillation is excited by an external quasi-steady flow. This finding indicates that the most powerful, lower-frequency spectral components of photospheric motions, which are well below the Alfvénic/kink cutoff, can reach the corona.

Figures (6)

• Figure 1: The region of study that displays the oscillating loops by AIA 171 Å image (a) and corresponding HMI LoS magnetogram (b). The box in panel a outlines the region of interest (ROI). The dotted curves sketch the loop of interest, and the red/blue circles denote their positive/negative footpoints. Panels (c--d) show the magnetic connectivity of the western footpoint of the analyzed loop. Blue/light blue/red contours indicate the magnetic field of -250/-100/250 G. An animation of panels (c) and (d) showing the temporal evolution of the Western footpoint of the studied coronal loop is available. The animation begins at 12:00 UT and ends at 16:59 UT. The real-time duration of the animation is 12 seconds.
• Figure 2: Kink oscillations in the analyzed loop bundle. (a) AIA 171 Å image showing the loop ensemble marked by the dotted curve. White slits across the loop are used to make time--distance maps that reveal the oscillatory signals. The white box locates the possible negative footpoint of the oscillating loop. (b-d) Representative time--distance maps exhibiting the decayless kink oscillations. The data is magnified by a factor (magk) of 8. The blue curves are oscillation signals extracted by the Gaussian fitting of the transverse intensity profiles.
• Figure 3: Periodicity analysis of the oscillations in the loop of interest. From top to bottom, each row is for oscillations in Slit 17, 26, 33 (blue curves in Figure \ref{['fig:50min_td']}b--d) and selected time interval [13:55 UT, 14:58 UT] in S33. First column: Original signals (black) with their trend (blue) in the upper sub-panel and detrended signals (red) in the bottom sub-panel. The relative variation of the signals is linearly magnified by a factor of 8. From the second to the fourth column are the Fourier power spectrum with a 95% confidence level (red line), EMD energy spectrum with a 95% confidence interval (red lines), and Wavelet spectrum with a 95% confidence level (black contour), respectively. In panel (i), the vertical lines indicate the time interval selected for further detection of shorter periodicity (5 minutes) shown in panels (m--p). In panels (b--n), the blue lines are the best-fitting power-law functions. In panels (c--o), the vertical lines indicate the threshold of reliable period estimation, the blue lines are the mean energy, and grey horizontal lines indicate error bars. In panels (d--p), the color bars indicate the normalized spectral power, the blue curves in the right subpanels are the global normalized wavelet power as a function of period, and the red dotted curves indicate the 95% confidence levels. Here, '' Mag.'', '' E'', '' a.u.'' stands for power magnitude, EMD modal energy and arbitrary units, respectively.
• Figure 4: Temporal variation of mean B$_{\rm LoS}$ in ROI$_1$. (a) The footpoint region (ROI$_1$) of the loop of interest is seen in the HMI LoS magnetogram. (b) Time series of average LoS magnetic field in ROI$_1$. The red dashed lines indicate the time duration of the observed 50-min kink oscillations. The blue lines indicate the selected time interval where the 50-min periodicity is detected by EMD analysis. The blue curve is the trend of the selected signals. (c) The detrended time series (black) is overlaid with the detected EMD mode 6 (red). (d) Wavelet spectrum of the mean magnetic field in ROI$_1$ from 12:45 UT to 19:00 UT. The global normalized spectrum (blue) and the 95% confidence level (red) are shown on the right of the wavelet spectrum. (e) EMD energy spectrum of the selected signals. The vertical dotted line indicates the threshold of detectable periodicity. (f) Hilbert spectrum of the EMD mode 6 shows the instantaneous period's time evolution. The red curve represents the values with maximum power. The dotted line indicates 50-min periodicity. (g) The trajectory of the centroid position of the loop footpoint. The color scheme from dark purple to yellow indicates the elapsed time since 12:00 UT. (h) Instantaneous period extracted from mode 6 as a function of the mean magnetic field. The color scheme is the same as in panel (j). '' Inst.'' means instantaneous and '' a.u.'' stands for arbitrary units.
• Figure 5: The spatial location of 50-min oscillation of the mean magnetic field in the study region. (a) HMI LoS magnetogram overlaid with 2 boxes outlining the areas exhibiting 50-min periodicity. The yellow spline depicts the oscillating loop. The filled area (labelled ROI$_{1}$) covers the footpoint area of the loop. (b) The detrended mean B$_{\rm LoS}$ in area ROI$_2$ (black). The red curve is the sixth EMD mode with a periodicity of $50.6\pm5.8$ min. (c) The detected 50-min oscillations of average magnetic field strength in areas ROI$_{1}$--ROI$_{2}$.