Ubiquitous high-frequency waves and disturbances in the active region corona observed with DKIST/Cryo-NIRSP

TL;DR

This paper uses the Cryo-NIRSP instrument on DKIST to observe the off-limb active-region corona in Fe XIII 1074 nm with sub-second cadence and high spatial resolution, enabling detailed study of high-frequency MHD waves. Through sit-and-stare and raster observations, the authors detect abundant high-frequency power extending up to ~100 mHz and identify an anti-correlation between line intensity and line width, signaling compressive MHD activity alongside Alfvénic signatures. A k–ω decomposition and PSD modeling reveal distinct propagation speeds: hundreds of km s⁻¹ within AR structures and up to ~1400 km s⁻¹ in open-field regions, with localized, high-frequency power indicating both slow and kink-mode activity. Coherence analysis shows strong coupling between line intensity and line width (antiphase), while Doppler fluctuations show more limited coherence, offering new constraints on wave dissipation and heating processes in the corona. Overall, the work showcases DKIST's power to map high-frequency coronal waves and informs wave-based heating scenarios, including potential PDI-related mechanisms.

Abstract

The plasma of the solar corona harbors a multitude of coronal wave modes, some of which could be dissipated to provide the required energy and momentum to heat the corona and accelerate the solar wind. We present observations of the corona acquired with the newly commissioned infrared slit spectropolarimeter Cryo-NIRSP at the Daniel K. Inouye Solar Telescope (DKIST), Haleakala, Hawaii to study the high frequency wave behavior in closed, active-region structures. Cryo-NIRSP observes the corona off the limb in the Fe XIII 1074 and 1079 nm forbidden atomic lines. The large aperture of DKIST allows us to explore the active region corona with temporal resolution faster than a second with an achieved spatial resolution of 2-5 arcseconds. Enhanced wave power is observed in the power spectra up to 100 mHz. Furthermore, we report on a statistically significant anti-correlation between the Fe XIII 1074 nm peak line intensity and line width in our data, possibly pointing to the presence of compressive magnetohydrodynamic (MHD) wave modes. These observations show how the powerful spectropolarimetric capabilities of DKIST offer great promise for furthering our knowledge of coronal MHD waves.

Figures (8)

• Figure 1: Overview from the SDO/AIA 171 Å and 193 Å channels of the coronal regions observed with Cryo-NIRSP during the observational campaign on July 6-7 2023. The top row, panels (a)-(c) show the observed active region in SDO/AIA channels 171 Å and 193 Å observed on July 6 at 19:50 UT. The bottom row follows the same organization of the panels for the observations on July 7 2023. The field of view of the Cryo-NIRSP raster is shown as the white rectangle, and the sit-and-stare observations are marked as the red line. The magnified subpanels (b), (c), (e), and (f) have RHEF applied.
• Figure 2: Overview of the DKIST observations for July 6. The top row shows the AIA context image and the wide raster taken with Cryo-NIRSP with the Fe$\;$ 1074 nm line intensity, Doppler velocity and line width (FWHM in nm) in panels (b)-(d). The corresponding AIA 211 Å image for the DKIST raster is shown in panel (a). The sit-and-stare (S&S) observations of the same region in the second row in panels (e)-(g), where the line properties are shown in the same order. The temporally filtered sit-and-stare data are shown in the bottom row, panels (h)-(j).
• Figure 3: Cryo-NIRSP DKIST observations for July 7 2023, following the same outline as for Figure \ref{['fig:DKIST_overview_Jul6']}.
• Figure 4: Synthetic AIA Artificial slit images for the corresponding time and position as the CryoNIRSP slit showing the relative intensity fluctuations. The images with removed running average and normalized to the mean intensity are shown at each row, to show the relative intensity fluctuations. Panel (a): July 6, AIA 171 Å data; panel (b): July 6, 193 Å; panel (c): July 6, AIA 211 Å; panel (d): July 7, AIA 171 Å; (e) July 7, AIA 193 Å; (f) July 7, AIA 211 Å.
• Figure 5: Decomposition of the upward and downward propagating fluctuations of the Cryo-NIRSP sit-and-stare data obtained on Jul 6 2023, based on a $k-\omega$ analysis. Top row: intensity fluctuations $I$; middle row: velocity fluctuations V$_{Dop}$; bottom row: line width $\sigma$ fluctuations. The left column (panels (a), (d),(g)) shows the original data, the middle column the downward (panels (b), (e), and (h)), component, and the right column (panels (c), (f), and (i)) the upward (positive $k$) component.