Xu Yang

Context . Quasi-periodic pulsations (QPPs) have been observed in a broad electromagnetic spectrum, encompassing radio, ultraviolet, white light, X-rays, and γ -rays. Yet, flare-associated QPPs remain rarely detected in mid-infrared emission. Aims . We explored dual-period QPPs in the mid-infrared waveband, hard X-rays (HXRs), and microwave emission during an X1.5 flare on 2024 December 30 (SOL2024-12-30T04:01). Methods . The X1.5 flare was captured simultaneously by the Accurate Infrared Magnetic field Measurements of the Sun (AIMS), Fermi, the Hard X-ray Imager (HXI), the Nobeyama Radio Polarimeters (NoRP), the White-light Solar Telescope (WST), and the Atmospheric Imaging Assembly (AIA). Dual quasi-periods were identified using fast Fourier transform and wavelet analysis methods. Hard X-ray images were reconstructed with the HXI_CLEAN algorithm. Differential emission measure (DEM) describes the temperature structure of optically thin plasmas in the solar corona, and its solution was applied in six AIA Extreme ultraviolet wavelengths. Results . Flare QPPs with dual quasi-periods at ∼8.5 s and ∼4.6 s were simultaneously detected in the AIMS 8–10 μm, Fermi 26– 50 keV, and HXI 20–50 keV wavebands during the impulsive phase. Imaging observations show that the flare emission sources in the mid-infrared, HXR, and white-light wavebands are spatially coincident. Mid-infrared emissions are primarily localized at the loop top and double footpoints, which are connected by a hot plasma loop. These observational features support intermittent and rapid energy release via oscillatory magnetic reconnection during the solar flare. Differential emission measure analysis confirms fast sausage waves in flaring loops, while the WST observation indicates a white-light flare. Conclusions . We localized the flare QPPs with double periods in mid-infrared, HXR, and microwave emissions during a white-light flare. The flare-associated QPPs may be attributed to a quasi-periodic regime of magnetic reconnection, with the double periods likely modulated by quasi-harmonics of sausage waves.

Using high-resolution photospheric and chromospheric observations taken by the Goode Solar Telescope, we studied two groups of bidirectional plasma jets occurring in active region NOAA 13110. Supplementary observations are also provided by Solar Dynamics Observatory’s Atmospheric Imaging Assembly and Helioseismic and Magnetic Imager. From the photospheric observations and magnetograms, the two successive bidirectional plasma jets were initially located in the vicinity of the polarity inversion lines and at the intersection of the umbra and penumbra of the sunspot, followed by magnetic flux emergence and cancellation. As the cool filamentary threads are continuously emerging from the lower chromosphere and interact with overlying horizontal magnetic loops, it leads to the bidirectional jets, erupting outflow plasmoids, and heating coronal magnetic loops. We find that the bidirectional jets extended from the central excitation location in opposite directions, at the speed of about dozens of km s ⁻¹ . For the first jet, the initial brightening first appears in 304 Å, about 30 s earlier than the H α observations, indicating that magnetic reconnection takes place in the transition region. Meanwhile, the initial reconnection for the second jet occurs simultaneously in H α and 304 Å, showing the recurrent eruptions. These observations confirm that the bidirectional plasma jets can be generated by magnetic reconnection between the rising filamentary threads or material and the overlying horizontal magnetic loops. Our results provide new insights into the generation of the bidirectional plasma jets and reconnection-based coronal heating.

In this paper, we report more than 30 quasiperiodic coronal jets observed by the 1 m New Vacuum Solar Telescope and the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory. Based on magnetograms and photospheric observations, the jets occur in a mixed-polarity region of active region 13468 on 2023 October 23, originating from intergranular lanes. The bright point at the jet base shows a southward motion along the polarity inversion lines. The small region with jets shows continuous magnetic flux emergence, convergence, and cancellation. According to AIA observations, dozens of recurrent coronal jets are observed with cool surges erupting almost cospatially and cotemporally. Coordinated observations of the H α line core and wings show an inverted Y-shaped structure, accompanied by upflows and downflows of plasma in the reconnection region. Simultaneously, we find that successive plasmoids rapidly erupt above the cusp of the jets (J1–J8), and two groups of quasiperiodic jets are identified with periods of 2–3 minutes. Furthermore, quasiperiodic brightenings in the chromospheric reconnection current sheet are regarded as evidence of continuous magnetic reconnection and are associated with quasiperiodic coronal jets (J4–J8). We propose that the quasiperiodic jets are driven by quasiperiodic magnetic reconnection, likely modulated by slow magnetoacoustic waves in the chromosphere.

Our study of H α line profiles of rapid blue- and redshifted excursions measured with Goode Solar Telescope revealed an asymmetrical three-peak structure present in the blue wing of the H α line, suggesting complex internal velocity fields that may include bidirectional flows and transverse and torsional motions. Blueshifted plasma predominates across the field of view (FOV), correlating with higher temperatures (>10 ⁴ K) and extending to greater heights. Conversely, redshifts are less spread over the FOV, are localized near network magnetic fields, and diminish rapidly with altitude. The frequency distribution associated with blueshifted events displays a bimodal structure with peaks centered at 7200 and 8800 K. The redshifted events display a much weaker and wide peak centered at about 9000 K. No significant difference in temperature distributions for blue- and redshifted events is observed in the range above 10,000 K. Variations of H α line profiles with height seem to indicate that the line-of-sight integration effects may be most significant within the 0–6 Mm layer above the photosphere, and it decreases with height.

We present a unique observation of the X6.4-class flare SOL2024-02-22T22:34 using the Mid-InfraRed Imager (MIRI) at the Goode Solar Telescope. Three ribbon-like flare sources and one unidentified source were detected in MIRI’s two mid-infrared (mid-IR) bands at 5.2 and 8.2 μm. The two stronger ribbons displayed maximum mid-IR enhancements of 21% and 18% above quiet-Sun levels and 10% in Helioseismic and Magnetic Imager (HMI) continuum intensity (I _c ). The weak ribbon and the unidentified source had maximum mid-IR enhancements of 7% but showed HMI/I _c dimmings, instead of excess emissions. Our result suggests that mid-IR emission forms in a higher layer during the flare and is more sensitive to flare heating than HMI/I _c emission. The MIRI observations have high temporal resolution (2.6 s cadence in these observations) and show apparent source motions. One flare ribbon extends along weak vertical magnetic-field channels in the sunspot umbra, light bridge, and penumbra, with an approximately 30 s delay between HMI/I _c and 8.2 μm emissions. Meanwhile, the unidentified source moved at an apparent speed of 130 km s⁻¹ from a mixed-polarity area to one flare ribbon with a strong HMI/I _c enhancement. We studied available hard X-ray/microwave imaging spectroscopy and used nonlinear force-free field extrapolation modeling to identify flare structures. The observational evidence strongly favors the chromospheric origin of the unidentified mid-IR source. Comparison with the X1.0 flare SOL2022-10-02T20:25 indicates that the total amount of high-energy electron (>60 keV) flux density is a key factor in determining the total brightening area and the maximum intensity enhancement in HMI/I _c emissions.

In this paper, we present a detailed analysis of the spatiotemporal evolution of photospheric vertical electric currents (VECs) during an X1.1 flare (SOL2013-11-10T05:08). The VEC on the solar surface is calculated using the 135 s high-temporal-resolution vector magnetograms obtained from the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory. In the region, a highly sheared magnetic channel that is also a polarity inversion line (PIL) divides the region into two parts. The spatial configuration of VEC ribbons is always conjugate footprints, and it takes the form of a sigmoid along two sides of the PIL at the beginning of the flare. The temporal evolution of the VECs shows a rapid enhancement associated with the impulsive phase of the flare, and mean horizontal fields in this region show similar temporal behavior. The most prominent enhancement of VECs not only shows up along the two sides of the enhancement B _h but also spreads outward along the PILs. The VECs in positive and negative fields have an initial separation motion and are followed by an apparent approaching motion. In contrast, the flaring loops and white-light flare ribbons have an initial contraction and later expansion motion. Our results show that the rapid change of magnetic fields related to flares has a predominant role in affecting the spatiotemporal evolution of VECs.

We analyze high-resolution observations of an X-1.0 white-light flare, triggered by a filament eruption, on 2022 October 2. The full process of filament formation and subsequent eruption was captured in the Hα passband by the Visible Imaging Spectrograph (VIS) on board the Goode Solar Telescope (GST) within its center field of view. White-light emissions appear in flare ribbons following the filament eruption and Hα ribbon brightening. GST Broadband Filter Imager data show that the continuum intensity, as compared to the nearby quiet-Sun area, has increased by up to 20% in the photospheric TiO band around 7057 Å. The Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory reported 10% contrast enhancement in the continuum near Fe i 6173 Å line. The separation motion of two white-light kernels is recorded by the high-cadence GST/TiO images and is well accompanied by the motion of the VIS Hα flare ribbon leading edge. One kernel, located in a 150 Gauss field within a granulation area, exhibited an average apparent motion speed of 55 km s⁻¹, which is the highest average speed ever reported. The other kernel drifted at 9 km s⁻¹ in an 800 Gauss magnetic field area. Hard X-ray (HXR) emissions reaching up to 300 keV have been observed for this flare. The simultaneous occurrence of high-cadence HXR, microwave, and white-light emissions strongly suggests that the energetic particles from the flare directly contribute to the heating. The inverted HXR energy flux density corresponding to 10% TiO brightening is 2.07 ± 0.23 × 10¹¹ erg cm⁻² s⁻¹ during the flare peak.

With the aid of high-resolution spatial and temporal observations from the Goode Solar Telescope, we present an investigation of the emergence, coalescence, and submergence of a moving magnetic feature (MMF) in the region surrounding a magnetic pore located at the periphery of a large sunspot. The results show that the MMF has a magnetic field strength greater than 500 G and is dominated by the horizontal magnetic component. We observe upflow at the inner part and downflow at the outer part, indicating a pattern of Evershed flow. The MMF emergence is accompanied by the expansion of a granule, which has several striations inside just like the twisted features found in the penumbra filament. Our analysis shows that although these striations have different properties of magnetic field and kinematics during the expansion of the granule, the overall magnetic and dynamic properties of the MMF remain stable. We find that the region where the MMF emerges and submerges becomes more penumbra-like, i.e., adjacent positive and negative values of elongated magnetic features that are parallel to each other, while the optical penumbra-like features are not apparent at the same time. Our work indicates that the dynamics of the MMF near the magnetic pore is important for the development of filamentary structure. The magnetic configuration produced by an MMF together with the elongation of a granule could thus be key to understand the formation of penumbra filaments.

We used 29 high-resolution line-of-sight magnetograms acquired with the Goode Solar Telescope (GST) in a quiet-Sun area to extrapolate a series of potential field configurations and study their time variations. The study showed that there are regions that consistently exhibit changes in loop connectivity, whereas other vast areas do not show such changes. Analysis of the topological features of the potential fields indicates that the photospheric footprint of the separatrix between open- and closed-loop systems closely matches the roots of rapid blue- and redshifted excursions, which are disk counterparts of type II spicules. There is a tendency for the footpoints of the observed H _α features to be cospatial with the footpoints of the loops that most frequently change their connectivity, while the area occupied by the open fields that did not show any significant and persistent connectivity changes is void of prominent jet and spicular activity. We also detected and tracked magnetic elements using the Southwest Automatic Magnetic Identification Suite and GST magnetograms, which allowed us to construct artificial magnetograms and calculate the corresponding potential field configurations. Analysis of the artificial data showed tendencies similar to those found for the observed data. The present study suggests that a significant amount of chromospheric activity observed in the far wings of the H _α spectral line may be generated by reconnecting closed-loop systems and canopy fields consisting of “open” field lines.

Plumes are bright structures in coronal holes extending from the solar surface into the corona and are considered as a possible source of the solar wind. Plumes are thought to be rooted in strong unipolar photospheric flux patches (network/plage region). The magnetic activities at the base of plumes may play a crucial role in producing outflows and propagating disturbances (PDs). However, the role of photospheric/chromospheric activities (e.g., jets/spicules) at the base of plumes and their connection to PDs is poorly understood. Using high-resolution observations of a plume taken on 2020 July 23 with the 1.6 m Goode Solar Telescope (GST), Interface Region Imaging Spectrograph (IRIS), and the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory, we analyzed chromospheric/transition region activities at the base of the plume and their connection to outflows/PDs in the plume. The GST Visible Imaging Spectrometer images reveal repetitive spicules with blueshifted emission (pseudo-Doppler maps) at the plume’s footpoint. In addition, the photospheric magnetograms provide evidence of mixed polarities at the base of the plume. The IRIS Mg ii k Dopplergrams show strong blueshifted emission (∼50 km s⁻¹) and a high brightness temperature (Mg ii k2 line) at the footpoint of the plume. The long-period PDs (P ≈ 20–25 minutes) along the plume (AIA 171 Å) match the periodicity of spicules in the chromospheric images, suggesting a close connection between the spicules and the PDs. We suggest that the interchange reconnection between the closed and open flux of the coronal bright point at the plume’s footpoint is the most likely candidate to produce upflows and associated PDs along the plume.