Tongjiang Wang

Quasiperiodic fast-propagating (QFP) wave trains are a distinctive form of magnetohydrodynamic (MHD) disturbance frequently observed in the solar corona. Yet their excitation mechanism and propagation characteristics are not well understood. In this study, we investigate a well-observed QFP wave event associated with an M6.5-class flare and coronal mass ejection that occurred in NOAA Active Region 12371 on 2015 June 22, by combining multiwavelength observations from the Solar Dynamics Observatory/Atmospheric Imaging Assembly (AIA) and Helioseismic and Magnetic Imager with data-inspired 3D MHD simulations. The QFP wave trains propagating at high speeds of 1140−1760 km s ⁻¹ are detected in the AIA 171 Å channel, following global extreme-ultraviolet (EUV) wave fronts visible at 171 and 193 Å traveling at considerably lower speeds of 300−510 km s ⁻¹ . Wavelet analysis reveals consistent 2–4 minutes periodicities in both the QFPs and flare quasiperiodic pulsations observed in UV/EUV and hard-X-ray emissions, suggesting a common origin likely linked to intermittent magnetic reconnection. Guided by these observations, we construct realistic 3D MHD models incorporating dense fan-loop structures and periodic drivers applied at different locations. The simulations reproduce the key characteristics of the observed wave trains. Comparison between cases with and without a coronal background (nonloop plasma emission) indicates that coronal density structuring significantly modifies the detected wave amplitudes and propagation patterns. Our results highlight the importance of realistic coronal magnetic configurations in modeling QFP dynamics and suggest that their observed association with fan loops in AIA 171 Å may represent a temperature-dependent visibility effect rather than a genuine confinement of the waves.

This paper presents a follow-up to previous work on correcting point-spread-function (PSF)-induced Doppler artifacts in observations by the SPICE spectrograph on Solar Orbiter. In a previous paper, we demonstrated the correction of these artifacts in the y − λ plane with PSF regularization, treating the forward problem with a method based on large sparse matrix inversion. It has since been found that similar apparent artifacts are also present in the x − λ direction, i.e., across adjacent slit positions. Correcting this is difficult (although not impossible) with the previous matrix inversion method due to the time variation between slit positions. We have therefore devised a new method that addresses both x − λ and y − λ artifacts simultaneously by applying wavelength-dependent shifts at each x − y plane of the spectral cube. This paper demonstrates the SPICE data issue, describes the new method, and shows a comparison with the previous one. We explore the time variation of the correction parameters for the SPICE data and show a clear orbit dependence. The results of the method are significantly higher-quality Doppler signals, which we estimate at less than ∼5 km/s uncertainty for brighter lines in the absence of other systematics. Furthermore, we show the new SPICE polar observation results as a demonstration. The correction codes are written in Python, publicly available on GitHub, and can be directly applied to SPICE level 2 datasets.

Quasiperiodic fast propagating (QFP) magnetosonic waves have been discovered in the solar corona in the extreme ultraviolet (EUV) since the launch of the Solar Dynamics Observatory (SDO) spacecraft more than a decade ago. The QFP waves are associated with flares and coronal mass ejections, providing information on flare pulsations as well as on the magnetic field by MHD wave seismology. Previous models of QFP waves primarily used idealized magnetic active region (AR) structures. However, more realistic AR numerical models are needed to improve the application of coronal seismology to observations of waves in coronal structures. Here, we extend the previous models by including a realistic magnetic configuration based on an observed coronal AR in a case study using AR 11166, observed on 2011 March 10 by the SDO Atmospheric Imaging Assembly, using potential field extrapolation of the photospheric magnetic field with realistic gravitationally stratified density structure and typical coronal temperature in our resistive 3D MHD model. We aim at reproducing the observed QFP properties, such as directionality, propagation, reflection, nonlinearity, and damping of these waves. We model various forms of excitation of QFPs through time-dependent boundary conditions and localized pulses at the base of the corona. We produce synthetic emission measure maps from the 3D MHD modeling results to facilitate comparison to EUV observations. We find that the present, more realistic model provides better qualitative agreement with observations compared to previous idealized models, improving the study of QFP wave excitation, propagation, and damping in coronal ARs, with potential applications to coronal seismology.

Multiwavelength observations of the propagating disturbances (PDs), discovered by Atmospheric Imaging Assembly (AIA) on board Solar Dynamics Observatory (SDO), are analyzed to determine their driving mechanism and physical nature. Two magnetic strands in the localized corona are observed to approach and merge with each other, followed by the generation of brightening, which further propagates in a cusp-shaped magnetic channel. Differential emission measure analysis shows an occurrence of heating in this region of interest. We extrapolate potential magnetic field lines at coronal heights from the observed Helioseismic and Magnetic Imager vector magnetogram via Green’s function method using MPI-AMRVAC. We analyze the field to locate magnetic nulls and quasi-separatrix layers (QSLs), which are preferential locations for magnetic reconnection. Dominant QSLs including a magnetic null are found to exist and match the geometry followed by PDs; therefore, this provides conclusive evidence of magnetic reconnection. In addition, spectroscopic analysis of Interface Region Imaging Spectrograph Si iv λ1393.77 line profiles show a rise of line width in the same time range depicting the presence of mass motion in the observed cusp-shaped region. PDs are observed to exhibit periodicities of around 4 minutes. The speeds of PDs measured by the surfing transform technique are close to each other in four different SDO/AIA bandpasses, i.e., 304, 171, 193, and 131 Å, excluding the interpretation of PDs in terms of slow magnetoacoustic waves. We describe comprehensively the observed PDs as quasiperiodic plasma flows generated as a result of periodic reconnection in the vicinity of a coronal magnetic null.

Whitepaper #333 in the Decadal Survey for Solar and Space Physics (Heliophysics) 2024-2033. Main topics: space weather applications; basic research. Additional topics: space weather research/operations/research loop; space weather research/applications/operations pipeline; […]

We present a detailed analysis of a reflecting intensity perturbation in a large coronal loop that appeared as a sloshing oscillation and lasted for at least one and a half periods. The perturbation is initiated by a microflare at one footpoint of the loop, propagates along the loop, and is eventually reflected at the remote footpoint where significant brightenings are observed in all of the Atmospheric Imaging Assembly extreme-ultraviolet channels. This unique observation provides us with the opportunity to better understand not only the thermal properties and damping mechanisms of the sloshing oscillation but also the energy transfer at the remote footpoint. Based on differential emission measures analysis and the technique of coronal seismology, we find that (1) the calculated local sound speed is consistent with the observed propagation speed of the perturbation during the oscillation, which is suggestive of a slow magnetoacoustic wave; (2) thermal conduction is the major damping mechanism of the wave but an additional damping mechanism such as anomalous enhancement of compressive viscosity or wave leakage is also required to account for the rapid decay of the observed waves; (3) the wave produced a nanoflare at the remote footpoint, with a peak thermal energy of ∼10²⁴–10²⁵ erg. This work provides a consistent picture of the magnetoacoustic wave propagation and reflection in a coronal loop, and reports the first solid evidence of a wave-induced nanoflare. The results reveal new clues for further simulation studies and may help with solving the coronal heating problem.

We introduce a new quantitative approach for assessing the quality of coronal magnetic field models. The method compares the location of the magnetic neutral line at a specified height in the magnetic field model with the locations of localized density peaks in the coronal electron density, as measured using coronal rotational tomography. This approach is flexible to the presence of pseudostreamers in the coronal magnetic field, as well as folds in the streamer belt. We present an example application during mid-2010 when the white-light streamer-belt structure is complex and the emergence of a large active region on the far side of the Sun presents a challenge for modeling the coronal magnetic structure.