We present observations of a quasi-periodic fast-propagating (QFP) magnetosonic wave on 23 April 2012, with high-resolution observations taken by the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory. Three minutes after the start of a C2.0 flare, wave trains were first observed along an open divergent loop system in 171 Å observations at a distance of 150 Mm from the footpoint of the guiding loop system and with a speed of 689 km s−1, then they appeared in 193 Å observations after their interaction with a perpendicular, underlaying loop system on the path; in the meantime; their speed decelerated to 343 km s−1 within a short time. The sudden deceleration of the wave trains and their appearance in 193 Å observations are interpreted through a geometric effect and the density increase of the guiding loop system, respectively. We find that the wave trains have a common period of 80 seconds with the flare. In addition, a few low frequencies are also identified in the QFP wave. We propose that the generation of the period of 80 seconds was caused by the periodic releasing of energy bursts through some nonlinear processes in magnetic reconnection, while the low frequencies were possibly the leakage of pressure-driven oscillations from the photosphere or chromosphere, which could be an important source for driving coronal QFP waves. Our results also indicate that the properties of the guiding magnetic structure, such as the distributions of magnetic field and density as well as geometry, are crucial for modulating the propagation behaviors of QFP waves.

Observations of a Quasi-periodic, Fast-Propagating MagnetosonicWave in Multiple Wavelengths and Its Interaction with Other Magnetic Structures

We present a case study for the global extreme-ultraviolet (EUV) wave and its chromospheric counterpart the Moreton-Ramsey Wave associated with the second X-class flare in Solar Cycle 25 and a halo coronal mass ejection (CME). The EUV wave was observed in the Hα and EUV passbands with different characteristic temperatures. In the 171 Å and 193/195 Å images, the wave propagates circularly with an initial velocity of 600–720 km s−1 and a deceleration of 110–320 m s−2. The local coronal plasma is heated from log(T/K) ≈ 5.9 to log(T/K) ≈ 6.2 during the passage of the wave front. The Hα and 304 Å images also reveal signatures of wave propagation with a velocity of 310–540 km s−1. With multiwavelength and dual-perspective observations, we found that the wave front likely propagates forwardly inclined to the solar surface with a tilt angle of ∼53°.2. Our results suggest that this EUV wave is a fast-mode magnetohydrodynamic wave or shock driven by the expansion of the associated CME, whose wave front is likely a dome-shaped structure that could impact the upper chromosphere, transition region, and corona.

https://iopscience.iop.org/article/10.3847/1538-4357/ac590d/pdf

Three-dimensional Propagation of the Global Extreme-ultraviolet Wave Associated with a Solar Eruption on 2021 October 28

We present high-resolution observations of a quiescent solar prominence which was consisted of a vertical and a horizontal foot encircled by an overlying spine, and counter-streaming mass flows were ubiquitous in the prominence. While the horizontal foot and the spine were connecting to the solar surface, the vertical foot was suspended above the solar surface and supported by a semicircular bubble structure. The bubble first collapsed and then reformed at a similar height, finally, it started to oscillate for a long time. We find that the collapsing and oscillation of the bubble boundary were tightly associated with a flare-like feature located at the bottom of the bubble. Based on the observational results, we propose that the prominence should be composed of an overlying horizontal spine encircling a low-lying horizontal and a vertical foot, in which the horizontal foot was consisted of shorter field lines running partially along the spine and with the both ends connecting to the solar surface, while the vertical foot was consisted of piling-up dips due to the sagging of the spine fields and supported by a bipolar magnetic system formed by parasitic polarities (i.e., the bubble). The upflows in the vertical foot were possibly caused by the magnetic reconnection at the separator between the bubble and the overlying dips, which intruded into the persistent downflow field and formed the picture of counter-streaming mass flows. In addition, the counter-streaming flows in the horizontal foot were possibly caused by the imbalanced pressure at the both ends.

Fine Magnetic Structure and Origin of Counter-Streaming Mass Flows in a Quiescent Solar Prominence

By direct measurements of the gas temperature, the Atacama Large Millimeter/sub-millimeter Array (ALMA) has yielded a new diagnostic tool to study the solar chromosphere. Here we present an overview of the brightness-temperature fluctuations from several high-quality and high-temporal-resolution (i.e., 1 and 2 sec cadence) time series of images obtained during the first two years of solar observations with ALMA, in Band 3 and Band 6, centred at around 3 mm (100 GHz) and 1.25 mm (239 GHz), respectively. The various datasets represent solar regions with different levels of magnetic flux. We perform Fast Fourier and Lomb-Scargle transforms to measure both the spatial structuring of dominant frequencies and the average global frequency distributions of the oscillations (i.e., averaged over the entire field of view). We find that the observed frequencies significantly vary from one dataset to another, which is discussed in terms of the solar regions captured by the observations (i.e., linked to their underlying magnetic topology). While the presence of enhanced power within the frequency range 3-5 mHz is found for the most magnetically quiescent datasets, lower frequencies dominate when there is significant influence from strong underlying magnetic field concentrations (present inside and/or in the immediate vicinity of the observed field of view). We discuss here a number of reasons which could possibly contribute to the power suppression at around 5.5 mHz in the ALMA observations. However, it remains unclear how other chromospheric diagnostics (with an exception of Halpha line-core intensity) are unaffected by similar effects, i.e., they show very pronounced 3-min oscillations dominating the dynamics of the chromosphere, whereas only a very small fraction of all the pixels in the ten ALMA data sets analysed here show peak power near 5.5 mHz.

An overall view of temperature oscillations in the solar chromosphere with ALMA

Abstract Type II radio bursts are often associated with coronal shocks that are typically driven by coronal mass ejections (CMEs) from the Sun. Here we conduct a case study of a type II radio burst that is associated with a C4.5-class flare and a blowout jet, but without the presence of a CME. The blowout jet is observed near the solar disk center in the extreme-ultraviolet (EUV) passbands with different characteristic temperatures. Its evolution involves an initial phase and an ejection phase with a velocity of 560 ± 87 km s −1 . Ahead of the jet front, an EUV wave propagates at a projected velocity of ∼403 ± 84 km s −1 in the initial stage. The velocity of the type II radio burst is estimated to be ∼641 km s −1 , which corresponds to the shock velocity against the coronal density gradient. The EUV wave and the type II radio burst are closely related to the ejection of the blowout jet, suggesting that both are likely the manifestation of a coronal shock driven by the ejection of the blowout jet. The type II radio burst likely starts lower than those associated with CMEs. The combination of the velocities of the radio burst and the EUV wave yields a modified shock velocity at ∼757 km s −1 . The Alfvén Mach number is in the range of 1.09–1.18, implying that the shock velocity is 10%–20% larger than the local Alfvén velocity. 

A Type II Radio Burst Driven by a Blowout Jet on the Sun

Using imaging and radio multi-wavelength observations, we studied the origin of two homologous accelerated electron beams and a quasiperiodic fast-propagating (QFP) wave train associated with a solar jet on 2012 July 14. The jet occurred in a small-scale fan-spine magnetic system embedded in a large-scale pseudostreamer associated with a GOES C1.4 flare, a jet-like coronal mass ejection (CME), a type II radio burst, and a type III radio burst. During the initial stage, a QFP wave train and a fast-moving on-disk radio source were detected in succession ahead of the jet along the outer spine of the fan-spine system. When the jet reached a height of about 1.3 solar radii, it underwent a bifurcation into two branches. Based on our analysis results, all the observed phenomena in association with the jet can be explained by using a fan-spine magnetic system. We propose that both the type III radio burst and the on-disk fast-moving radio source were caused by the same physical process, i.e., energetic electrons accelerated by magnetic reconnection at the null point, and these energetic electrons were propagating along the open field lines of the pseudostreamer and the closed outer spine of the fan-spine structure, respectively. Due to the bifurcation of the jet body, the lower branch along the closed outer spine of the fan-spine structure fell back to the solar surface, while the upper branch along the open field lines of the pseudostreamer caused the jet-like CME in the outer corona.

Homologous Accelerated Electron Beams, a Quasiperiodic Fast-propagating Wave, and a Coronal Mass Ejection Observed in One Fan-spine Jet

Large-scale extreme-ultraviolet (EUV) waves are frequently observed as an accompanying phenomenon of flares and coronal mass ejections (CMEs). Previous studies mainly focused on EUV waves with single wave fronts that are generally thought to be driven by the lateral expansion of CMEs. Using high spatiotemporal resolution multi-angle imaging observations taken by the Solar Dynamics Observatory and the Solar Terrestrial Relations Observatory, we present the observation of a broad quasiperiodic fast-propagating (QFP) wave train composed of multiple wave fronts along the solar surface during the rising phase of a GOES M3.5 flare on 2011 February 24. The wave train transmitted through a lunate coronal hole (CH) with a speed of ∼840 ± 67 km s−1, and the wave fronts showed an intriguing refraction effect when they passed through the boundaries of the CH. Due to the lunate shape of the CH, the transmitted wave fronts from the north and south arms of the CH started to approach each other and finally collided, leading to a significant intensity enhancement at the collision site. This enhancement might hint at the occurrence of interference between the two transmitted wave trains. The estimated magnetosonic Mach number of the wave train is about 1.13, which indicates that the observed wave train was a weak shock. Period analysis reveals that the period of the wave train was ∼90 s, in good agreement with that of the accompanying flare. Based on our analysis results, we conclude that the broad QFP wave train was a large-amplitude fast-mode magnetosonic wave or a weak shock driven by some nonlinear energy release processes in the accompanying flare.

Observations of a Flare-ignited Broad Quasiperiodic Fast-propagating Wave Train

Electromagnetic wave lensing, a common physical phenomenon recognized in visible light for centuries, finds extensive applications in manipulating light in optical systems such as telescopes and cameras. Magnetohydrodynamic wave is a common perturbation phenomenon in the corona. By using high spatio-temporal resolution observations from the Solar Dynamics Observatory, here, we report the observation of a magnetohydrodynamic wave lensing in the highly ionized and magnetized coronal plasma, where quasi-periodic wavefronts emanated from a flare converged at a specific point after traversing a coronal hole. The entire process resembles an electromagnetic wave lensing from the source to the focus. Meanwhile, the magnetohydrodynamic wave lensing is well reproduced through a magnetohydrodynamic numerical simulation with full spatio-temporal resolution. We further investigate potential applications for coronal seismology, as the lensing process encodes information on the Alfv\'en speed, in conjunction with favorable geometric and density variations. 

pdf/resolved-magnetohydrodynamic-wave-lensing-in-the-solar-xt2n0fhcem.pdf

Resolved magnetohydrodynamic wave lensing in the solar corona

Quasi-periodic fast-propagating (QFP) magnetosonic wave trains are commonly observed in the low corona at extreme ultraviolet wavelength bands. Here, we report the ﬁrst white-light imaging observation of a QFP wave train propagating outwardly in the outer corona ranging from 2 to 4 R (cid:12) . The wave train was recorded by the Large Angle Spectroscopic Coronagraph on board the Solar and Heliospheric Observatory (SOHO) , and was associated with a GOES M1.5 ﬂare in NOAA active region AR12172 at the southwest limb of the solar disk. Measurements show that the speed and period of the wave train were about 218 km s − 1 and 26 minutes, respectively. The extreme ultraviolet imaging observations taken by the Atmospheric Imaging Assembly on board the Solar Dynamic Observatory reveal that in the low corona the QFP wave train was associated with the failed eruption of a breakout magnetic system consisting of three low-lying closed loop systems enclosed by a high-lying large-scale one. Data analysis results show that the failed eruption of the breakout magnetic system was mainly because of the magnetic reconnection that occurred between the two lateral low-lying closed-loop systems. This reconnection enhances the conﬁnement capacity of the magnetic breakout system because the upward-moving reconnected loops continuously feed new magnetic ﬂuxes to the high-lying large-scale loop system. For the generation of the QFP wave train, we propose that it could be excited by the intermittent energy pulses released by the quasi-periodic generation, rapid stretching, and of the upward-moving, strongly bent reconnected loops.

/pdf/white-light-qfp-wave-train-and-the-related-failed-breakout-det17wel.pdf

White-light QFP wave train and the related failed breakout eruption


 The fine magnetic structure is vitally important to understanding the formation, stabilization and eruption of solar filaments, but so far, it is still an open question yet to be resolved. Using stereoscopic observations taken by the Solar Dynamics Observatory and Solar TErrestrial RElations Obsevatory, we studied the generation mechanism of a two-sided-loop jet (TJ) and the ejection process of the jet plasma into the overlying filament-cavity system. We find that the generation of the two-sided-loop jet was due to the magnetic reconnection between an emerging flux loop and the overlying filament. The jet’s two arms ejected along the filament axis during the initial stage. Then, the north arm bifurcated into two parts at about 50 Mm from the reconnection site. After the bifurcation, the two bifurcated parts were along the filament axis and the cavity which hosted the filament, respectively. By tracing the ejecting plasma flows of the TJ inside the filament, we not only measured that the magnetic twist stored in the filament was at least 5π but also found that the fine magnetic structure of the filament-cavity flux rope system is in well agreement with the theoretical results of Magnetic flux rope models.

/pdf/stereoscopic-diagnosing-of-a-filament-cavity-flux-rope-1zcriuep.pdf

Stereoscopic diagnosing of a filament-cavity flux rope system by tracing the path of a two-sided-loop jet

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