arXiv subjects

Zhenghua Huang

Publications and source records attributed to Zhenghua Huang.

At least 19 recordsLinked to original sources

arXiv2026

Magnetic loops in the solar transition region

Transition region (TR) loops are arcade-like features in the solar transition region, with temperatures roughly between $2\times10^4$ K and $6\times10^5$ K. They are a fundamental building block of TR, which are results of the coupling between the magnetic field and the TR plasma. Their dynamics is closely related to the transport of energy and mass through the TR. Studies on this class of loops since the launch of the Interface Region Imaging Spectrograph (IRIS) have revealed that they are distinct from coronal loops. Observations have revealed that they are associated with many small-scale dynamic phenomena in the TR, from which one can infer the physics behind the energy and mass transfer in a magnetically confined environment at TR temperature. This review summarises the observational results of TR loops, showing their morphology, dynamics, plasma parameters, their relationship with flux emergence, their heating properties, and their implication in the heating of the solar atmosphere. This class of magnetic loops is much less well understood than their coronal counterparts. This review also concludes with several critical questions that need to be answered in the coming era with more advanced observational techniques and more precise and realistic simulations.

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arXiv2026

Statistics of blob properties in two types of coronal streamers

Previous studies have shown that a streamer blob might originate in the lower corona and thus be affected by activity in that region. While the base of one streamer might differ from that of another, it can be cataloged into two distinct types: active region streamers (ARSs) that have active regions at their base, and quiet equatorial streamers (QESs) that do not have an active region underneath.The difference between the blob properties in ARSs and those in QESs remains unknown. By analyzing the whole-year observations from SOHO/LASCO/C2 in 2018, we carried out a statistical analysis of the properties of propagating blobs in ARSs and QESs. We found that the properties of streamer blobs are very different from one blob to another. The occurrence rate of blobs in ARSs is about twice as high as that in QESs. On average, the ARS blobs have significantly higher initial velocities and slightly higher accelerations, but slightly lower heights of first appearance than the QES blobs. There is a weak positive correlation between the initial velocities and heights of first appearance in the two groups of streamer blobs. The correlation between the accelerations and heights of first appearance in ARS blobs is negative, while that in QES blobs is positive. Our results provide statistical evidence that a higher degree of activity at the coronal base of a streamer can cause more dynamic blobs higher up, and that it affects the structures of the solar wind originating in the region.

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arXiv2026

Statistics of transition-region loop brightenings and their heating implication

Transition-region loops are a type of critical magnetic structure in the solar atmosphere, yet their physical properties and evolutionary characteristics remain statistically poorly constrained. We aim to statistically characterize the physical properties of propagating brightening events in transition-region loops and to explore the underlying heating mechanism responsible for these brightenings.Using coordinated observations from the Extreme Ultraviolet Imager onboard the Solar Orbiter and the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory, we analyze 42 propagating brightening events in loops that are unambiguously detected in both instrument data. Each of these events evolve simultaneously in the AIA 94, 131, 171, 193, 211, 304, and 335 passband images, suggesting that they are in the transition-region or low-coronal temperature range. Our analyses show that these brightenings are impulsive, with an average brightening time of 118.4 s and a mean intensity decreasing time of 159.4 s. The propagating brightenings are predominantly subsonic, with velocities in the range of 0-90 km/s and an average of 51.3 km/s. The lengths of brightenings range from 3 to 11 Mm, with an average and standard deviation of 6.3 Mm, which are closely related to the propagation velocity and the lifetime. The initial brightening sites are predominantly located near the footpoints of these loops, and the number of brightening events decreases systematically with increasing of loop height. Our results are consistent with an energizing mechanism regulated by enthalpy flows and radiative cooling.

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arXiv2026

Propagating Kink Waves in Chromospheric Jet-like Structures and Coronal Plumelets

Coronal plumes and chromospheric jet-like structures are believed to be highly dynamic. We report the first direct observations of a propagating kink wave in a chromospheric jet-like structure and its associated plumelet structure in the upper corona of the solar polar region, using data from the High Resolution Imager (HRI) of the Extreme Ultraviolet Imager (EUI) on board Solar Orbiter (SO). The dark jet-like structure exhibits transverse oscillation during upward propagation, with a period of approximately 95s and a displacement of about 193km. The corresponding plumelet also displays transverse motion, with an oscillation period of around 99s and a displacement of about 315km. Given that both the dark jet-like structure and the plumelet share the same magnetic skeleton and have similar oscillation period, we suggest that these oscillations are the same transverse propagating wave originating in the chromosphere. This scenario is further supported by a 3D magnetohydrodynamic (MHD) simulation, in which both vertical and transverse perturbations were introduced in a stratified magnetic flux tube. The simulation successfully reproduces the upward propagation of a kink wave through both the chromospheric jet-like structure and the coronal plumelet. These results highlight the potential role of transverse waves in transferring energy from the lower solar atmosphere to the corona.

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arXiv2026

The fine dynamics in homologous and recurrent jets induced by persistent rising loops and mini-filaments

Jets are common eruptive phenomena in the solar atmosphere which may occur repeatedly. Many studies of their fine dynamics have been conducted. However, the fine dynamics of persistent interactions among various features that drive recurrent coronal jets have not been studied in detail. In this paper, we use observations from the Solar Orbiter to report persistent interactions between rising loops/mini-filaments and a fan-spine-like structure, which produced more than 22 ejections. Many loops and mini-filaments under the fan-spine-like structure rose with speeds of $8 - 58\,\mathrm{km~s^{-1}}$ and an average of $27\,\mathrm{km~s^{-1}}$. These rising loops and mini-filaments interacted with the fan-spine-like structure successively, producing ejections with speeds ranging from 25 to 186\,\rm km\,s$^{-1}$ and an average at $80\,\rm km~s^{-1}$. We observed the fine dynamics of the drivers of these recurrent jets in detail, including partial eruption of mini-filaments, formation of a new mini-filament by contraction of remaining threads from the partially-erupted mini-filament, and interaction between rising loops (or mini-filaments) and the fan-spine-like structure. Brightenings appeared near the footpoint of these rising structures, followed by the formation of current sheets. Some arcades at the outflow region contracted with speeds of around $10\,\rm km~s^{-1}$, and the outflow region moved at around $8\,\rm km~s^{-1}$ toward the opposite direction. Bright blobs were observed in the current sheets, and they propagated at speeds averaging at $21\,\rm km\,s^{-1}$ and had an average width of 296\,km. We emphasize the vital roles of persistent rising loops and/or mini-filaments in producing recurrent jets by interacting with the fan-like structure, and show their detailed dynamics with unprecedentedly-high-resolution observations.

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arXiv2025

The Influence of Magnetic Complexity of Active Regions on Solar Wind Properties During Solar Cycles 23 and 24

Linking solar wind properties to the activities and characteristics of its source regions can enhance our understanding of its origin and generation mechanisms. Using the Mount Wilson magnetic classification (MWMC), we categorize all active regions (ARs) between 1999 and 2020 into three groups: alpha, beta, and complex ARs. Subsequently, we classify the near-Earth AR solar wind into the corresponding three types based on the magnetic type of ARs. Our results show that alpha, beta, and complex ARs account for 19.99%, 66.67%, and 13.34% of all ARs, respectively, while their corresponding AR solar wind proportions are 16.96%, 45.18%, and 37.86%. The properties of solar wind from different types of ARs vary significantly. As the magnetic complexity of ARs increases, the corresponding AR solar wind exhibits higher magnetic field strength, charge states, helium abundance (A_He), and first ionization potential (FIP) bias. Our results demonstrate that complex ARs are more effective at generating solar wind. Additionally, the strong magnetic fields and frequent magnetic activities in complex ARs can heat the plasma to higher temperatures and effectively transport helium-rich materials from the lower atmosphere to the upper corona.

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arXiv2025

Witnessing Magnetic Reconnection in Tangled Superpenumbral Fibrils Around a Sunspot

Three-dimensional magnetic reconnection is a fundamental plasma process crucial for heating the solar corona and generating the solar wind, but resolving and characterizing it on the Sun remains challenging. Using high-quality data from the Chinese New Vacuum Solar Telescope, the Solar Dynamics Observatory, and the Interface Region Imaging Spectrograph, this work presents highly suggestive direct imaging evidence of magnetic reconnection during the untangling of braided magnetic structures above a sunspot. These magnetic structures, visible as bright superpenumbral threads in extreme ultraviolet passbands, initially bridge opposite-polarity magnetic fluxes and then gradually tangle in their middle section. Magnetic extrapolation reveals the fibrils to form a small flux rope that is twisted and braided, possibly created by persistent and complex photospheric motions. During untangling, repetitive reconnection events occur inside the flux rope, accompanied by transient plasma heating, bidirectional outflowing blobs, and signatures of nanojets. Emission analysis reveals that the outflowing blobs are multi-thermal structures with temperatures well below 1 MK, undergoing rapid cooling and leaving emission imprints in Hα images. The measured reconnection angles indicate that 16%-22% of the magnetic field along each thread is anti-parallel, with the remaining field acting as a guide field. The estimated energy released during these reconnection events is comparable to nanoflares, which can be powered by up to 6% of the magnetic energy stored in the anti-parallel field. This work presents a textbook example of magnetic flux rope reconnection in the solar atmosphere, providing new insights into fine-scale energy release processes within sunspot superpenumbral fibrils.

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arXiv2025

Sequential ejections of plasma blobs due to unbraiding of tangled loops in the solar atmosphere

Nanoflares, which are consequences of braids in tangled magnetic fields, are an important candidate to heat the solar corona to million degrees. However, their observational evidence is sparse and many of their observational characteristics are yet to be discovered. With the high-resolution observations taken by the Extreme Ultraviolet Imager onboard the Solar Orbiter, here we study a series of ejections of plasma blobs resulted from a braided magnetic loops in the upper transition region and reveal some critical characteristics of such processes. The cores of these ejections have a size of about 700\,km, a duration less than 1 minute and a speed of about 90\,\kms. An important characteristic is that these plasma blobs are apparently constrained by the post-reconnection magnetic loops, along which they show an extension of up to about 2\,000\,km. The propagation of unbraiding nodes along the main axis of the tangled loops has a speed of about 45\,\kms. The separation angles between the post-reconnection loops and the main axis of the tangled loops are about 30\degree. The observations from the Atmospheric Imaging Assembly reveal that the braiding loops are upper transition region structures. Based on these observations, the typical magnetic free energy producing a blob is estimated to be about $3.4\times10^{23}$\,erg, well in the nano-flare regime, while the kinematic energy of a blob is about $2.3\times10^{23}$\,erg, suggesting that a majority of magnetic free energy in a magnetic braid is likely transferred into kinematic energy.

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arXiv2025

Multi-episodes of remote brightenings driven by a coronal EUV jet on the Sun

Remote brightening (RB) is compact brightening at footpoints of magnetic loops, which are remotely-connecting to and confining an eruption in the solar atmosphere. Here, we report on observations of an RB resulting from an EUV jet with a speed of about 90\,km\,s$^{-1}$. The loops connecting the RB and the jet have an apparent length of about 59\,Mm. Intriguingly, the RB exhibits at least two episodes of brightenings, as characterised by two peaks in its lightcurve. The energies, which sustain the first and second peaks of the RB, are $6.3\times10^{26}$\,erg and $8.4\times10^{26}$\,erg, respectively, and take a significant proportion of the total energy. The first peak of the RB brightenings coincides with the jet's peak with a time delay of 12 seconds, while the second peak lags behind by 108 seconds. Besides the flows of the ejecta, we have identified two additional flows originating from the eruption site. One is relatively cool with a temperature of $log_{10}T/K=5.8-6.1$ and has a speed of about $275\pm15$\,km\,s$^{-1}$. The other is hot with a temperature of $log_{10}T/K=7.0-7.3$ and travels much faster with a speed of about 750$\pm$\,70\,km\,s$^{-1}$. We attribute the second peak of RB directly to this hot flow, which our numerical experiments suggest is the result of a slow shock wave. Considering the minimal time delay between the first peak of RB and the eruption, we infer this first episode is due to heating by nonthermal electrons. Our research demonstrates that the dynamics in an RB can offer vital insights into the nature of the corresponding eruption and help understand how the energy is distributed throughout the solar atmosphere.

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arXiv2024

Tracking an eruptive prominence using multiwavelength and multiview observations on 2023 March 7

In this paper, we carry out multiwavelength and multiview observations of the prominence eruption, which generates a C2.3 class flare and a coronal mass ejection (CME) on 2023 March 7. For the first time, we apply the revised cone model to three-dimension reconstruction and tracking of the eruptive prominence for ~4 hrs. The prominence propagates non-radially and makes a detour around the large-scale coronal loops in active region NOAA 13243. The northward deflection angle increases from ~36 degrees to ~47 degrees before returning to ~36 degrees and keeping up. There is no longitudinal deflection throughout the propagation. The angular width of the cone increases from ~30 degrees and reaches a plateau at ~37 degrees. The heliocentric distance of the prominence rises from ~1.1 to ~10.0 solar radii, and the prominence experiences continuous acceleration (~51 m/s^2) over two hours, which is probably related to the magnetic reconnection during the C-class flare. The true speed of CME front is estimated to be ~829 km/s, which is ~1.2 times larger than that of CME core (prominence). It is concluded that both acceleration and deflection of eruptive prominences in their early lives could be reproduced with the revised cone model.

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arXiv2024

The differences in the origination and properties of the near-Earth solar wind between solar cycles 23 and 24

The dependence of the sources and properties of the near-Earth solar wind on solar cycle activity is an important issue in solar and space physics. We use the improved two-step mapping procedure that takes into account the initial acceleration processes to trace the near-Earth solar winds back to their source regions from 1999 to 2020, covering solar cycles (SCs) 23 and 24. Then the solar wind is categorized into coronal hole (CH), active region (AR), and quiet Sun (QS) solar wind based on the source region types. We find that the proportions of CH and AR (QS) wind during SC 23 are higher (lower) than those during SC 24. During solar maximum and declining phases, the magnetic field strength, speed, helium abundance (AHe), and charge states of all three types of solar wind during SC 23 are generally higher than those during SC 24. During solar minimum, these parameters of solar wind are generally lower during SC 23 than those during SC 24. There is a significant decrease in the charge states of all three types of solar wind during the solar minimum of SC 23. The present statistical results demonstrate that the sources and properties of the solar wind are both influenced by solar cycle amplitude. The temperatures of AR, QS, and CH regions exhibit significant difference at low altitudes, whereas they are almost uniform at high altitudes.

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arXiv2024

Electron densities of Transition Region Loops derived from IRIS O IV spectral data

Loops are fundamental structures in the magnetized atmosphere of the sun. Their physical properties are crucial for understanding the nature of the solar atmosphere. Transition region loops are relatively dynamic and their physical properties have not yet been fully understood. With spectral data of the line pair of O IV 1399.8 Å& 1401.2 Å($T_{max}=1.4\times10^5$ K) of 23 transition region loops obtained by IRIS, we carry out the first systematic analyses to their loop lengths ($L$), electron densities ($n_e$) and effective temperatures. We found electron densities, loop lengths and effective temperatures of these loops are in the ranges of $8.9\times10^{9}$-$3.5\times10^{11}$ cm$^{-3}$, 8-30 Mm and $1.9\times10^5$-$1.3\times10^6$ K, respectively. At a significant level of 90\%, regression analyses show that the relationship between electron densities and loop lengths is $n_e[cm^{-3}]\varpropto (L[Mm])^{-0.78\pm0.42}$, while the dependences of electron densities on effective temperatures and that on the line intensities are not obvious. These observations demonstrate that transition region loops are significantly different than their coronal counterparts. Further studies on the theoretical aspect based on the physical parameters obtained here are of significance for understanding the nature of transition region loops.

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arXiv2024

Formation of a streamer blob via the merger of multiple plasma clumps below 2Rs

Context. Propagating streamer blobs could be an important source of disturbances in the solar wind. Direct observations on formation of streamer blobs could be a proxy for understanding the formation of small-scale structures and disturbances in the solar wind. Aims. We aim to investigate how a streamer blob is formed before it is observed in the outer corona. Methods. Usingspecialcoordinated-observationsfromSOHO/LASCO,GOES/SUVIandSDO/AIA, we study the precursors of a streamer blob as seen in the corona below 2.0 solar radii (Rs). Results. We found that the streamer blob was formed due to the gradual merging of three clumps of brightenings initiated from the lower corona at about 1.8Rs, which is likely driven by expansion of the loop system at the base of the streamer. The acceleration of the blob starts from 1.9Rs or lower. It propagates along the south flank of the streamer where an expanding elongated brightening occurs coincidently. Conclusions. Our observations demonstrate that formation of a streamer blob is a complex process. We suggest that the expansion of the loop results in a pinching-off flux-rope-like blob at the loop apex below 2Rs. When the blob moves outward, it can be transferred across the overlying loops through interchange/component magnetic reconnection and then is released into the open field system. When the blob moves toward open field lines, interchange magnetic reconnections might also occur, and that can accelerate the plasma blob intermittently whilst allow it to transfer across the open field lines. Such dynamics in a streamer blob might further trigger small-scale disturbances in the solar wind such as switchbacks in the inner heliosphere.

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arXiv2023

The contribution and FIP bias of three types of materials inside ICMEs associated with different flare intensities

The studies on the origination and generation mechanisms of ICME materials are crucial for understanding the connection between CMEs and flares. The materials inside ICMEs can be classified into three types, coming from corona directly (corona-materials), heated by magnetic reconnection in corona (heated-corona-materials), and generated by chromospheric evaporation (chromospheric-evaporation-materials). Here, the contribution and First Ionization Potential (FIP) bias of three types of materials inside ICMEs associated with different flare intensities are analyzed and compared. We find that the speeds and scales of near-Earth ICMEs both increase with flare intensities. The proportions of heated-corona-materials are nearly constant with flare intensities. The contributions of corona-materials (chromospheric-evaporation-materials) are significantly decreased (increased) with flare intensities. More than two-thirds of materials are chromospheric-evaporation-materials for ICMEs associated with strong flares. The FIP bias of corona-materials and heated-corona-materials is almost the same. The FIP bias of chromospheric-evaporation-materials is significantly higher than that of corona-materials and heated-corona-materials, and it is increased with flare intensities. The above characteristics of FIP bias can be explained reasonably by the origination and generation mechanisms of three types of ICME materials. The present study demonstrates that the origination and generation mechanisms of ICME materials are significantly influenced by flare intensities. The reasons for the elevation of FIP bias, if ICMEs are regarded as a whole, are that the FIP bias of chromospheric-evaporation-materials is much higher, and the chromospheric-evaporation-materials contributed significantly to the ICMEs which associated with strong flares.

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arXiv2023

Internal activities in a solar filament and heating to its threads

Filaments are one of the most common features in the solar atmosphere, and are of significance in solar, stellar and laboratory plasma physics. Using data from the Chinese H$α$ Solar Explorer, the Solar Upper Transition Region Imager and the Solar Dynamics Observatory, we report on multiwavelength imaging and spectral observations of the activation of a small filament. The filament activation produces several localized dynamic brightenings, which are probably produced by internal reconnections of the braided magnetic fields in the filament. The filament expands during the activation and its threads reconnect with the ambient magnetic fields, which leads to the formation of hot arcades or loops overlying the filament. The thermal energy of each of these localized brightenings is estimated in the order of $10^{25}-10^{27} erg$ and the total energy is estimated to be $\sim1.77 \times 10^{28} erg$. Our observations demonstrate that the internal magnetic reconnections in the filament can lead to localized heating to the filament threads and prompt external reconnections with ambient corona structures, and thus could contribute to the energy and mass transferring into the corona.

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arXiv2023

Why "solar tsunamis" rarely leave their imprints in the chromosphere

Solar coronal waves frequently appear as bright disturbances that propagate globally from the eruption center in the solar atmosphere, just like the tsunamis in the ocean on Earth. Theoretically, coronal waves can sweep over the underlying chromosphere and leave an imprint in the form of Moreton wave, due to the enhanced pressure beneath their coronal wavefront. Despite the frequent observations of coronal waves, their counterparts in the chromosphere are rarely detected. Why the chromosphere rarely bears the imprints of solar tsunamis remained a mystery since their discovery three decades ago. To resolve this question, all coronal waves and associated Moreton waves in the last decade have been initially surveyed, though the detection of Moreton waves could be hampered by utilising the low-quality H$α$ data from Global Oscillations Network Group. Here, we present 8 cases (including 5 in Appendix) of the coexistence of coronal and Moreton waves in inclined eruptions where it is argued that the extreme inclination is key to providing an answer to address the question. For all these events, the lowest part of the coronal wavefront near the solar surface appears very bright, and the simultaneous disturbances in the solar transition region and the chromosphere predominantly occur beneath the bright segment. Therefore, evidenced by observations, we propose a scenario for the excitation mechanism of the coronal-Moreton waves in highly inclined eruptions, in which the lowest part of a coronal wave can effectively disturb the chromosphere even for a weak (e.g., B-class) solar flare.

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arXiv2023

The properties of small magnetic flux ropes inside the solar wind come from coronal holes, active regions, and quiet Sun

The origination and generation mechanisms of small magnetic flux ropes (SFRs), which are important structures in solar wind, are not clearly known. In present study, 1993 SFRs immersed in coronal holes, active regions, and quiet Sun solar wind are analyzed and compared. We find that the properties of SFRs immersed in three types of solar wind are signicantly different. The SFRs are further classifed into hot-SFRs, cold-SFRs, and normal-SFRs, according to whether the O7+/O6+ is 30% elevated or dropped inside SFRs as compared with background solar wind. Our studies show that the parameters of normal-SFRs are similar to background in all three types of solar wind. The properties of hot-SFRs and cold-SFRs seem to be lying in two extremes. Statistically, the hot-SFRs (cold-SFRs) are associated with longer (shorter) duration, lower (higher) speeds and proton temperatures, higher (lower) charge states, helium abundance, and FIP bias as compared with normal-SFRs and background solar wind. The anti-correlations between speed and O7+/O6+ inside hot-SFRs (normal-SFRs) are different from (similar to) those in background solar wind. Most of hot-SFRs and cold-SFRs should come from the Sun. Hot-SFRs may come from streamers associated with plasma blobs and/or small-scale activities on the Sun. Cold-SFRs may be accompanied by small-scale eruptions with lower-temperature materials. Both hot-SFRs and cold-SFRs could also be formed by magnetic erosions of ICMEs that do not contain or contain cold-filament materials. The characteristics of normal-SFRs can be explained reasonably by the two originations, from the Sun and generated in the heliosphere both.

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arXiv2022

Solar Ring Mission: Building a Panorama of the Sun and Inner-heliosphere

Solar Ring (SOR) is a proposed space science mission to monitor and study the Sun and inner heliosphere from a full 360° perspective in the ecliptic plane. It will deploy three 120°-separated spacecraft on the 1-AU orbit. The first spacecraft, S1, locates 30° upstream of the Earth, the second, S2, 90° downstream, and the third, S3, completes the configuration. This design with necessary science instruments, e.g., the Doppler-velocity and vector magnetic field imager, wide-angle coronagraph, and in-situ instruments, will allow us to establish many unprecedented capabilities: (1) provide simultaneous Doppler-velocity observations of the whole solar surface to understand the deep interior, (2) provide vector magnetograms of the whole photosphere - the inner boundary of the solar atmosphere and heliosphere, (3) provide the information of the whole lifetime evolution of solar featured structures, and (4) provide the whole view of solar transients and space weather in the inner heliosphere. With these capabilities, Solar Ring mission aims to address outstanding questions about the origin of solar cycle, the origin of solar eruptions and the origin of extreme space weather events. The successful accomplishment of the mission will construct a panorama of the Sun and inner-heliosphere, and therefore advance our understanding of the star and the space environment that holds our life.

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