arXiv subjects

Chuanyang Li

Publications and source records attributed to Chuanyang Li.

At least 19 recordsLinked to original sources

arXiv2026

Type I Solar Radio Bursts Modulated by Solar Flares

Type I solar radio bursts (noise storms) are persistent meter-wave nonthermal emissions above active regions, with their occurrence and proper?ties closely related to the local magnetic configuration and nonthermal electron acceleration. This study examines a type I noise storm on 24 December 2023 and its relation to flare activity. The noise-storm source was co-spatial with active region AR 3529 and showed frequency-dependent spatial dispersion. The associated M2.9 flare strongly modulated the emission, with the storm intensity decreasing at flare onset, recovering afterward, and shifting to higher frequencies. Based on multiwavelength observations, we suggest that pre-flare small-scale reconnection supplied nonthermal electrons to overlying closed magnetic struc?tures and maintained the storm. During the flare, magnetic reconnection above the active region produced bidirectional plasma ejections and type III bursts with bidirectional frequency drifts; the gradually decreasing starting frequency of these bursts may indicate an upward-moving reconnection site. The resulting magnetic reconfiguration disrupted electron trapping and suppressed the storm, whereas post-flare magnetic recovery allowed the emission to resume. These results show that flares can modulate type I noise storms through magnetic restructuring and provide insight into the generation mechanism of noise storms.

astro-ph.SR↗

arXiv2026

Coronal Diagnostics Via Modelling Periodic-Beaded Stripes of Solar Radio Bursts

Using high-resolution data from the Chashan Broadband Solar radio spectrometer at meter wavelengths (CBSm) of the Chinese Meridian Project-Phase II (CMP-II), Li et al. (2025) identified a novel fine spectral structure of solar radio bursts, termed periodic beaded stripes, and proposed a generation mechanism. Here we report additional events and develop a quantitative method to determine the physical conditions in the emission region. Periodic stripes tend to occur in the post-phase of flares and are associated with complex magnetic configurations. They repeat on sub-second timescales and show $\sim$0.1 s bead-like modulations, often accompanied by low-frequency absorptions. Modeling the chained stripes with linear kinetic theory of the double plasma resonance (DPR) instability constrains the source-region magnetic field to 0.2-1.7 G and the plasma density to (1-7) $\times 10^8$ cm $^{-3}$. The former follows the drift of individual stripes, and the latter tracks the overall trend. This study summarizes the key properties of periodic beaded stripes and establishes a quantitative DPR-based framework for coronal diagnostics.

astro-ph.SR↗

arXiv2025

HistCAD: A Constraint-Aware Parametric History-Based CAD Representation, Dataset, and Benchmark with Industrial Complexity

Parametric CAD sequences are reusable because dimensional and geometric constraints govern how parameter changes propagate. Existing CAD generation datasets and benchmarks emphasize reconstruction fidelity, execution validity, or static shape similarity, leaving preservation of design intent under edits largely unmeasured. We introduce HistCAD, a representation standard, dataset, and benchmark for executable parametric CAD with explicit constraints. HistCAD defines an intermediate language independent of CAD software, recording sketch primitives, constraints, feature operations, and 3D point boundary references for operations such as fillet and chamfer. The dataset contains 170,236 executable sequences aligned with native CAD models, STEP files, rendered views, and text annotations, combining academic scale with professionally authored industrial complexity. Building on this representation, the Constraint-Aware Editability Benchmark applies parameter edits and reports Edit Reachability, conditional preserved constraint satisfaction, and Overall Editable Success, abbreviated ER, cPCSR, and OES; these metrics separate failures to reach a valid edited state from failures to preserve required constraints. Experiments show that explicit constraints are essential for preserving design intent after edits, and that HistCAD supports supervised CAD generation from text and direct LLM workflows. We argue that HistCAD reframes CAD generation from static shape imitation to the synthesis of reusable parametric sequences with explicit constraints.

cs.GR↗

arXiv2025

The Liouville theorem on H-type groups

In this paper we obtain a Liouville type theorem to the semilinear subcritical elliptic equation on H-type groups. The semilinear subcritical elliptic equation studied in this paper is a generalization of a classical semilinear subcritical elliptic equation on the Heisenberg group. The proofs are based on an {\it a priori} integral estimate and a generalized differential identity which found by Jerison and Lee [J. Diff. Geom, 29 (1989)].

math.DG↗

arXiv2025

A Novel Fine Spectral Structure of Solar Radio Bursts with Periodic Beaded Stripes Observed by CBSm of CMP-II

A novel fine spectral structure in solar radio bursts has been discovered using the Chashan broadband solar radio spectrometer at meter wavelengths (CBSm), an instrument of the Chinese Meridian Project-Phase II (CMP-II). The structure features periodic narrow-band stripes with a typical recurrence time $< 1 $ s (occasionally reaches 8 s), often drifting from high to low frequencies and accompanied by absorptions, with trailing stripes appearing at the end of preceding ones. Some stripes exhibit periodic beaded enhancements with a periodicity of $\sim$0.1 s. The beaded stripes are reported for the first time ever. Data from the DAocheng Radio Telescope (DART) indicate a radio emission brightness temperature exceeding $10^{9}$ K, originating above brightening loops in active region AR 13664. We proposed a novel generation mechanism of the periodic stripes on the basis of the double plasma resonance (DPR) instability, and explained the beaded substructure in terms of modulation by low-frequency magnetohydrodynamic (MHD) waves. The study highlights the CBSm's capability to detect high-resolution fine spectral structures and offers novel insights into the emission mechanism and source characteristics of solar radio bursts.

astro-ph.SR↗

arXiv2023

High-harmonic Plasma Emission Induced by Electron Beams in Weakly Magnetized Plasmas

Electromagnetic radiation at higher harmonics of the plasma frequency ($ω\sim nω_{pe}, n > 2$) has been occasionally observed in type II and type III solar radio bursts, yet the underlying mechanism remains undetermined. Here we present two-dimensional fully kinetic electromagnetic particle-in-cell simulations with high spectral resolution to investigate the beam-driven plasma emission process in weakly magnetized plasmas of typical coronal conditions. We focused on the generation mechanisms of high-harmonic emission. We found that a larger beam velocity ($u_d$) favors the generation of the higher-harmonic emission. The emissions grow later for higher harmonics and decrease in intensity by $\sim$2 orders of magnitude for each jump of the harmonic number. The second and third harmonic ($\rm H_2$ and $\rm H_3$) emissions get closer in intensity with larger $u_d$. We also show that (1) the $\rm H_3$ emission is mainly generated via the coalescence of the $\rm H_2$ emission with the Langmuir waves, i.e., $\rm H_2 + L \rightarrow H_3$, wherein the coalescence with the forward-propagating beam-Langmuir wave leads to the forward-propagating $\rm H_3$, and coalescence with the backward-propagating Langmuir wave leads to the backward-propagating $\rm H_3$; and (2) the $\rm H_4$ emission mainly arises from the coalescence of the $\rm H_3$ emission with the forward- (backward-) propagating Langmuir wave, in terms of $\rm H_3 + L \rightarrow H_4$.

astro-ph.SR↗

arXiv2023

Excitation of extraordinary modes inside the source of Saturn's kilometric radiation

The electron cyclotron maser instability (ECMI) of extraordinary mode waves was investigated with the parameters observed in Saturn's kilometric radiation (SKR) sources. Previous studies employed simplified dispersion relations, and did not consider the excitation of the relativistic (R) mode. This mode is introduced by considering the relativistic effect in plasmas consisting of both cold and hot electrons. Using particle-in-cell simulations, we investigated the excitation of R and X modes based on the measured data. Using the reported value of the density ratio of energetic to total electrons $n_e/n_0=24\%$, the most unstable mode is the R mode. The escaping X-mode emissions are amplified only if the energetic electrons are dominant with $n_e/n_0 \ge 90\%$. For these cases, only the X mode is excited and the R mode disappears due to its strong coupling. The results are well in line with the linear kinetic theory of ECMI. The properties of both the R and X modes are consistent with the observed SKR emissions. This raises questions about the nature of the measured electric field fluctuations within ``presumed'' SKR sources. The study provides new insights into the ECMI process relevant to SKR emission mechanisms.

astro-ph.EP↗

arXiv2022

Plasma emission induced by ring-distributed energetic electrons in overdense plasmas

According to the standard scenario of plasma emission, escaping radiations are generated by the nonlinear development of the kinetic bump-on-tail instability driven by a single beam of energetic electrons interacting with plasmas. Here we conduct fully-kinetic electromagnetic particle-in-cell simulations to investigate plasma emission induced by the ring-distributed energetic electrons interacting with overdense plasmas. Efficient excitations of the fundamental (F) and harmonic (H) emissions are revealed with radiation mechanism(s) different from the standard scenario: (1) The primary modes accounting for the radiations are generated through the electron cyclotron maser instability (for the upper-hybrid (UH) and Z modes) and the thermal anisotropic instability (for the whistler (W) mode); the F emission is generated by the nonlinear coupling of the Z and W modes and the H emission by the nonlinear coupling of the UH modes. This presents an alternative mechanism of coherent radiation in overdense plasmas.

physics.plasm-ph↗

arXiv2022

Verification of the standard theory of plasma emission with particle-in-cell simulations

The standard theory of plasma emission is based on kinetic couplings between a single beam of energetic electrons and unmagnetized thermal plasmas, involving multi-step nonlinear wave-particle and wave-wave interactions. The theory has not yet been completely verified with fully-kinetic electromagnetic particle-in-cell (PIC) simulations. Earlier studies, greatly limited by available computational resources, are controversial regarding whether the fundamental emission can be generated according to the standard theory. To resolve the controversy, we conducted PIC simulations with a large domain of simulation and a large number of macroparticles, among the largest ones of similar studies. We found significant fundamental emission if the relative beam density is small enough (say, $\le$ 0.01), in line with earlier study with a much-smaller domain; the relative intensity (normalized by the total initial beam energy) of all modes, except the mode associated with the beam-electromagnetic Weibel instability, decreases with increasing relative density of the beam. We also found significant transverse magnetic component associated with the superluminal Langmuir turbulence, which has been mistakenly regarded as evidence of the F emission in earlier study. Further investigations are required to reveal their origin.

physics.plasm-ph↗

arXiv2022

Plasma Emission Induced By Electron Beam in Weakly Magnetized Plasmas

Previous studies on the beam-driven plasma emission process were done mainly for unmagnetized plasmas. Here we present fully-kinetic electromagnetic particle-in-cell simulations to investigate such process in weakly-magnetized plasmas of the solar corona conditions. The primary mode excited is the beam-Langmuir (BL) mode via the classical bump-on-tail instability. Other modes include the whistler (W) mode excited by the electron cyclotron resonance instability, the generalized Langmuir (GL) waves that include a superluminal Z-mode component with smaller wave number $k$ and a thermal Langmuir component with larger $k$, and the fundamental (F) and harmonic (H) branches of plasma emission. Further simulations of different mass and temperature ratios of electrons and protons indicate that the GL mode and the two escaping modes (F and H) correlate positively with the BL mode in intensity, supporting that they are excited through nonlinear wave-wave coupling processes involving the BL mode. We suggest that the dominant process is the decay of the primary BL mode. This is consistent with the standard theory of plasma emission. Yet, the other possibility of the Z+W$\rightarrow$O--F coalescing process for the F emission cannot be ruled out completely.

physics.plasm-ph↗

arXiv2021

Harmonic maser emissions from electrons with loss-cone distribution in solar active regions

Electron cyclotron maser emission (ECME) is regarded as a plausible source for the coherent radio radiations from solar active regions (e.g., solar radio spikes). In this Letter, we present a 2D3V fully kinetic electromagnetic particle-in-cell (PIC) simulation to investigate the wave excitations and subsequent nonlinear processes induced by the energetic electrons in the loss-cone distribution. The ratio of the plasma frequency to the electron gyrofrequency $ω_{pe}/Ω_{ce}$ is set to 0.25, adequate for solar active region conditions. As a main result, we obtain strong emissions at the second-harmonic X mode (X2). While the fundamental X mode (X1) and the Z mode are amplified directly via the electron cyclotron maser instability, the X2 emissions can be produced by the nonlinear coalescence between two Z modes and between Z and X1 modes. This represents a novel generation mechanism for the harmonic emissions in plasmas with a low value of $ω_{pe}/Ω_{ce}$, which may resolve the escaping difficulty of explaining solar radio emissions with the ECME mechanism.

astro-ph.SR↗

arXiv2021

Harmonic elctron-cyclotron maser emissions driven by energetic electrons of the horseshoe distribution with application to solar radio spikes

Content. Electron-cyclotron maser emission (ECME) is the favored mechanism for solar radio spikes and has been investigated extensively since the 1980s. Most studies relevant to solar spikes employ a loss-cone-type distribution of energetic electrons, generating waves mainly in the fundamental X/O mode (X1/O1), with a ratio of plasma oscillation frequency to electron gyrofrequency ($ω_ {pe}/Ω_{ce}$) lower than 1. Despite the great progress made in this theory, one major problem is how the fundamental emissions pass through the second-harmonic absorption layer in the corona and escape. This is generally known as the escaping difficulty of the theory. Aims. We study the harmonic emissions generated by ECME driven by energetic electrons with the horseshoe distribution to solve the escaping difficulty of ECME for solar spikes. Methods. We performed a fully kinetic electromagnetic PIC simulation with $ω_ {pe}/Ω_{ce}$ = 0.1, corresponding to the strongly magnetized plasma conditions in the flare region, with energetic electrons characterized by the horseshoe distribution. We also varied the density ratio of energetic electrons to total electrons ($n_e/n_0$) in the simulation. Results. We obtain efficient amplification of waves in Z and X2 modes, with a relatively weak growth of O1 and X3. With a higher-density ratio, the X2 emission becomes more intense, and the rate of energy conversion from energetic electrons into X2 modes can reach $\sim$0.06% and 0.17%, with $n_e/n_0$= 5% and 10%, respectively. Conclusions. We find that the horseshoe-driven ECME can lead to an efficient excitation of X2 and X3 with a low value of $ω_ {pe}/Ω_{ce}$, providing novel means for resolving the escaping difficulty of ECME when applied to solar radio spikes. The simultaneous growth of X2 and X3 can be used to explain some harmonic structures observed in solar spikes.

astro-ph.SR↗

arXiv2021

An alternative form of the fundamental plasma emission through the coalescence of Z-mode waves with whistlers

Plasma emission (PE), i.e., electromagnetic radiation at the plasma frequency and its second harmonic, is a general process occurring in both astrophysical and laboratory plasmas. The prevailing theory presents a multi-stage process attributed to the resonant coupling of beam-excited Langmuir waves with ion-acoustic waves. Here we examine another possibility of the fundamental PE induced by the resonant coupling of Z-mode and whistler (W) waves. Earlier studies have been controversial in the plausibility and significance of such process in plasmas. In this study we show that the matching condition of three wave resonant interaction (Z+W ! O) can be satisfied over a wide regime of parameters based on the magnetoionic theory, demonstrate the occurrence of such process and further evaluate the rate of energy conversion from the pumped Z or W mode to the fundamental O mode with particle-in-cell (PIC) simulations of wave pumping. The study presents an alternative form of the fundamental PE, which could possibly play a role in various astrophysical and laboratory scenarios with both Z and W modes readily excited through the electron cyclotron maser instability.

physics.plasm-ph↗

arXiv2021

PIC Simulation of Double Plasma Resonance and Zebra Pattern of Solar Radio Bursts

Latest study reports that plasma emission can be generated by energetic electrons of DGH distribution via the electron cyclotron maser instability (ECMI) in plasmas characterized by a large ratio of plasma oscillation frequency to electron gyro-frequency ($ω_{pe}/Ω_{ce}$). In this study, on the basis of the ECMI-plasma emission mechanism, we examine the double plasma resonance (DPR) effect and the corresponding plasma emission at both harmonic (H) and fundamental (F) bands using PIC simulations with various $ω_{pe}/Ω_{ce}$. This allows us to directly simulate the feature of zebra pattern (ZP) observed in solar radio bursts for the first time. We find that (1) the simulations reproduce the DPR effect nicely for the upper hybrid (UH) and Z modes, as seen from their variation of intensity and linear growth rate with $ω_{pe}/Ω_{ce}$, (2) the intensity of the H emission is stronger than that of the F emission by $\sim$ 2 orders of magnitude and vary periodically with increasing $ω_{pe}/Ω_{ce}$, while the F emission is too weak to be significant, therefore we suggest that it is the H emission accounting for solar ZPs, (3) the peak-valley contrast of the total intensity of H is $\sim 4$, and the peak lies around integer values of $ω_{pe}/Ω_{ce}$ (= 10 and 11) for the present parameter setup. We also evaluate the effect of energy of energetic electrons on the characteristics of ECMI-excited waves and plasma radiation. The study provides novel insight on the physical origin of ZPs of solar radio bursts.

astro-ph.SR↗

arXiv2019

Effect of the Temperature of Background Plasma and the Energy of Energetic Electrons on Z-Mode Excitation

It has been suggested that the Z-mode instability driven by energetic electrons with a loss-cone type velocity distribution is one candidate process behind the continuum and zebra pattern of solar type-IV radio bursts. Both the temperature of background plasma ($T_0$) and the energy of energetic electrons ($v_e$) are considered to be important to the variation of the maximum growth rate ($γ_{max}$). Here we present a detailed parameter study on the effect of $T_0$ and $v_e$, within a regime of the frequency ratio ($10 \leq \frac{ω_{pe}}{Ω_{ce}} \leq 30$). In addition to $γ_{max}$, we also analyze the effect on the corresponding wave frequency ($ω^r_{max}$) and propagation angle ($θ_{max}$). We find that (1) $γ_{max}$ in-general decreases with increasing $v_e$, while its variation with $T_0$ is more complex depending on the exact value of $v_e$; (2) with increasing $T_0$ and $v_e$, $ω^r_{max}$ presents step-wise profiles with jumps separated by gradual or very-weak variations, and due to the warm-plasma effect on the wave dispersion relation $ω^r_{max}$ can vary within the hybrid band (the harmonic band containing the upper hybrid frequency) and the band higher; (3) the propagation is either perpendicular or quasi-perpendicular, and $θ_{max}$ presents variations in line with those of $ω^r_{max}$, as constrained by the resonance condition. We also examine the profiles of $γ_{max}$ with $\frac{ω_{pe}}{Ω_{ce}}$ for different combinations of $T_0$ and $v_e$ to clarify some earlier calculations which show inconsistent results.

astro-ph.SR↗

arXiv2018

Formation of Large Scale Coronal Loops Interconnecting Two Active Regions Through Gradual Magnetic Reconnection and Associated Heating Process

Coronal loops interconnecting two active regions, called as interconnecting loops (ILs), are prominent large-scale structures in the solar atmosphere. They carry a significant amount of magnetic flux, therefore are considered to be an important element of the solar dynamo process. Earlier observations show that eruptions of ILs are an important source of CMEs. It is generally believed that ILs are formed through magnetic reconnection in the high corona (>150-200"), and several scenarios have been proposed to explain their brightening in soft X-rays (SXRs). Yet, the detailed IL formation process has not been fully explored and the associated energy release in the corona still remains unresolved. Here we report the complete formation process of a set of ILs connecting two nearby active regions, with successive observations by STEREO-A on the far side of the Sun and SDO and Hinode on the Earth side. We conclude that ILs are formed by gradual reconnection high in the corona, in line with earlier postulations. In addition, we show evidence supporting that ILs become brightened in SXRs and EUVs through heating at or close to the reconnection site in the corona (i.e., through direct heating process of reconnection), a process that has been largely overlooked in earlier studies on ILs

astro-ph.SR↗

arXiv2018

Harmonics of Solar Radio Spikes at Metric Wavelengths

This paper presents the latest observations from the newly-built solar radio spectrograph at the \emph{Chashan Solar Observatory}. On July 18 2016, the spectrograph records a solar spike burst event, which has several episodes showing harmonic structures, with the second, third, and fourth harmonics. The lower harmonic radio spike emissions are observed later than the higher harmonic bands, and the temporal delay of the second (third) harmonic relative to the fourth harmonic is about 30\ --\ 40 (10) ms. Based on the electron cyclotron maser emission mechanism, we analyze possible causes of the temporal delay and further infer relevant coronal parameters, such as the magnetic field strength and the electron density at the radio source.

astro-ph.SR↗

arXiv2017

EUV and Magnetic Activities Associated with Type-I Solar Radio Bursts

Type-I bursts (i.e. noise storms) are the earliest-known type of solar radio emission at the metre wavelength. They are believed to be excited by non-thermal energetic electrons accelerated in the corona. The underlying dynamic process and exact emission mechanism still remain unresolved. Here, with a combined analysis of extreme ultraviolet (EUV), radio and photospheric magnetic field data of unprecedented quality recorded during a type-I storm on 30 July 2011, we identify a good correlation between the radio bursts and the co-spatial EUV and magnetic activities. The EUV activities manifest themselves as three major brightening stripes above a region adjacent to a compact sunspot, while the magnetic field there presents multiple moving magnetic features (MMFs) with persistent coalescence or cancelation and a morphologically similar three-part distribution. We find that the type-I intensities are correlated with those of the EUV emissions at various wavelengths with a correlation coefficient of 0.7-0.8. In addition, in the region between the brightening EUV stripes and the radio sources there appear consistent dynamic motions with a series of bi-directional flows, suggesting ongoing small-scale reconnection there. Mainly based on the induced connection between the magnetic motion at the photosphere and the EUV and radio activities in the corona, we suggest that the observed type-I noise storms and the EUV brightening activities are the consequence of small-scale magnetic reconnection driven by MMFs. This is in support of the original proposal made by Bentely et al. (Solar Phys. 193, 227, 2000).

astro-ph.SR↗