arXiv subjects

Baolin Tan

Publications and source records attributed to Baolin Tan.

At least 19 recordsLinked to original sources

arXiv2025

Multiwavelength Observations for a Double-decker Filament Channel in AR 13102

We present the observational evidence of the existence of a double-decker filament channel (FC) by using observations in extreme ultraviolet and H{\alpha} wavelengths. For both FCs, the east foot-point roots in the active region (AR), while the west one roots in the remote quiet region. The bottom FC (FC1) appears as intermittent filaments. Within the AR, the FC1 appears as an S-shaped filament (F1), which consisted of two J-shaped filaments (F1S/F1N for the south/north one). For the upper one (FC2), only the east part is filled with dark plasma and visible as a small filament (F2). Its east foot-point roots around the junction of F1S and F1N. Initially, due to the recurrent reconnections, F1N and F1S link to each other and form a new filament (F3) thread by thread. Meanwhile, the heated plasma, which appears as brightening features, flows from the east foot-point of F2 to the west, and becomes invisible about 1.1$\times$10^{5} km away. The failed eruption of F1S is triggered by the reconnection, which appears as the brightening threads changing their configuration from crossed to quasiparallel in between the F1S and F3, and is confined by the upper magnetic field. Associated with the eruption, the distant invisible plasma becomes visible as a brightening feature. It continuously flows to the remote foot-point, and becomes invisible before reaching it. The brightening plasma flow outlines the skeleton of FC2 gradually. The observations show the existence of a double-decker FC, as a magnetic structure, before they appear as a brightening/dark feature when fully filled with hot/cool plasma.

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arXiv2025

JW-Flare: Accurate Solar Flare Forecasting Method Based on Multimodal Large Language Models

Solar flares, the most powerful explosive phenomena in the solar system, may pose significant hazards to spaceborne satellites and ground-based infrastructure. Despite decades of intensive research, reliable flare prediction remains a challenging task. Large Language Models, as a milestone in artificial intelligence, exhibit exceptional general knowledge and next-token prediction capabilities. Here we introduce JW-Flare, the first Multimodal Large Language Models (MLLMs) explicitly trained for solar flare forecasting through fine-tuning on textual physic parameters of solar active regions and magnetic field images. This method demonstrates state-of-the-art (SOTA) performance for large flares prediction on the test dataset. It effectively identifies all 79 X-class flares from 18,949 test samples, yielding a True Skill Statistic (TSS) of 0.95 and a True Positive Rate (TPR) of 1.00, outperforming traditional predictive models. We further investigate the capability origins of JW-Flare through explainability experiments, revealing that solar physics knowledge acquired during pre-training contributes to flare forecasting performance. Additionally, we evaluate models of different parameter scales, confirming the Scaling_Law of Large Language Models in domain-specific applications, such as solar physics. This study marks a substantial advance in both the scale and accuracy of solar flare forecasting and opens a promising avenue for AI-driven methodologies in broader scientific domains.

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arXiv2025

Heating Mechanisms and Radio Response from the Solar Chromosphere to Corona

Heating mechanism in the solar atmosphere (from chromosphere to corona) is one of the top-challenges in modern astronomy. The classic mechanisms can be divided into two categories: wave heating (W) and magnetic reconnection heating (X). Both of them still face some problems currently difficult to overcome. Recently, we proposed a new mechanism, called magnetic-gradient pumping heating (MGP, or P) which seems to overcome those difficulties, but still lacks sufficient observational evidence. Which one really explained the physics of hot corona exactly? How can observations be used to identify and verify the heating mechanism? Since different heating mechanism will generate non-thermal particles from different accelerations and experience different propagations, they will have different response on the broadband spectral radio observations. Among them, the non-thermal electrons from W mechanisms are closely related to shock-wave acceleration, and their radio response should be group of spike bursts with random distribution of drifting rates; the non-thermal electrons from X mechanisms are accelerated by reconnecting electric field with bidirectional flow, and their radio response should be type III pairs or spike pairs; P mechanism will produce energetic particle upflows, and their radio response should be unidirectional fiber bursts with moderate negative drifting rates. Therefore, the heating mechanism can be identified and verified from the the broadband dynamic spectral radio observations. Additionally, using high-resolution radioheliographs and spectral-imaging observations, the heating mechanisms in different regions can be identified and verified separately, thereby demonstrating the physical essence of hot corona.

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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.

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arXiv2025

A Flare-related Decimetric Type-IV Radio Burst Induced by the X2 Radiation of Electron Cyclotron Maser Emission

The radiation mechanism of decimetric wideband and pulsating radio bursts from the Sun (in terms of decimetric type-IV (t-IVdm) burst) and other flaring stars is a long-standing problem. Early investigations were based on the leading-spot hypothesis for the sun and yielded contradictory results. Here, we analyzed the flare-associated t-IVdm burst on 20110924 with medium-strong levels of polarization and from sources near a sunspot. We found that the emission is intermittent and the maximum $T_B$ exceeds 10$^{11}$ K, with well-defined upper and lower frequency cutoffs. The radio sources are left-handed polarized, located above the sunspot with a negative polarity. The sources align well with the sites of the second harmonic of the local electron gyrofrequency. These findings provide essential evidence that the burst is induced by the electron cyclotron maser emission (ECME) in the harmonic X mode. We further modeled the transport of downward-streaming energetic electrons along a coronal loop and found most electrons get mirrored within the specific altitude range of 20-100 Mm. This explains why such bursts tend to have well-defined spectral ranges. We also found the ECME-radiating energetic electrons exhibit a shell-like VDF instead of the generally-presumed loss-cone distribution. The study greatly expands the application of ECME in solar radio astronomy and provides solar samples for similar bursts from other flaring stars.

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arXiv2025

The occurrence of powerful flares stronger than X10 class in Solar Cycles

Solar flares stronger than X10 (S-flares, >X10) are the highest class flares which significantly impact on the Sun's evolution and space weather. Based on observations of Geostationary Orbiting Environmental Satellites (GOES) at soft X-ray (SXR) wavelength and the daily sunspot numbers (DSNs) since 1975, we obtained some interesting and heuristic conclusions: (1) Both S-flares and the more powerful extremely strong flares (ES-flares, >X14.3) mostly occur in the late phases of solar cycles and low-latitude regions on the solar disk; (2) Similar to X-class flares, the occurrence of S-flares in each solar cycle is somewhat random, but the occurrence of ES-flares seems to be dominated by the mean DSN (Vm) and its root-mean-square deviation during the valley phase (Vd) before the cycle: the ES-flare number is strongly correlated with Vd, and the occurrence time of the first ES-flare is anti-correlated with Vd and Vm. These facts indicate that the higher the Vm and Vd, the stronger the solar cycle, the more the ES-flares and the earlier they occurred. We proposed that the Sun may have a low-latitude active zone (LAZ), and most ES-flares are generated from the interaction between LAZ and the newly emerging active regions. The correlations and the linear regression functions may provide an useful method to predict the occurrence of ES-flares in an upcoming solar cycle, which derives that solar cycle 25 will have about 2 ES-flares after the spring of 2027.

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arXiv2024

Failure of a solar filament eruption caused by magnetic reconnection with overlying coronal loops

Failure of a filament eruption caused by magnetic reconnection between the erupting filament and the overlying magnetic field has been previously proposed in numerical simulations. It is, however, rarely observed. In this study, we report the reconnection between an erupting filament and its overlying coronal loops, that results in the failure of the filament eruption. On 2023 September 24, a filament was located in active region 13445. It slowly rose, quickly erupted, rapidly decelerated, and finally stopped, with an untwisting motion. As a failed eruption, the event is associated with an M4.4 flare but no coronal mass ejection. During the eruption, the filament became bright, and the overlying loops appeared first in the high-temperature channels. They have average temperatures of ~12.8 and ~9.6MK, respectively, indicating that both of them were heated. Two sets of new loops, separately connecting the filament endpoints and the overlying loop footpoints, then formed. Subsequently, the heated overlying loops were seen sequentially in the low-temperature channels, showing the cooling process, which is also supported by the light curves. Plasmoids formed, and propagated bidirectionally along the filament and the overlying loops, indicating the presence of plasmoid instability. These results suggest that reconnection occurs between the erupting filament and the overlying loops. The erupting filament eventually disappeared, with the appearance of more newly-formed loops. We propose that the reconnection between the erupting filament and the overlying loops ruins the filament completely, and hence results in the failed eruption.

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arXiv2024

A Multi-Peak Solar Flare with a High Turnover Frequency of The Gyrosynchrotron Spectra from the Loop-Top Source

The origin of multiple peaks in lightcurves of various wavelengths remains illusive during flares. Here we discuss the flare of SOL2023-05-09T03:54M6.5 with six flux peaks as recorded by a tandem of new microwave and Hard X-ray instruments. According to its microwave spectra, the flare represents a high-turnover frequency (>15 GHz) event. The rather-complete microwave and HXR spectral coverage provides a rare opportunity to uncover the origin of such event together with simultaneous EUV images. We concluded that (1) the microwave sources originates around the top section of the flaring loops with a trend of source spatial dispersion with frequency;(2) the visible movement of the microwave source from peak to peak originates from the process of new flaring loops appearing sequentially along the magnetic neutral line; 3) the optically-thin microwave spectra are hard with the indices varying from -1.2 to -0.4, and the turnover frequency always exceeds 15 GHz; 4) higher turnover/peak frequency corresponds to stronger peak intensity and harder optically-thin spectra. Using the Fokker-Planck and GX simulator codes we obtained a good fit to the observed microwave spectra and spatial distribution of the sources at all peaks, if assuming the radiating energetic electrons have the same spatial distribution and single-power-law spectra but with the number density varying in a range of 30%. We conclude that the particle acceleration in this flare happens in a compact region nearing the looptop. These results provide new constraints on the acceleration of energetic electrons and the underlying flare intermittent reconnection process.

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arXiv2024

Long-term evolution of solar activity and prediction of the following solar cycles

Solar activities have a great impact on modern high-tech systems, such as human aerospace, satellite communication and navigation, deep space exploration, and related scientific research. Therefore, studying the long - term evolution trend of solar activity and accurately predicting the future solar cycles is highly anticipated. Based on wavelet transform and empirical function fitting of the longest recorded data of the annual average relative sunspot number (ASN) series of 323 years to date, this work decisively verified the existence of the solar century cycles and confirmed that its length is about 104.0 years, and the magnitude has a slightly increasing trend on the time scale of several hundreds of years. Based on this long-term evolutionary trend, we predicted solar cycle 25 and 26 by using phase similar prediction methods. As for the solar cycle 25, its maximum ASN will be about $146.7\pm 33.40$, obviously stronger than solar cycle 24. The peak year will occur approximately in 2024, and the period is about $11\pm 1$ years. As for the solar cycle 26, it will start around 2030, reach the maximum between 2035 and 2036, with maximum ASN of about $133.0\pm 3.200$, and the period is about 10 years.

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arXiv2023

The physics of solar spectral imaging observations in dm-cm wavelengths and the application on space weather

Recently, several new solar radio telescopes have been put into operation and provided spectral-imaging observations with much higher resolutions in decimeter (dm) and centimeter (cm) wavelengths. These telescopes include the Mingantu Spectral Radioheliograph (MUSER, at frequencies of 0.4 - 15 GHz), the Expanded Owens Valley Solar Array (EOVSA, at frequencies of 1 - 18 GHz), and the Siberian Radio Heliograph (SRH, at frequencies of 3 - 24 GHz). These observations offer unprecedented opportunities to study solar physics and space weather, especially to diagnose the coronal magnetic fields, reveal the basic nature of solar eruptions and the related non-thermal energy release, particle accelerations and propagation, and the related emission mechanisms. These results might be the important input to the space weather modeling for predicting the occurrence of disastrous powerful space weather events. In order to provide meaningful reference for other solar physicists and space weather researchers, this paper mainly focus on discussing the potential scientific problems of solar radio spectral-imaging observations in dm-cm wavelengths and its possible applications in the field of space weather. These results will provide a helpful reference for colleagues to make full use of the latest and future observation data obtained from the above solar radio telescopes.

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arXiv2023

Imaging Preflare Broadband Pulsations in the Decimetric-metric Wavelengths

Preflare activities contain critical information about the pre-cursors and causes of solar eruptions. Here we investigate the characteristics and origin of a group of broadband pulsations (BBPs) in the decimetric-metric wavelengths, taking place during the preflare stage of the M7.1 flare dated on 2011 September 24. The event was recorded by multiple solar instruments including the Nan\c{c}ay Radioheliograh that measure the properties of the radio source. The BBPs start $\sim$24 min before the flare onset, extending from $<$ 360 to above 800 MHz with no discernible spectral drift. The BBPs consist of two stages, during the first stage the main source remains stationary, during the second stage it moves outward along with a steepening extreme-ultraviolet (EUV) wave driven by the eruption of a high-temperature structure. In both stages, we observe frequent EUV brightenings and jets originating from the flare region. During the second stage, the BBPs become denser in number and stronger in general, with the level of the polarization increasing gradually from $<$ 20% to $>$ 60% in the right-handed sense. These observations indicate the steepening EUV wave is important to the BBPs during the second stage, while the preflare reconnections causing the jets and EUV brightenings are important in both stages. This is the first time such a strong association of an EUV wave with BBPs is reported. We suggest a reconnection plus shock-sweeping-across-loop scenario for the cause of the BBPs.

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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{\deg} perspective in the ecliptic plane. It will deploy three 120{\deg}-separated spacecraft on the 1-AU orbit. The first spacecraft, S1, locates 30{\deg} upstream of the Earth, the second, S2, 90{\deg} 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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arXiv2022

Diagnostic functions of solar coronal magnetic fields from radio observations

In solar physics, it is a big challenge to measure the magnetic fields directly from observations in the upper solar atmosphere, including the chromosphere and corona. Radio observations are regarded as the most feasible approach to diagnose the magnetic field in solar chromosphere and corona. However, because of the complexity and diversity of the emission mechanisms, the previous studies have only presented the implicit diagnostic functions of the magnetic field for specific mechanism from solar radio observations. This work collected and sorted out all methods for diagnosing coronal magnetic field from solar radio observations, which are expressed as a set of explicit diagnostic functions. In particular, this work supplemented some important diagnostic methods missed in other reviews. This set of diagnostic functions can completely cover all regions of the solar chromosphere and corona, including the quiet region, active region and flaring source regions. At the same time, it also includes incoherent radiation such as bremsstrahlung emission of thermal plasma above the quiet region, cyclotron and gyro-synchrotron emissions of magnetized hot plasma and mildly relativistic nonthermal electrons above the active regions, as well as coherently plasma emission around flaring source regions. Using this set of diagnostic functions and the related broadband spectral solar radio imaging observations, we can derive the magnetic fields of almost all regions in the solar atmosphere,which may help us to make full use of the spectral imaging observations of the new generation solar radio telescopes (such as MUSER, EVOSA and the future FASR, etc.) to study the solar activities, and provide a reliable basis for the prediction of disastrous space weather events.

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arXiv2021

The early evolution of solar flaring plasma loops

Plasma loops are the elementary structures of solar flaring active regions which dominate the whole processes of flaring eruptions. The standard flare models are well explained the evolution and eruption after magnetic reconnection around the hot cusp-structure above the top of plasma loops, however, the early evolution of the plasma loops before the onset of magnetic reconnection has been poorly understood. Considering that magnetic-gradients are ubiquitous in solar plasma loops, this work applies the magnetic-gradient pumping (MGP) mechanism to study the early evolution of flaring plasma loops. The results indicate that the early evolution depend on the magnetic field distribution and the geometry of the plasma loops which dominates the balance between the accumulation and dissipation of energy around loop-tops. Driven by MGP process, both of the density and temperature as well as the plasma beta value around the looptop will increase in the early phase of the plasma loops evolution. In fact, the solar plasma loops will have two distinct evolutionary results: the low, initial dense plasma loops with relatively strong magnetic fields tend to be stable for their maximum beta value always smaller than the critical value, while the higher, initial dilute solar plasma loops with relatively weak magnetic fields tend to be unstable for their beta values exceeding the critical value at a time of about one hour after the formation of the solar magnetized plasma loop. The latter may produce ballooning instability and finally trigger the following magnetic reconnection and eruptions. These physical scenarios may provide us a new viewpoint to understand the nature and origin of solar flares.

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arXiv2021

Energy and spectral analysis of confined solar flares from radio and X-ray observations

The energy and spectral shape of radio bursts may help us understand the generation mechanism of solar eruptions, including solar flares, CMEs, eruptive filaments, and various scales of jets. The different kinds of flares may have different characteristics of energy and spectral distribution. In this work, we selected 10 mostly confined flare events during October 2014 to investigate their overall spectral behavior and the energy emitted in microwaves by using radio observations from microwaves to interplanetary radio waves, and X-ray observations of GOES, RHESSI, and Fermi/GBM. We found that: All the confined flare events were associated with a microwave continuum burst extending to frequencies of 9.4 - 15.4 GHz, and the peak frequencies of all confined flare events are higher than 4.995 GHz and lower than or equal to 17 GHz. The median value is around 9 GHz. The microwave burst energy (or fluence) as well as the peak frequency are found to provide useful criteria to estimate the power of solar flares. The observations imply that the magnetic field in confined flares tends to be stronger than that in 412 flares studied by Nita et al. 2004. All 10 events studied did not produce detectable hard X-rays with energies above 300 keV indicating the lack of efficient acceleration of electrons to high energies in the confined flares.

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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.

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arXiv2020

Sub-second time evolution of Type III solar radio burst sources at fundamental and harmonic frequencies

Recent developments in astronomical radio telescopes opened new opportunities in imaging and spectroscopy of solar radio bursts at sub-second timescales. Imaging in narrow frequency bands has revealed temporal variations in the positions and source sizes that do not fit into the standard picture of type III solar radio bursts, and require a better understanding of radio-wave transport. In this paper, we utilise 3D Monte Carlo ray-tracing simulations that account for the anisotropic density turbulence in the inhomogeneous solar corona to quantitatively explain the image dynamics at the fundamental (near plasma frequency) and harmonic (double) plasma emissions observed at \sim 32~MHz. Comparing the simulations with observations, we find that anisotropic scattering from an instantaneous emission point source can account for the observed time profiles, centroid locations, and source sizes of the fundamental component of type III radio bursts (generated where f_{pe} \approx 32~MHz). The best agreement with observations is achieved when the ratio of the perpendicular to the parallel component of the wave vector of anisotropic density turbulence is around 0.25. Harmonic emission sources observed at the same frequency (\sim 32~MHz, but generated where f_{pe} \approx 16~MHz) have apparent sizes comparable to those produced by the fundamental emission, but demonstrate a much slower temporal evolution. The simulations of radio-wave propagation make it possible to quantitatively explain the variations of apparent source sizes and positions at sub-second time-scales both for the fundamental and harmonic emissions, and can be used as a diagnostic tool for the plasma turbulence in the upper corona.

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arXiv2020

Microwave diagnostics of magnetic field strengths in solar flaring loops

We have performed microwave diagnostics of the magnetic field strengths in solar flare loops based on the theory of gyrosynchrotron emission. From Nobeyama Radioheliograph observations of three flare events at 17 and 34 GHz, we obtained the degree of circular polarization and the spectral index of microwave flux density, which were then used to map the magnetic field strengths in post-flare loops. Our results show that the magnetic field strength typically decreases from ~800 G near the loop footpoints to ~100 G at a height of 10--25 Mm. Comparison of our results with magnetic field modeling using a flux rope insertion method is also discussed. Our study demonstrates the potential of microwave imaging observations, even at only two frequencies, in diagnosing the coronal magnetic field of flaring regions.

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