Solar Physics最新文献

Accurate identification of solar radio bursts (SRBs) is of great significance for solar physics research and space-weather forecasting. Most existing studies focus on the mere detection of SRB occurrence or the identification of a single class (e.g., Type III bursts), which fails to meet the demand for precise detections of various solar radio bursts. Additionally, current mainstream SRBs detection models often employ complex architectures and redundant parameters, resulting in low computational efficiency. To address these limitations, we constructed a spectrogram dataset based on the e-CALLISTO platform, comprising Type II, Type III, Type IV, and Type V bursts. The dataset contains 8752 images with 10,822 annotated instances, where samples of types IV and V are incredibly scarce. To overcome the challenge of pretraining with few-shot classes, this paper proposes a pretraining method that integrates a stable diffusion generative model with a self-supervised learning strategy, effectively enhancing the model’s learning capability for few-shot classes. Building on this, this paper presents a detection model for various solar radio bursts, VitDet-SRBs (Vision Transformer Detector for Solar Radio Bursts), which incorporates a channel attention mechanism into the feature fusion module to enhance performance while controlling model complexity. Experimental results show that VitDet-SRBs achieve an average precision at a single Intersection-over-Union threshold of 0.50 (AP@50, AP with IoU = 0.50) of 81.2% on the SRBs dataset, outperforming existing mainstream methods in both precision and recall. This study not only provides a novel approach for efficient detections of various solar radio bursts but also offers a feasible solution for other few-shot astronomical data processing problems, with broad application prospects.

Solar radio type II bursts are slow-drifting bursts that exhibit various distinct features such as Fundamental (F) and Harmonic (H) emissions, band-splitting, and discrete fine structures in the dynamic spectra. Observationally, it has been found that in some cases the F emission is stronger than the H emission, and vice versa. The reason for such behavior has not been thoroughly investigated. To investigate this, we studied 58 meter wave (20 – 500 MHz) type II solar radio bursts showing both F and H emissions, observed during the period from 13 June 2010 to 25 December 2024, using data obtained with the Compound Astronomical Low frequency Low cost Instrument for Spectroscopy and Transportable Observatory (CALLISTO) spectrometers at different locations and Gauribidanur LOw-frequency Solar Spectrograph (GLOSS). We examined the intensity ratios of the H ((I_{mathrm{H}})) and F ((I_{mathrm{F}})) emissions and analyzed their variation with heliographic longitude. We found that 14 out of 19 bursts originating from heliographic longitudes beyond (pm 75^{circ }) exhibited an (I_{mathrm{H}}/I_{mathrm{F}}) ratio greater than unity. In contrast, 32 out of 39 bursts originating from longitudes within (pm 75^{circ }) showed a intensity ratio less than unity. From these results, we conclude that the relative strength of the F and H emissions can be influenced by refraction due to density gradient in the solar corona, directivity and viewing angle of the bursts.

Increasing interest in understanding the formation and dynamics of cool coronal condensations like solar prominences leads to complex magneto-hydrodynamical (MHD) simulations which assume a variety of physical processes responsible for energy balance. Formation of cool structures and their maintenance over the observed periods requires detailed treatment of heating/cooling processes of which the radiative ones are critically important. Most of up-to-date models use the so-called optically-thin radiative losses to account for radiative cooling. In this article, we present radiative-transfer simulations which demonstrate the importance of optically-thick line and continuum transitions. We model the process of free relaxation of prominence kinetic temperature towards the radiative equilibrium which demonstrates the formation of condensations in case where the radiative processes dominate the energy balance. We show a grid of isobaric models and how they relax to radiative equilibrium where the radiative losses are balanced by radiative gains. We also compare our results with previous works. Finally we stress the importance of realistic net radiative cooling rates for MHD modeling of cool coronal condensations.

We review the development of the non-LTE (i.e. departures from Local Thermodynamic Equilibrium) radiative-transfer modeling of cool coronal condensations, namely solar prominences. The period considered covers five decades, but we particularly focus on current trends and advancements. Our main goal is to critically discuss various issues of the model geometries and how the assumed geometry couples to the specification of the incident illumination from the surrounding atmosphere. We start with initial one-dimensional (1D) models and continue with the discussion of 2D models and the current 3D approaches. A special attention is devoted to highly heterogeneous prominence structures and to fast-moving eruptive prominences currently well observed by the Metis and EUI instruments onboard Solar Orbiter and by the ASPIICS large coronagraph onboard the Proba-3 formation-flight mission.

Solar activity and related space weather have a significant impact on the Solar System and Earth. Therefore, reliable prediction of solar activity is becoming increasingly important. To predict the remainder of Solar Cycle 25 and the amplitude and timing of the maximum of Solar Cycle 26, we applied the Simplex Projection method to the monthly mean sunspot number (SSN). While most prediction studies rely on 13-month smoothed SSN, we deliberately used unsmoothed monthly mean SSN for long-term solar cycle postcasts and obtained quite successful single and double cycle predictions for Solar Cycles 20 – 24. We defined the “split point” between the library and prediction sets as an important setting parameter; when this parameter was optimized, prediction ability improved significantly. We predicted that Solar Cycle 26 will be slightly weaker than Solar Cycle 25 and stronger than Solar Cycle 24. Its cycle profile is expected to show either a well-defined double peak or a slightly fluctuating flat peak, both resembling Solar Cycle 20. We predicted that the Solar Cycle 25 minimum will occur in the mid-2030. For Solar Cycle 26, the maximum is predicted for June 2035 with 150.6 – 181.5 monthly mean SSN (13-month smoothed 137.4 – 146.2), and the minimum for late 2040. The similarity between Solar Cycles 20 and 26 may reflect Gleissberg Cycle modulation.

We report long duration observations of changes in the 5303 Å (Fe XIV) solar coronal emission line parameters at heliocentric distance (r{approx }1.07text{R}_{odot }), using data obtained with the Visible Line Emission Coronagraph (VELC) onboard Aditya-L1 in the sit and stare mode. The observed changes are due to a flare near the east limb of the Sun. The intensity and width of the line are enhanced during the event. There is no change in the Doppler velocity. Our analysis indicates that the increase in line width is most likely due to an increase in temperature due to flare heating.

Solar type II radio bursts are associated with shock waves driven by coronal mass ejection (CME). Their shapes in the solar radio dynamic spectrum depend on the shock velocity and the electron density traversed by their radio sources. This study examines a stationary type II radio burst. By analyzing observations from the Daocheng Solar Radio Telescope and the Solar Dynamics Observatory/Atmospheric Imaging Assembly, we aim to determine the spatial relationship between type II burst sources and shock fronts. Observations suggest that the radio sources are located in the interaction region between the CME shocks and the coronal streamer. Extensive analysis of their fine structures, particularly the type II herringbones, shows that the radio sources are generally distributed in a frequency order from downstream to upstream regions of the shocks, or only in the upstream region. The observations confirm the existence of type II bursts and associated energetic electrons in the regions upstream and downstream of a shock wave.

Solar filaments are cool and dense plasma structures suspended in the solar corona against gravity. We present observations of a quiescent filament eruption that occurs on 13 July 2015. The eruption is associated with a two-ribbon GOES B8.9 class flare. Photospheric magnetic-flux cancellation is present below the filament during days. This builds up a flux rope which progressively rises until it gets unstable, first leading to a confined eruption and pre-flare brightenings, then to an ejection which starts ≈ 20 min later with the flare onset. An interesting feature of this event is the presence of a large circular brightening formed around the erupting region. This brightening is produced due to interchange reconnection of the ejected magnetic configuration with the surrounding open magnetic field. This null-point topology is confirmed by a potential-field extrapolation. The EUV loops located on the southern side of the filament eruption first contract during the null-point reconnection, then expand as the flux rope is ejected. The associated CME has both a classical flux rope shape and plasma ejected along open field lines on the flux rope side (a trace of interchange reconnection). Finally, we set all this disparate observations within a coherent framework where magnetic reconnection occurs both below and above the erupting filament.

This study investigates the properties of waves that propagate along a density interface in partially ionised plasmas, separating two regions of different properties, including ionisation degree. Our analysis covers frequencies that are much smaller than the collisional frequency of particles, so we are using a single-fluid approximation, where the partial ionisation aspect of the plasma appears through the ambipolar diffusion in the generalised Ohm’s law. The derived dispersion relation is solved numerically. Our results show that guided waves along a density interface undergo very little change in their propagation speed (frequency); however, their damping rate shows variation with the ionisation degree and plasma-(beta ) parameter. We find that waves can only propagate when plasma-(beta >1.2), indicating pressure-driven dynamics relevant to photospheric structures with moderate magnetic fields. The damping rate increases with higher neutral particle content but decreases with higher plasma-(beta ) values. For ionisation degrees close to fully ionised plasma, the damping is minimal but becomes more significant as the neutral particle concentration increases. These findings provide important insights into wave behaviour in partially ionised plasma interfaces and lay the groundwork for future studies of wave propagation in partially ionised plasma slab waveguides.

Joy’s law is a well-established statistical property of solar active regions that any theory of active region emergence must explain. This tilt angle of the active region away from an east-west alignment is a critical component for converting the toroidal magnetic field to poloidal magnetic field in some leading dynamo theories, and observations show its importance for the reversal of the sign of the global solar magnetic dipole. This review aims to synthesise observational results related to the onset of Joy’s law, placing them within the broader context that describes active region emergence as a largely passive process occurring near the surface of the Sun.