Search Results (55)

The Forbush effects (FEs) in cosmic rays associated with interplanetary disturbances caused by the disappearance of solar filaments (DSFs) outside active regions (ARs) are considered. In total, 481 FEs were detected for 1995–2023 using the database of Forbush Effects and Interplanetary Disturbances (FEID). The behavior of the cosmic ray density was calculated using the Global Survey Method (GSM). The distributions of the FE numbers depending on their duration and magnitude, as well as on the characteristics of the interplanetary and near-Earth medium, were obtained. It is found that the average duration of such FEs (33.4 ± 0.5 h) is almost the same as for events associated with CMEs from ARs, but the average magnitude is much smaller (0.83 ± 0.03%). It is also shown that coronal mass ejections (CMEs) caused by DSFs are often low-speed interplanetary disturbances (with an average maximum SW speed of 423.2 ± 3.5 km/s), the velocities of which are close to the speed of the background solar wind (SW). During FEs associated with CMEs after DSFs outside ARs, on average, unsettled geomagnetic activity is observed. Magnetic storms were recorded only in 19% of events. Lower values of FE magnitude and geomagnetic activity are associated with weakened magnetic fields and low speeds of such interplanetary disturbances. Full article

About ten years ago, we established the first coronagraph that has been continuously operating on the high plateau of western China. This coronagraph is an internal occulting, 10 cm aperture instrument, installed at Lijiang Station through a collaboration with the Norikura Station of the National Astronomical Observatory of Japan. To ensure high efficiency in current and future coronal observations, developing integrated observation systems is essential for reliable, autonomous, and remote operation of coronagraphs. This paper introduces an advanced integrated observation and control system, based on the Lijiang 10 cm coronagraph. The coronagraph focuses on the observations for the solar inner corona, capturing the coronal green-line emission within a field range from $1.03R_{⨀}$ to $2.5R_{⨀}$. To enhance the observational precision and efficiency, a comprehensive integrated system has been designed, incorporating various subsystems, including precise pointing and tracking mechanisms, a multi-band filter system, a protective dome system, and a robust data storage infrastructure. This paper details the hardware architecture and software frameworks supporting each subsystem. Results from extended operational testing confirm the stability of the system, its capacity for autonomous and remote observations, and significant improvements in the automation and efficiency of coronal imaging. The automated observation system will be further improved and used for our future coronagraphs to be developed for coronal magnetism diagnosis. Full article

Bipolar emerging flux regions (EFRs) form active regions (ARs) that generally evolve into a pre-existing magnetic environment in the solar atmosphere. Reconfiguration of the small- and large-scale magnetic connectivities is invoked to explain a plethora of energy-release phenomena observed at the sites of EFRs. These include brightening events, surges, and jets, whose triggers and relationships are still unclear. In this context, we study the formation of a proto-spot in AR NOAA 11462 by analyzing spectropolarimetric and spectroscopic measurements taken by the Interferometric Bidimensional Spectrometer along the Fe I 630.2 nm and Ca II 854.2 nm lines on 17 April 2012. We complement these high-resolution data with simultaneous SDO satellite observations. The proto-spot forms from magnetic flux and emerges into the photosphere, coalescing following plasma flows in its surroundings. The chromospheric and higher atmosphere observations show that flux emergence occurs in a pre-existing magnetic environment, with small- and large-scale coronal arcades that seemingly shape the proto-spot formation in the upper atmospheric layers. In addition, in the chromosphere, we observe an arch filament system and repeated intense brightening events and surges, likely due to magnetic interactions of the new flux with the pre-existing overlying coronal field. These phenomena have been observed since the early stages of the new flux emergence. Full article

We estimated the relative location of the solar rotation axis and the magnetic axis of the solar dipole, which were defined as centers of polar coronal holes. We used observations of polar coronal hole data, which were originally obtained with Solar Dynamic Observatory (SDO) spacecraft. To calculate the tilt of the magnetic axis relative to the rotation axis of the Sun, an empirical method for the estimation of the coronal hole centers is proposed. As a result, it was found that these axes do not coincide. The average deviation of the magnetic dipole axis from the rotation axis is ∼5 degrees of latitude. Using the wavelet transform method, it was found that the magnetic axis rotates around the rotation axis with a main period of 15–16 days. This period is related to the sector structure of the global magnetic field in the polar zones of the Sun. Full article

On 1 December 2023, a strong geomagnetic storm was triggered by an interplanetary shock caused by a coronal mass ejection (CME). This study used data from 193 Global Navigation Satellite System (GNSS) observation stations in China to study the three-dimensional morphological total electron content (TEC) disturbances during this storm. By analyzing GNSS TEC data from 15 GNSS stations along the magnetic field lines, it was found that TEC disturbances spread from low to high latitudes, confirmed by ionosonde NmF2 data. The TEC disturbance first appeared at the LJHP station, (21.68° N) at 11:30 UT and propagated to the BJFS station (39.60° N) at 13:30 UT with a propagation speed of about 217 m/s and maximum amplitude of ±0.2 m. The TEC disturbance lasted the longest, approximately 4 h, between latitudes 25° N and 32° N. Additionally, this study investigated the ionosphere’s three-dimensional electron density distribution in the Guangxi region using an ionospheric tomography algorithm. Results showed that the TEC disturbances were mainly concentrated between 450 and 580 km in altitude. At 12:00 UT, the maximum change in electron density occurred at a 580 km height at 26° N, 112° E, increasing by 20.54 total electron content unit (TECU). During the main phase of the geomagnetic storm, the electron density expanded from higher to lower layers, while during the recovery phase, it recovered from the lower layers to the higher layers. Full article

High-energy particles may be accelerated widely in stellar coronae; probably by the same processes we find in the Sun. Here, we have learned of two physical mechanisms that dominate the acceleration of solar energetic particles (SEPs). The highest energies and intensities are produced in “gradual” events where shock waves are driven from the Sun by fast and wide coronal mass ejections (CMEs). Smaller, but more numerous “impulsive” events with unusual particle compositions are produced during magnetic reconnection in solar jets and flares. Jets provide open magnetic field lines where SEPs can escape. Closed magnetic loops contain this energy to produce bright, hot flares; perhaps even contributing to heating the low corona in profuse nanoflares. Streaming protons amplify Alfvén waves upstream of the shocks. These waves scatter and trap SEPs and, in large events, modify the element abundances and flatten the low-energy spectra upstream. Shocks also re-accelerate the residual ions from earlier impulsive events, when available, that characteristically dominate the energetic heavy-ion abundances. The large CME-driven shock waves develop an extremely wide longitudinal span, filling much of the inner heliosphere with energetic particles. Full article

Solar supergranulation is a large-scale convective structure on the solar surface, whose formation mechanism and dynamical properties are closely related to key physical processes such as solar magnetic field evolution, coronal heating, and solar wind acceleration. This paper reviews recent research progress on solar supergranulation, focusing on the latest achievements in high-resolution observations, theoretical models, and numerical simulations. By analyzing the flow field structure, magnetic field distribution, and their relationship with the solar activity cycle, the crucial role of supergranulation in solar physics is revealed. Studies indicate that supergranulation is not only a crucial component of the solar convection zone but also drives coronal heating and solar wind acceleration through mechanisms such as magnetic reconnection and Alfvén wave propagation. Furthermore, the interaction between supergranulation and larger-scale convective patterns (e.g., giant cells) provides new insights into the dynamics of the solar interior. Despite significant progress in recent years, the formation mechanism and dynamical nature of supergranulation remain unresolved. Future research should combine high-resolution observations, theoretical modeling, and numerical simulations to further elucidate the complex dynamical processes and the central role of supergranulation in solar physics. Full article

The origin and acceleration of high-energy particles, constituting cosmic rays, is likely to remain an important topic in modern astrophysics. Among the two categories galactic and solar cosmic rays, the latter are much less investigated. The primary source of solar cosmic ray particles are impulsive explosions of the magnetized plasma, known as solar flares and coronal mass ejections. These particles, however, are characterized by relatively low energies compared to their galactic counterparts. In this work, we explore the resonance wave–wave (RWW) interaction between the polarized electromagnetic radiation emitted by the solar active regions and the quantum waves associated with high-energy, relativistic electrons generated during solar flares. Mathematically, the RWW interaction problem boils down to analyzing a Klein–Gordon Equation (spinless electrons) embedded in the electromagnetic field. We find that RWW could accelerate the relativistic electrons to enormous energies even comparable to energies in the galactic cosmic rays. Full article

The study aims to understand the role of solar wind current sheets (CSs) in shaping the spectrum of turbulent fluctuations and driving dissipation processes in space plasma. Local non-adiabatic heating and acceleration of charged particles in the solar wind is one of the most intriguing challenges in space physics. Leading theories attribute these effects to turbulent heating, often associated with magnetic reconnection at small-scale coherent structures in the solar wind, such as CSs and flux ropes. We identify CSs observed at 1 AU in different types of the solar wind around and within an interplanetary coronal mass ejection (ICME) and analyze the corresponding characteristics of the turbulent cascade. It is found that the spectra of fluctuations of the interplanetary magnetic field may be reshaped due to the CS impact potentially leading to local disruptions in energy transfer along the cascade of turbulent fluctuations. Case studies of the spectra behavior at the peak of the CS number show their steepening at MHD scales, flattening at kinetic scales, and merging of the spectra into a single form, with the break almost disappearing. In the broader vicinity of the CS number peak, the behavior of spectral parameters changes sharply, but not always following the same pattern. The statistical analysis shows a clear correlation between the break frequency and the CS number. These results are consistent with the picture of turbulent reconnection at CSs. The CS occurrence is found to be statistically linked with the increased temperature. In the ICME sheath, there are two CS populations observed in the hottest and coldest plasma. Full article

Solar filaments are a significant solar activity phenomenon, typically observed in full-disk solar observations in the H-alpha band. They are closely associated with the magnetic fields of solar active regions, solar flare eruptions, and coronal mass ejections. With the increasing volume of observational data, the automated high-precision recognition of solar filaments using deep learning is crucial. In this study, we processed full-disk H-alpha solar images captured by the Chinese H-alpha Solar Explorer in 2023 to generate labels for solar filaments. The preprocessing steps included limb-darkening removal, grayscale transformation, K-means clustering, particle erosion, multiple closing operations, and hole filling. The dataset containing solar filament labels is constructed for deep learning. We developed the Attention U²-Net neural network for deep learning on the solar dataset by introducing an attention mechanism into U²-Net. In the results, Attention U²-Net achieved an average Accuracy of 0.9987, an average Precision of 0.8221, an average Recall of 0.8469, an average IoU of 0.7139, and an average F1-score of 0.8323 on the solar filament test set, showing significant improvements compared to other U-net variants. Full article

The solar atmosphere is a complex, coupled, highly dynamic plasma environment, which shows rich structuring due to the presence of gravitational and magnetic fields. Several features of the Sun’s atmosphere can serve as guiding media for magnetohydrodynamic (MHD) waves. At the same time, these waveguides may contain flows of various magnitudes, which can then destabilise the waveguides themselves. MHD waves were found to be ubiquitously present in the solar atmosphere, thanks to the continuous improvement in the spatial, temporal, and spectral resolution of both space-born and ground-based observatories. These detections, coupled with recent theoretical advancements, have been used to obtain diagnostic information about the solar plasma and the magnetic fields that permeate it, by applying the powerful concept of solar magneto-seismology (SMS). The inclusion of asymmetric shear flows in the MHD waveguide models used may considerably affect the seismological results obtained. Further, they also influence the threshold for the onset of the Kelvin–Helmholtz instability, which, at high enough relative flow speeds, can lead to energy dissipation and contribute to the heating of the solar atmosphere—one of the long-standing and most intensely studied questions in solar physics. Full article

Anterior cruciate ligament (ACL) tears are prevalent knee injures, particularly among active individuals. Accurate and timely diagnosis is essential for determining the optimal treatment strategy and assessing patient prognosis. Various previous studies have demonstrated the successful application of deep learning techniques in the field of medical image analysis. This study aimed to develop a deep learning model for detecting ACL tears in knee magnetic resonance Imaging (MRI) to enhance diagnostic accuracy and efficiency. The proposed model consists of three main modules: a Dual-Scale Data Augmentation module (DDA) to enrich the training data on both the spatial and layer scales; a selective group attention module (SG) to capture relationships across the layer, channel, and space scales; and a fusion module to explore the inter-relationships among various perspectives to achieve the final classification. To ensure a fair comparison, the study utilized a public dataset from MRNet, comprising knee MRI scans from 1250 exams, with a focus on three distinct views: axial, coronal, and sagittal. The experimental results demonstrate the superior performance of the proposed model, termed SGNET, in ACL tear detection compared with other comparison models, achieving an accuracy of 0.9250, a sensitivity of 0.9259, a specificity of 0.9242, and an AUC of 0.9747. Full article

Geomagnetic storms (GSs) are major disturbances in the terrestrial atmosphere caused by the reconnection process between the incoming plasma ejecta in the solar wind and the planetary magnetosphere. The strongest GSs can lead to auroral displays even at lower latitudes, and cause both satellite and ground-based infrastructure malfunctions. The early recognition of geoeffective events based on specific features on the solar photosphere is crucial for the development of early warning systems. In this study, we explore 16 magnetic field parameters provided by the Space-weather HMI Active Region Patch (SHARP) database from the SDO/HMI instrument. The analysis includes 64 active regions that produced strong GS during solar cycle (SC) 24 and the ongoing SC25. We present the statistical results between the SHARP and solar parameters, in terms of Pearson and Spearman correlation coefficients, and discuss their space weather potential. Full article

Flares, sometimes accompanied by coronal mass ejections (CMEs), are the result of sudden changes in the magnetic field of stars with high energy release through magnetic reconnection, which can be observed across a wide range of the electromagnetic spectrum from radio waves to the optical range to X-rays. In our observational review, we attempt to collect some fundamental new results, which can largely be linked to the Big Data era that has arrived due to the expansion of space photometric observations over the last two decades. We list the different types of stars showing flare activity and their observation strategies and discuss how their main stellar properties relate to the characteristics of the flares (or even CMEs) they emit. Our goal is to focus, without claiming to be complete, on those results that may, in one way or another, challenge the “standard” flare model based on the solar paradigm. Full article

Coronal loops are bright, filamentary structures formed by thermal plasmas constrained by the sun’s magnetic field. Studying coronal loops provides insights into magnetic fields and their role in coronal heating processes. We propose a new automatic coronal loop detection method to optimize the problem of existing algorithms in detecting low-intensity coronal loops. Our method employs a line-Gaussian filter to enhance the contrast between coronal loops and background pixels, facilitating the detection of low-intensity ones. Following the detection of coronal loops, each loop is extracted using a method based on approximate local direction. Compared with the classical automatic detection method, Oriented Coronal Curved Loop Tracing (OCCULT), and its improved version, OCCULT-2, the proposed method demonstrates superior accuracy and completeness in loop detection. Furthermore, testing with images from the Transition Region and Coronal Explorer (TRACE) at 173 Å, the Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory (SDO) at 193 Å, and the High-Resolution Coronal Imager (Hi-C) at 193 Å and 172 Å confirms the robust generalization capabilities of our method. Statistical analysis of the cross-section width of coronal loops shows that most of the loop widths are resolved in Hi-C images. Full article