Solar Physics最新文献

Based on data obtained from Wilcox Solar Observatory, the solar polar magnetic field reversals in Cycles 21 – 25 are considered. The results indicate that the polarity reversal occurs at the maximum of sunspot activity of each cycle, but the beginning, end, and duration of the reversals did not demonstrate any association with the Wolf numbers, which are characteristics of local magnetic fields. Moreover, during the periods of polarity reversal, the correlation between global magnetic field (GMF) parameters and Wolf numbers decreased and even moved into an anti-correlation mode.

The polarity reversal occurred during periods of sharp structural changes in the GMF, accompanied by a redistribution of the positive- and negative-polarity magnetic field domination in the North and South hemispheres. All parameters of the GMF demonstrate characteristic changes associated with polarity reversal.

The polar field reversals are determined by the GMF flows of positive- and negative-polarity magnetic fields, which cyclically migrate from one pole to the opposite pole. The magnetic fields of the new polarity are delivered to the poles by a certain flow, and then carried away by the same flow to the opposite pole. In each cycle, the increase in the polar magnetic field strength to its maximal values at the solar activity minimum and following decrees to the cycle maximum coincides with the latitudinal changes in corresponding magnetic field flow. The differences in start, duration, and end times of the polarity reversal at each pole are a consequence of the different width and speed of the corresponding flow.

Interaction with magnetic fields of active regions during the passage of the GMF pole-to-pole meridional flows through low latitudes leads to the formation of longitudinal magnetic structures and a sectorial structure of the GMF.

Equations for calculating the meridional circulation of positive- and negative-polarity magnetic field flows are proposed. They allow to predict the time of polarity reversals, and since polarity reversals occur at the maxima of cycles, then also predict the time of maxima of both the future and past cycles.

We present a novel Bayesian model and a corresponding robust, probabilistic calibration procedure for the CORSAIR polarimeter that can be applied to other polarimeters. Our calibration procedure combines existing Mueller matrix representations of polarimeters with Bayesian methods, and computes the posterior distribution of the parameters by collecting data from the polarimeter at different states. We show that the algorithm is able to converge and recover a well-constrained posterior of the free parameters with a credible interval that is consistent with the ground truth values. Posterior predictive checks indicate that our generative model with inferred parameters can reproduce the calibration data within the predictive uncertainty, and captures the dominant systematic effects of the calibration procedure. We further show that we can propagate calibration uncertainties in the distributions to downstream reconstructions of Stokes measurements and magnetic-field estimates. We find that the contribution of calibration uncertainty towards the reconstructed results is minimal relative to that of the photon noise uncertainty, indicating that estimates using our Bayesian calibration algorithm can achieve photon noise-limited measurements in the magnetic-field parameters. Finally, we test the Bayesian calibration algorithm on a lab prototype of the CORSAIR polarimeter, and show that it converges and closely recovers theoretical estimates of the free parameters from real-world measurements.

We performed a Sun-to-Earth analysis of Earth-directed eruptive events observed with the H(alpha ) solar telescope at the Hvar Observatory, examining the consistency between their remote and in situ signatures. Filaments/prominences (283 events) and flares (91 events) reported in the Hvar catalog (2010 – 2019) were associated with coronal mass ejections (CMEs) listed in the SOHO/LASCO CME catalog, resulting in 42 H(alpha ) eruptive events with CME counterparts. These CMEs were subsequently linked to their interplanetary counterparts (ICMEs) near Earth using the Drag-Based Model (DBM) and its probabilistic implementation, DBEMv4, and cross-checked against three independent ICME catalogs. To refine and confirm these associations, we performed three-dimensional Graduated Cylindrical Shell (GCS) reconstructions, re-ran DBEMv4 using 3D parameters, and analysed in situ ICME signatures. We identified eight reliable H(alpha ) eruptive event–CME–ICME associations, for which we derived the axial field orientation, inclination, and chirality. Only one event (12.5%) exhibited full consistency between the remotely inferred and in situ flux rope properties, increasing to 75% when intermediate inclinations (approximately 45^∘) were considered a match. Our results, consistent with previous studies, reveal substantial variability between flux rope properties derived from remote and in situ observations. This variability likely arises from both measurement uncertainties and intrinsic evolutionary effects, which cannot yet be clearly disentangled. These findings underscore the importance of multi-spacecraft and multi-instrument observations for understanding CME evolution and emphasise the continued value of H(alpha ) imaging in constraining the early physical properties of solar flare signatures exhibit characteristic ribbon structures.

In this paper, we present a unique decimetric radio burst that oscillates not only in time but also in frequency. Its duration, exceeding 80 minutes, is significantly longer than any radio oscillations previously reported in the literature. The oscillation period of the burst was about 3 minutes, suggesting a connection with sunspot oscillations observed in EUV and radio wavelengths. We detected the same periodicity in a 3000 MHz radio source located in a loop anchored to sunspots and spanning the entire active region, where flares occurred during the burst. Based on these observations, we propose that the frequency-oscillating burst is generated in the loop, serving as a reservoir of accelerated electrons, by the electron-cyclotron mechanism. Waves originating in the sunspot penetrate into the loop containing the source of the frequency-oscillating burst, and the resonant period of this loop appears to be close to that of the incoming waves. As a result, the radio emission of the burst oscillated for about 80 minutes with a 3-minute period. The magnetic-field strength in the burst source was estimated to be about 250 G.

We analyze decay phase observations of the GOES class C6.7 flare SOL2022-08-19T20:31 by the Visible Spectropolarimeter (ViSP) on the National Science Foundation’s Daniel K. Inouye Solar Telescope (DKIST). The data include the first flare-time DKIST observations of the chromospheric Ca II H 396.8 nm and H(epsilon ) 397.0 nm spectral lines. These diagnostics have rarely been studied together during the modern era of high-resolution solar flare observations, and never at the spectral and spatial resolution of the DKIST. We directly compare DKIST spectra to state-of-the-art RADYN+RH simulations, including one heated by a nonthermal electron beam and one by in-situ thermal conduction. While certain salient properties of the spectra such as the width of H(epsilon ) are reproduced, the models severely underestimate the width of Ca II H in the red wing and fail to reproduce the exact relative intensity of Ca II H to H(epsilon ). The models exhibit a range of chromospheric electron densities spanning over an order of magnitude. Unlike the modeled lower-order Balmer-series lines, we find that the width of H(epsilon ) is not solely related to the high-density upper chromosphere; the widths and intensities are also sensitive to the deeper flare layers. We outline possible avenues towards improvement of flare models, such as a comprehensive evaluation of flare heating mechanisms in the context of both impulsive and decay phase high-resolution data.

The twin Solar TErrestrial Relations Observatory (STEREO) A and B spacecraft were launched in October 2006 into heliocentric orbits at (sim 1) AU, advancing ahead of or lagging behind Earth, respectively, at (sim 22^{circ })/year. The spacecraft provide in situ observations of the solar wind and energetic particle populations, as well as remote sensing observations of solar activity and the corona. In particular, the High Energy Telescopes (HETs) on the STEREO spacecraft observe 0.7 – 4 MeV electrons and 13 – 100 MeV protons. This article summarizes observations of solar energetic particle (SEP) events made by the STEREO HETs from the beginning of the mission through Solar Cycle 24 to December 2023, approaching the maximum of Solar Cycle 25 and encompassing STEREO A first full orbit of the Sun relative to Earth, completed in August 2023; contact with STEREO B was lost in October 2014. Specifically, the catalog of SEP events including (sim,25text{ MeV}) protons observed by the STEREO HETs and/or instruments on spacecraft near Earth in Richardson et al. (Solar Phys. 289, 3059, 2014) is updated to include (sim 450) SEP events and a total of (sim 1000) separate observations of these events from the various spacecraft locations. These extensive observations can provide unique insight into the propagation of energetic protons in the inner heliosphere and how the properties of the particle events are related to those of the associated solar eruptions. In particular, we examine the association of coronal mass ejections (CMEs) and SEP events with all 397 M and X-class solar X-ray flares in the period June 2010 – January 2014 and demonstrate that, for these events, the occurrence of a CME accompanying a flare is required for the detection of a (sim 25text{ MeV}) proton event. On the other hand, many flares accompanied by CMEs are not followed by detected SEP events. The longitudinal width and intensity of the associated SEP events generally increase with the CME speed and the flare intensity. We also note evidence for a (sim 150) day “Rieger-like” periodicity in the SEP occurrence rate in 2020 – 2023 during the rising phase of Solar Cycle 25.

We investigate the long-assumed relationship between sunspot group properties and coronal mass ejection (CME) speed using a manually verified dataset of 1488 M- and X-class flare-CME associations spanning Solar Cycles 23, 24, and 25. For each event, the associated sunspot area, Hale magnetic classification, and McIntosh class were compiled based on the active region identified at the flare time, animated GOES X-ray flux plots, and movies from the Large Angle and Spectrometric Coronagraph. Contrary to operational forecasting expectations, we find that these traditional photospheric parameters are consistently poor predictors of CME speed. Across all three solar cycles and CME speed categories; Pearson and Spearman correlation coefficients and multivariable regression models show that these metrics only account for less than 4% variance in CME speed. These results demonstrate that even large and magnetically complex active regions do not reliably produce fast CMEs, while some of the fastest events originate from small or simple regions. These results highlight the limitations of traditional sunspot indicators, which exclude key magnetic structures such as plages, in capturing the full eruptive potential of active regions and fail to capture coronal conditions that govern CME acceleration. Improved CME forecasting may require greater emphasis on coronal magnetic topology and non-spot magnetic environments.

In order to investigate the temporal evolution of the solar magnetic field and different classes of solar flares, and to probe the relationship between them, we study the time-series of the sunspot area and solar flares of M and X class observed on the full solar disk during complete Solar Cycle 24 and the ascending phase of current Solar Cycle 25 i.e., from January 2009 to April 2025, following the new NOAA scaling system. We study periodic and quasi-periodic behavior of the solar indices. It has been established that the solar indices referring to the phenomena occurring at different solar layers exhibit different periodicities, which are confined to various phases of the solar cycle. Our investigation indicates that sunspot area as well as the flare index have higher amplitudes during Cycle 25 than Cycle 24. We noticed that both sunspot area (representing solar magnetic activity) and energetic flares show a number of short and intermediate term periodicities during both Cycle 24 and 25. During Cycle 24 and 25, in the high-frequency range, this covers the solar rotation periods as well as prominent 17 – 60-day periods in the flare data sets. On the other hand, in the intermediate-frequency range, we measured a series of significant quasi-periodicities of 76 – 85, 104 – 120, 147 – 176 days, 183 – 196, 237 – 243, 273 – 295, 328 – 392 days and 1.1 – 1.5 year and ∼ 2.7 year in different phases of Cycle 24 and 25. We have observed that the well-known Rieger-type of periods and Quasi-biennial oscillations of about 1.3 years reappeared during the maximum phase of Cycle 25 in both sunspot area and energetic flare data sets. The cross-correlation and cross-wavelet analysis reveal that both M and X class flares are positively correlated with the sunspot areas with phase mixing (asynchronicity) in both cycles. We discuss our results with the existing numerical models.

Sunspot groups often emerge in spatial–temporal clusters, known as nests or complexes of activity. Quantifying how frequently such nesting occurs is important for understanding the organisation and recurrence of solar magnetic fields. We introduce an automated approach based on kernel density estimation and DBSCAN clustering to identify nests in the longitude–time domain and to measure the fraction of sunspot groups that belong to them. The method combines a smooth representation of emergence patterns with a density-based clustering procedure, validated using synthetic solar-like cycles and corrected for variations in data density.

We apply this method to 151 years of sunspot-group observations from the Royal Greenwich Observatory Photoheliographic Results (RGO, 1874 – 1976) and Kislovodsk Mountain Astronomical Station (KMAS, 1955 – 2025) catalogues. Across all cycles and latitude bands, the mean nesting degree is (langle Drangle = 0.61 pm 0.12), implying that about 60 percent all sunspot groups emerge within nests. Nesting is strongest at mid-latitudes (10^∘ – 20^∘), and results from the two independent datasets agree in the period of overlap. The nesting degree significantly correlates with the solar activity level, with the correlation strengthening when small groups are excluded. The characteristic inter-nest spacing contracts from ∼ 200 – 500 Mm at low activity to ∼ 60 – 100 Mm at solar maximum, approaching typical sunspot-group dimensions. The identified nests range from compact clusters to long-lived, drifting structures, offering new quantitative constraints on the persistence and organisation of solar magnetic activity.