Solar Physics最新文献

We study the long-term variation of the zonal and meridional flows from Solar Cycle 23 to 25 derived with ring-diagram analysis applied to Global Oscillation Network Group (GONG) and Helioseismic and Magnetic Imager (HMI) Dopplergrams. We focus mainly on the subsurface flows averaged over depths from 2.0 Mm to 11.6 Mm since their long-term variations are sufficiently similar. First, we examine their temporal variations for systematic artifacts. We find that the GONG-derived zonal flows increase almost linearly with time until about 2020, which we correct with a linear regression. Then we determine the average differences between the GONG- and HMI-derived flows. The average offset is (0.15 pm 0.53) m s⁻¹ for the zonal flow and (0.65 pm 0.08) m s⁻¹ for the meridional flow within (pm 30.0^{circ }) latitude. The average difference of the meridional flow is nearly constant with latitude in this range, whereas that of the zonal flow varies similarly to that of the magnetic activity. At latitudes of 45.0^∘ and higher, the differences increase and are larger than those at lower latitudes, which is most likely due to the combined effect of different spatial resolution between GONG and HMI and geometric projection effects. Finally, we combine the GONG- and HMI-derived flows and find, as expected, that the solar-cycle variation is the dominant long-term variation. At each latitude within (pm 30.0^{circ }), the meridional-flow pattern appears ahead of the zonal-flow pattern by an average lag of (0.926 pm 0.126) years. The equatorward and poleward branches of the solar-cycle variation occur at 52.5^∘ with the poleward branches present near 60.0^∘ and the equatorward ones at lower latitudes. The zonal flows at 52.5^∘ and 60.0^∘ show an additional trend and decrease by (2.9 pm 0. 3) m s⁻¹ over 11 years. This decrease might nevertheless be related to the solar cycle and imply that the flow amplitudes are anticorrelated with the strength of the associated solar cycle.

This study explores the multi-fractal properties of cosmic-ray (CR) counts collected from two mid-latitude neutron-monitor stations, Newark (NEWK) and Irkutsk 3 (IRK3), and two high-latitude stations, Thule (THUL) and Inuvik (INVK), during periods of severe geomagnetic storms. By employing multi-fractal along with time-series analysis, we did an in-depth examination of CR count variations to demonstrate the effectiveness of these methods in analyzing complex signals associated with astrophysical and solar phenomena. The findings reveal that CR count rates across stations at different latitudes exhibit multi-fractal characteristics, reflecting a range of scaling exponents that capture varying degrees of correlation and variability within the system. The results underscore that solar activity, geomagnetic events, and interactions with Earth’s magnetic field play a more crucial role in determining multi-fractality than the geographic location of the measurement station. Moreover, the study shows that geomagnetic events exert a stronger influence on the multi-fractal properties of CR count rate than the geographic location of station, underscoring the impact of solar storms and Earth’s magnetic field on the distribution and intensity of CRs. This work emphasizes the value of multi-fractal analysis as a powerful tool for investigating the complex nature of CR counts and its sensitivity to both extraterrestrial and terrestrial factors.

Effective predicting sunspot numbers (SSN) is the complex task of studying space weather, solar activity, satellite communication, and Earth’s climate. Developing a reliable SSN forecasting model is difficult because SSN time series exhibit complex patterns, nonlinearity, and nonstationarity characteristics. The state-of-the-art shows that deep-learning models often need help capturing SSN data’s intricate dynamics and long-term dependencies. The SSN time series’ decomposed trend and seasonal and residual characteristics may provide better information on long-term dependencies and associated dynamics for effective learning. In this research, the vipin-deep-decomposed-recomposed rolling-window (vD2R2w) models have been proposed with a combination of time-series decomposition, deep-learning models, and a rolling-window method to predict the SSN accurately. The proposed vD2R2w models have been evaluated over four datasets and consistently outperform traditional deep-learning models. The model improves the performance in terms of RMSE, MAPE, and (R^{2}) over the datasets as SSN_Daily: 84.18% (RMSE), 10.38% (MAPE), and 3.504% ((R^{2})); SSN_Monthly: 39.5% (RMSE), 26.06% (MAPE), and 7.258% ((R^{2})); SSN_MonthlyMean: 178.32% (RMSE), 54.83% (MAPE), and 1.56% ((R^{2})); and SSN_Yearly: 6.06% (RMSE), 10.36% (MAPE), and 1.366% ((R^{2})). Further, the superiority of the vD2R2w models is validated through AIC & BIC, Diebold Mariano test, and Friedman ranking statistical tests. Additionally, the vD2R2w model has forecasted the peak value of Solar Cycles (SC) and time, i.e., SC25: 127.16 (± 6.83) in 2025 and SC26: 191.71 (± 43.37) in 2035. The analysis of proposed model performances and statistical validation over various measures with four SSNs have concluded that the vD2R2w model outperforms the traditional models and is a reliable framework for SSN time series forecasting. Implementing the proposed model may benefit domains such as space-weather monitoring, satellite communication planning, and solar energy forecasting that rely on accurate SSN predictions.

Solar type V radio bursts are associated with type III bursts. Several processes have been proposed to interpret the association, electron distribution, and emission. We present the observation of a unique type V event observed by e-CALLISTO on 7 May 2021. The type V radio emission follows a group of U bursts. Unlike the unpolarized U bursts, the type V burst is circularly polarized, leaving room for a different emission process. Its starting edge drifts to higher frequency four times slower than the descending branch of the associated U burst. The type V processes seem to be ruled by electrons of lower energy. The observations conform to a coherent scenario where a dense electron beam drives the two-stream instability (causing type III emission) and, in the nonlinear stage, becomes unstable to another instability, previously known as the electron firehose instability (EFI). The secondary instability scatters some beam electrons into velocities perpendicular to the magnetic field and produces, after particle loss, a trapped distribution prone to electron cyclotron masering (ECM). A reduction in beaming and the formation of an isotropic halo are predicted for electron beams continuing to interplanetary space, possibly observable by Parker Solar Probe and Solar Orbiter.

This study investigates penumbrae and light bridges based on photospheric and chromospheric flow fields and photospheric magnetic fields in active region NOAA 13096. The improved High-resolution Fast Imager (HiFI+) and the GREGOR Infrared Spectrograph (GRIS) acquired high-resolution imaging and spectropolarimetric data at the 1.5-meter GREGOR solar telescope at the Observatorio del Teide, Izaña, Tenerife, Spain. Background-Subtracted Activity Maps (BaSAMs) have been used to locate areas of enhanced activity, Local Correlation Tracking (LCT) provides horizontal proper motions, and near-infrared full-Stokes polarimetry offers access to magnetic fields and line-of-sight velocities. The results show that the decaying active region is characterized by a triangular region between the three leading, positive-polarity sunspots with unfavorable conditions for penumbra formation. This region has a spongy appearance in narrow-band H(alpha ) images, shows signs of enhanced activity on small spatial scales, is free of divergence centers and exploding granules, lacks well-ordered horizontal flows, has low flow speeds, and is dominated by horizontal magnetic fields. Umbral cores are inactive, but the interface between pores and penumbral filaments often shows enhanced activity. Moat flows and superpenumbrae are almost always observed, when penumbral filaments are present, even in very small penumbral sectors. However, evidence of the moat flow can also be seen around pores, surviving longer than the decaying penumbral filaments. Light bridges have mainly umbral temperatures, reaching quiet-Sun temperatures in some places, show strong intensity variations, and exhibit weak photospheric horizontal flows, while narrow-band H(alpha ) flow maps show substantial inflows.

With the steady improvement of the observing capabilities and numerical simulations, an efficient data management of large data volumes has become mandatory. The Institute for Solar Physics (KIS) has developed the Science Data Centre (SDC), a data infrastructure to store, curate, and disseminate science-ready data from the German solar-observing facilities and other partner institutions. The SDC was also conceived to create and disseminate higher-level data products of added value like inversions from spectropolarimetric data. The SDC archive infrastructure consists of a back-end based on the Rucio science data-management and MongoDB systems and a front-end web interface that allows the user to search and discover data based on search parameters like instrument, date, wavelength range, and target. The SDC archive also provides data access via API and TAP services. The SDC currently offers access to 1299 science-ready datasets from the GRIS instrument at the GREGOR telescope (Tenerife) since 2014, a set of 610 spectra from the LARS at the Vacuum Solar Telescope (VTT, Tenerife) and 202 404 full-disc solar images from the Chromospheric Telescope (ChroTel). The SDC also offers to the community Milne–Eddington inversions of the GRIS spectropolarimetric archived data that can be downloaded as well as tools for data visualization and advanced analysis (e.g., GRISView tool). Many SDC activities have been carried out within the framework of large international data projects like the Horizon 2020 ASTERICS and ESCAPE EU-funded projects under the FAIR (Findable, Accessible, Interoperable, Reusable) principles. New and planned SDC activities include the ingestion of solar data from GREGOR context imaging instruments, flare observations from Ondřejov Observatory (Czech Republic), archiving and dissemination of in-house magnetohydrodynamic simulations, and creation of high-level data products using machine learning. The KIS Science Data Centre is a state-of-the-art data-management infrastructure that curates, archives, and provides access to ground-based science-ready spectropolarimetric and imaging solar data. SDC also provides advanced data visualization and analysis tools and invites data providers to publish their data to the solar and broader (astro)physics community via the SDC data archive.

The study of the solar corona is a prominent focus in the field of solar physics. However, conducting ground-based observations of the corona is a challenging task due to the interference caused by the diffused sky brightness, which obscures the faint coronal signal. As a result, such observations are primarily carried out during total solar eclipses. The requirement of a sky-brightness level as low as (10^{-6}) times the solar disk brightness ((B_{odot })) is met by few places on Earth, and currently there are only two sites hosting solar observatories that satisfy this criterion, Mauna Loa and Haleakala, both located in Hawaii. Nevertheless, another candidate coronagraphic site was discovered in the Concordia Station at Dome C plateau, Antarctica ((simeq 3300) m a.s.l.). In this article, we show the last results of the Extreme Solar Coronagraphy Antarctic Program Experiment (ESCAPE) during the 38th summer campaign of the Italian Piano Nazionale di Ricerche in Antartide (PNRA). Here, we report a model for estimating the air column, which allows for the first time to account for variations in the Sun’s altitude above the horizon during different observation periods, and we use it to compare the obtained results with previous campaigns. Our results confirm that Dome C is an ideal coronagraphic site with the required sky-brightness level, reaching (1.0-0.7times 10^{-6}B_{odot }) in optimal conditions.

The first adiabatic exponent profile, noted ({{Gamma }_{1}}), computed along adiabatic coordinates ((T), (rho )), is in the focus of our study. Under conditions of almost fully ionized hydrogen and helium, the ({{Gamma }_{1}}) profile is quite sensitive to heavy elements ionization. ({{Gamma }_{1}}) decreases in regions where an element is partially ionized. The recent helioseismic structural inversion is obtained with an accuracy better than ({{10}^{-4}}) in the most of the adiabatic convective zone that allows to study ionization variations. The aim is to determine the major heavy elements content in the solar convective zone. The method of our research is synthesis of the (Gamma _{1}) profile, which is based on a linear combination of the contributions of individual heavy elements. The idea of the approach was proposed and justified by Baturin et al. (2022). We find the best approximation of the inverted profile ({{Gamma }_{1}}) adjusting the abundances of major elements (C, N, O, Ne), meanwhile the abundances of elements heavier than neon are fixed. We synthesize the theoretical ({{Gamma }_{1}}) profile using the SAHA-S equation of state, and are able to reproduce the inverted profiles with an accuracy of ((1-2)cdot {{10}^{-5}}). Total mass fraction of heavy elements found with this method is (Z=0.0148pm 0.0004). The oxygen logarithmic abundance is (8.70pm 0.03), carbon (8.44pm 0.04), nitrogen (8.12pm 0.08), and neon (8.17pm 0.09). The obtained estimations of oxygen and carbon agree with spectroscopic abundances by Asplund, Amarsi, and Grevesse (2021).

The aim of this work is to study the dispersion of acoustic waves in the rarefied high-temperature plasma of the solar corona and its role in propagating intensity disturbances (PDs) occurring in this region. We believe that a multi-periodicity in wavelet spectra, recorded when observing PDs in coronal holes and loops, is due to a result of the combined effect of dispersion and damping of compression waves. Observations show the presence of continuous spectra, where periods are distinguished by suitable maxima. The shape of the spectra is characteristic of localized disturbances. This study is based on our previously proposed clear model of nonadiabatic waves in high-temperature plasma, which takes into account the properties of thermal conduction, radiative cooling, and constant heating. Thermal conduction forms a local minimum of group speed, separating groups of waves with short and long periods. Waves of the first group have strong dispersion and weak damping while waves of the second group have the opposite properties. This effect leads to the fact that the initial pulse disturbance eventually acquires a form in which the indicated groups are clearly separated. Two maxima appear in the wavelet spectrum which determine the short period (P_{s}) and the long period (P_{l}). Two groups of waves with dominant periods propagate at the same speed, which is less than the sound speed. We assume that the form of PDs can indeed arise in the corona under the influence of small-scale disturbances in the lower atmosphere. The speed of the observed disturbances is also less than the sound speed. This is usually explained by the projection effect, but can also be explained by the fact that PDs propagate with a group speed. The time signals in the corona recorded by observing PDs bear little resemblance to the superposition of just a few harmonic components. The observed periods are not regular, they can change several times during the entire observation time (often 2 – 3 hours). We propose to consider PDs as a sequence of independent pulse disturbances. Two periods occur only in a given pulse, the duration of which is on the order of a long period (P_{l}), often 20 – 30 minutes. They may change in the next pulse, since they depend on the length of the initial pulse formed at the boundary of the corona and the lower atmosphere.

We investigate the angular rotation velocities of stable recurrent sunspot groups characterized by a leading unipolar sunspot with an initially well-developed penumbra, similar to the H or J types in the Zürich classification. These structures are tracked for two (class I) or three (class II) solar rotations. The Debrecen Photoheliographic Data sunspot catalogue (1977 – 2017) used in this study provides the daily positions and areas of observable sunspots and sunspot groups with great precision. This allows the calculation of the angular rotation synodic velocities from a least-squares fit to the sunspot positions over a given disk passage. After converting to sidereal coordinates, the velocities were used to obtain the solar rotation parameters via a least-squares fit to the solar differential rotation law. Comparison is made with the solar differential rotation laws obtained in two previous studies considering the same classes of sunspot groups, and over comparable time periods, using the data from the Greenwich Photoelectric Results (GPR) catalogue. We find that, on average, the sunspots exhibit a braking tendency, aligning with previous findings. The common results across the three studies, when examined in the context of simulations for sunspot formation and evolution, suggest a scenario in which recurrent unipolar sunspots are anchored at a shallow subsurface layer. The observed braking effect is attributed to gradual fragmentation, leading to disconnection and a transition to dynamics increasingly influenced by surface flows.