Solar Physics最新文献

Many questions must be answered before understanding the relationship between the emerging magnetic flux through the solar surface and the extreme geoeffective events. The main ingredients for getting X-ray class flares and large interplanetary Coronal Mass Ejections (CMEs) are the buildup of electric current in the corona, the existence of magnetic free energy, magnetic energy/helicity ratio, twist, and magnetic stress in active regions (ARs). The upper limit of solar energy in the space research era, as well as the potential for experiencing superflares and extreme solar events, can be predicted using MHD simulations of CMEs.

To address this problem, we consider the recent events of May 2024 and use three MHD models:

1) OHM (“Observationally driven High order scheme Magnetohydrodynamic code”) for investigating the magnetic evolutions at a synthetic dipole structure.

2) TMF (time-dependent magneto-friction) for setting up an initial non-potential magnetic field in the active region. A zero-beta MHD model for tracing the magnetic evolution of active regions.

3) EUHFORIA (“European heliospheric forecasting information asset”) for interplanetary CME propagations.

For the eruptive flares with CMEs, magnetic solar energy is computed along with data-constrained MHD simulations for the May 2024 events. We show the consistency between the data-initiated, realistic simulation of the May 2024 big event and energy scalings from an idealised simulation of a bipolar eruption using OHM. The estimated free magnetic energy did not surpass (5.2 times 10^{32}text{ erg}). Good arrival time predictions ((<3) hours) are achieved with the EUHFORIA simulation with the cone model. We note the interest in coupling all the chains of codes from the Sun to the Earth and developing different approaches to test the results.

Doppler shifts in chromospheric and transition-region lines during solar flares are often interpreted as chromospheric condensation or evaporation. However, alternative sources of Doppler-shifted emission have been suggested, such as filament eruptions, jets or chromospheric bubbles. We analyse high-cadence scans from SORCE/SOLSTICE, which provide one-minute resolution profiles of the transition-region Si iii (1206 Å, (textrm{T} = 10^{4.6},textrm{K})) line. 11 X-, M-, and C-class events observed during these scans with clear impulsive phase Si iii enhancements were identified. By subtracting a quiet-Sun profile and fitting Gaussian profiles to the Si iii line, measurements of flare-induced Doppler shifts were made. After correcting for a systematic trend in these shifts with solar longitude, two of the 11 events were found to exhibit a significant Doppler shift, one with a (201.36pm 21.94;textrm{km,s}^{-1}) redshift and the other with a (-39.75pm 11.00;textrm{km,s}^{-1}) blueshift. Intriguingly, SDO/AIA 304 Å and 1600 Å imaging revealed a bright eruption coincident with the event that exhibited a blueshift, suggesting the shift may have resulted from the eruption rather than evaporation alone. Our results highlight Si iii as a useful diagnostic of flaring dynamics at a temperature that has received limited attention to date. Future comparisons of these observations with radiative hydrodynamic simulations, along with new observations from state-of-the-art spectrometers such as SOLAR-C/EUVST and MUSE, should clarify the mechanisms behind the observed shifts in this study.

We use subsurface-flow velocity maps inferred by time–distance helioseismology from Doppler measurements with the Helioseismic and Magnetic Imager (HMI) of the Solar Dynamics Observatory (SDO) to investigate variations of large-scale convection during Solar Cycles 24 and 25 in the 19-Mm-deep layer. The spatial power spectra of the horizontal-flow divergence reveal well-defined characteristic scales of solar supergranulation in the upper 4 Mm layer, while the giant-cell scale is prominent below levels of (d sim 8) Mm. We find that the characteristic scales of supergranulation remain stable while the giant scales increase during the periods of the 11-year activity cycle maxima. The power of the giant-cell scales increases with the enhancement of solar activity. This may be due to large-scale flows around active regions and, presumably, solar-cycle variations of the convection-zone stratification.

We present an overview of magnetohydrodynamic (MHD) simulations of prominence-forming coronal flux ropes and the development of coronal mass ejection (CME) with associated prominence eruption. The simulations found the formation of a prominence–cavity system that qualitatively reproduces several observed features including the cavity, the prominence “horns”, and the central “cavity” enclosed in the “horns” above the prominence. We discuss the magnetic structure corresponding to these observed features and the effect of the prominence weight on the stability and eruption of the flux rope.

Aditya-L1 is an observatory class mission designed and developed by the Indian Space Research Organisation (ISRO) to study the Sun and the inner heliosphere. Aditya-L1, currently orbiting around the first Lagrange point L1, is in a periodic halo orbit located approximately at 1.5 million km from Earth on the Sun–Earth line (about 1% of the Sun-Earth distance and closer to Earth). The orbital parameters of Aditya-L1 around L1 are Ax = 208,951 km, Ay = 670,024 km and Az = 120,000 km, where Ax, Ay and Az are semi-diameters of the orbit with an orbital period of 177.86 days. The primary objective of the Aditya-L1 mission is to understand the coronal and chromospheric dynamics of the Sun along with its influence on the heliosphere, especially at the L1 location. To achieve these goals, the spacecraft is configured to accommodate seven payloads of which four are remote sensing and three are in situ experiments. The scientific payloads are designed and developed by various Indian Research Institutes in close collaboration with different ISRO centers. The spacecraft is configured with the modified Mars orbiter mission (MOM) bus and is a three-axis stabilized spacecraft with a lift of mass of 1480.73 kg and power generation of ≈ 1820 W. Pointing stability will be better than 15 arcsec as required by the coronagraph payload. Aditya-L1 payload produces around 240 Gbits of science data per day (≈ 90% data is from the imaging payloads). Planning, coordination, and operation of the spacecraft and the scientific payloads are conducted from ISRO telemetry, tracking, and command network in Bengaluru, India. Aditya-L1 was launched on board the Polar Satellite Launch Vehicle (PSLV C57) at 11:50 Indian standard time (IST) from the second launch pad of the Satish Dhawan Space Centre (SDSC), Sriharikota, India on 2 September 2023. It was inserted at the L1 point on 6 January 2024, at 4:17 pm IST. The spacecraft, mission, and operation aspects of the Aditya-L1 spacecraft are discussed in this paper.

Ellerman bombs (EBs) are small and short-lived magnetic reconnection events in the lower solar atmosphere, most commonly reported in the line wings of the H(alpha ) line. These events are thought to play a role in heating the solar chromosphere and corona, but their size, short lifetime, and similarity to other brightenings make them difficult to detect. We aim to automatically detect and statistically analyze EBs at different heliocentric angles to find trends in their physical properties. We developed an automated EB detection pipeline based on a star-finding algorithm. This pipeline was used on ten high-resolution H(alpha ) datasets from the 1-meter Swedish Solar Telescope (SST). This pipeline identifies and tracks EBs in time, while separating them from visually similar pseudo-EBs. It returns key parameters such as size, contrast, lifetime, and occurrence rates based on a dynamic threshold and the more classical static ‘contrast threshold’ of 1.5 times the mean quiet-Sun (QS) intensity. For our dynamic threshold we found a total of 2257 EBs from 28,772 individual detections across our datasets. On average, the full detection set exhibits an area of 0.44 arcsec² (0.37 Mm²), a peak intensity contrast of 1.4 relative to the QS, and a median lifetime of 2.3 min. The stricter threshold yielded 549 EBs from 15,997 detections, with a higher median area of 0.66 arcsec² (0.57 Mm²), an intensity contrast of 1.7, and a median lifetime of 3 min. These comparisons highlight the sensitivity of EB statistics to selection thresholds and motivate further work towards consistent EB definitions. Several long-lived EBs were observed with lifetimes exceeding one hour. While the EB intensity contrast increases towards the limb, no clear trends were found between the other EB parameters and the heliocentric angle, suggesting that the local magnetic complexity and evolutionary stage dominate EB properties.

Coronal holes (CHs) are magnetically open regions that allow hot coronal plasma to escape from the Sun and form the high-speed solar wind. This wind can interact with Earth’s magnetic field. For this reason, developing an accurate understanding of CH regions is vital for understanding space weather and its effects on Earth. The process of identifying CH regions typically relies on extreme ultraviolet (EUV) imagery, leveraging the fact that CHs appear dark at these wavelengths. Accurate identification of CHs in EUV, however, can be difficult due to a variety of factors, including stray light from nearby regions, limb brightening, and the presence of filaments (which also appear dark, but are not sources of solar wind). In order to overcome these issues, this work incorporates photospheric magnetic-field data into a classical EUV-based segmentation algorithm based on the Active Contours Without Edges (ACWE) segmentation method. In this work magnetic-field data are incorporated directly into the segmentation process, serving both as a method for removing non-CH regions in advance, and as a method to constrain evolution of the segmented CH boundary. This reduces the presence of filaments while allowing the segmentation to include CH regions that may be difficult to identify due to inconsistent intensities.

We investigated the interplanetary source of the October 2024 major storm and determined that it was triggered by a sheath region and a magnetic cloud (MC), with the sheath region playing a decisive role. The MC has a larger and longer duration of southward interplanetary magnetic field (IMF) and solar wind electric field compared to the sheath, and the largest southward IMF and solar wind electric field were observed within the MC. As expect, the solar wind density in the sheath region is much larger than that in the MC. The results of this study not only provide direct evidence that solar wind density controls the evolution of the ring current, but also demonstrate that the correlation coefficients between the largest southward IMF and geomagnetic storm intensity, as well as between the largest solar wind electric field and geomagnetic storm intensity, lack physical meaning. The contribution of the sheath region to the intensity of the major storm, as estimated by the empirical formula developed by Burton, McPherron, and Russell (1975) (hereafter referred to as the BMR equation), was found to be smaller than that of the MC. However, actual observations indicate the opposite. This discrepancy suggests that the BMR equation is not capable of accurately estimating the ring current variation. The injection term in the BMR equation is merely a linear function of the solar wind electric field, without considering the solar wind density. This indicates that if we overlook the influence of solar wind density on the evolution of the ring current, estimating the intensity of a geomagnetic storm based solely on the integral of the solar wind electric field during the main phase of the storm would yield incorrect results. The October 2024 major storm also provides direct evidence that solar wind velocity, density, and the southward component of the IMF are all important parameters in the evolution of the ring current.

The 11-yr cycle of sunspots undergoes amplitude modulation over longer timescales. As a part of this long-term modulation in solar activity, the decennial rhythm occasionally breaks, with quiescent phases with very few sunspots observed over multiple decades. These episodes are termed as solar grand minima. Observation of solar magnetic activity proxies complemented by solar dynamo simulations suggests that the large-scale solar polar fields become very weak during these minima phases with a temporary halt in the polar field reversal. Eventually, with the accumulation of sufficient polar fluxes, the polarity reversal and regular cyclic activity is thought to resume, Using multi-millennial dynamo simulations with stochastic forcing, we quantify the polar flux threshold necessary to recover global solar polarity reversal and surmount grand minima phases. We find that the duration of a grand minimum is independent of the onset rate and does not affect the recovery rate. Our results suggest a method to forecast the Sun’s recovery from a grand minima phase. However, based on our approach, we could not identify specific precursors that signal entry in to a grand minima phase – implying that predicting the onset of grand minima remains an outstanding challenge.

Coronal holes (CHs) are widely considered as the main sources of high-speed solar wind streams. We validate this thesis comparing the smoothed time series of solar wind speed measured by the Advanced Composition Explorer (ACE) and various indices of CH areas constructed from the CH catalog compiled at the Kislovodsk Mountain Astronomical Station for the period 2010 – 2025. The main result is that we find specific indices of CH areas that give a strong correlation with smoothed solar wind speed variations. As an example, 1-year averaged areas of CHs located within 30 degrees of the solar equator yield a correlation of 0.9 with 1-year averaged solar wind speed. This strong correlation is a feature of the particular CH catalog, and considering an alternative CH catalog obtained using the Spatial Possibilistic Clustering Algorithm (SPoCA) from the Heliophysics Event Knowledgebase (HEK), the same index provides a correlation of only 0.3. Although the fact that the correlation significantly depends on the catalog requires a separate discussion, we conclude that if some of the catalogs can be used to construct a reliable indicator of solar wind speed variations, then this methodology should be maintained further. Additionally, we present time-latitude diagrams of rolling correlation between CH areas and solar wind speed, which, in our opinion, can be used to reveal source CHs for high-speed solar wind streams.