Solar Physics最新文献

Sunspots or active regions with a (delta )-magnetic configuration are known to be associated with strong eruptions such as flares and mass ejections. This article, investigates the relationship between (delta ) active regions (ARs) and flares over the course of three solar cycles, from 1996 to 2024, with respect to the (delta ) AR areas, lifetimes, latitudinal distributions, and the phase of their magnetic complexity. Solar Cycle 25, while still in progress, has produced the least number of (delta )-active regions in comparison to the previous two solar cycles, yet the number of M- and X-class flares exceed that of Cycle 24 by 25%. Flare occurrence is higher in C-, M-, and X-class events during the presence of the (delta ) configuration in an active region, which is seen in all three solar cycles. The total number of flares produced by (delta ) and non-(delta ) active regions were 15,875 and 17,033, respectively, along all three solar cycles. The latter are dominated by B- and C-class flares, while the number of M- and X-class flares along all three solar cycles was significantly less than compared to (delta ) ARs. The median lifetime of an active region in the (delta ) phase is about five days while it is about eight days in the non-(delta ) phase. The typical number of flares produced by a (delta ) active region is 20, with maximum values ranging from 80 – 156 for lifetimes between 6 – 13 days. However, about 30% of (delta ) active regions do not produce flares when their lifetimes are between 6 – 12 days. The latitudinal distribution of (delta ) active regions across the northern and southern hemispheres is nearly symmetric on either side of the equator for Solar Cycles 23 and 24, peaking around ({pm},10^{circ }) – (20^{circ }). For Solar Cycles 23 and 24, about 30% of the host (delta ) active regions have an area exceeding the mean value over the above latitudinal belt while for Solar Cycle 25, there is a large scatter possibly due to the cycle still being in progress. It remains to be seen if the latter phase of Solar Cycle 25 will be as active as its earlier phase and whether the number of (delta ) active regions emerging during that period scale with the total sunspot number.

Solar Orbiter conducted a series of flare-optimised observing campaigns in 2024 using the Major Flare Solar Orbiter Observing Plan (SOOP). Dedicated observations were performed during two distinct perihelia intervals in March/April and October, during which over 22 flares were observed, ranging from B- to M-class. These campaigns leveraged high-resolution and high-cadence observations from the mission’s remote-sensing suite, including the High-Resolution EUV Imager (EUI/HRI_EUV), the Spectrometer/Telescope for Imaging X-rays (STIX), the Spectral Imaging of the Coronal Environment (SPICE) spectrometer, and the High Resolution Telescope of the Polarimetric and Helioseismic Imager (PHI/HRT), as well as coordinated ground-based and Earth-orbiting observations. EUI/HRI_EUV, operating in short-exposure modes, provided two-second-cadence, non-saturated EUV images, revealing structures and dynamics on scales not previously observed. Simultaneously, STIX captured hard X-ray imaging and spectroscopy of accelerated electrons, while SPICE acquired EUV slit spectroscopy to probe chromospheric and coronal responses. Together, these observations offer an unprecedented view of magnetic reconnection, energy release, particle acceleration, and plasma heating across a broad range of temperatures and spatial scales. These campaigns have generated a rich dataset that will be the subject of numerous future studies addressing Solar Orbiter’s top-level science goal: “How do solar eruptions produce energetic particle radiation that fills the heliosphere?”. This paper presents the scientific motivations, operational planning, and observational strategies behind the 2024 flare campaigns, along with initial insights into the observed flares. We also discuss lessons learned for optimizing future Solar Orbiter Major Flare campaigns and provide a resource for researchers aiming to utilize these unique observations.

Understanding the Sun’s role in past climate change requires knowledge of solar variability over millennia. While direct sunspot records span only the last 400 years, longer-term changes are inferred from cosmogenic radionuclides like ¹⁴C and ¹⁰Be in tree rings and ice cores. Their production reflects variations in galactic cosmic ray flux, modulated by Earth’s and Sun’s magnetic fields - the latter is tied to solar activity. We present a Bayesian model that jointly reconstructs solar modulation and the global geomagnetic field over the Holocene. Extending previous work, our model directly incorporates ¹⁴C and ¹⁰Be production rate data and thermoremanent magnetic records. A flexible prior allows for bimodality and explicit long-term trends in solar activity. The reconstruction shows a clear separation of grand solar minima and a normal mode. Additionally, we explore the recovery of an 11-year cycle in solar modulation.

We study the long-term variation of the zonal and meridional flows from Solar Cycle 23 to 26 throughout the near-surface shear layer (NSSL) derived with ring-diagram analysis (RDA) applied to Dopplergrams obtained mainly by Global Oscillation Network Group (GONG) and Helioseismic and Magnetic Imager (HMI) and compare them with global helioseismic results. We also create super-synoptic maps of the divergence of the meridional and the acceleration of the zonal flow. The bands of decelerating zonal and converging meridional flows of a given solar cycle coincide with the locations of magnetic activity at mid- to low latitudes. They begin their latitudinal migration near 50^∘ at or shortly after the maximum of the previous cycle, such as near 2015 for Solar Cycle 25, while the band of fast zonal flow is close to two years ahead of these bands at mid- to low latitudes. The patterns move (5.20 pm 0.29^{circ })/Yr from 37.5^∘ to 7.5^∘ averaged over both hemispheres during Solar Cycle 25. The zonal-flow patterns vary little with depth throughout the NSSL at 7.5^∘ to 30.0^∘ where most active regions are present. However, the bands of converging meridional flows appear somewhat earlier at greater depths than at shallower ones. The bands of fast zonal flow of Solar Cycle 25 have reached latitudes near the equator during 2024, which is close to Solar Cycle 25 maximum. A band of fast zonal flow appeared at about 50^∘ at the same time and thus indicates the beginning of Solar Cycle 26. The amplitudes of the bands of fast zonal flows are anti-correlated with the strength of the associated solar cycles except close to the equator. The divergence minima are also anti-correlated with magnetic activity, while the acceleration minima are only weakly anti-correlated. With the derived flow parameters, we estimate the timing and strength of Solar Cycle 26 and predict that it will be close to an average sunspot cycle.

This review surveys recent advances in the numerical modeling of solar prominences and coronal rain achieved with the fully open-source adaptive-grid, parallelized Adaptive Mesh Refinement Versatile Advection Code (MPI-AMRVAC). We examine how these models have contributed to our understanding of the formation and evolution of cool plasma structures in the solar corona. We first discuss prominence models that focus on prominence formation and their dynamic behaviour. We then turn to coronal rain, highlighting its connection to thermal instability and its role in the exchange of mass and energy between the corona and chromosphere. Particular attention is given to the growing efforts to connect simulations with observations through synthetic emission and spectral diagnostics.

Sunrise iii is a balloon-borne solar observatory dedicated to the investigation of the processes governing the physics of the magnetic field and the plasma flows in the lower solar atmosphere. The gondola hosts a 1-m aperture telescope that feeds three post-focus instruments.

One of these instruments, the Tunable Magnetograph (TuMag), is a tunable imaging spectropolarimeter in visible wavelengths. It is designed to probe the vector magnetic field, (bf{B}), and the line-of-sight (LoS) velocity, (v_{mathrm{LoS}}), of the photosphere and the lower chromosphere. It provides polarized images with a (63^{prime prime }times , 63^{prime prime }) field of view (FoV) of the Sun in four polarization states. These images can later be processed on ground to retrieve maps of the aforementioned solar physical quantities. The quasi-simultaneous observation of two spectral lines sensitive to (bf{B}) and (v_{mathrm{LoS}}) in the photosphere and lower chromosphere provides excellent diagnostic measurements of the magnetic and dynamic coupling in these layers. When combined with the other two instruments on board, observing in the infrared and ultraviolet regions of the spectrum, TuMag’s diagnostic potential is expected to be greatly enhanced.

Building upon heritage of instruments like IMaX and SO/PHI, the key technologies employed for TuMag are a liquid-crystal-variable-retarder-based polarimeter and a solid, LiNbO₃ Fabry–Pérot etalon as a spectrometer. However, it also incorporates several innovative features, such as in-house-made, high-sensitivity scientific cameras and a double filter wheel. The latter makes TuMag the first balloon-borne instrument of its type capable of tuning between spectral lines. Specifically, it can sequentially observe any two out of the three spectral lines of Fe i at 525.02 and 525.06 nm and of Mg i at 517.3 nm. Time cadences range from 30 to 100 seconds, depending on the observing mode and the specific pair of spectral lines targeted.

Laboratory measurements have demonstrated good image quality, spectral resolution, and polarimetric efficiency. Here we report on the concept, design, calibration, and integration phases of the instrument, as well as on the data reduction pipeline.

The galactic cosmic ray (GCR) unidirectional latitudinal gradient ((G_{bot })) is important for the understanding of the physical mechanism of solar modulation in the three-dimensional heliosphere. This work calculates the south-north (SN) asymmetry the GCR intensity from six neutron monitor (NM) stations with different geographic locations and cutoff rigidities ((P_{mathrm{c}})). The (P_{mathrm{c}}) values are divided into three groups: low (P_{mathrm{c}}) (1 – 5 GV) for the McMurdo and Thule NMs, medium (P_{mathrm{c}}) (6 – 11 GV) for the Tsumeb NM and Mexico NM, and high (P_{mathrm{c}}) (> 12 GV) for the Haleakala NM and Princess Sirindhorn NM. The SN GCR intensities are corrected by the secular change method and the heliospheric current sheet (HCS) tilt angle for Earth’s excursions in helio-latitudes to calculate the unidirectional latitudinal gradients ((G_{bot })) in the course of solar rotations during the (A > 0) (1996 – 1998 and 2015 – 2019) and (A < 0) epochs (2004 – 2008). We find that the directions of (G_{bot }) are opposite to the (north-South) NS offset of the HCS. The effect of the asymmetric HCS tilt on the (G_{bot }) is more prominent in the (A < 0) than in the (A > 0) epochs. The NS asymmetry in the HCS tilt and solar wind speed simultaneously contribute to the (G_{bot }) throughout both magnetic polarities. When the asymmetric solar wind speed is absent, the effect of the asymmetric HCS tilt on the (G_{bot }) is clearly observed in the (A < 0) epoch not in the (A > 0) epochs, and the magnitudes of (G_{bot }) are proportional to the size of the offset. However, when the asymmetric HCS tilt is none, the effect of the NS asymmetric solar wind speed on (G_{bot }) cannot be discriminated in both magnetic polarities. The slope of the SN asymmetric GCR intensity to the asymmetric solar wind speed in the (A > 0) (2015 – 2019) is larger than in the (A < 0) by about 1.3 – 1.8 times. The yearly GCR asymmetric latitudinal gradients tend to depend on directions of the HCS and solar wind speed offsets rather than on the solar magnetic polarities. The rigidity and asymptotic dependences of the (G_{bot }) are discussed.

Long-term reconstructions of sunspot number (SSN) and group number (GN) often tacitly assume that the basic characteristics of solar activity remain unchanged even over long times, e.g., that the number of sunspots and the number of sunspot groups now and, say, 100 or 500 years ago have the same relation. However, this assumption needs examination, especially as the long-term homogeneity between sunspots and several other solar activity parameters has recently been challenged (Mursula et al. 2024). Here we use long series of sunspot observations to study if and how the number of sunspots per group varies at different time scales. We use observations from the Kislovodsk Mountain Astronomical Station (KMAS) and the Solar Observing Optical Network (SOON) to create a reference series for the overlapping period of 1982 – 2016. We then scale other historical data to this reference series in order to have a unified time series for 1749 – 2024. We find that the yearly mean number of sunspots per group varies between about 2 and 10 (average of 6.8), closely in phase with the solar cycle over the whole 270-year time interval. We also find that the number of sunspots per group depicts a very similar secular variation as the sunspot number.

Solar eruptions may occur at different evolutionary stages of active regions, during which the photospheric motions manifest in various forms, including flux emergence, sunspot rotation, shearing, converging, and magnetic flux diffusion. However, it remains unclear what the specific roles played by these different motions are in leading to eruptions. Here, we employ high resolution magnetohydrodynamic simulations to demonstrate how solar eruptions can be initiated in a single bipolar configuration, driven by first shearing and then flux diffusion at the bottom surface. Flux diffusion disperses the photospheric magnetic flux, driving portions of it toward the polarity inversion line (PIL). This process leads to the expansion of core field, enhancing the pinching effect to form the current sheet. When magnetic reconnection occurs within this current sheet, the eruption is initiated, characterized by a rapid release of magnetic energy and accompanied by the formation of a erupting flux rope. Additionally, flux diffusion contributes to magnetic cancellation near the PIL, leading to the formation of a weakly twisted magnetic flux rope prior to the eruption. However, this pre-existing flux rope plays a limited role in eruption initiation, as its spatial position remains largely unchanged throughout the eruption. These findings demonstrate that the primary role of flux diffusion is to facilitate current sheet formation, highlighting the critical role of current sheet formation in eruption initiation.