Solar Physics最新文献

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.

In situ measurements of kinetic scale current sheets in the solar wind show that they are often approximately force-free although the plasma (beta) is of order one. They frequently display systematic asymmetric and anti-correlated spatial variations of their particle density and temperature across the current sheet, leaving the plasma pressure essentially uniform. These observations of asymmetries have previously been modelled theoretically by adding additional terms to both the ion and electron distribution functions of self-consistent force-free collisionless current sheet models with constant density and temperature profiles. In this article we present the results of a modification of these models in which only the electron distribution function has an additional term, whereas the ion distribution function is kept as a thermal (Maxwellian) distribution function. In this case the nonlinear quasineutrality condition no longer has a simple analytical solution and therefore has to be solved alongside Ampère’s law. We find that while the magnetic field remains approximately force-free, the non-zero quasineutral electric field gives rise to an additional spatial substructure of the plasma density inside the current sheet. We briefly discuss the potential relation between our theoretical findings and current sheet observations.

Solar flares exhibit precursor soft X-ray emission at high temperatures (the Hot Onset Precursor Event, here HOPE for short). This phenomenon is readily seen for events at or above the GOES C-class, but at present we do not know whether or not a “pure” filament-eruption event, such as one coming from the polar-crown filament zone, also exhibits this property. We study this question using both older and more modern GOES/XRS soft X-ray data. The currently operating GOES-R spacecraft (GOES-16 through GOES-19) have different sensor technology and also higher cadence than in the earlier satellites in the series, and so we devote an Appendix to describing these data from the point of view of a user interested in the detection of faint sources; most GOES/XRS users focus on flare observations, rather than the quiet Sun. Because the HOPE signatures appear at the very beginning of the development of a flare, they require study at the lowest flux levels. Our searches both with GOES-R and earlier data do not detect HOPE in purely filament-eruption events. At a representative HOPE temperature of 10 MK, the emission measure for any HOPE source must be less than about (10^{46}text{ cm}^{-3}).