Solar Physics最新文献

The Ly(alpha ) Solar Telescope (LST) is the first instrument to achieve imaging of the full solar disk and the coronal region in both white light (WL) and ultraviolet (UV) H i Ly(alpha ), extending up to 2.5 solar radii (Rs), contributing to solar physics research and space weather forecasting. Since its launch on 9 October 2022, LST has captured various significant solar activity phenomena, including flares, filaments, prominences, and coronal mass ejections (CMEs). On-orbit observation and test results show that LST covers a continuous spatial range and the wavelengths of 121.6, 360, and 700 nm. The Ly(alpha ) Solar Disk Imager (SDI) has a field of view (FOV) of 38.4′ and a spatial resolution of around 9.5″, while the White-Light Solar Telescope (WST) has an FOV of 38.43′ and a spatial resolution of around 3.0″. The FOV of the Ly(alpha ) Solar Corona Imager (SCI) reaches 81.1′ and its spatial resolution is 4.3″. The stray-light level in the 700 nm waveband is about 7.8 × 10⁻⁶ MSB at 1.1 Rs and 7.6 × 10⁻⁷ MSB at 2.5 Rs, and in Ly(alpha ) waveband it is around 4.3 × 10⁻³ MSB at 1.1 Rs and 4.1 × 10⁻⁴ MSB at 2.5 Rs (MSB: mean solar brightness). This article will detail the results from on-orbit tests and calibrations.

Romashets and Vandas (2024) derived a method for the determination of Euler potentials at a spherical surface and applied it to the geomagnetic field. Here, we apply it to find Euler potentials at the source surface. A regular mesh defined by Euler potentials divides the source surface to surface elements with the same magnetic flux. By tracing magnetic-field lines away from the source surface, Euler potentials can be extended into the heliosphere.

The present study uses machine learning and time series spectral analysis to develop a novel technique to forecast the sunspot number (S_N) in both hemispheres for the remainder of Solar Cycle 25 and Solar Cycle 26. This enables us to offer predictions for hemispheric S_N until January 2038 (using the 13-month running average). For the Northern hemisphere, we find maximum peak values for Solar Cycles 25 and 26 of 58.5 in April 2023 and 51.5 in November 2033, respectively (root mean square error of 6.1). For the Southern hemisphere, the predicted maximum peak values for Solar Cycles 25 and 26 are 77.0 in September 2024 and 70.1 in November 2034, respectively (root mean square error of 6.8). In this sense, the results presented here predict a Southern hemisphere prevalence over the Northern hemisphere, in terms of S_N, for Solar Cycles 25 and 26, thus continuing a trend that began around 1980, after the last period of Northern hemisphere prevalence (which, in turn, started around 1900). On the other hand, for both hemispheres, our findings predict lower maxima for Solar Cycles 25 and 26 than the preceding cycles. This fact implies that, when predicting the total S_N as the sum of the two hemispheric forecasts, Solar Cycles 24 – 26 may be part of a centennial Gleissberg cycle’s minimum, as was the case in the final years of the 19th century and the start of the 20th century (Solar Cycles 12, 13, and 14).

This study introduces a novel method for predicting the sunspot number ((mathrm{S}_{mathrm{N}})) of Solar Cycles 25 (the current cycle) and 26 using multivariate machine-learning techniques, the Sun’s polar flux as a precursor parameter, and the fast Fourier transform to conduct a spectral analysis of the considered time series. Using the 13-month running average of the version 2 of the (mathrm{S}_{mathrm{N}}) provided by the World Data Center—SILSO, we are thus able to present predictive results for the (mathrm{S}_{mathrm{N}}) until January 2038, giving maximum peak values of 131.4 (in July 2024) and 121.2 (in September 2034) for Solar Cycles 25 and 26, respectively, with a root mean square error of 10.0. These predicted dates are similar to those estimated for the next two polar flux polarity reversals (April 2024 and August 2034). Furthermore, the values for the (mathrm{S}_{mathrm{N}}) maxima of Solar Cycles 25 and 26 have also been forecasted based on the known correlation between the absolute value of the difference between the polar fluxes of both hemispheres at an (mathrm{S}_{mathrm{N}}) minimum and the maximum (mathrm{S}_{mathrm{N}}) of the subsequent cycle, obtaining similar values to those achieved with the previous method: 142.3 ± 34.2 and 126.9 ± 34.2 for Cycles 25 and 26, respectively. Our results suggest that Cycle 25 will have a maximum amplitude that lies below the average and Cycle 26 will reach an even lower peak. This suggests that Solar Cycles 24 (with a peak of 116.4), 25, and 26 would belong to a minimum of the centennial Gleissberg cycle, as was the case in the final years of the 19th and the early 20th centuries (Solar Cycles 12, 13, and 14).

In the Sun and solar-type stars, there is a critical dynamo number for the operation of a large-scale dynamo, below which the dynamo ceases to operate. This region is known as the subcritical region. Previous studies showed the possibility of operating the solar-like large-scale (global) dynamo in the subcritical region without a small-scale dynamo. As in the solar convection zone, both large- and small-scale dynamos are expected to operate at the same time and location, we check the robustness of the previously identified subcritical dynamo branch in a numerical model in which both large- and small-scale dynamos are excited. For this, we use the Pencil Code and set up an (alpha Omega ) dynamo model with uniform shear and helically forced turbulence. We have performed a few sets of simulations at different relative helicity to explore the generation of large-scale oscillatory fields in the presence of small-scale dynamo. We find that in some parameter regimes, the dynamo shows hysteresis behavior, i.e., two dynamo solutions are possible depending on the initial parameters used. A decaying solution when the dynamo was started with a weak field and a strong oscillatory solution if the dynamo was initialized with a strong field. Thus, the existence of the sub-critical branch of the large-scale dynamo in the presence of small-scale dynamo is established. However, the regime of hysteresis is quite narrow with respect to the case without the small-scale dynamo. Our work supports the possible existence of large-scale dynamo in the sub-critical regime of slowly rotating stars.

We studied the radio emission occurring as narrowband decimetric spikes observed during the 10 May 2022 and 26 August 2022 flares. In the radio spectra, these spikes were distributed in groups that occurred quasi-periodically with the periods 5.1 s in the 10 May 2022 flare and 9.1 s in the 26 August 2022 flare. In some parts of these groups, even subgroups of spikes distributed with the quasi-periods of 0.19 s (10 May 2022 flare), and 0.17 s and 0.21 s (26 August 2022 flare) were found. Some of these subgroups even drifted to higher or lower frequencies, which was observed for the first time. At the time of the dm-spikes observation, a pair of reconnecting loops are identified in the SDO/AIA EUV observations of the 10 May 2022 flare, one of which is interpreted as belonging to a small erupting filament. We propose that these loops reconnect in the dynamic quasi-periodic regime (the period 0.19 s) and this reconnection is modulated by an oscillation of one of the interacting loops (the period 5.1 s). Accelerated electrons from this process are trapped in reconnecting plasma outflows, and thus the drifting groups of spikes are generated. The 26 August 2022 flare is a complex event with several systems of bright loops; nevertheless, it also shows a disintegrating erupting filament similar to the 10 May 2022 flare, meaning that the dm-spikes are likely generated by similar reconnection processes.

HXI on ASO-S and STIX onboard Solar Orbiter are the first simultaneously operating solar hard X-ray imaging spectrometers. ASO-S’s low Earth orbit and Solar Orbiter’s periodic displacement from the Sun–Earth line enables multi-viewpoint solar hard X-ray spectroscopic imaging analysis for the first time. Here, we demonstrate the potential of this new capability by reporting the first results of 3D triangulation of hard X-ray sources in the SOL2023-12-31T21:55 X5 flare. HXI and STIX observed the flare near the east limb with an observer separation angle of 18°. We triangulated the brightest regions within each source, which enabled us to characterise the large-scale hard X-ray geometry of the flare. The footpoints were found to be in the chromosphere within uncertainty, as expected, while the thermal looptop source was centred at an altitude of 15.1 ± 1 Mm. Given the footpoint separation, this implies a more elongated magnetic-loop structure than predicted by a semi-circular model. These results show the strong diagnostic power of joint HXI and STIX observations for understanding the 3D geometry of solar flares. We conclude by discussing the next steps required to fully exploit their potential.

High spectral resolution imaging spectroscopy plays a crucial role in solar observation, regularly serving as a backend instrument for solar telescopes. These instruments find direct application in deriving Doppler velocity from hyperspectral images, offering insights into the dynamic motion of matter on the solar surface. In this study, we present the development of a Fabry–Pérot interferometer (FPI) based imaging spectrometer operating at the Fe I (617.3 nm) wavelength for precise Doppler velocity measurements. The spectrometer features a moderate spectral resolution of (lambda/Deltalambdaapprox60{,}000), aiming to balance the imaging signal-to-noise ratio (SNR). The instrument underwent successful observational experiments on the 65-cm Educational Adaptive-Optics Solar Telescope (EAST) at the Shanghai Astronomy Museum. Obtained Doppler velocities were compared with data from the Helioseismic and Magnetic Imager (HMI), the maximum column and row correlation coefficients are 0.9261 and 0.9603, respectively. The estimated cut-off normalized frequency of the power spectral density (PSD) curve for velocity map is approximately 0.4/0.21 times higher than that observed in the HMI data, with potentially higher spatial resolution achievable under better seeing conditions. Based on the estimated imaging SNR levels, the accuracy of velocity measurements is approximately 50 m s⁻¹.

To estimate the hemispheric flux generation rate of the large-scale radial magnetic field in Solar Cycles 23 and 24, we use the photospheric observations of the solar magnetic fields and results of the mean-field dynamo models. Results of the dynamo model show the strong impact of the radial turbulent diffusion on the surface evolution of the large-scale poloidal magnetic field and on the hemispheric magnetic flux generation rate. To process the observational data set, we employ the parameters of the meridional circulation and turbulent diffusion from the Surface Flux-Transport (SFT) models. We find that the observed evolution of the axisymmetric vector potential contains the time–latitude patterns which can result from the effect of turbulent diffusion of the large-scale poloidal magnetic field in the radial direction. We think that the SFT models can reconcile the observed rate of hemispheric magnetic flux generation by considering radial turbulent diffusion and lower values of the diffusion coefficient.

Improvement of the model providing the boundary condition of the solar-wind speed near the Sun is essential for gaining a better forecast of space weather. We optimized the parameters of the distance from the coronal hole boundary (DCHB) model and the Wang–Sheeley (WS) model, which enabled the determination of solar-wind speed from observations of the Sun’s magnetic field. In this study, we used solar-wind speed data derived from interplanetary scintillation (IPS) observations at the Institute for Space-Earth Environmental Research (ISEE) for six Carrington rotations in Solar Cycle 23 as reference data. A comparison of IPS observations and optimized DCHB models demonstrated strong-to-moderate positive correlations and small deviations, except for solar maximum data. The degraded correlation at the solar maximum is ascribed to the effect of the rapid structural evolution of the solar wind and coronal magnetic field. The performance of the optimized DCHB model was better than that of the optimized WS model. To solve a limitation of the DCHB model in reproducing slow-wind speeds, we propose a modified version of the DCHB model and optimize it for IPS observations. The optimized solutions for the modified DCHB model demonstrate performance comparable to that of the original model. The results obtained in this study suggest that the DCHB acts better as a controlling parameter for the solar-wind speed than the expansion factor and that both the optimized DCHB model and its modified version are useful for improving the estimation of the solar-wind speed at the source surface from magnetograph observations.