Solar Physics最新文献

A long-term prediction approach for solar cycles is proposed by including the century-scale modulation in the SODA (Solar Dynamo Amplitude) and XSODA (Extended Solar Dynamo Amplitude) indices of Schatten and Pesnell, MSODA and MXSODA. Additionally, we also introduce a new technique, the minimal fluctuation method, to reduce temporal fluctuations. By combining this method with MSODA, we predict that Solar Cycle 26 will reach a maximum sunspot number of (109.14pm 32.92) in the year (2035.3 pm 2.3). Using MXSODA, the most reliable indicator, the peak is expected to reach a maximum amplitude of (160.70pm 47.83) on the same date.

We examine the statistical properties of extreme solar activity levels through the application of the extreme value theory to the annual sunspot number series reconstructed from ¹⁴C data spanning the last millennium. We have used the extreme value theory to study long-term solar variability by applying the peaks-over-threshold technique to an annual sunspot number series reconstructed from ¹⁴C data for the last millennium. We have obtained a negative value of the shape parameter of the generalized Pareto distribution implying that an upper bound has been reached by the extreme sunspot number value distribution during the past millennium. The results obtained from the same analysis applied to two subperiods of the series, are consistent with that considering the whole series. We have also estimated return levels and periods for the extreme sunspot numbers. The maximum annual sunspot number (273.6) observed during the past millennium is slightly higher (lower) than that considering a 1000-year (10,000-year) return level, but they are within the 95% confidence interval in both cases. It approximately corresponds to a 3500-year return period. Our result implies that solar activity has reached its upper limit, and it would be unlikely to observe, in the near future, sunspot numbers significantly higher than those already observed during the past millennium.

Data on the (B_{y}) and (B_{z}) components of the heliospheric magnetic field (HMF) were used to study the relationships between the Power Spectral Density (PSD) ((PSDpropto f^{-nu } ), (f) is the frequency) of HMF turbulence and the rigidity spectrum variation (RSV) of the galactic cosmic ray (GCR) intensity ((delta D(R)/D(R) propto R^{- gamma } )). A new common exponent (nu _{yz}) was constructed to account for the contributions of both the (B_{y}) and (B_{z}) components of the HMF. The period from 1969 to 2022 was considered, divided into five subperiods based on the global solar magnetic field (GSMF) polarities: i) 1969 – 1979 ((A>0)) (positive polarity—magnetic field lines directed away from the Sun’s northern hemisphere), ii) 1980 – 1990 ((A<0)) (negative polarity—magnetic field lines directed towards the Sun’s northern hemisphere), iii) 1991 – 2002 ((A>0)), iv) 2003 – 2013 ((A<0)), and v) 2014 – 2022 ((A>0)). The analysis of these five subperiods confirmed a close relationship between the PSD and the RSV, determined by the exponents (nu _{yz}) and (gamma ), respectively. These exponents, calculated from independent sources, may be important parameters in the study of long-term GCR variations in the heliosphere.

Solar active regions (ARs), characterized by intense magnetic fields, are prime locations for solar flares. Understanding the properties of these magnetic fields is crucial for predicting and mitigating space weather events. In this study, the non-potential magnetic field parameters of active region (AR) NOAA 9077 are investigated; this AR experienced a super-strong X5.7 solar flare. Using advanced extrapolation techniques, the 3D magnetic field structure from vector magnetograms is obtained using the Solar Magnetic Field Telescope (SMFT) at Huairou Solar Observing Station (HSOS). Then, various non-potential parameters are calculated, including current density, shear angle, quasi-separatrix layers (QSLs), twist, and field line helicity. By analyzing the spatial and temporal distributions of these parameters, we aim to shed light on the relationship between magnetic field properties and solar flare occurrence. Our findings reveal that high twist and complex magnetic field configurations are prevalent before flares, while these features tend to weaken after the eruption. Additionally, we observe decreases in helicity and free energy after the flare, while the free energy peaks approximately 1.5 days prior to the onset of the flare. Furthermore, we investigate the distribution of quasi-separatrix layers and twist, finding high degrees of complexity before flares. Multiple patterns of high current density regions suggest unstable magnetic structures prone to flaring, coinciding with the shear angle distribution. Relative field line helicity patterns exhibit distinct characteristics compared to current density, concentrating before flares and diverging afterward. Overall, our results highlight the contrasting nature of current density and relative field line helicity patterns in relation to solar flares, in addition to the aforementioned features in the set of commonly derived non-potential parameters for this particular event.

The primary objective of our research is to validate direct measurements of the solar magnetic field through calculating the splitting of polarized spectral lines. The data are collected by the Solar Magnetism and Activity Telescope (SMAT) located at the Huairou Solar Observing Station (HSOS). The number of sampling points of the spectral line profile was varied from 5 to 31. By fitting the profiles of left- and right-circularly polarized light intensities, we determined the spectral line splitting, and the error between the magnetic-field strength determined from this and the true value was less than 2%. We found that the correlation between the magnetic-field strength measured in the active regions by SMAT and that observed by Helioseismic and Magmetic Imager (HMI) on board the Solar Dynamics Observatory (SDO) reached about 80%, but in the quiet region, this correlation was very low.

Magnetic reconnection is one of the fundamental dynamical processes in the solar corona. The method of studying reconnection in active region-scale magnetic fields generally depends on non-local methods (i.e. requiring information across the magnetic field under study) of magnetic topology, such as separatrix skeletons and quasi-separatrix layers. The theory of General Magnetic Reconnection is also non-local, in that its measure of the reconnection rate depends on determining the maxima of integrals along field lines. In this work, we complement the above approaches by introducing a local description of magnetic reconnection, that is one in which information about reconnection at a particular location depends only on quantities at that location. This description connects the concept of the field line slippage rate, relative to ideal motion, to the underlying local geometry of the magnetic field characterized in terms of the Lorentz force and field-aligned current density. It is argued that the dominant non-ideal term for the solar corona, discussed in relation to this new description, is mathematically equivalent to the anomalous resistivity employed by many magnetohydrodynamic simulations. However, the general application of this new approach is adaptable to the inclusion of other non-ideal terms, which may arise from turbulence modelling or the inclusion of a generalized Ohm’s law. The approach is illustrated with two examples of coronal magnetic fields related to flux ropes: an analytical model and a nonlinear force-free extrapolation. In terms of the latter, the slippage rate corresponds to the reconnection that would happen if the given (static) force-free equilibrium were the instantaneous form of the magnetic field governed by an Ohm’s law with non-ideal terms.

Tomography is a powerful technique for recovering the three-dimensional (3D) density structure of the global solar corona. In this work, we present an improved tomography method by introducing radial weighting in the regularization term. Radial weighting provides balanced smoothing of density values across different heights, helping to recover finer structures at lower heights while also stabilizing the solution and preventing oscillatory artifacts at higher altitudes. We apply this technique to reconstruct the 3D electron density of Carrington Rotation (CR) 2098 using two weeks of polarized brightness (pB) observations from the inner coronagraph (COR1) on board spacecraft-B of the twin Solar Terrestrial Relations Observatory (STEREO), where the radial weighting function is taken as the inverse intensity background, calculated by averaging all the pB images used. Comparisons between density distributions at various heights from the tomography and magnetohydrodynamics (MHD) simulations show good agreement. We find that radial weighting not only effectively corrects the oversmoothing effect near the inner boundary in reconstructions using second-order smoothing but also significantly improves reconstruction quality when using zero-order smoothing. Additionally, comparing reconstructions for CR 2091 from single-satellite data with that from multiviewpoint data suggests that coronal evolution and dynamics may significantly impact on the reconstructed density structures. This improved tomography method has been used to create a database of 3D densities for CRs 2052 to 2154, based on STEREO/COR1-B data, covering the period from 08 January 2007 to 17 September 2014.

Probing the solar wind at different distances from the Sun provides a great opportunity to explore turbulence development in the unlimited space. Recent measurements from the near-Sun plasma demonstrate the evolution of turbulence from an undeveloped to a fully developed state on the path from the Sun to the Earth. On the other hand, the properties of turbulence are known to be altered for the solar-wind streams of different origin. The present study adopts measurements during two Solar Orbiter and Wind alignments with separations of 0.1 and 0.5 AU to analyze changes in the properties of turbulence for the same plasma parcels embedded in the solar-wind streams of various origins. The results demonstrate that at scales spectra become shallower toward the Earth’s orbit, while Kolmogorov scaling stays unchanged at the MHD scales. The power of the fluctuations within the inertial range is shown to be an important factor that determines the evolution of the turbulent fluctuations in the inner heliosphere, regardless of the origin of the solar-wind stream.

Based on observations from Parker Solar Probe, this paper studies the dependence of the correlations between the transition-range spectral index of the magnetic energy spectrum and four parameters (inertial-range cross-helicity and magnetic energy density, transition-range magnetic helicity, and bulk proton temperature) on solar wind speed and heliocentric distance. Results show significant correlations between the spectral index and both cross-helicity and magnetic energy density. Notably, at lower speeds or closer distances, the correlation coefficient (CC) between the cross-helicity and spectral index is smaller than that between the magnetic energy density and spectral index. Conversely, at higher speeds or greater distances, the correlation with cross-helicity becomes comparable to or even exceeds that with magnetic energy density. Additionally, as the speed increases or the heliocentric distance decreases, cross-helicity, magnetic energy density, proton temperature, and the absolute values of the spectral index show a mostly upward trend. Moreover, cross-helicity, absolute values of the spectral index, and CC between the magnetic energy density and spectral index exhibit a similar trend with the speed, initially rising and then declining at the highest speed bin. We discuss the results using the recently proposed “helicity barrier” effect.

Using the energy method and the thin magnetic flux tube approximation, we find the wave dispersion relation for magnetohydrodynamic kink oscillations of a force-free magnetic flux rope with uncompensated longitudinal electric current under solar coronal conditions. The eigenvectors are shown to impose restrictions on the conditions of the kink instability of a flux rope. The observed weak twist of coronal loops with a small ((lesssim 1)) number of turns of the magnetic field lines around the axis indicates the dominance of unshielded magnetic flux ropes in the corona of the Sun, in which the longitudinal electric currents do not exceed (10^{11}) – (10^{12}) A. These restrictions can be associated with the absence of solar superflares. The period of kink oscillations of twisted coronal loops should decrease with decreasing longitudinal electric current, which can be used to study its dynamics in solar flares. No dependence of compact and eruptive solar flares on the twist of flux ropes can be explained by the coexistence of both shielded and unshielded electric currents in the corona.