Solar Physics最新文献

We investigate the temporal variations and distribution functions of daily sunspot area and magnetic flux data from 2011 to 2023. The yearly distribution of sunspot area on the solar full disc, southern hemisphere and northern hemisphere, and magnetic flux on the solar full disc are positively skewed for all the years from 2011 to 2023. We analyzed the variations of yearly maximum, median, first quartile, third quartile, interquartile range and mean of the daily sunspot area and magnetic flux on the solar full disc and found their maxima and minima for sunspot area and magnetic flux. Maxima occur in the years 2014 and 2015 for sunspot area and magnetic flux, respectively, whereas their minima occur in the years 2018 and 2019. We found the correlations between the descriptive statistical measures of sunspot area and magnetic flux, kernel density estimator, and lognormal functions to describe the distributions of daily sunspot area and magnetic flux. We found a positive correlation of 0.96 between the distribution functions of sunspot area and magnetic flux on the solar full disc during 2011 – 2023. We demonstrated that the distribution function for daily sunspot area correlates linearly well with the distribution function for magnetic flux during 2011 – 2023.

The statistical analysis of solar flares is essential for understanding their characteristics and properties, serving as a fundamental tool to interpret flare distributions and constrain the physical mechanisms driving their occurrence. In this paper, we investigated the statistical properties of these energetic phenomena over the last four solar cycles, spanning the period from September 1975 to June 2017. Specifically, we analysed the temporal (i.e., waiting time and duration) and energetic (i.e., peak intensity) aspects of soft X-ray (SXR) flares from the GOES catalogue in terms of flare occurrence rates and frequency distributions. We found that (i) the duration of most of the events increases with the increase of the intensity of a given flare, i.e. with its class. X-class flares exhibit a second peak centred around the 80th minute after its formation. (ii) Waiting times, i.e. the interval between the starting time of two consecutive flares, correlate with the solar activity variation within the solar cycle. (iii) In all solar cycles considered here, the flare and CME waiting-time distributions (WTDs) show similar power-law indices of the frequency event distribution and time variation, especially in the tail of the power-law distribution. (iv) Peak-intensity energy does not correlate with the waiting time, contrary to the idea that the more time elapses between two consecutive events the higher the intensity of the flare is.

In this article, Part 1, we have synthetically resonance scattered and Thomson scattered a measured solar chromospheric (mathrm{Ly}alpha ) spectral radiance (CLSR) spectrum off the neutral hydrogen [(N_{1})] atoms in ground state and free electrons [(N_{mathrm{e}})], respectively, contained in a 3D coronal model of the 14 July 2000 (“Bastille Day”) Coronal Mass Ejection (CME). From these two scatters, we have computed maps of the associated resonance scattered spectral radiance (RSSR) spectrum and the Thomson scattered spectral radiance (TSSR) spectrum in ultraviolet (UV) from 121.3 to 121.8 nm with a wavelength resolution of 0.1 nm, which encompasses the (mathrm{Ly}alpha ) center line at 121.57 nm. We then integrated the maps over the above wavelength range and have created two 2D resonance scattered radiance (RSR) and Thomson scattered radiance (TSR) maps. As expected, the TSSR spectrum is (approx 1000) times dimmer than the RSSR spectrum, which we can deem for it to contribute towards noise in the center of the RSSR spectrum. In a follow up article, Part 2, we intend to do the following with these maps. First, we will use the computed RSSR spectra along each line of sight (LOS) to derive the proton temperature [(T_{mathrm{p}})] and speed [(V_{mathrm{p}})] using the Doppler Dimming technique (DDT). Second, we will compare these derived proton parameters along each LOS with the actual values contained within the Bastille Day CME model at the plane of the sky and compute the differences. If we find they are different we will then determine where along the LOS they closely match and their distances from the plane of the sky. Finally, we will quantify an estimate of the systematic error from using DDT to measure the proton parameters at the plane of the sky, which is different from the statistical error margins reported in the literature from real RSSR experiments conducted from space-based instruments.

We report on the 2024 September 9 sustained gamma-ray emission (SGRE) event observed by the Large Area Telescope (LAT) on board the Fermi satellite. The hevent was associated with a backside solar eruption observed by multiple spacecraft such as the Solar and Heliospheric Observatory (SOHO), Solar Terrestrial Relations Observatory (STEREO), Parker Solar Probe (PSP), Solar Orbiter (SolO), Solar Dynamics Observatory (SDO), Wind, and GOES, and by ground-based radio telescopes. Fermi/LAT observed the SGRE after the EUV wave from the backside eruption crossed the limb to the frontside of the Sun. SolO’s Spectrometer Telescope for Imaging X-rays (STIX) imaged an intense (X3.3) flare, which occurred ≈ 41° behind the east limb, from heliographic coordinates S13E131. Forward modeling of the coronal mass ejection (CME) flux rope revealed that it impulsively accelerated (3.54 km s⁻²) to attain a peak speed of 2162 km s⁻¹. SolO’s energetic particle detectors (EPD) observed protons up to ≈ 1 GeV from the extended shock and electrons that produced a complex type II burst and possibly type III bursts. The durations of SGRE and type II burst are consistent with the linear relation between these quantities obtained from longer duration (> 3 hours) SGRE events. All these observations are consistent with an extended shock surrounding the CME flux rope, which is the likely source of high-energy protons required for the SGRE event. We compare this event with six other behind-the-limb (BTL) SGRE eruptions and find that they are all consistent with energetic shock-driving CMEs. We also find a significant east-west asymmetry (3:1) in the BTL source locations.

We study solar differential rotation for solar cycle No. 19 (1954 – 1964) by tracing sunspot groups on the sunspot drawings of Kanzelhöhe Observatory for Solar and Environmental Research (KSO). Our aim is to extend previous differential rotation (DR) analysis from the KSO data (1964 – 2016) to the years prior to 1964 to create a catalog of sunspot group positions and photospheric DR parameters from KSO sunspot drawings and white light images. Synodic angular rotation velocities were first determined using the daily shift (DS) and robust linear least-squares fit (rLSQ) methods, then converted to sidereal velocities, and subsequently used to derive solar DR parameters. We compare the DR parameters obtained from different sources and analyse the north–south asymmetry of rotation for solar cycle No. 19. It has been shown that our results for the equatorial rotation velocity (parameter (A)) and the gradient of DR (parameter (B)) coincide with earlier results from the KSO data (performed with a different method), as well as with results from the Kodaikanal Solar Observatory (KoSO) and the Yunnan Observatories (YNAO). In contrast, the values of parameter (A) from three different earlier studies based on the Greenwich Photoheliographic Results (GPR) exhibit statistically significant differences when compared to the values of parameter (A) derived from KSO, KoSO and YNAO. These findings suggest that the GPR data have the largest inconsistency compared to the other three data sources, highlighting the need for further analysis to identify the causes of these discrepancies. The analysis of the north-south asymmetry in the solar rotation profile using two different methods shows that the DR parameters of the hemispheres coincide, indicating a rotational symmetry around the equator. This is consistent with previous results from KSO and YNAO data. However, all sources indicate slightly higher equatorial rotation velocities in the southern hemisphere.

Understanding the long-term variability of the solar dynamo remains a key challenge in solar physics. In this work, we apply the Sparse Identification of Nonlinear Dynamical Systems (SINDy) framework to reconstruct a low-order dynamo model directly from 275 years of sunspot number data. Our data-driven approach for discovering governing equations from time series enables us to identify a minimal yet accurate dynamical system that captures the essential features of solar activity cycles. We demonstrate that, when interpreted as a low-order dynamo model, the solar dynamo is governed by an unstable saddle point, with nonlinear evolution leading to cyclic behavior. In particular we find that the underlying dynamics is described by a cubic nonlinearity driven by a (B_{phi }dot{B}_{phi }^{2}) term, which results in a phase space not necessarily of the Van der Pol universality class. Additionally, we show that higher-order nonlinearities are disfavored, and we discuss how to interpret our findings in terms of a mean-field dynamo model with a novel quenching term.

In this work we compare the full-disk line-of-sight magnetic field measurements of the Helioseismic and Magnetic Imager (HMI) with the magnetograms from multiple sources including the Global Oscillation Network Group (GONG), the Michelson Doppler Imager (MDI), the Synoptic Optical Long-term Investigations of the Sun (SOLIS) instrument, the Mount Wilson Observatory (MWO), and the Wilcox Solar Observatory (WSO). A scaling factor is then derived that matches the magnetograms from these instruments to those of HMI. The scaling factors are (1.438pm 0.000) for GONG, (0.701pm 0.001) for MDI, (1.038pm 0.001) for SOLIS, (2.795pm 0.002) for MWO, and ({3.582pm 0.006}) for WSO. This scaling factor varies with the center-to-limb distance and field strength. Distortion maps for these instruments are also determined using the HMI data as a reference.

Solar activity seems quite understandable when considered on the scales comparable with a solar cycle, i.e. about 11 years, and on a short time scale of about a year. A solar cycle looks basically (anti)symmetric with respect to the solar equator, while the sunspot distribution is more or less random. We investigated the difference in the spatial distribution of magnetic structures on both time scales in terms of sunspots and the surface large-scale magnetic field and arrived at the conclusion that the structures of each type are created by a specific mechanism. For long-term structures, it is the mean-field dynamo. For the short-term ones, it is the spot production considered as a separate physical mechanism. The relationship between the mean-field dynamo mechanism and the processes of sunspot formation is a complex problem of current interest. The 11-year cycle itself is created by the mean-field dynamo and is most likely determined by processes in the convection zone. However, the transformation of magnetic flux into spots and active regions occurs, apparently, on significantly shorter time scales and probably develops directly in the subsurface layers, i.e., Near-Surface Shear Layer (NSSL) or leptocline.

We investigate the relationship between the gamma-ray emission measured with the Large Area Telescope on board Fermi (Fermi-LAT9 and radio signatures of coronal shock waves in four behind-the-limb (BTL) solar flares. All events were associated with metric type II radio bursts. Both start and end times of the radio bursts were synchronized with the gamma-ray emission. The type II bursts associated with the BTL gamma-ray flares had higher speeds and lower formation heights than those of an average sample. These findings support the notion that the highly relativistic ions that produce the gamma-rays in BTL flares are accelerated at CME-driven propagating coronal shock waves rather than in large-scale coronal loops.

Solar eruptive events such as flares and coronal mass ejections can accelerate charged particles up to nearly relativistic energies producing so-called solar energetic particles (SEPs). Some of those SEPs can propagate towards Earth and be registered by, e.g., particle detectors onboard satellites. Favourable acceleration conditions make strong SEP events possible with a high flux of high-energy (> 500 MeV) protons, which can be registered even on the ground by neutron monitors (NMs) as rapid enhancements of their count rate over the background. Such events are accordingly called ground-level enhancements (GLEs). GLEs are rare, with only 73 events registered from 1942 to 2023, and three more GLEs 74 – 76 occurred in 2024, close to the maximum of solar activity. In this work, we report GLE 75 that happened on 8 June 2024, initially missed during real-time monitoring, but identified retrospectively. The SEP event, which induced the GLE, was associated with a flare from the solar active region 13697 (13664 on the previous solar rotation). It caused statistically significant increases in the count rate of NMs Dome C, South Pole, and Peawanuck, as well as in the proton intensity measured by Geostationary Operational Environmental Satellite GOES-16. Here, we show the GLE in NM data, describe the procedure of evaluation of its statistical significance, and present the analysis with reconstruction of the spectral and angular SEP distributions.