Solar Physics最新文献

We perform a statistical analysis of 112 proton events from 24 November 2000 to 20 December 2014, accompanied by an increase in the intensity of solar energetic particles (SEPs) with energy (E_{p} > 1)–850 MeV using GOES data. All events were accompanied by metric type II radio bursts in the frequency range of 25–180 MHz observed with the Radio Solar Telescope Network. A correlation in the peak proton integral intensity (I_{p}) with the intensity of type II radio bursts (I_{i}) and the frequency drift rate (V) is shown. Taking into account the helio-longitudinal weakening, i.e. the dependence of SEP intensity on the heliographic longitude of the flare, we find that the correlation coefficients between (I_{p}) and (I_{i}), as well as between (I_{p}) and (V) for protons with (E_{p} > 30) MeV are 0.79 and 0.71, respectively. This suggests that non-thermal electrons, which drive type II radio bursts, and energetic protons are generated at the front of the same shock wave. The correlation coefficients mentioned above decrease for (E_{p} gtrsim100) MeV. Therefore, the contribution of high energetic protons to the integral intensity (I_{p}) is rather determined by accelerated processes in the flare energy release region. The weak dependence of SEP intensity on the helio-longitudinal weakening is discussed.

The open solar flux (OSF) is the integrated unsigned magnetic flux leaving the top of the solar atmosphere to form the heliospheric magnetic field. As the OSF modulates the intensity of galactic cosmic rays at Earth, the production rate of cosmogenic isotopes – such as ¹⁴C and ¹⁰Be stored in tree rings and ice sheets – is closely related to the OSF. Thus on the basis of cosmogenic isotope data, OSF can be reconstructed over millennia. As sunspots are related to the production of OSF, this provides the possibility of reconstructing sunspot number (SSN) and hence properties of the solar cycles prior to the first sunspot telescopic observations in 1610. However, while models exist for estimating OSF on the basis of SSN, the hysteresis present in OSF and the lack of a priori knowledge of the start/end dates of individual solar cycles means that directly inverting these models is not possible. We here describe a new method that uses a forward model of OSF to estimate SSN and solar cycle start/end dates through a Monte Carlo approach. The method is tested by application to geomagnetic reconstructions of OSF over the period 1845-present, and compared to the known SSN record for this period. There is a substantial improvement in reconstruction of both the SSN time series and the solar cycle start/end dates compared with existing OSF-SSN regression methods. This suggests that more accurate solar-cycle information can be extracted from cosmogenic isotope records by forward modelling, and also provides a means to assess the level of agreement between independent SSN and OSF reconstructions. We find the geomagnetic OSF and observed SSN agree very well after 1875, but do differ during the early part of the geomagnetic record, though still agree within the larger observational uncertainties.

Numerical simulations of a propagating slow magnetoacoustic wave guided by a field-aligned low-(beta ) plasma nonuniformity are performed in terms of ideal magnetohydrodynamics, aiming at modeling propagating extreme ultraviolet (EUV) emission disturbances observed in the solar corona. The perpendicular profiles of the equilibrium density and temperature are smoothly nonuniform, resulting in smoothly nonuniform profiles of the sound and tube speeds. It is found that an initially plane wavefront perpendicular to the magnetic field experiences a growing deformation with the distance from the driver. The segments of the wavefront located at higher sound speed regions propagate along the field faster. This results in progressively increasing phase mixing. At some distance from the wave driver, at a certain perpendicular cross-section of the nonuniformity, there are opposite phases of the wave. As local perpendicular phase and group speeds are opposite to each other, the slow wave energy tends towards regions of the higher local sound speed. This effect increases with the increase in the plasma-(beta ). Thus, plasma nonuniformities with temperature decreases are slow magnetoacoustic anti-waveguides, while those with temperature increases are waveguides. In the optically thin radiation regime, typical for the EUV emission from the solar corona, phase mixing of slow waves leads to apparent damping of the waves. This damping is not connected with any dissipative process, and is caused by the destructive interference of slow perturbations with different phases, integrated along the line of sight. The apparent damping depends on the combination of magnetic-field strengths, plasma-(beta ), and viewing angles. This effect could be responsible for nonsystematic dependencies of the damping length upon the oscillation periods and the plasma temperature, appearing in observations.

Magnetic bright points (MBPs) are located in intergranular channels on the solar surface. Studying the properties and evolution process of MBPs can help us to better understand solar activity and predict solar events that have a significant impact on Earth. In this study, we performed a statistical analysis of MBPs at different latitudes and longitudes. Data from the quiet-Sun (QS) in the eastward-equator (8 June 2021) and in the southern hemisphere (31 July 2020), as well as data from the QS near the disk center (30 July 2020), are analyzed. We studied the properties of MBPs, including lifetime, intensity contrast, and velocity. Moreover, we analyzed the intensity contrast of isolated MBPs at the moments of their birth and disappearance at different latitudes and longitudes, as well as the variation in the number of MBPs that appeared and disappeared in each frame. The results show that non-isolated MBPs have longer lifetimes than isolated MBPs, and the average lifetime of non-isolated MBPs located in the southern hemisphere (SH) is significantly shorter than that of MBPs near the disk center (DC) in the eastward-equator (EE). We find that the lifetime of non-isolated MBPs in the SH is negatively correlated with the intensity contrast, with higher intensity contrast associated with a shorter lifetime. The velocities of isolated MBPs at different latitudes and longitudes follow a Rayleigh distribution, while the velocities of non-isolated MBPs follow a log-normal distribution. Non-isolated MBPs exhibit higher horizontal velocities, with the maximum horizontal velocity reaching 8 km s⁻¹. Finally, we find that the number of isolated MBPs per square Mm at different latitudes and longitudes remains stable during consecutive periods, and the intensity contrast of isolated MBPs is similar at the moment of their birth and disappearance.

Several strong eruptive events that occurred near the solar limb were reported generating off-limb features detectable in the SDO/HMI’s continuum intensity. These observations offer new insights into the emission mechanisms of off-limb flaring loops, magnetic strength in the loops, and electron density distributions, among others. However, only a limited number of such events were reported, and it is unclear whether off-limb white-light features are popular or only associated with specific eruptions. In this study, we surveyed all the flaring events that occurred between May 2010 and August 2023 with a magnitude stronger than M2.0 and a heliographic longitude larger than (65^{circ }). We found that among the 189 flares that met our selection criteria, 78 (41.3%) had off-limb features associated with them. Further statistical analysis showed, unsurprisingly, that the stronger the flare, the more likely it has an off-limb white-light feature, and the closer the flare is to the limb, the more likely an off-limb feature is detectable. We then categorized these off-limb white-light events into four types, closed-loop eruptions, open-loop eruptions, fast ejection, and flare arcades, and identified the events with visible flare ribbons. Coupling two examples of the white-light observations with simultaneous UV/EUV observations, we demonstrate the usefulness of the former in studying the flare dynamics and emission mechanisms. Our catalogue provides a rather complete list of the off-limb white-light events, which will benefit the community interested in studying such events.

We consider variations of the azimuthal magnetic fields of the Sun in the 23 – 25 activity cycles according to observations with SDO/HMI, SOHO/MDI, and Kislovodsk/STOP telescopes. To identify azimuthal magnetic fields, the daily observations of LOS magnetic fields from the regions near the solar limb were analyzed. It is shown that with a sufficiently large averaging of the data, large-scale structures are distinguished, which can be interpreted by horizontal magnetic fields along the east – west direction. Azimuthal magnetic fields are visible at both low and high latitudes. Azimuthal fields at the same latitudes have opposite directions in the northern and southern hemispheres and also change sign in even and odd cycles of activity.

The mechanism of formation of global azimuthal magnetic fields and their role in the cycle of solar activity is discussed. The near-surface azimuthal magnetic field is closely related to the activity cycle. Apparently, the azimuthal field is formed from U-shaped flux tubes of active regions (AR). Due to the presence of the tilt angle AR during differential rotation, the subsurface magnetic fields are pulled in the azimuthal direction. The role of azimuthal magnetic fields in solar activity cycles is considered. A scheme for the generation of a magnetic field different from Babcock – Leighton dynamo models is proposed.

The solar physics community is entering a golden era that is ripe with next-generation ground- and space-based facilities, advanced spectral inversion techniques, and realistic simulations that are becoming more computationally streamlined and efficient. With ever-increasing resolving power stemming from the newest observational telescopes, it becomes more challenging to obtain (near-)simultaneous measurements at high spatial, temporal and spectral resolutions, while operating at the diffraction limit of these new facilities. Hence, in recent years there has been increased interest in the capabilities integral field units (IFUs) offer towards obtaining the trifecta of high spatial, temporal and spectral resolutions contemporaneously. To date, IFUs developed for solar physics research have focused on mid-optical and infrared measurements. Here, we present an IFU prototype that has been designed for operation within the near-ultraviolet to mid-optical wavelength range, which enables key spectral lines (e.g., Ca ii H/K, H(beta ), Sr ii, Na i D₁/D₂, etc.) to be studied, hence providing additional spectral coverage to the instrument suites developed to date. The IFU was constructed as a low-budget proof-of-concept for the upcoming (2text{ m}) class Indian National Large Solar Telescope and employs circular cross-section fibres to guide light into a Czerny–Turner configuration spectrograph, with the resulting spectra captured using a high quantum efficiency scientific CMOS camera. Mapping of each input fibre allows for the reconstruction of two-dimensional spectral images, with frame rates exceeding (20text{ s}^{-1}) possible while operating in a non-polarimetric configuration. Initial commissioning of the instrument was performed at the Dunn Solar Telescope, USA, during August 2022. The science verification data presented here highlights the suitability of fibre-fed IFUs operating at near-ultraviolet wavelengths for solar physics research. Importantly, the successful demonstration of this type of instrument paves the way for further technological developments to make a future variant suitable for upcoming ground-based and space-borne telescope facilities.