Solar Physics最新文献

Active regions (ARs) appear in the solar atmosphere as a consequence of the emergence of magnetic-flux ropes (FR). In this study, we use Bayesian methods to analyze line-of-sight magnetograms of emerging ARs. We employ a FR model consisting of a half-torus field structure based on eight parameters. The goal is to derive constrained physical parameters of the originating FR that are consistent with the observations. Specifically, we aim to obtain a precise estimation of the AR tilt angle and magnetic twist at different stages of the emergence process. To achieve this, we propose four temporal methods that correlate the field-parameter evolutions with a single coherent FR. These methods differ from each other in the size of the explored parameter space. We test the methods on four bipolar ARs observed with the Michelson Doppler Imager on board the Solar and Heliospheric Observatory. We find that tilt angles are typically consistent between the temporal methods, improving previous estimations at all stages of the emergence. The twist sign derived from the temporal methods is consistent with previous estimations. The standard errors of all the methods used are similar, indicating that they model the observations equally well. These results indicate that the proposed methods can be used to obtain global magnetic parameters of ARs during their early evolution. The derived parameters contribute to a better understanding of the formation of FRs, and the role of ARs in the magnetic recycling process along the solar cycle.

The association of coronal mass ejections (CMEs) with flares is related to the question of whether reconnection is necessary for the CME eruption. Indeed, if reconnection happens during a CME eruption, the plasma is heated, which can be observed as a flare. In this work, we study the CME-flare association using data obtained with the Mg xii spectroheliograph on board the Complex Orbital Observations Near-Earth of Activity on the Sun (CORONAS-F) satellite. This instrument is sensitive only to the emission of plasma with a temperature greater than 4 MK, which makes it a convenient tool for detection of flaring activity. During our analysis, we first searched for CMEs detected during the Mg xii observations by the Large Angle and Spectroscopic Coronagraph (LASCO). Then, we visually checked the Mg xii images for flaring activity. We found that during the Mg xii observations (2001 – 2003), 198 CMEs were detected by LASCO. One hundred sixty of them (81%) are associated with flares seen in the Mg xii images. The strength of flares associated with narrow CMEs – jet-like ejecta – is uniformly distributed in the A – C GOES class range. The speed of narrow CMEs does not depend on the flare strength. For normal CMEs (motion of both magnetic field and plasma), the flare strength varies from A to X class with a peak of the distribution at the C level. The median speed and the kinetic energy of normal CMEs weakly depend on flare strength for weak flares (below C) and strongly for strong ones (M and X). Our results suggest that at solar maximum reconnection occurs during most CMEs. For strong flares (M and X), the reconnection is a dominant acceleration mechanism. For weak flares (C and below), other mechanisms start to play a bigger role.

Observations have shown that the chromosphere networks are rich in features with density higher than the ambient atmosphere. To investigate the effect of horizontal density-inhomogeneity on spicules, here we carry out two-dimensional magnetohydrodynamic (MHD) simulations based on the shock scenario. In a gravitationally stratified solar atmosphere, we insert a vertical preexisting density structure (PeDS) that has higher density than the ambient regions, and then we drive a spicule by a velocity pulse at the bottom of the chromosphere. We find a horizontal flow of 2 km s⁻¹ caused by a rarefaction wave that may have a certain material supplement effect for the spicules and a V-shaped shock front in the chromosphere. An interesting feature found in our experiment is that the existence of PeDS leads to the formation of multiple threads in spicules. Their formation results from the larger density, lower transition region, and higher speeds of magnetoacoustic waves in the PeDS than at its outer boundaries. Parameter studies show that multiple threads of a spicule can be more pronounced in cases with wider velocity pulses and a larger internal/external density ratio in the PeDS. Our study shows that the horizontal density-inhomogeneity in the solar atmosphere is an important factor that is responsible for the complexity of a spicule.

We analyze the magnetic evolution of solar active region (AR) NOAA 11476 that, between May 9 and 10, 2012, produced a series of surge-type eruptions accompanied by GOES X-ray class-M flares. Using force-free models of the AR coronal structure and observations at several wavelengths, in previous works we studied the detailed evolution of those eruptions, relating them to the characteristic magnetic topology of the AR and reconstructing the involved reconnection scheme. We found that the eruptions were due to the ejection of minifilaments, which were recurrently ejected and reformed at the polarity-inversion line of a bipole that emerged in the middle of the positive main AR magnetic polarity. The bipole was observed to rotate for several tens of hours before the events. In this article we analyze, for the full AR and the rotating bipole, the evolution of a series of magnetic parameters computed using the Helioseismic and Magnetic Imager (HMI) vector magnetograms. We combine this analysis with estimations of the injection of magnetic energy and helicity obtained using the Differential Affine Velocity Estimator for Vector Magnetograms (DAVE4VM) method that determines, from vector magnetograms, the affine velocity field constrained by the induction equation. From our results, we conclude that the bipole rotation was the main driver that provided the magnetic energy and helicity involved in the minifilament destabilizations and ejections. The results also suggest that the observed rotation is probably due to the emergence of a kinked magnetic flux rope with negative writhe helicity.

Solar radio bursts are intense radio radiation sources that occur during the energy-release process and represent a hot topic in solar-physics and space-weather research. In this paper, we present a multimode prediction model for daily solar radio bursts. The model uses deep learning and machine learning to obtain data information from different dimensions and to establish the relationship between the characteristics of the solar active region on the solar surface and solar radio bursts. For this model, we use data from the Solar and Heliospheric Observatory (SOHO)/Michelson Doppler Imager (MDI) total solar magnetic map, the Royal Observatory of Belgium World Data Centre in Brussels, and NOAA sunspot parameters (including number, area, and type of sunspots) as inputs. The output results are then compared with the list of solar radio bursts recorded by the Radio Solar Telescope Network (RSTN) to determine whether solar radio bursts are present and to determine the key parameters for determining radio bursts. Based on 5449 days of observational data, we find that the prediction accuracy of the model is 0.898 ± 0.011, and that the number of sunspots is a key parameter in determining the occurrence of solar radio bursts. Specifically, when the number of sunspots is greater than 15, the probability of occurrence of solar radio bursts is greater than 90%. We have identified the key parameters and thresholds for determining solar radio bursts and highlighted the key parameters for space-weather prediction. In addition, the prediction model can also be used for predicting in other fields.