Solar Physics最新文献

Geomagnetic storms resulting from solar disturbances impact telecommunication and satellite systems. Satellites are positioned at Lagrange point L1 to monitor these disturbances and give warning 30 min to 1 h ahead. As propagation delay from L1 to Earth depends on various factors, estimating the delay using the assumption of ballistic propagation can result in greater uncertainty. In this study, we aim to reduce the uncertainty in the propagation delay by using machine-learning (ML) models. Solar-wind velocity components ((V_{ mathrm{x}}), (V_{mathrm{y}}), (V_{mathrm{z}})), the position of Advanced Composition Explorer (ACE) at all three coordinates ((r_{mathrm{x}}), (r_{mathrm{y}}), (r_{mathrm{z}})), and the Earth’s dipole tilt angle at the time of the disturbances are taken as input parameters. The target is the time taken by the disturbances to reach from L1 to the magnetosphere. The study involves a comparison of eight ML models that are trained across three different speed ranges of solar-wind disturbances. For low and very high-speed solar wind, the vector-delay method fares better than the flat-plane propagation method and ML models. Ridge regression performs consistently better at all three speed ranges in ML models. For high-speed solar wind, boosting models perform well with an error of around 3.8 min better than the vector-delay model. Studying the best-performing models through variable-importance measures, the velocity component (V_{mathrm{x}}) is identified as the most important feature for the estimation and aligns well with the flat-plane propagation method. Additionally, for slow solar-wind disturbances, the position of ACE is seen as the second most important feature in ridge regression, while high-speed disturbances emphasize the importance of other vector components of solar-wind speed over the ACE position. This work improves our understanding of the propagation delay of different solar-wind speed and showcases the potential of ML in space weather prediction.

The AIA 304 Å channel on board the Solar Dynamics Observatory (SDO) offers a unique view of (approx 10^{5}text{ K}) plasma emitting in the He ii 304 Å line. However, when observing off-limb, the emission of the (small) cool structures in the solar atmosphere (such as spicules, coronal rain and prominence material) can be of the same order as the surrounding hot coronal emission from other spectral lines included in the 304 Å passband, particularly over active regions. In this paper, we investigate three methods based on temperature and morphology that are able to distinguish the cool and hot emission within the 304 Å passband. The methods are based on the Differential Emission Measure (DEM), a linear decomposition of the AIA response functions (RFit) and the Blind Source Separation (BSS) technique. All three methods are found to produce satisfactory results in both quiescent and flaring conditions, largely removing the diffuse corona and leading to images with cool material off-limb in sharp contrast with the background. We compare our results with co-aligned data from the Interface Region Imaging Spectrograph (IRIS) in the SJI 1400 Å and 2796 Å channels, and find the RFit method to best match the quantity and evolution of the cool material detected with IRIS. Some differences can appear due to plasma emitting in the (log T=5.1,text{--},5.5) temperature range, particularly during the catastrophic cooling stage prior to rain appearance during flares. These methods are, in principle, applicable to any passband from any instrument suffering from similar cool and hot emission ambiguity, as long as there is good coverage of the high-temperature range.

The solar eruption that occurred on 28 November 2023 (SOL2023-11-28) triggered an intense geomagnetic storm on 1 December 2023. The associated terrestrial auroras manifested at the most southern latitudes in the northern hemisphere observed in the past two decades. In order to explore the profound geoeffectiveness of this event, we conducted a comprehensive analysis of its solar origin to offer potential factors contributing to its impact. Magnetic flux ropes (MFRs) are twisted magnetic structures recognized as significant contributors to coronal mass ejections (CMEs), thereby impacting space weather greatly. In this event, we identified multiple MFRs in the solar active region and observed distinct slipping processes of the three MFRs: MFR1, MFR2, and MFR3. All three MFRs exhibit slipping motions at a speed of 40 – 137 km s⁻¹, extending beyond their original locations. Notably, the slipping of MFR2 extends to (sim 30text{ Mm}) and initiates the eruption of MFR3. Ultimately, MFR1’s eruption results in an M3.4-class flare and a CME, while MFR2 and MFR3 collectively produce an M9.8-class flare and another halo CME. This study shows the slipping process in a multi-MFR system, showing how one MFR’s slipping can trigger the eruption of another MFR. We propose that the CME–CME interactions caused by multiple MFR eruptions may contribute to the significant geoeffectiveness.

The combination of the H i Ly(alpha ) (121.6 nm) line formation mechanism with ultraviolet (UV) Ly(alpha ) and white-light (WL) observations provides an effective method for determining the electron temperature of coronal mass ejections (CMEs). A key to ensuring the accuracy of this diagnostic technique is the precise calculation of theoretical Ly(alpha ) intensities. This study performs a modeled CME and its driven shock via the three-dimensional numerical magneto-hydrodynamic simulation. Then, we generate synthetic UV and WL images of the CME and shock within a few solar radii to quantify the impact of different assumptions on the theoretical Ly(alpha ) intensities, such as the incident intensity of the solar chromospheric Ly(alpha ) line ((I_{disk})), the geometric scattering function ((p(theta ))), and the kinetic temperature ((T_{ boldsymbol{n}})) assumed to be equal to either the proton ((T_{p})) or electron ((T_{e})) temperature. By comparing differences of the Ly(alpha ) intensities of the CME and shock under these assumptions, we find that: (1) Using the uniform or Carrington maps of the disk Ly(alpha ) emission underestimates the corona Ly(alpha ) intensity (with relative uncertainties below 10%) compared to the synchronic map, except for a slight overestimate (<4%) observed in the partial CME core. The Carrington map yields lower uncertainties than the uniform disk. (2) Neglecting the geometric scattering process has a relatively minor impact on the Ly(alpha ) intensity, with a maximum relative uncertainty of no more than 5%. The Ly(alpha ) intensity is underestimated for the most part but overestimated in the CME core. (3) Compared to the assumption (T_{boldsymbol{n}}=T_{p}), using (T_{boldsymbol{n}}=T_{e}) leads to more complex relative uncertainties in CME Ly(alpha ) intensity. The CME core and void are both overestimated, with the maximum relative uncertainty in the core exceeding 50% and in the void remaining below 35%. An appropriate increasing proton-to-electron temperature ratio can reduce the uncertainty in the CME core and void. In the CME front, both overestimates and underestimates exist with relative uncertainties of less than 35%. The electron temperature assumption has a smaller impact on the shock, with an underestimated relative uncertainty of less than 20%.

In this study, we investigate the decay of sunspots in the active region NOAA 13229 using data from the ASO-S/FMG and SDO/HMI. We closely examine the decay patterns of sunspots S1 and S2, which reveal different decay rates and features due to the mechanisms of magnetic cancellation, dispersion, and the role of horizontal flows. Our analysis highlights the significant impact of magnetic flux changes, including the decrease of both the sunspot area and magnetic flux over time, which adheres to distinct decay laws. This study elucidates the complex interplay between magnetic submergence, cancellation, and dispersion in the sunspot decay process, contributing to our understanding of the underlying mechanisms driving these phenomena. Our results emphasize the importance of horizontal flow dynamics in shaping the decay characteristics of sunspots, providing insights for the role played by the magnetic and plasma processes in solar active regions.

The long-term study of the temporal variation of the rotation period of the solar photosphere, chromosphere, and corona has been widely undertaken. To date it is unclear whether the temporal variation of the rotation period of the solar transition region has a systematic periodicity. In this article we perform a study on the temporal variation of the rotation period of the solar transition region. For this purpose, we use the Lyman (alpha ) line emission at a wavelength of 121.56 nm corresponding to the solar transition region from the year 1965 to 2019, covering four complete solar cycles (i.e., Cycles 21, 22, 23, 24) as well as descending and ascending phases of Cycles 20 and 25, respectively. An autocorrelation analysis depicts that the average sidereal rotation period of the transition region (from 1965 to 2019) is 24.8 days. Furthermore, we find that a significant periodicity of about 12 years exists in the temporal variation of the sidereal rotation period of the solar transition region. The results indicate that this periodicity is closely linked to the 11-year Schwabe cycle. A cross-correlation analysis between the time series of the sidereal rotation period and sunspot numbers (as a function of lag in years) exhibits a positive correlation between these aforementioned parameters. From this result, we can state that the sidereal rotation period of the solar transition region leads the solar activity by about six months. This correlation again proves the periodicity of about 11 years in the rotation period of the transition region which is closely linked to the 11-year Schwabe cycle. Furthermore, long-term variation of rotation periods also demonstrates a decreasing trend from 1965 to 2019, which is similar to that in the sunspot numbers. From this long-term study, it seems that solar activity is largely driven by solar rotation.

Sympathetic eruptions of solar prominences have been studied for decades, however, it is usually difficult to identify their causal links. Here, we present two failed prominence eruptions on 26 October 2022 and explore their connections. Using stereoscopic observations, the South prominence (PRO-S) erupts with untwisting motions, flare ribbons occur underneath, and new connections are formed during the eruption. The North prominence (PRO-N) rises up along with PRO-S, and its upper part disappears due to catastrophic mass draining along an elongated structure after PRO-S failed eruption. We suggest that the eruption of PRO-S initiates due to a kink instability, and fails to erupt due to reconnection with surrounding fields. The elongated structure connecting PRO-N overlies PRO-S, which causes the rising up of PRO-N along with PRO-S and mass drainage after PRO-S eruption. This study suggests that a prominence may end its life through mass drainage forced by an eruption underneath.

Filament eruptions often result in flares and coronal mass ejections (CMEs). Most studies attribute the filament eruptions to their instabilities or magnetic reconnection. In this study, we report a unique observation of a filament eruption whose initiation process has not been reported before. This large-scale filament, with a length of about 360 Mm crossing an active region, is forced to erupt by two small-scale erupting filaments pushing out from below. This process of multifilament eruption results in an M6.4 flare in the active region NOAA 13229 on 25 February 2023. The whole process can be divided into three stages: the eruptions of two active-region filaments, F1 and F2; the interactions between the erupting F1, F2, and the large-scale filament F3; and the eruption of F3. Though this multifilament eruption occurs near the northwest limb of the solar disk, it produces a strong halo CME that causes a significant geomagnetic disturbance. Our observations present a new filament eruption mechanism in which the initial kinetic energy of the eruption is obtained from and transported to by other erupting structures. This event provides us a unique insight into the dynamics of multifilament eruptions and their corresponding effects on the interplanetary space.

We present a new iterative rotation inversion technique based on the Simultaneous Algebraic Reconstruction Technique developed for image reconstruction. We describe in detail our algorithmic implementation and compare it to the classical inversion techniques like the Regularized Least Squares (RLS) and the Optimally Localized Averages (OLA) methods. In our implementation, we are able to estimate the formal uncertainty on the inferred solution using standard error propagation, and derive the averaging kernels without recourse to any Monte-Carlo simulation. We present the potential of this new technique using simulated rotational frequency splittings. We use noiseless sets that cover the range of observed modes and associate to these artificial splittings observational uncertainties. We also add random noise to present the noise magnification immunity of the method. Since the technique is iterative we also show its potential when using an a priori solution. With the correct regularization, this new method can outperform our RLS implementation in precision, scope, and resolution. Since it results in very different averaging kernels where the solution is poorly constrained, this technique infers different values. Adding such a technique to our compendium of inversion methods will allow us to improve the robustness of our inferences when inverting real observations and better understand where they might be biased and/or unreliable, as we push our techniques to maximize the diagnostic potential of our observations.

We analyzed Interface-Region Imaging Spectrograph (IRIS) and Solar Dynamics Observatory/Atmospheric Imaging Assembly (SDO/AIA) observations of a small coronal jet that occurred at the solar west limb on 29 August 2014. The jet source region, a small bright point, was located at an active-region periphery and contained a fan-spine topology with a mini-filament. Our analysis has identified key features and timings that motivated the following interpretation of this event. As the stressed core flux rises, a current sheet forms beneath it; the ensuing reconnection forms a flux rope above a flare arcade. When the rising filament-carrying flux rope reaches the stressed null, it triggers a jet via explosive interchange (breakout) reconnection. During the flux-rope interaction with the external magnetic field, we observed brightening above the filament and within the dome, along with a growing flare arcade. EUV images reveal quasi-periodic ejections throughout the jet duration with a dominant period of 4 minutes, similar to coronal jetlets and larger jets. We conclude that these observations are consistent with the magnetic breakout model for coronal jets.