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We estimate the contributions to the solar-cycle variation of solar meridional and zonal flows near the surface expected solely from local magnetic regions. Maps of flows near magnetic regions are obtained using helioseismic holography and averaged over ensembles of such regions with similar magnetic flux. These averaged flows are assigned to the positions and times of all magnetic regions identified from daily magnetograms over an 11 yr period. Residuals are obtained after averaging both meridional and zonal-flow components over longitude for each Carrington rotation and subtracting the temporal mean at each latitude. Results indicate that magnetic regions produce solar-cycle variations of both components in the active latitude range with peak amplitudes of about 1 m s−1, which represents only a fraction of the known variations in either the residual zonal or meridional flow with amplitudes around 3 and 5 m s−1, respectively. Thus it is unlikely that active regions, and compact magnetic concentrations in general, are the primary source of the 11 yr variation in these global flows. A threshold magnetic flux of 5 × 1020 Mx, below which no significant flows are observed, is identified as a check on the completeness of the set of magnetic regions. We also find that inflows around most magnetic regions are confined to within 10°–12° of their centers, in contrast with recent evidence of more extended inflows. [ABSTRACT FROM AUTHOR]

Mars lacks a global intrinsic dipole field but possesses localized crustal fields, making it unique in the solar system. Recent observations revealed that electrons can be injected into the crustal fields, and exhibit drift-dispersed bursts due to the magnetic drift motion, which are characterized by increases or decreases in energy over time in the energy spectrum. However, the source of the drift-dispersed electrons and the mechanism of their injection into the crustal fields remains unclear. Here, by leveraging data from the Mars Atmosphere and Volatile EvolutioN mission, along with test-particle simulations, we reveal that the source of dispersed electrons is the precipitating electrons injected into the crustal fields via open field lines. These electrons display as dispersionless bursts near the source location, and as dispersed bursts as they drift away from the source. Thus, the dispersed electrons represent a later stage in the evolution of dispersionless electrons. This evolutionary process closely mirrors that observed within Earth's dipole field, affirming that the crustal fields function similarly to a mini-magnetosphere. [ABSTRACT FROM AUTHOR]

Coronal mass ejections from the Sun are not always initiated along a radial trajectory; such non-radial eruptions are well known to be caused by the asymmetry of the pre-eruption magnetic configuration, which is primarily determined by the uneven distribution of magnetic flux at the photosphere. Therefore, it is naturally expected that the non-radial eruptions should be rather common, at least as frequent as radial ones, given the typically asymmetrical nature of photospheric magnetic flux. However, statistical studies have shown that only a small fraction of eruptions display non-radial behaviour. Here we aim to shed light on this counterintuitive fact, based on a series of numerical simulations of eruption initiation in bipolar fields with different asymmetric flux distributions. As the asymmetry of the flux distribution increases, the eruption direction tends to deviate further away from the radial path, accompanied by a decrease in eruption intensity. In case of too strong asymmetry, no eruption is triggered, indicating that excessively inclined eruptions cannot occur. Therefore, our simulations suggest that asymmetry plays a negative role in producing eruption, potentially explaining the lesser frequency of non-radial solar eruptions compared to radial ones. With increasing asymmetry, the degree of non-potentiality the field can attain is reduced. Consequently, the intensity of the pre-eruption current sheet decreases, and reconnection becomes less efficient, resulting in weaker eruptions. [ABSTRACT FROM AUTHOR]

Based on the consecutive synoptic magnetic maps, we devise a new method to calculate the solar differential rotation coefficients. This method is very easy to implement and has a high accuracy. Firstly, based on the two-term or three-term differential rotation formula, we simulate a synoptic map CR |$_{n}$| evolves one Carrington Rotation (CR) time only under the effect of the differential rotation, and thereby a stretched synoptic map CR |$_{n*}$| is obtained. Then, through searching the maximum covariance between the maps CR |$_{n*}$| and CR |$_{n+1}$| by the grid search method, the rotation coefficients can be determined. Based on the synoptic maps of CRs 1625 to 2278 (during the years 1975–2023), the two-term coefficients A and B for latitude region between |$\pm 40^{\circ }$| are calculated. The rotation coefficient B shows an obvious 11-yr period. From the time series of B , we find that the Sun usually rotates more differentially in the rising phases of the sunspot cycles than in the falling phases. Moreover, the strong magnetic field corresponds to an increasing of B (note that B has a negative sign) or decreasing of differential. The evolutionary trend of B also indicates that there are several years until the maximum value of B will be reached in solar cycle 25, and the coefficient B will be still in the rising phase in the few coming years. The two-term rotation coefficients for the two hemispheres are also calculated separately, and in the studied time-scale, the largest N–S asymmetry of the rotation rate appeared in October 2007. [ABSTRACT FROM AUTHOR]

Emerging active regions are associated with convective flows on the spatial scale and lifetimes of supergranules. To understand how these flows are involved in the formation of active regions, we aim to identify where active regions emerge in the supergranulation flow pattern. We computed supergranulation scale flow maps at the surface for all active regions in the Solar Dynamics Observatory Helioseismic Emerging Active Region Survey. We classified each of the active regions into four bins based on the amplitude of their average surface flow divergence at emergence. We then averaged the flow divergence over the active regions in each bin as a function of time. We also considered a corresponding set of control regions. We found that, on average, the flow divergence increases during the day prior to emergence at a rate independent of the amount of flux that emerges. By subtracting the averaged flow divergence of the control regions, we found that active region emergence is associated with a remaining converging flow at 0.5–1 d prior to emergence. This remnant flow, |$\Delta \, \mathrm{div} \, \boldsymbol {v}_{\rm h} = (-4.9 \pm 1.7) \times 10^{-6}\,{\rm s}^{-1}$|⁠ , corresponds to a flow speed of 10–20 m s−1 (an order of magnitude less than supergranulation flows) out to a radius of about 10 Mm. We show that these observational results are qualitatively supported by simulations of a small bipole emerging through the near-surface convective layers of the Sun. The question remains whether these flows are driving the emergence, or are caused by the emergence. [ABSTRACT FROM AUTHOR]

After days of intense solar activity, active region AR3664 launched seven CMEs toward Earth producing an extreme G5 geomagnetic storm commencing at 17:05 UT on 10 May 2024. The storm impacted power grids, disrupted precision navigational systems used by farming equipment, and generated aurora seen around the globe. The storm produced remarkable effects on composition, temperature, and dynamics in the Earth's thermosphere that were observed by NASA's Global‐scale Observations of the Limb and Disk (GOLD) mission and are reported here for the first time. We use synoptic disk images of ΣO/N2 and neutral temperature (at ∼160 km) measured by GOLD to directly link dynamics resulting from the storm with dramatic changes in thermospheric composition and temperature. We observe a heretofore unseen spatial morphology simultaneously in ΣO/N2, neutral temperature, and total electron content. Equator‐to‐pole temperature differences reach 400 K with high latitude peak neutral temperatures near 160 km exceeding 1400 K. Plain Language Summary: On Saturday 10 May 2024, the sun launched a wave of energized plasma toward the Earth. A large disturbance in the Earth's magnetic field associated with the solar wind resulted in an extreme geomagnetic storm. The storm impacted power grids, disrupted navigational systems used by farming equipment, and produced aurora seen around the globe. The storm produced remarkable effects in the Earth's upper atmosphere that were observed by NASA's Global‐scale Observations of the Limb and Disk (GOLD) mission. In this letter, we use images measured by GOLD to directly link atmospheric dynamics resulting from the May 10–12 superstorm with dramatic changes in composition, temperature, and global circulation in the Earth's upper atmosphere. We observe previously unseen structure in the upper atmosphere associated with equator‐to‐pole temperature differences exceeding 400 K. Peak neutral temperatures near 160 km exceed 1400 K at high latitudes. Key Points: GOLD disk images of ΣO/N2 and neutral temperature link storm time dynamics with changes in thermospheric composition and temperatureWe observe a previously unseen spatial morphology in ΣO/N2, neutral temperature, and total electron contentPeak equator‐to‐pole temperature differences exceed 400 K but relax to pre‐storm conditions well before ΣO/N2 [ABSTRACT FROM AUTHOR]

Magnetic null points are an important aspect of the magnetic field structure of the solar corona and can be sites of enhanced dissipation. This paper uses analytical and numerical models to investigate the plasma structure around a heated null. It is shown that the temperature profile not only differs significantly from that in a uniform field, but also that the profile depends significantly on the spatial structure of the heating. Field lines close to the separatrices and the null point have higher temperatures than a uniform field for the same heating input. The dependence of the results near the null on both the ratio of perpendicular to parallel conduction, and numerical resolution is also explored. The comparison between analytic and numerical solutions also provides a useful benchmark to compare MHD codes with anisotropic thermal conduction. [ABSTRACT FROM AUTHOR]

The long‐standing "energy crisis" at the giant planets refers to the anomalous heating of planetary thermospheres compared to the available energy from solar irradiance. The coupling between planetary magnetospheres and their upper atmospheres is thought to address these crises, though the sources and pathways of energy transport have not been fully explored at each system. In particular, the total available energy from the upstream solar wind at each planet has not been comprehensively quantified. Here we apply recently developed models of energy conversion by magnetic reconnection and the Kelvin‐Helmholtz instability to each of the Giant Planets, providing estimates of the average external energy inputs for each system between 1985 and 2020. We find that external energy associated with solar‐wind‐magnetospheric coupling significantly exceeds that from solar extreme ultraviolet photons. While internal energy sources are known to dominate at Jupiter and Saturn, external sources may be significant at Uranus and Neptune. Plain Language Summary: The upper atmospheres of Jupiter, Saturn, Uranus, and Neptune are all hotter than would be predicted by their exposure to sunlight alone. The space plasma environment around each planet provides an additional reservoir of energy that can be used to provide this heating. Here we quantify the average energy input to each planetary system due to variation of the photons and plasmas emitted from the Sun. We find that the interaction between a planetary magnetic field and the solar interplanetary magnetic field provides a strong source of external energy at each of the planets, on average significantly more than that of light from the Sun. Key Points: Solar wind‐magnetospheric‐coupling provides higher energy input than solar extreme ultraviolet at the giant planetsSolar activity drives solar‐wind‐magnetospheric coupling much more strongly than planetary seasonThe solar wind may drive the energy input to the upper atmospheres at Uranus and Neptune [ABSTRACT FROM AUTHOR]

The occurrence of space weather events, notably geomagnetic storms driven by various solar wind structures, can significantly alter Earth's electromagnetic environment. In this study, we examined the interplanetary origins and statistical distribution of 384 geomagnetic storms ( D s t m i n   ≤ −50 nT) that occurred from September 1996 to December 2023. We statistically analyzed the correlations between storm intensity and solar wind parameters (SWPs) across different subsets. The results indicate that (1) the solar activity level, indicated by the sunspot number (SSN), and the number of geomagnetic storms during the first four years of the 25th solar cycle were intermediate, compared to the first four years of the 23rd and 24th solar cycles. Specifically, ICME-related structures caused 80% of the strong storms ( D s t m i n   ≤ −100 nT) and 34% of the moderate storms (−100 nT < D s t m i n   ≤ −50 nT) from 2020 to 2023. (2) The storm intensity correlated with the peak and/or time-integral values of the southward interplanetary magnetic field (IMF B s ), the dawn–dusk electric field ( E y ), the Akasofu's function (ε), and dynamic pressure ( P s w ) to varying extents. Strong storms exhibited higher correlation levels than moderate ones and ICME-related storms showed larger correlation levels compared to those driven by other sources. (3) Compared with the storms from 1996-09 to 2000-08, the storms that occurred from 2020 to 2023 had lower correlations with the peak values of the IMF B s and E y but higher correlations with the peak value of ε and the time-integral values of the IMF B s , E y , P s w , and ε. (4) Among the 174 events that featured continuous southward IMF during the storm's main phase, the duration of southward IMF during about 66.7% of moderate storms and 51.5% of strong storms were less than 13 h. Continuous southward IMF resulted in more direct and efficient energy coupling, enhancing the correlation between the peak values of SWPs and storm intensity but weakening the relationships with the time-integral values of SWPs. Notably, when the southward IMF persisted for a longer duration (e.g., ∆t > 13 h), the continuous energy input further enhanced correlations with both peak and integral values of SWPs, leading to stronger overall correlations with storm intensity. This analysis sheds light on the intricate relationships between geomagnetic storms and their solar wind drivers, emphasizing the significant influence of ICME-related structures and the duration of southward IMF on storm intensity. [ABSTRACT FROM AUTHOR]

Alfvén-wave turbulence is known as a plasma heating mechanism associated with the acceleration of fast solar wind, found emanating from open magnetic fields adjacent to coronal holes. In this study, we expand the scope of this mechanism to investigate the thermodynamics of Alfvénic slow solar wind, a phenomenon originating from open fields near a streamer, as observed in recent inner heliospheric missions. We demonstrate a one-dimensional two-fluid model that incorporates three components: (1) low-frequency Alfvén-wave turbulence, serving as the primary dissipation mechanism, (2) a curved magnetic field that reproduces the streamer's boundary, and (3) the kinetic instabilities to address proton temperature anisotropy. Our findings suggest that this dissipation mechanism can be applied in common to both fast and Alfvénic slow solar winds. We identify the proton-cyclotron instability near the Sun and the oblique and parallel firehose instabilities occurring close to 1 au as crucial factors governing temperature anisotropy. This study contributes to our understanding of the complex thermodynamics of solar winds and provides valuable insights for future space missions. [ABSTRACT FROM AUTHOR]

We extend our model of magnetic braking (MB), driven by an α–Ω dynamo mechanism, from fully convective M-dwarfs (FCMDs) to explain the surface and internal spin |$P_\mathrm{spin}$| evolution of partly convective dwarfs (PCDs) starting from the disc-dispersal stage to the main-sequence turn-off. In our model, the spin of the core is governed by shear at the core-envelope boundary while the spin of the envelope is governed by MB and shear. We show that (1) the most massive FCMDs experience a stronger spin-down than PCDs and less massive FCMDs, (2) the stalled spin-down and enhanced activity of K-dwarfs and the pile-up of G-dwarfs older than a few Gyr are stellar-structure and MB-dependent, and weakly dependent on core-envelope coupling effects, (3) our expression of the core-envelope convergence time-scale |$\tau _{\text{converge}}(M_\ast , P_{\text{spin}})$| between a few 10 to 100 Myr strongly depends on stellar structure but weakly on MB strength and shear, such that fast and massive rotators achieve corotation earlier, (4) our estimates of the surface magnetic fields are in general agreement with observations and our wind mass loss evolution explains the weak winds from the solar analog |$\pi ^1$| UMa, and (5) with our model the massive young Sun hypothesis as a solution to the faint young Sun problem can likely be ruled out, because the maximum mass lost by winds from our Sun with our model is about an order of magnitude smaller than required to solve the problem. [ABSTRACT FROM AUTHOR]

Since solar cycle 16, the heliospheric current sheet (HCS) has been found to be shifted southward during the late declining to minimum phase. However, this trend is broken at the end of solar cycle 24. In this paper, we analyse the shift of the HCS by using information obtained from coronal model and in situ data provided by the near-Earth OMNI data base and the Parker Solar Probe (PSP). Coronal potential field source surface modelling results show that the northward shift is established at the beginning of 2018 and remains stable for about 2 yr. Interplanetary magnetic field data obtained from and within 1 au also support the northward shift, as the southern polarity T appears more frequently than the northern polarity A between 2018 and 2020. Both model results and in situ observation obtained by PSP imply that the HCS shift is established in the corona, and then propagates into the heliosphere. The quadrupole term still has a significant influence on the formation of the HCS shift. [ABSTRACT FROM AUTHOR]

Sunspots and active regions observed on the solar surface are widely believed to be manifestations of compact predominantly toroidal magnetic field structures ("flux tubes") that emerge by magnetic buoyancy from the deeper interior of the Sun. Much work has examined the evolution of such magnetic structures, typically considering them as idealized isolated magnetic entities and not as more realistic magnetic concentrations in a volume-filling background magnetic field. Here, we report results that explore the buoyant rise dynamics of magnetic concentrations in a volume-filling field in the full three dimensions. Earlier 2.5D work in this series established the remarkable fact that the twist orientation of a flux concentration relative to the background field affected its likelihood to rise and emerge, regardless of whether the buoyant rise took place in the absence or presence of convection. The contrasting dynamics between structures with differing orientations lead to a selection mechanism that reproduces characteristics of the "solar hemispheric helicity rule(s)" observations strikingly well. Here, we show that this two-dimensional selection mechanism persists in the face of the added complexity of three-dimensional dynamics. Arching of the magnetic structure in the third dimension, as might be expected in the solar application, is introduced. The role of tension force leading to this selection mechanism is elucidated and subtle differences that arise due to the three-dimensional geometry are discussed. [ABSTRACT FROM AUTHOR]

Efficient forecasting of solar flares is of significant importance for better risk prevention. Currently, there is relatively rare research on multi/four-classification of flares, and the influence of the number of time steps and data feature dimensions on the prediction performance of multi-class models has not been considered. In this study, we utilize the Space-weather HMI Active Region Patch (SHARP) data to develop two categories of models for multiclass flare prediction within 24 hr, including direct output four-classification models and four-classification models using a cascading scheme. The former encompasses Random Forest (RF) model, Long Short-Term Memory (LSTM) model, and Bidirectional LSTM (BLSTM) model, while the latter includes BLSTM Cascade (BLSTM-C) model and BLSTM Cascade with Attention Mechanism (BLSTM-C-A) model. These two categories of models are employed to contrast the impact of different numbers of time steps and the predictive performance in solar flare multi/four-classification. Additionally, we conduct, for the first time, feature importance analysis for multi/four-classification solar flare prediction using deep learning models. The main results are as follows: (1) As the number of time steps increases, the True Skill Statistic (TSS) scores of the four deep learning models improve, showing an overall upward trend in predictive performance. The models achieve their optimal performance when the number of time steps reaches 120. (2) Among the direct output four-class models, deep learning models (LSTM and BLSTM) outperform traditional machine learning model (RF). In both multi-class and binary-class predictions using deep learning, the BLSTM-C model performs better than other deep learning models (LSTM, BLSTM, and BLSTM-C-A). (3) In the feature importance analysis, the top-ranked important features include SAVNCPP and R_VALUE, while the least important features include SHRGT45 and MEANPOT. [ABSTRACT FROM AUTHOR]

In the Sun and solar-type stars, there is a critical dynamo number for the operation of a large-scale dynamo, below which the dynamo ceases to operate. This region is known as the subcritical region. Previous studies showed the possibility of operating the solar-like large-scale (global) dynamo in the subcritical region without a small-scale dynamo. As in the solar convection zone, both large- and small-scale dynamos are expected to operate at the same time and location, we check the robustness of the previously identified subcritical dynamo branch in a numerical model in which both large- and small-scale dynamos are excited. For this, we use the Pencil Code and set up an α Ω dynamo model with uniform shear and helically forced turbulence. We have performed a few sets of simulations at different relative helicity to explore the generation of large-scale oscillatory fields in the presence of small-scale dynamo. We find that in some parameter regimes, the dynamo shows hysteresis behavior, i.e., two dynamo solutions are possible depending on the initial parameters used. A decaying solution when the dynamo was started with a weak field and a strong oscillatory solution if the dynamo was initialized with a strong field. Thus, the existence of the sub-critical branch of the large-scale dynamo in the presence of small-scale dynamo is established. However, the regime of hysteresis is quite narrow with respect to the case without the small-scale dynamo. Our work supports the possible existence of large-scale dynamo in the sub-critical regime of slowly rotating stars. [ABSTRACT FROM AUTHOR]

To estimate the hemispheric flux generation rate of the large-scale radial magnetic field in Solar Cycles 23 and 24, we use the photospheric observations of the solar magnetic fields and results of the mean-field dynamo models. Results of the dynamo model show the strong impact of the radial turbulent diffusion on the surface evolution of the large-scale poloidal magnetic field and on the hemispheric magnetic flux generation rate. To process the observational data set, we employ the parameters of the meridional circulation and turbulent diffusion from the Surface Flux-Transport (SFT) models. We find that the observed evolution of the axisymmetric vector potential contains the time–latitude patterns which can result from the effect of turbulent diffusion of the large-scale poloidal magnetic field in the radial direction. We think that the SFT models can reconcile the observed rate of hemispheric magnetic flux generation by considering radial turbulent diffusion and lower values of the diffusion coefficient. [ABSTRACT FROM AUTHOR]

Improvement of the model providing the boundary condition of the solar-wind speed near the Sun is essential for gaining a better forecast of space weather. We optimized the parameters of the distance from the coronal hole boundary (DCHB) model and the Wang–Sheeley (WS) model, which enabled the determination of solar-wind speed from observations of the Sun's magnetic field. In this study, we used solar-wind speed data derived from interplanetary scintillation (IPS) observations at the Institute for Space-Earth Environmental Research (ISEE) for six Carrington rotations in Solar Cycle 23 as reference data. A comparison of IPS observations and optimized DCHB models demonstrated strong-to-moderate positive correlations and small deviations, except for solar maximum data. The degraded correlation at the solar maximum is ascribed to the effect of the rapid structural evolution of the solar wind and coronal magnetic field. The performance of the optimized DCHB model was better than that of the optimized WS model. To solve a limitation of the DCHB model in reproducing slow-wind speeds, we propose a modified version of the DCHB model and optimize it for IPS observations. The optimized solutions for the modified DCHB model demonstrate performance comparable to that of the original model. The results obtained in this study suggest that the DCHB acts better as a controlling parameter for the solar-wind speed than the expansion factor and that both the optimized DCHB model and its modified version are useful for improving the estimation of the solar-wind speed at the source surface from magnetograph observations. [ABSTRACT FROM AUTHOR]

Low and Lou (Astrophys. J.352, 343, 1990) presented a family of nonlinear force-free magnetic fields that have established themselves as the gold standard for extrapolating force-free magnetic fields in solar physics. Building upon this important work, our study introduces a novel grid-free machine-learning-based method to effectively solve the equilibria proposed by Low and Lou. Through extensive numerical experiments, our results unequivocally demonstrate the efficient capability of the machine-learning algorithm in deriving numerical solutions for Low and Lou's equilibria. Furthermore, we explore the opportunities and challenges of applying artificial-intelligence technology to real observed solar active regions. [ABSTRACT FROM AUTHOR]

This work focuses on the analysis of the mean longitudinal magnetic field as a stellar activity tracer in the context of small exoplanet detection and characterization in radial-velocity (RV) surveys. We use Solar Dynamics Observatory/Helioseismic and Magnetic Imager filtergrams to derive Sun-as-a-star magnetic field measurements, and show that the mean longitudinal magnetic field is an excellent rotational period detector and a useful tracer of the solar magnetic cycle. To put these results into context, we compare the mean longitudinal magnetic field to three common activity proxies derived from HARPS-N Sun-as-a-star data: the full width at half-maximum, the bisector span, and the S-index. The mean longitudinal magnetic field does not correlate with the RVs and therefore cannot be used as a one-to-one proxy. However, with high cadence and a long baseline, the mean longitudinal magnetic field outperforms all other considered proxies as a solar rotational period detector, and can be used to inform our understanding of the physical processes happening on the surface of the Sun. We also test the mean longitudinal magnetic field as a 'stellar proxy' on a reduced solar data set to simulate stellar-like observational sampling. With a Gaussian Process regression analysis, we confirm that the solar mean longitudinal magnetic field is the most effective of the considered indicators, and is the most efficient rotational period indicator over different levels of stellar activity. This work highlights the need for polarimetric time series observations of stars. [ABSTRACT FROM AUTHOR]

Studying the hemispheric distribution of active regions (ARs) with different magnetic morphologies may clarify the features of the dynamo process that is hidden under the photospheric level. The magnetic flux data for 3047 ARs from the CrAO catalogue (https://sun.crao.ru/databases/catalog-mmc-ars), between May 1996 and December 2021 (cycles 23 and 24) were used to study ARs cyclic variations and perform correlation analysis. According to the magneto-morphological classification (MMC) of ARs proposed earlier, subsets of the regular (obeying empirical rules for sunspots) and irregular (violating these rules) ARs were considered separately. Our analysis shows the following: For ARs of each MMC type, in each of the hemispheres, time profiles demonstrate a multipeak structure. The double-peak structure of a cycle is formed by ARs of both MMC types in both hemispheres. For the irregular ARs, the pronounced peaks occur in the second maxima (close to the polar field reversal). Their significant hemispheric imbalance might be caused by a weakening of the toroidal field in one of the hemispheres due to the interaction between the dipolar and quadrupolar components of the global field, which facilitates the manifestation of the turbulent component of the dynamo. The similarity of the irregular ARs activity that was found in adjacent cycles in different hemispheres also hints at realization of the mix-parity dynamo solution. For the quadrupolar-like component of the flux (compiled in the simple axisymmetric approximation), signs of oscillations with a period of about 15 years are found, and they are pronounced specifically for the irregular groups. This MMC type ARs might also contribute in |$\alpha$| -quenching. [ABSTRACT FROM AUTHOR]

Studies of active region (AR) lifetimes are mostly restricted to short-lived ARs. The aim of this paper is to include recurrent ARs, which should be identified unambiguously. The first step is the algorithmic listing of possible returns; then, the candidates are visually checked using the unique HTML-feature of the Debrecen sunspot database. The final step is application of an asymmetric Gaussian function, introduced in previous articles, for short-lived ARs. This function has a surprisingly good fit to the data on correctly identified recurrent sunspot groups over several rotations enabling the reconstruction of the development on the far side of the sun. The Gnevyshev–Waldmeier rule for the area–lifetime relationship is not applicable for recurrent ARs; however, as a novel approach, a linear regression analysis extended to long lifetimes made it possible to recognize two populations of sizes for which two different area–lifetime relationships can be obtained. The lifetimes exhibit weak dependencies on the heliographic latitude and solar cycle phase. If an asymmetric Gaussian cannot be fit to the data, then they presumably belong to consecutive members of an active nest. [ABSTRACT FROM AUTHOR]

The Huairou Solar Observing Station (HSOS) has conducted solar vector magnetic field observations for 40 years and developed multiple vector magnetographs (including one space magnetic field observation instrument). Using these accumulated magnetic field observation data, HSOS has achieved significant progress in solar physics research, including important advancements in the helicity sign rule of solar active regions, the helicity characteristics of strong and weak magnetic fields in active regions, the chromospheric magnetic field characteristics of the Sun, the evolution of magnetic fields in active regions, and the extraction of magnetic field characteristics for flare precursors. However, due to historical reasons, the calibration of vector magnetic field data in HSOS are not standardized. Therefore, this paper summarizes past historical experiences and introduces the standardized calibration procedure for vector magnetic field processing in detail. These calibration procedures are the basic steps of the calibration process for the space vector magnetograph (Full-Disk Vector MagnetoGraph, abbreviated as FMG) observation data, and are also applicable to the calibration of other instrument observation data at HSOS. They mainly include basic processing of polarization data and in-depth processing of vector magnetic fields. We believe that such calibration processing of the historical data collected by HSOS over the past 40 years will help us to accurately measure and analyze the solar magnetic field, further revealing the laws of solar activity and its impact on the Earth's environment. [ABSTRACT FROM AUTHOR]

Geomagnetic storms (GSs) are major disturbances in the terrestrial atmosphere caused by the reconnection process between the incoming plasma ejecta in the solar wind and the planetary magnetosphere. The strongest GSs can lead to auroral displays even at lower latitudes, and cause both satellite and ground-based infrastructure malfunctions. The early recognition of geoeffective events based on specific features on the solar photosphere is crucial for the development of early warning systems. In this study, we explore 16 magnetic field parameters provided by the Space-weather HMI Active Region Patch (SHARP) database from the SDO/HMI instrument. The analysis includes 64 active regions that produced strong GS during solar cycle (SC) 24 and the ongoing SC25. We present the statistical results between the SHARP and solar parameters, in terms of Pearson and Spearman correlation coefficients, and discuss their space weather potential. [ABSTRACT FROM AUTHOR]

The evolution of solar magnetic fields is significant for understanding and predicting solar activities. And our knowledge of solar magnetic fields largely depends on the photospheric magnetic field. In this paper, based on the spherical harmonic expansion of the photospheric magnetic field observed by Wilcox Solar Observatory, we analyze the time series of spherical harmonic coefficients and predict Sunspot Number as well as synoptic maps for Solar Cycle 25. We find that solar maximum years have complex short-period disturbances, and the time series of coefficient g70 is nearly in-phase with Sunspot Number, which may be related to solar meridional circulation. Utilizing Long Short-Term Memory networks (LSTM), our prediction suggests that the maximum of Solar Cycle 25 is likely to occur in June 2024 with an error of 8 months, the peak sunspot number may be 166.9±22.6, and the next solar minimum may occur around January 2031. By incorporating Empirical Mode Decomposition, we enhance our forecast of synoptic maps truncated to Order 5, validating their relative reliability. This prediction not only addresses a gap in forecasting the global distribution of the solar magnetic field but also holds potential reference value for forthcoming solar observation plans. [ABSTRACT FROM AUTHOR]

Experimental data on solar activity (sunspot number, induction of solar polar magnetic field Bp, and others), characteristics of interplanetary space, and cosmic ray fluxes testify that the Sun has entered a deep minimum of its activity similar to the Dalton minimum. An almost functional relationship was found between maximum values of Bpmax observed in the solar activity minimum of the 11-year cycle and the next sunspot maximum. Based on this relationship, a simple method of forecasting maximum number of sunspots Rzmax and time course Rz(t) was developed. A forecast of the 25th solar cycle is given. [ABSTRACT FROM AUTHOR]

The August 2024 issue of Astronomy & Geophysics covers a wide range of topics in astronomy. It includes information about the upcoming Caroline Herschel Prize Lecture, which will discuss the use of artificial intelligence in finding exploding stars and black holes. The winners of the 2023 RAS Thesis Prize are also announced, and details about National Astronomy Week in 2025 are provided. The issue features scientific discoveries such as the most distant known galaxy, the cause of water loss on Venus, evidence of space weathering on asteroid Ryugu, and the presence of liquid rock droplet clouds on exoplanet WASP-43b. Other topics covered include sunspots, Pluto's heart-shaped feature, alternative eclipse observation methods, quasar mergers, planet-forming disks, gas outflows in galaxies, supermassive black hole growth, early galaxy mergers, magnetar bursts, the Sun's magnetic field formation, a vent near the Milky Way's black hole, and a new model explaining phosphorus abundance. A new Earth-sized exoplanet called SPECULOOS-3 b has been discovered orbiting a nearby ultra-cool dwarf star, and researchers found that primordial inhomogeneities in molecular clouds can create chemical differences in stars with the same origin. Another study suggests that massive stars can collapse into black holes without becoming supernovae. [Extracted from the article]

• Sunspot number (SN) is linearly relating with sunspot-group area (WSGA). • A decreasing trend exists in the slope of this relation during Solar Cycles 12–24. • In the cases of Solar Cycles 14, 17, and 24 a nonlinear fit is better than linear fit. • A 77-year cycle is found in the ratio SN/WSGA at the maximum epoch of Solar cycle. • We predicted that Solar Cycle 25 will be larger than both Cycles 24 and 26. • Using an our earlier methods we predicted 141 and 127 for the amplitude of Solar Cycle 25. • We predicted Solar Cycle 25 will have similar shape as Solar Cycle 13. • Hence, we predicted 135 for the amplitude of Solar Cycle 25. • We predicted March/2024 for the maximum epoch of Solar Cycle 25. • We predicted March/2032 will be the end of Solar Cycle 25 with SN 4. Prediction of the amplitude of solar cycle is important for understanding the mechanism of solar cycle and solar activity influence on space-weather. We analysed the combined data of sunspot groups from Greenwich Photoheliographic Results (GPR) during the period 1874–1976 and Debrecen Photoheliographic Data (DPD) during 1977–2017 and determined the monthly mean, annual mean, and 13-month smoothed monthly mean whole sphere sunspot-group area (WSGA). We also analysed the monthly mean, annual mean, and 13-month smoothed monthly mean version 2 of international sunspot number ( SN T ) during the period 1874–2017. We fitted the annual mean WSGA and SN T data during each of Solar Cycles 12–24 separately to the linear and nonlinear (parabola) forms. In the cases of Solar Cycles 14, 17, and 24 the nonlinear fits are found better than the linear fits. We find that there exists a secular decreasing trend in the slope of the WSGA– SN T linear relation during Solar Cycles 12–24. A secular decreasing trend is also seen in the coefficient of the first order term of the nonlinear relation. The existence of ≈ 77-year variation is clearly seen in the ratio of the amplitude to WSGA at the maximum epoch of solar cycle. From the pattern of this long-term variation of the ratio we inferred that Solar Cycle 25 will be larger than both Solar Cycles 24 and 26. Using an our earlier method (now slightly revised), i.e. using high correlations of the amplitude of a solar cycle with the sums of the areas of sunspot groups in 0– 10 ° latitude intervals of the northern hemisphere during 3.75-year interval around the minimum–and the southern hemisphere during 0.4-year interval near the maximum–of the corresponding preceding solar cycle, we predicted 127 ± 26 and 141 ± 19 for the amplitude of Solar Cycle 25, respectively. Based on ≈ 130-year periodicity found in the cycle-to-cycle variation of the amplitudes of Solar Cycles 12–24 we find the shape of Solar Cycle 25 would be similar to that of Solar Cycle 13 and predicted for Solar Cycle 25 the amplitude 135 ± 8 , maximum epoch 2024.21 (March 2024) ± 6-month, and the following minimum epoch 2032.21 (March 2032) ± 6-month with SN T ≈ 4. [ABSTRACT FROM AUTHOR]

Minifilaments are widespread small-scale structures in the solar atmosphere. To better understand their formation and eruption mechanisms, we investigate the entire life of a sigmoidal minifilament located below a large quiescent filament observed by Big Bear Solar Observatory/Goode Solar Telescope on 2015 August 3. The H α structure initially appears as a group of arched threads, then transforms into two J-shaped arcades, and finally forms a sigmoidal shape. Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly observations in 171 Å show that two coronal jets occur around the southern footpoint of the minifilament before the minifilament eruption. The minifilament eruption starts from the southern footpoint, then interacts with the overlying filament and fails. The aforementioned observational changes correspond to three episodes of flux cancellations observed by SDO/Helioseismic and Magnetic Imager. Unlike previous studies, the flux cancellation occurs between the polarity where the southern footpoint of the minifilament is rooted and an external polarity. We construct two magnetic field models before the eruption using the flux rope insertion method and find a hyperbolic flux tube above the flux cancellation site. The observation and modeling results suggest that the eruption is triggered by the external magnetic reconnection between the core field of the minifilament and the external fields due to flux cancellations. This study reveals a new triggering mechanism for minifilament eruptions and a new relationship between minifilament eruptions and coronal jets. [ABSTRACT FROM AUTHOR]

Attributed to the lack of an Earth-like global intrinsic dipole magnetic field on Mars, the induced electromagnetic field environment plays a crucial role in the evolution of its atmosphere. The dominant motional electric field ( E M ) induced by the bulk motion of the magnetic field within the Martian magnetosheath serves to accelerate ions toward escape velocity, thereby forming a plume escape channel. However, the distribution morphology of E M itself has received limited attention in previous research. In this study, by taking advantage of the multi-fluid Hall-MHD model cooperating with the Martian crustal field model, we focus on elucidating the physical mechanisms underlying the asymmetrical distribution of E M and examining the influence of the crustal field on this asymmetry. The results obtained from the simulation conducted in the absence of the crustal field indicate that the E M is more intense within the − Z M S E magnetosheath, where E M is directed toward Mars, primarily due to its corresponding higher velocity and a stronger magnetic field at lower solar zenith angles. The Martian crustal field has the ability to enhance the local E M around the inner boundary of the magnetosheath by amplifying both the magnetic field and its associated velocity. Accordingly, these findings provide valuable insights into the asymmetric nature of E M within the Martian magnetosheath under typical quiet-time solar wind conditions. [ABSTRACT FROM AUTHOR]

We survey crossings of Jupiter's dawn magnetopause during the Juno prime mission to identify and characterize Jupiter's magnetopause boundary layer. Using plasma and magnetic field observations from Jovian Auroral Distributions Experiment and Juno Magnetic Field investigation, we identify 53 boundary layer events from the 62 magnetopause crossings studied here. We find that the boundary layer generally exhibits mixed properties of magnetosheath and magnetosphere electron distributions, including lower characteristic electron energies and denser ion populations than in the magnetosphere, but higher characteristic electron energies and less dense ion populations than in the magnetosheath. Boundary layer proton speeds are on average slower than both the magnetosheath and magnetosphere. Other proton parameters in the boundary layer have intermediate values between the magnetosheath and magnetosphere. Through ion composition analysis in regions adjacent to the magnetopause, we find evidence of solar wind and magnetospheric plasma in the boundary layer that suggests plasma is transported across the magnetopause in both directions. This mass and energy transport may be the result of solar wind interactions such as magnetic reconnection and Kelvin‐Helmholtz instabilities. However, many boundary layer events do not exhibit local signatures of these solar wind interactions and plasma may be transported by a non‐local process or diffusively transported. Plain Language Summary: Jupiter has the strongest planetary magnetic field in the solar system and over one metric ton per second of sulfur and oxygen is ejected via volcanic activity on the moon, Io. These two factors inflate Jupiter's magnetosphere as material from Io slowly travels outward from Jupiter to near the magnetopause, the boundary between the magnetosphere and magnetosheath. Jupiter's magnetopause boundary layer is located between its outer magnetosphere and surrounding magnetosheath. The magnetosheath is a region of primarily solar wind plasma between the bow shock and the magnetopause and is draped over the magnetosphere. We find that the dawnside boundary layer that separates the magnetosphere and the magnetosheath is comprised of plasma from both regions and travels across this region due to a variety of physical processes. Additionally, we find solar wind plasma in the magnetosphere and plasma from Io in the magnetosheath. This result implies that plasma travels across the boundary layer in both directions. Lastly, our survey shows the plasma in the dawnside boundary layer moves in the opposite direction of Jupiter's rotation, contrary to the plasma located closer to Jupiter. Key Points: The primary characteristic of Jupiter's magnetopause boundary layer is a dual distribution of magnetosphere and magnetosheath electronsIon composition in the boundary layer and adjacent regions show that plasma is transported across the magnetopause in both directionsIon flow speeds in Jupiter's dawn flank magnetopause boundary layer are hundreds of km/s tailward, opposite to corotation on the dawnside [ABSTRACT FROM AUTHOR]

We report a rare regime of Earth's magnetosphere interaction with sub‐Alfvénic solar wind in which the windsock‐like magnetosphere transforms into one with Alfvén wings. In the magnetic cloud of a Coronal Mass Ejection (CME) on 24 April 2023, NASA's Magnetospheric Multiscale mission distinguishes the following features: (a) unshocked and accelerated low‐beta CME plasma coming directly against Earth's dayside magnetosphere; (b) dynamical wing filaments representing new channels of magnetic connection between the magnetosphere and foot points of the Sun's erupted flux rope; (c) cold CME ions observed with energized counter‐streaming electrons, evidence of CME plasma captured due to by reconnection between magnetic‐cloud and Alfvén‐wing field lines. The reported measurements advance our knowledge of CME interaction with planetary magnetospheres, and open new opportunities to understand how sub‐Alfvénic plasma flows impact astrophysical bodies such as Mercury, moons of Jupiter, and exoplanets close to their host stars. Plain Language Summary: Like supersonically fast fighter jets creating sonic shocks in the air, planet Earth typically moves in the magnetized solar wind at super‐Alfvénic speeds and generates a bow shock. Here we report unprecedented observations of Earth's magnetosphere interacting with a sub‐Alfvénic solar wind brought by an erupted magnetic flux rope from the Sun, called a coronal mass ejection (CME). The terrestrial bow shock disappears, leaving the magnetosphere exposed directly to the cold CME plasma and the strong magnetic field from the Sun's corona. Our results show that the magnetosphere transforms from its typical windsock‐like configuration to having wings that magnetically connect our planet to the Sun. The wings are highways for Earth's plasma to be lost to the Sun, and for the plasma from the foot points of the Sun's erupted flux rope to access Earth's ionosphere. Our work indicates highly dynamic generation and interaction of the wing filaments, shedding new light on how sub‐Alfvénic plasma wind may impact astrophysical bodies in our solar and other stellar systems. Key Points: MMS observed a rare regime of magnetosphere interaction with unshocked low‐beta CME plasmaWing filaments represent dynamical channels of magnetic connection between the magnetosphere and foot points of the Sun's erupted flux ropeCold CME ions observed on closed field lines, likely generated by dual‐wing reconnection [ABSTRACT FROM AUTHOR]

Since the launch of the Solar Dynamics Observatory (SDO) in 2010 and throughout the solar cycle 24, the Sun has produced few tens of X-class flares, which are the most energetic solar events. Those flares are produced in regions where the magnetic flux/energy is large and the magnetic configurations are complex. To provide more insights into the flaring process, we investigate the properties of magnetic null points (MNPs) and their correlation with the energy release sites. During solar cycle 24, we identify 17 X-class flares satisfying selection criteria. From SDO /HMI magnetograms, we perform potential extrapolations around the peak time of the flare to access the 3D coronal magnetic field and thus investigate the existence of coronal MNPs. We then correlate the flaring sites with the existing MNPs using SDO /AIA 171 Å; EUV observations, and deduce their properties (sign, spine, and fan). Six active regions out of 10 possess at least one MNP which is stable and with large magnetic field gradients: this implies that 35  per cent of X-class flares are associated with an MNP; of which 87.5 per cent of MNPs are of positive type. The MNPs associated with the flare sites are predominantly located at a height between 0.5 and 2 Mm, and with a vertical/radial spine field line. We also find a slight correlation between the MNPs not associated with a flare and negative-type MNPs (55 per cent) within the active region. Regarding the physics of flares, the association between the enhanced intensity at the flaring site and an MNP represents about a third of the possible scenarios for triggering X-class flares. [ABSTRACT FROM AUTHOR]

It is well known that the dominant frequency of oscillations in the solar photosphere is ≈3 mHz, which is the result of global resonant modes pertaining to the whole stellar structure. However, analyses of the horizontal motions of nearly 1 million photospheric magnetic elements spanning the entirety of solar cycle 24 have revealed an unexpected dominant frequency, ≈5 mHz, a frequency typically synonymous with the chromosphere. Given the distinctly different physical properties of the magnetic elements examined in our statistical sample, when compared to largely quiescent solar plasma where ≈3 mHz frequencies are omnipresent, we argue that the dominant ≈5 mHz frequency is not caused by the buffeting of magnetic elements, but instead is due to the nature of the underlying oscillatory driver itself. This novel result was obtained by exploiting the unmatched spatial and temporal coverage of magnetograms acquired by the Helioseismic and Magnetic Imager (HMI) on board NASA's Solar Dynamics Observatory (SDO). Our findings provide a timely avenue for future exploration of the magnetic connectivity between sub-photospheric, photospheric, and chromospheric layers of the Sun's dynamic atmosphere. [ABSTRACT FROM AUTHOR]

Aims. Kink oscillations are frequently observed in coronal loops. This work aims to numerically clarify the influence of the loop curvature on horizontally and vertically polarized kink oscillations. Methods. Working within the framework of ideal magnetohydrodynamics (MHD), we conduct three-dimensional (3D) simulations of axial fundamental kink oscillations in curved density-enhanced loops embedded in a potential magnetic field. Both horizontal and vertical polarizations are examined, and their oscillation frequencies are compared with Wentzel-Kramers-Brillouin (WKB) expectations. We discriminate between two different density specifications. In the first (dubbed "uniform density"), the density is axially uniform and varies continuously in the transverse direction toward a uniform ambient corona. Some further stratification is implemented in the second specification (dubbed "stratified"), allowing us to address the effect of evanescent barriers. Results. Examining the oscillating profiles of the initially perturbed uniform-density loops, we found that the frequencies for both polarizations deviate from the WKB expectation by ∼10%. In the stratified loop, however, the frequency of the horizontal polarization deviates to a larger extent (∼25%). We illustrate the lateral leakage of kink modes through wave tunneling in 3D simulations, for the first time. Despite this, in the uniform density and the stratified loops, the damping time-to-period ratios are similar and are close to the analytical predictions for straight configurations under the thin-tube-thin-boundary (TTTB) assumption. Conclusions. The WKB expectation for straight configurations can reasonably describe the eigenfrequency of kink oscillations only in loops without an asymmetrical cross-loop density profile perpendicular to the oscillating direction. Lateral leakage via wave tunneling is found to be less efficient than resonant absorption, meaning that the latter remains a robust damping mechanism for kink motions even when loop curvature is included. [ABSTRACT FROM AUTHOR]

Context. Filament eruption is a common phenomenon in solar activity, but the triggering mechanism is not well understood. Aims. We focus our study on a filament eruption located in a complex nest of three active regions close to a coronal hole. Methods. The filament eruption is observed at multiple wavelengths: by the Global Oscillation Network Group (GONG), the Solar Terrestrial Relations Observatory (STEREO), the Solar Upper Transition Region Imager (SUTRI), and the Atmospheric Imaging Assembly (AIA) and Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamic Observatory (SDO). Thanks to high-temporal-resolution observations, we were able to analyze the evolution of the fine structure of the filament in detail. The filament changes direction during the eruption, which is followed by a halo coronal mass ejection detected by the Large Angle Spectrometric Coronagraph (LASCO) on board the Solar and Heliospheric Observatory (SOHO). A Type III radio burst was also registered at the time of the eruption. To investigate the process of the eruption, we analyzed the magnetic topology of the filament region adopting a nonlinear force-free-field (NLFFF) extrapolation method and the polytropic global magnetohydrodynamic (MHD) modeling. We modeled the filament by embedding a twisted flux rope with the regularized Biot-Savart Laws (RBSL) method in the ambient magnetic field. Results. The extrapolation results show that magnetic reconnection occurs in a fan-spine configuration resulting in a circular flare ribbon. The global modeling of the corona demonstrates that there was an interaction between the filament and open field lines, causing a deflection of the filament in the direction of the observed CME eruption and dimming area. Conclusions. The modeling supports the following scenario: magnetic reconnection not only occurs with the filament itself (the flux rope) but also with the background magnetic field lines and open field lines of the coronal hole located to the east of the flux rope. This multiwavelength analysis indicates that the filament undergoes multiple magnetic reconnections on small and large scales with a drifting of the flux rope. [ABSTRACT FROM AUTHOR]

Context. Inferences of the magnetic field in the solar atmosphere by means of spectropolarimetric inversions (i.e., Stokes inversion codes) yield magnetic fields that are non-solenoidal (∇ ⋅ B ≠ 0). Because of this, results obtained by such methods are sometimes put into question. Aims. We aim to develop and implement a new technique that, in conjunction with Stokes inversion codes, can retrieve magnetic fields that are simultaneously consistent with observed polarization signals and with the null divergence condition. Methods. The method used in this work strictly imposes ∇ ⋅ B = 0 by determining the vertical component of the magnetic field (Bz) from the horizontal ones (Bx, By). We implement this technique, which we refer to as solenoidal inversion, into the FIRTEZ Stokes inversion code and apply it to spectropolarimetric observations of a sunspot observed with the Hinode/SP instrument. Results. We show that the solenoidal inversion retrieves a vertical component of the magnetic field that is consistent in 80% of the analyzed three-dimensional (x, y, z) domain, with the vertical component of the magnetic field inferred from the non-solenoidal inversion. We demonstrate that the solenoidal inversion is capable of a better overall fitting to the observed Stokes vector than the non-solenoidal inversion. In fact, the solenoidal magnetic field fits Stokes V worse, but this is compensated by a better fit to Stokes I. We find a direct correlation between the worsening in the fit to the circular polarization profiles by the solenoidal inversion and the deviations in the inferred Bz with respect to the non-solenoidal inversion. Finally, we also show that the spatial distribution of the electric currents given by ∇ × B does not change significantly after imposing the null divergence condition. Conclusions. In spite of being physically preferable, solenoidal magnetic fields are topologically very similar in 80% of the analyzed three-dimensional domain to the non-solenoidal fields obtained from spectropolarimetric inversions. These results support the idea that common Stokes inversion techniques fail to reproduce ∇ ⋅ B = 0 mainly as a consequence of the uncertainties in the determination of the individual components of the magnetic field. In the remaining 20% of the analyzed domain, where the Bz inferred by the solenoidal and non-solenoidal inversions disagree, it remains to be proven that the solenoidal inversion is to be preferred because even though the overall fit to the Stokes parameters improves, the fit to Stokes V worsens. It is in these regions where the application of the Stokes inversion constrained by the null divergence condition can yield new insights about the topology of the magnetic field in the solar photosphere. [ABSTRACT FROM AUTHOR]

Context. Understanding the role of magnetic reconnection in the heating and dynamics of the solar atmosphere requires detailed observational data of any observable aspect of the reconnection process, including small-scale features such as plasmoids. Aims. Here, we examine the capability of active and upcoming instruments to detect plasmoids generated by reconnection in the corona including low-density regimes. Methods. We used the Bifrost code to perform simulations of plasmoid-mediated reconnection in the corona with a 2D idealized setup: a fan-spine topology with uniform density including thermal conduction. Through a forward-modeling of extreme-ultraviolet (EUV) observables, we checked whether our simulated plasmoids could be detected with the instruments of Solar Dynamics Observatory (SDO) and Solar Orbiter (SO), as well as the upcoming Multi-Slit Solar Explorer (MUSE) and Solar-C missions. Results. Short-lived (∼10 − 20 s) small-scale (∼0.2 − 0.5 Mm) coronal plasmoids are not resolvable with the Atmospheric Imaging Assembly (AIA) on board SDO. In contrast, they could be captured with the EUV High-Resolution Imager at the Extreme Ultraviolet Imager (EUI-HRIEUV) of SO. The spatial and temporal high-resolution planned for the MUSE spectrograph (SG) is adequate to obtain full spectral information of these plasmoids. To achieve a sufficient signal-to-noise ratio (S/N) for ∼0.8 MK plasmoids in the MUSE/SG 171 Å channel, full-raster images are attainable for regions with electron densities above 109 cm−3, while sit-and-stare observations are recommended for lower-density regions. The future Solar-C mission could also capture these coronal plasmoids using the EUV High-Throughput Spectroscopic Telescope (EUVST), considering rapid changes in Doppler shift and line widths in different EUV lines caused by plasmoid motions along the current sheet. Conclusions. With the combined spectra of MUSE/SG and Solar-C/EUVST in multiple emission lines, along with high-resolution images from SO/EUI-HRIEUV and MUSE/CI, it should be possible to gain new insights about plasmoid formation in the corona. [ABSTRACT FROM AUTHOR]

We present a catalog that contains depth-dependent information about the atmospheric conditions inside sunspot groups of all types. The catalog, which we named MODEST, is currently composed of 944 observations of 117 individual active regions with sunspots and covers all types of features observed in the solar photosphere. We used the SPINOR-2D code to perform spatially coupled inversions of the Stokes profiles observed by Hinode/SOT-SP at high spatial resolution. SPINOR-2D accounts for the unavoidable degradation of the spatial information due to the point spread function of the telescope. The sunspot sample focuses on complex sunspot groups, but simple sunspots are also part of the catalog for completeness. Sunspots were observed from 2006 to 2019, covering parts of solar cycles 23 and 24. The catalog is a living resource, as with time, more sunspot groups will be included. [ABSTRACT FROM AUTHOR]

Context. Solar Orbiter is a new space observatory that provides unique capabilities to understand the heliosphere. In particular, it has made several observations of the far-side of the Sun and therefore provides unique information that can greatly improve space weather monitoring. Aims. In this study, we aim to quantify how the far-side data will affect simulations of the corona and the interplanetary medium, especially in the context of space weather forecasting. Methods. To do so, we focused on a time period with a single sunspot emerging on the far-side in February 2021. We used two different input magnetic maps for our models: one that includes the far-side active region and one that does not. We used three different coronal models typical of space weather modeling: a semi-empirical model (potential field source surface or PFSS) and two different magnetohydrodynamic models (Wind Predict and Wind Predict-AW). We compared all the models with both remote sensing and in situ observations in order to quantify the impact of the far-side active region on each solution. Results. We find that the inclusion of the far-side active region in the various models has a small local impact due to the limited amount of flux of the sunspot (at most 8% of the total map flux), which leads, for example, to coronal hole changes of around 7% for all models. Interestingly, there is a more global impact on the magnetic structure seen in the current sheet, with clear changes, for example, in the coronal hole boundaries visible in extreme ultra-violet (EUV) on the western limb, which is opposite to the active region and the limb most likely to be connected to Earth. For the Wind Predict-AW model, we demonstrate that the inclusion of the far-side data improves both the structure of the streamers and the connectivity to the spacecraft. Conclusions. In conclusion, the inclusion of a single far-side active region may have a small local effect with respect to the total magnetic flux, but it has global effects on the magnetic structure, and thus it must be taken into account to accurately describe the Sun-Earth connection. The flattening of the heliospheric current sheet for all models reveals that it causes an increase of the source surface height, which in return affects the open and closed magnetic field line distributions. [ABSTRACT FROM AUTHOR]

We seek to understand the composition and variability of fast solar wind (FSW) and slow Alfvénic solar wind emerging from coronal holes (CHs). We leverage an opportune conjunction between Solar Orbiter and Parker Solar Probe (PSP) during PSP Encounter 11 to include compositional diagnostics from the Solar Orbiter Heavy Ion Sensor as these variations provide crucial insights into the origin and nature of the solar wind. We use potential field source surface and magnetohydrodynamic models to connect the observed plasma at PSP and Solar Orbiter to its origin footpoint in the photosphere and compare these results with the in situ measurements. A very clear signature of a heliospheric current sheet crossing as evidenced by enhancements in low first ionization potential (FIP) elements, ion charge state ratios, proton density, low Alfvénicity, and polarity estimates validates the combination of modeling, data, and mapping. We identify two FSW streams emerging from small equatorial CHs with low ion charge state ratios, low FIP bias, high Alfvénicity, and low footpoint brightness, yet anomalously low alpha particle abundance for both streams. We identify high-Alfvénicity slow solar wind emerging from the overexpanded boundary of a CH having intermediate alpha abundance, high Alfvénicity, and dips in ion charge state ratios corresponding to CH boundaries. Through this comprehensive analysis, we highlight the power of multi-instrument conjunction studies in assessing the sources of the solar wind. [ABSTRACT FROM AUTHOR]

The details of the dynamo process in the Sun are an important aspect of research in solar-terrestrial physics and astrophysics. The surface part of the dynamo can be constrained by direct observations, but the subsurface part lacks direct observational constraints. The torsional oscillations, a small periodic variation of the Sun's rotation with the solar cycle, are thought to result from the Lorentz force of the cyclic magnetic field generated by the dynamo. In this study, we aim to discriminate between three Babcock–Leighton dynamo models by comparing the zonal acceleration of the three models with the observed one. The property that the poleward and equatorward branches of the torsional oscillations originate from about ±55° latitudes with their own migration time periods serves as an effective discriminator that could constrain the configuration of the magnetic field in the convection zone. The toroidal field, comprising poleward and equatorward branches separated at about ±55° latitudes, can generate the two branches of the torsional oscillations. The alternating acceleration and deceleration bands in time are the other property of the torsional oscillations that discriminates between the dynamo models. To reproduce this property, the phase difference between the radial (B r ) and toroidal (B ϕ ) components of the magnetic field near the surface should be about π /2. [ABSTRACT FROM AUTHOR]

The article focuses on the solar dynamo process, examining the generation, propagation, and emergence of magnetic fields on the Sun. Topics include early observations of sunspots and their historical impact, advancements in solar magnetism studies with the introduction of new tools like the solar magnetograph, and the role of helioseismology in understanding the Sun's internal dynamics and magnetic cycles.

This paper analyzes the Three events of Solar Parameters and Interplanetary Coronal Mass Ejections in the maximum phase of Solar Cycle 24 and focuses on the magnetic activity of interplanetary coronal mass ejection during the solar cycle 24. We investigate the magnetic field magnitude (B), Proton temperature (Tp), Proton density (Np). From this study, we find the highest peak of IP (Interplanetary) shocks on disk center MC (Magnetic cloud) events during the solar cycle 24 and also we investigate the magnetic activity of the solar cycle. In this study, we find that the ACE spacecraft shows the fastest coronal mass ejection and highest interplanetary shock wave on solar cycle 24. It is important to note that extreme events can happen at any time during a cycle. In solar cycle 24, from July 13, 2012 to July 15, 2012 largest storm occurred because the magnetic field was -52nT and linear speed was 1500 kms-1 observed. [ABSTRACT FROM AUTHOR]

The space weather effects at the Earth's magnetosphere are mostly driven by the solar wind that carries the interplanetary magnetic field (IMF). In this paper, we use 2 years of data in the solar wind from lunar orbiting ARTEMIS and MMS spacecraft upstream of the Earth's bow shock to study the structure of the IMF. We determine the lag times of IMF structures and their dependence on spacecraft positions by conducting an information theory analysis and comparing it with two traditional analysis methods: cross‐correlation (CC) analysis and minimum variance of magnetic field analysis (MVAB). For the events with long time intervals (i.e., >4 hr) and with small‐spatial separation between the MMS and ARTEMIS along the yGSM‐direction (i.e., <40Re, where Re is the Earth's radius), the lag times based on the CC and the mutual information (MI) analyses statistically agree with each other, with p‐values of 1.675 × 10−7 and 4.833 × 10−9, with the confidence of 95%. Both the results based on MI and CC have a large deviation from the results from MVAB. For some of the events, such a deviation could be improved by taking the fast mode speed into account; however, p‐tests showed that they were not statistically significant to the 95% confidence level. Plain Language Summary: Typically, single‐point measurements from the Earth‐Sun Lagrange Point‐1 are used to forecast space weather. However, it is important to understand that multi‐point measurements are required to further understand and predict geo‐effective solar wind structures. Three analysis methods using multi‐point measurements from the MMS and THEMIS missions of large solar wind structures as they move from regions around the Moon to regions around Earth's bow shock, are presented and compared in this paper. Information theory analysis (specifically Mutual Information) determines dependence between two variables by quantifying the entropy (uncertainty) in the two variables. Minimum variance analysis calculates the direction of least change in a magnetic field and assumes the solar wind is propagating in that direction. Lag time is calculated by taking the dot products of this direction with both the displacement vector between the two spacecraft, to get a distance, and the ion velocity (from ARTEMIS) to get a speed. The distance is divided by the speed to get a lag time. Cross‐Correlation analysis is a traditional method for measuring similarity between two variables. This paper shows that information theory analysis along with cross‐correlation analysis could be used successfully for space weather forecasting. Key Points: The solar wind data by MMS and THEMIS are analyzed by using information theory to understand the propagation of solar wind structuresMutual information, linear cross‐correlation, and minimum variance analyses sometimes give different lag‐timesInformation theory analysis along with the traditional method of cross‐correlation analysis could be used successfully for space weather forecasting [ABSTRACT FROM AUTHOR]

We use MHD simulations to study the time sequence of magnetospheric responses to a synthetic event with a southward interplanetary magnetic field (IMF) turning. The onset of dayside magnetopause reconnection launches a weak rarefaction wave and sunward flow in the equatorial magnetosphere simultaneously with a tailward flow through the polar cap. This convection results in the accumulation of magnetic flux in the tail lobes and thinning of the tail current layer which provides favorable conditions for the onset of nightside reconnection. The onset of nightside reconnection about 40 min later closes the Dungey convection cycle, resulting in a second increase in the sunward flow in the equatorial plane. Variations of the magnetopause standoff distance as well as the size of the polar cap (PC) may indicate the onsets of the dayside and nightside reconnections. We compare the results of two MHD models and discuss their differences. Plain Language Summary: The auroras and other space weather phenomena are produced by the interaction of the solar wind with the Earth's magnetic environment. The fundamental plasma process of magnetic reconnection modulates this interaction, which then drives a circulation of magnetic field and plasma within the magnetosphere known as the Dungey cycle. Reconnection occurs when the magnetic field in the solar wind points southwards but turns off when it is northwards. The sequence of events within the magnetosphere in response to a southwards turning of the magnetic field is currently poorly understood. In this study, we model the interaction with two magnetohydrodynamic simulation codes. These show a rarefaction wave from the front of the magnetosphere toward the magnetotail in response to the turn‐on of reconnection. Thereafter magnetic reconnection occurs in the magnetotail to complete the cycle. Although the simulations differ in the details, the two agree on this sequence of events, providing new insights into the dynamics of the magnetosphere. Key Points: We investigate magnetospheric convection after southward turning and highlight the differences between the two MHD modelsTwo‐step response in convection after dayside and nightside reconnectionVariations in the magnetopause standoff distance may indicate variations in the magnetic flux [ABSTRACT FROM AUTHOR]