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In this paper, we present for the first time a comprehensive statistical study between type II radio bursts from the metric (m) to the dekameric–hectometric (DH) domain and their associated solar and space weather (SW) phenomena, namely, solar flares (SFs), sunspot (SN) configurations, filament eruptions, coronal mass ejections (CMEs), their interplanetary (IP) counterparts (ICMEs) and shocks, in situ detected particles and geomagnetic storms (GSs). The m-only and m + DH radio signatures are identified from dynamic spectra provided by the ground-based RSTN stations distributed over the globe together with Wind/WAVES satellite data. The DH-only type IIs are adopted from a ready catalog based on Wind/WAVES spacecraft data. We perform the temporal and spatial association between the radio emission and the listed above activity events during solar cycle (SC) 24, separately for the three sub-categories, m-only, m + DH and DH-only type IIs. A quantitative assessment on the occurrence rates is presented as a function of the strength of the specific SW phenomena: highest rates are obtained with CMEs, SFs, filament eruptions, and SN configurations, whereas a much weaker relationship is found with ICMEs, IP shocks, energetic particles, and GSs. The potential of the obtained rates to be used in empirical or physics-based models for SW forecasting is discussed. [ABSTRACT FROM AUTHOR]

We analysed a GOES C6.2 class solar flare that occurred on 27 October 2003 at the heliographic position S20E29. Utilising a database developed from a simplified 3D magnetic loop model, we inferred a set of geometric and physical parameters to characterise the flare. This model, based on general properties of known solar flares and adjusted for instrument resolution, was used to replicate observations from the Nobeyama Radio Polarimeter (NoRP) spectra and the Nobeyama Radioheliograph (NoRH) brightness maps. We identified a possible range of parameters by comparing observed spectra and brightness distribution maps with modelled counterparts. The analysis involved computing a weighted mean of the one hundred best-fit model parameters, ranked by increasing χ 2 values.Across six discrete time intervals representing the gradual, impulsive, and decay phases of the flare, we observed slight variations in values for ten analysed parameters, with notable exceptions at the burst maxima, including an energy spectral index of approximately ∼ 2.34 , a photospheric magnetic field strength of around ∼ 2 308 G , and a non-thermal electron density of about ∼ 10 7.11 cm - 3 . In general, our results replicated the soft-hard-soft behaviour in the gradual-peak-decay phases of a solar flare. Therefore, we infer that the physical parameters (magnetic field strength, energy spectral index, and non-thermal electron density) were accurately recovered. However, fitting geometric parameters such as inclination, asymmetry, azimuth, loop radius, loop height, and footpoint separation proved challenging due to the limited resolution of the instruments, which affects the precise determination of loop-like flare geometries. [ABSTRACT FROM AUTHOR]

We present a novel deep Convolutional Neural Network model with one-against-rest approach (OAR-CNN) and modify the hybrid Convolutional Neural Network (H-CNN) model of Zheng et al. (2019) for multiclass flare prediction to forecast whether an active region generates multiclass flare within 24 h. Additionally, in the OAR-CNN and H-CNN models, we employ the decision strategies of majority voting and probability threshold, respectively, comparing the prediction outcomes of these two strategies. Our models undergo training and testing on the same 10 cross-validation datasets as employed by Zheng et al. (2019) , and then compare the results with previous studies using forecast verification metrics, with a focus on the true skill statistic (TSS). The major results are summarized as follows. (1) This is the first attempt to utilize the decision strategies of majority voting and probability threshold in the OAR-CNN model for multiclass solar flare prediction. (2) In both the OAR-CNN and H-CNN models, the predictive results with the probability threshold decision strategy are higher than those with majority voting across all six classes (i.e., No-flare, C, M, X, ⩾ C, and ⩾ M class), except for a slight decrease in the C class in the OAR-CNN model. (3) The OAR-CNN and modified H-CNN models with the probability threshold decision strategy demonstrate comparable statistical scores across all categories and outperform previous studies. (4) In the prediction of four-class flare, our proposed OAR-CNN model with the probability threshold decision strategy achieves relatively high mean TSS scores of 0.744, 0.429, 0.567, and 0.630 for No-flare, C, M, and X class, respectively, surpassing or comparable to results from prior studies. Furthermore, our model achieves high TSS scores of 0.744 ± 0.042 for ⩾ C–class and 0.764 ± 0.089 for ⩾ M-class predictions. [ABSTRACT FROM AUTHOR]

This work presents a summary of the continuous non-stop (hereinafter 24/7) real-time measurement and warning system for EUV solar activity, which is based on worldwide multifrequency Global Navigation Satellite Systems (GNSS) observations. The system relies on continuous tracking of the intensity of expected global patterns in the Earth's ionosphere's free electron distribution, which are associated with solar flares. The paper includes a discussion on the foundations of GNSS Solar Astronomy, along with details on its real-time implementation that began in 2011. Furthermore, a summary of the corresponding validation is provided, comparing it to external and direct solar EUV flux measurements obtained from SOHO-SEM. Finally, there will be a brief mention of the ongoing efforts to extend this technique to detect huge extra-solar sources. [ABSTRACT FROM AUTHOR]

• The SFE amplitude depends linearly on the perpendicular maximum flare X-ray flux. • The X-ray radiation affects the EEJ three times more strongly than the Sq current. • The weak linear relationship found for two SFE parameters might be a coincidence. Solar flares effects (SFE) are short geomagnetic disturbances (mainly in the horizontal component) observed during the development of solar flares. SFE are caused by current enhancements in multiple layers of the ionosphere induced by the flare ionizing radiation. Despite their origin, very few research studies have focused on the connection between the horizontal SFE amplitude and the maximum flare X-ray flux. By analyzing measurements from the magnetic station at Huancayo, Peru, located in the American sector of the equatorial electrojet (EEJ) current, we computed the horizontal SFE amplitudes triggered by X-class solar flares of Solar Cycle 24 by using a novel method. The EEJ contribution to the horizontal SFE amplitude was calculated using data from the geomagnetic observatory at Pilar, Argentina, located outside the EEJ belt. We found that the EEJ contribution to the horizontal SFE amplitude is linearly dependent on the perpendicular component of the maximum flare X-ray flux for two states of the EEJ current. We also found that the flare X-ray ionizing effect is around three times stronger in the EEJ current than in the solar quiet current, being the EEJ current the most important contributor to the horizontal SFE amplitude. In addition, our results suggest that the weak linear relationship between the pre-flare horizontal geomagnetic variation and the EEJ component of the horizontal SFE amplitude found by a previous study might be only a coincidence, instead of a real connection between both parameters. Exceptional SFE were studied separately. [ABSTRACT FROM AUTHOR]

Ionosphere has important influences on the performances of Global Navigation Satellite System (GNSS) in terms of signal quality and ranging errors. This study discusses the impact of ionosphere disturbances caused by the solar flare and geomagnetic storm events in September 2017 and October 2021 on signal quality and positioning accuracy. To identify the occurrence and also to study the magnitude of the storm, we have evaluated the Solar Activity parameters and constructed global Rate of TEC Index maps. In regard of the GNSS signal, both the signal-in-space ranging error and cycle slip occurrence are adopted to study the influence of the solar flare on the accuracy of the broadcast ephemeris and the quality of phase observation. Furthermore, the kinematic precise point positioning experiments with 39 International GNSS Service (IGS) stations are carried out, and the positioning errors of north, east, and up components are calculated to assess the precise positioning accuracy during the storm. The presented results suggest that the kinematic precise point positioning accuracy of the selected IGS stations in low- and high-latitude areas degraded at 8th September 2017 and 12th October 2021, implying that the GNSS precise positioning are less reliable during the solar flare events. [ABSTRACT FROM AUTHOR]

In association with the X28 solar flare on November 4, 2003, the muon telescope installed in Mexico City observed an enhancement in its counting rate between 19:55 and 20:00 UT. Based on a numerical simulation, we found that the entry of a high-energy solar neutron, with energy range from 0.2 to 2 GeV, is capable of producing muon flux that reach the atmospheric depth of Mexico City. Furthermore, we also found that this muon flux is of the order of 3% with respect to the average muon flux recorded by the telescope. Therefore it is very likely that the excess signals observed in the muon telescope are due to muons generated by solar neutrons in the Earth's atmosphere. [ABSTRACT FROM AUTHOR]

The origin of fast radio bursts (FRBs), the brightest cosmic explosion in radio bands, remains unknown. We introduce here a novel method for a comprehensive analysis of active FRBs' behaviors in the time-energy domain. Using "Pincus Index" and "Maximum Lyapunov Exponent", we were able to quantify the randomness and chaoticity, respectively, of the bursting events and put FRBs in the context of common transient physical phenomena, such as pulsar, earthquakes, and solar flares. In the bivariate time-energy domain, repeated FRB bursts' behaviors deviate significantly (more random, less chaotic) from pulsars, earthquakes, and solar flares. The waiting times between FRB bursts and the corresponding energy changes exhibit no correlation and remain unpredictable, suggesting that the emission of FRBs does not exhibit the time and energy clustering observed in seismic events. The pronounced stochasticity may arise from a singular source with high entropy or the combination of diverse emission mechanisms/sites. Consequently, our methodology serves as a pragmatic tool for illustrating the congruities and distinctions among diverse physical processes. [ABSTRACT FROM AUTHOR]

Ionospheric scintillation is a common phenomenon in the equatorial, auroral, and polar areas, posing a threat to the Global Navigation Satellite System's (GNSS) operation. This ionospheric effect is thought to impact satellite signal propagation, hence, lowering positioning accuracy. Therefore, detecting ionospheric scintillation is critical in enhancing GNSS performance, particularly at low latitudes with severe amplitude scintillation. This paper investigates the effects of ionospheric scintillation on GPS signals at UNIMAS station, the East part of Malaysia. This study aims to identify the occurrence of ionospheric scintillation by calculating the index of scintillation strength during solar maximum 2014. The amplitude scintillation, which is measured in the S 4 index is obtained and classified accordingly from the data recorded at the UNIMAS station. The results have shown that strong scintillation (S 4 ≥ 0.5) occurred in the spring (April) and autumn (September and October) seasons, reaching 8 incidents. This paper also presents the diurnal, seasonal, and solar activity dependence of ionospheric scintillation. It is evident that the occurrence of amplitude scintillation is influenced by variations in solar activity, including solar flares and sunspots, as well as diurnal and seasonal changes. These findings provide valuable insights into the behaviour of the ionosphere and its impact on space-based communication and navigation systems. [ABSTRACT FROM AUTHOR]

Based on satellite observations, the study examines the effect of an X1.7 flare (which occurred on January 27, 2012) on neutral winds and the formation of wave perturbations in Earth's thermosphere. The Gravity field and steady state Ocean Circulation Explorer (GOCE) observations of the thermospheric zonal wind speed show an increase of 100 m/s in the north polar and 400S to south polar regions on the day side associated with the X1.7 solar flare. This feature is absent for the geomagnetically quiet days in January 2012, when there are no X-class flares. The wave perturbations in thermosphere, derived from the zonal winds are observed to be strongest in the flare day, than in non-flare days, with power index 40. During the flare day, wave perturbation with a wavelength of about 1110 km is dominant and is found preferentially in southern latitudes (above 400S) on the day side. When compared to non-flare days, the TIMED-derived neutral temperature increases by 45 K around the equatorial zone. The measurements also show the substantial temperature gradients over latitude and longitude in the flare situation. This demonstrates the presence of high thermal gradients in the thermosphere caused by the X1.7 solar flare, which causes zonal wind amplification and the launching of strong waves in the thermosphere. [ABSTRACT FROM AUTHOR]

Flare stacks , used for emergency venting of redundant hydrogen, can cause jet fires that pose thermal hazards to the surrounding environment. To accurately predict the hazard distance of hydrogen flare, it is necessary to develop a new flare radiation model. Also, the numerical simulations of hydrogen flame are carried out to assess the radiation hazard area of the flares. The results show that the hazard distances predicted by the numerical method and the new model agree well with the HSL data fitted by exponential regression, and the errors are less than ±5%. Furthermore, the new model and simulations were used to analyze the distribution of thermal radiation for hydrogen flare under various release conditions. Increasing the release rates will drive the hazard boundary of flare system to expand. Additionally, as flare height increases, the radiation damage from the flare flame on ground is reduced due to buoyancy of combustion products. • A appropriate flare hazard distance can effectively prevent potential thermal hazards. • A new model for predicting the hazard distance of hydrogen flares is developed. • Simulations and the new model improved prediction accuracy of hydrogen flare hazard distance. • The hydrogen flare radiation model was applied to various release conditions. [ABSTRACT FROM AUTHOR]

We have investigated the dependence of the peak intensities of energetic storm particles (ESPs) on various parameters characterising the coronal mass ejections (CMEs) and associated phenomena. The aim of this study is to suggest empirical models for forecasting the peak intensities of ESP events at 1 AU based on solar and interplanetary (IP) space observations. For this study we searched for the associations of front-side full and partial halo CMEs with linear speeds > 400 km s−1during the years 1996–2015 with IP shocks at 1 AU and ESP events observed near the time when the shock passes the observer. We found 88 CME-driven IP shocks associated with ESP events at proton energy range 5.0–7.2 MeV (nominal energy 6.0 MeV) and 59 shocks at the energy range 15.1–21.9 MeV (nominal energy 18.2 MeV). At these two energies 71 % and 68 % of the ESP events were associated with solar energetic particle (SEP) events, 85 % and 84 % were associated with decametric–hectometric (DH) type II radio bursts while 67 % and 66 % were associated with both. For each CME - shock pair we calculated the predicted shock transit speed ( V TR ) by using the method of Belov et al. (2022) and used this as the primary parameter in the investigation. We performed correlation analyses between the logarithm of the peak intensities of the ESP events (log 10 [ I ESP peak ]) and the solar parameters related to the CMEs, solar flares, IP shocks, SEP events, and type II radio bursts. When using a single explanatory variable, we found best correlation coefficients for V TR (0.68 ± 0.05 and 0.71 ± 0.06), the CME space speed ( V CME space ) (0.59 ± 0.05 and 0.68 ± 0.07), and the logarithm of SEP peak intensity (log 10 [ I SEP peak ]) (0.55 ± 0.08 and 0.70 ± 0.08) at 6.0 and 18.2 MeV, respectively. Weak to moderate correlations were found for the logarithm of the soft X-ray flux (log 10 [SXRF]) and the logarithm of the duration of DH type II radio burst (log 10 [ D TII ]). Using linear combinations of two or more variables improved the correlations. The best two-variable combination explaining log 10 [ I ESP peak ] was V TR combined with log 10 [ I SEP peak ] and the best three- and four-variable combinations also included these two parameters. We found two methods for forecasting ESP peak intensities, one of which can be used for long lead time and the other for medium lead time forecasting. For long lead time forecasting V TR , V CME space and log 10 [SXRF] are used. The correlation coefficients between the calculated and observed log 10 [ I ESP peak ] were 0.71 ± 0.05 at 6.0 MeV and 0.74 ± 0.06 at 18.2 MeV. This method only depends on the coronagraph and X-ray observations at the Sun. For medium lead time forecasting the four parameters used are V TR , log 10 [ I SEP peak ], V CME space (or log 10 [SXRF]), and log 10 [ D TII ]. The correlation coefficients were 0.80 ± 0.04 at 6.0 MeV and 0.84 ± 0.05 at 18.2 MeV. Coronagraph observations at the Sun and solar energetic particle and DH type II burst measurements in IP space are required for this method. The medium lead time forecasting provides an average warning time of 30 ± 16 h. [ABSTRACT FROM AUTHOR]

• Geomagnetic response to strong X-ray emissions was presented. • Innovative simultaneous observations of the main GMF level and its fluctuations. • The levels of the main GMF and its fluctuations were measured at midlatitudes. • X-class solar flares induced crochet effect & GMF quasi-sinusoidal variations. • The observed results aligned with theoretical magnetic disturbance estimates. This study analyzes the variations in the levels of the Earth's magnetic field and its fluctuations in the range of periods of 1–1000 s that accompanied X-class solar flare on 6, 7, and 10 September 2017. Variations of the main Geomagnetic field (GMF) and the fluctuations in the range of periods 1–1000 s were measured by the magnetometer (located at 49.93°N, 36.95°E). The X9.3-class solar flare (SF) on 6 September 2017 induced substantial decreases in X-, Y-, and Z-component levels (−30 nT, −60 nT, and −15 nT, respectively), i.e., crochet effect. These reductions were restored within approximately 60, 150, and 5 min. Additionally, measurements from a magnetometer-fluxmeter (located at 49.64°N, 36.93°E) revealed a temporary sharp decrease in X- (approximately −3 nT) and Y-component (approximately −6 nT) fluctuations, followed by a subsequent increase/restoration lasting 12–15 min. The X8.2 solar flare that occurred on 10 September induced a minor reduction (<10 nT) in the levels of all local GMF components. Concurrently, it triggered a 1.5- to 2-fold amplification of quasi-sinusoidal oscillations in the Y-component fluctuations, characterized by a period of ∼10–12 min and a duration of ∼60 min. The study also discusses the mechanism of variations in the level of the GMF. [ABSTRACT FROM AUTHOR]

• The solar flare effect on the low equatorial latitude ionosphere during the peak of solar cycle 24 is analyzed using GPS TEC. • We have analyzed 05 X-class solar flares, 49 M-class solar flares, and 396 solar flares of C-class that occurred in the year 2014. • Two popular methods (baseline method and the mean method) of VTEC change estimation due to flare are compared, baseline method showed better results. We describe the newly discovered response of differential vertical total electron content (DVTEC) in the low-equatorial latitude ionosphere to the solar flares during the peak of solar cycle 24 i.e., the year 2014. GPS TEC data for the existing investigation has been acquired from the international GNSS services network station in Bangalore, India (geomagnetic latitude 4.58οN). For the year 2014, we inspected five X-class solar flares, forty-nine M-class solar flares, and three hundred ninety-six C-class solar flares in the current study. To ascertain the relationship between ΔDVTEC and the ΔX-ray and ΔEUV fluxes, the two main ionizing radiation fluxes during flare events are used. Additionally, to identify electron density change in the ionosphere due to solar flares, we used two well-known methodologies, the baseline method and the mean method. The baseline method provides a better correlation between ΔDVTEC and ΔX-ray for X-, M-, and C-class flares. For M- and C- class flares, both methods do not show any meaningful correlation. The Solar disc location effect shows an enhanced (0.573) correlation between ΔDVTEC and ΔX-ray*cos (CMD) for the X-class flares, whereas for M- and C-class flares, no significant change was observed, which indicates feeble or no CMD effect for lower class solar flares while it is opposite for X-class flares. Here we suggest that the high solar activity, and location of the observation station to the EIA trough region might be the possible reason for the observed results. [ABSTRACT FROM AUTHOR]

• Solar flare effect may suppress irregularities. • Positive ionospheric storm noticed during storm recovery phase. • Geomagnetic storm and solar flare impact affect TEC values. This study investigates the impact of geomagnetic storms and solar flares on total electron content (TEC) of the ionosphere of high-latitude auroral station at Tromso(Geog. Lat. 69.66 ° N, Geog.Long. 18.94 ° E, and Geomag.Lat. 66 °). The rate of increase or decrease in TEC value indicator ( ROTI ave ) are used as the ionospheric irregularities proxy to prob occurrence of TEC alteration during months of July, August, September, October and November 2021. The deviation of TEC (in percentage) denoted by Δ TEC (%) was utilized to examine the impact of geomagnetic storms and solar flares on the ionospheric storms over aurora region. The study finds that a remarkable boost of TEC values up to the order of about 7–10 TECU was noticed over Tromso station during moderate geomagnetic storms of 28 August 2021, 12 and 17 October 2021 and a strong geomagnetic storm of 4 November 2021. The investigation also finds suppression of ionospheric irregularities during peak of X-type solar flare of 28 October 2021. The suppression is probably attributed to effect of accelerated energetic particles associated to solar flare eruption and coronal mass ejection (CME). On the other hand, moderate occurrence of irregularity was observed during main and recovery storm phase of 4 November 2021 at 18:00–24:00 UT and 1:00 UT-3:00 UT. This article presents the consequence of geomagnetic storms and solar flare on characteristics evolution of phase fluctuations and ionospheric storm during July, August, September, October and November. [ABSTRACT FROM AUTHOR]

We explore the correlation between different parameters of space weather events associated with intense geomagnetic disturbances that occurred during the solar cycles (SCs) 23 and 24 (1996–2019). The space weather events under this study are the Solar Flares (SFs), Coronal Mass Ejections (CMEs), Geomagnetic Storms (GSs), Solar Energetic Protons (SEPs) and Electrons (SEEs), respectively. The severity of the GSs is identified based on the Dst ⩽ - 100 nT and a list of 111 GSs with their associated space weather counterparts is obtained over the pre-selected time period. The utilized association procedure between the different space weather events is described and their observed properties are listed. For the performed analysis, Pearson correlation metrics is employed. The results are summarized and discussed. [ABSTRACT FROM AUTHOR]

Magnetic reconnection is a fundamental process in astrophysical and space plasmas which is responsible for particle acceleration, in particular, in solar flares. Separator reconnection is one type of steady-state three-dimensional magnetic reconnection. In this paper, by considering static electric and magnetic fields associated with separator reconnection, we investigate first the acceleration features of a test-particle and then discuss acceleration of a randomly injected large population of protons and electrons in the vicinity of reconnection site with input parameters for the solar corona. It is shown that protons and electrons can be accelerated up to tens of MeV and even higher kinetic energies. The variation of energy spectra for different strengths of electric field amplitude is also discussed. [ABSTRACT FROM AUTHOR]

Very Low Frequency (VLF) signal amplitude is enhanced during solar flare events. Hence, it can be used as remote sensing for tracking solar flares and studying the lower ionosphere. However, the enhancement is not directly proportional to the magnitude of a solar flare hindering the effectiveness of the VLF signal as a remote sensor for tracking solar flare. Preliminary analysis shows that the level of enhancement recorded for a particular solar flare occurrence depends on the background fluctuations. Thus, this study aims to explore the background fluctuations of the VLF signal using quiet-day data and investigate the impact of background fluctuations on solar flare detectability using the VLF signal. The VLF data used for this study were collected using a VLF receiver installed at KolaDaisi University, Ibadan (KDU-I). The VLF data were from three stations; GBZ (Freq.: 19.8 kHz, Lat.: 21.82°, Long.: 114.17°), NWC (Freq.: 19.58 kHz, Lat.: 54.91°, Long.: 003.28°) and VTX4 (Freq.: 19.2, kHz Lat.: 08.38°, Long.: 077.75°) recorded between 2019 and 2022 at Ibadan (Lat.: 7.6248°, Long.: 3.9131°). The results revealed that the time series has a cyclic pattern that corresponds to each global season classification in the northern hemisphere (Summer, autumn, winter and spring) with an upward trend from wet to dry season. This observation shows that similar geophysical parameters that drive meteorology also have an impact on the background fluctuations of VLF amplitude. It was also observed that the sensitivity of VLF amplitude in sensing solar flare depends on the background fluctuation. It is recommended that the effect of meteorology and background fluctuation be considered when modelling VLF amplitude as a remote sensor for tracking solar flares. [ABSTRACT FROM AUTHOR]

The newly installed CALLISTO spectrometer, hosted by the Department of Space Environment, Institute of Basic and Applied Sciences- EJUST, commenced operation on August 14, 2021. The system contains a cross dipole long-wavelength array antenna with high sensitivity to monitor solar radio transients. Its antenna was strategically positioned and appeared to be in the center of the CALLISTO network of spectrometers. Moreover, in the northern section of Africa, the Egypt-Alexandria CALLISTO and ALGERIA-CRAAG stations are the only ones operating. There are no stations in the West African region, while stations in the eastern part of Africa are not working. Thus, Egypt- Alexandria station serves as a reference for other stations within the e-CALLISTO network. Despite the low solar activity, the instrument detected several solar radio bursts not limited to type II, type III, and type V. A vigorous case study was conducted on two selected radio burst events to validate the authenticity of the recorded events. Other solar radio stations at different geographical locations recorded all the radio bursts detected by the spectrometer. The case study included brief analyses that indicated a type II radio burst observed on October 09, 2021, between 06:30 and 07:00 UT, was associated with an M1.6 solar flare located at N18E08 within NOAA-AR 2882 and a CME with a shock front speed of ∼ 978 km/s. However, the type III radio burst is neither CME nor solar flare associated. These analyses examine the instrument's capacity to provide real-time solar radio transient data 24 h a day to mitigate the challenges of data gaps faced in the African continent. Hence, the instrument has become an integral part of space weather monitoring and forecasting over the region and other parts of the globe. [ABSTRACT FROM AUTHOR]

Solar physics specializes the study of the fundamental processes occurred in the Sun and their influences on the interplanetary space. It deals with detailed measurements that are possible only for our closest star which is a natural plasma laboratory with multi-scale processes taking place. In addition, solar activities have a high impact on the space weather and habitability of the Earth, major solar eruptive events such as solar flare and coronal mass ejection have harmful effects on communication systems, satellites, power grid, and so forth. The study of the Sun not only helps us to understand the universe, the solar-terrestrial relationship, and the planetary habitability, but also serves national strategies in space and aerospace security. In the 21st century, there has been considerable progress in solar physics due to the development of detecting the Sun from space. In this paper, recent space exploration development trends of solar physics are examined both at home and abroad, key fields of the future space exploration development of solar physics in China are summarized, the disciplinary layout is optimized, and high-quality development of solar physics is promoted. [ABSTRACT FROM AUTHOR]

Collisionless magnetic reconnection, which converts the magnetic energy into the kinetic energy of plasma particles via the heating or acceleration, has been believed widely to be able to explain various eruptive phenomena such as solar flares and geomagnetic storms. However, the microphysical mechanism of anomalous resistivity in the collisionless magnetic reconnection is still an unsolved fundamental problem. Among the many physical mechanisms of anomalous resistivity generation, chaos-induced resistivity based on the chaos of the charged particle orbits near the magnetic neutral point is not the most popular formation mechanism, but its microscopic physical picture is the clearest. This paper first briefly reviews the early research and physical model of the chaos-induced resistivity in collisionless magnetic reconnection region, introduces the recent research progress of the chaos-induced resistivity, and expounds the future research direction of the chaos-induced resistivity. [ABSTRACT FROM AUTHOR]

The characteristics of X-class flares of solar cycles 23 and 24 are examined based on the soft X-ray (0.1–0.8 nm) and EUV (26–34 nm) light curves. First, the commonly used correction factors for the center-to-limb variation of EUV flux are compared. Subsequently, enhancements in X-ray and EUV levels are used to calculate the relative apportionment of flare energy released in these two bands. The X-ray to EUV proportion of energy is found to be larger in the high X-class flares (X9.0 and stronger) as compared to the flares weaker than X9.0. The X-ray and EUV light curves revealed that the time of impulsive and thermal EUV peaks differed from X-ray peak by ∼ 0–25 min. The time differences had a broad range for weaker flares but reduced to within ∼ 7 min for high X-class flare events. Therefore, the present study brings out the general energetics and temporal evolution of phases of the X-class flares. Implications of the findings on solar flare studies and flare impact on terrestrial atmosphere are discussed. [ABSTRACT FROM AUTHOR]

A novel neuro-adaptive control design approach is presented to maintain a high-precision Sun-pointing attitude of a spacecraft on a Sun–Earth L 1 halo orbit. In the presence of parametric inaccuracies and unknown disturbances, the proposed method effectively learns the modeling uncertainty and adapts the control action to achieve its objective. First, large attitude errors are driven towards zero by applying a conventional back-stepping approach that uses the standard quadratic Lyapunov function (QLF). Once the errors are within the required error bounds, a barrier Lyapunov function-based (BLF) approach is excited, ensuring that the attitude errors remain constrained from thereon. Moreover, following the philosophy of meta-cognition, learning is purposefully stopped when the attitude error becomes too small but excited again whenever it grows large. The robustness of the proposed control law is illustrated by carrying out several simulations incorporating modeling uncertainties and disturbance torques, including high-magnitude solar flares. Finally, the effectiveness of the proposed BLF-based adaptive control law is demonstrated by comparing it with a QLF-based adaptive control law following the same philosophy. • A robust neuro-adaptive controller is designed to track a desired spacecraft attitude. • Despite uncertainties and SRP torque, a BLF enforces attitude error constraints. • Disturbance approximation is switched on/off using principle of meta-cognition. • The controller achieves a high-precision Sun-pointing attitude on a halo orbit. • Robustness is demonstrated by incorporating modelling uncertainties and disturbances. [ABSTRACT FROM AUTHOR]

Solar energetic particle (SEP) events originate from solar flares and coronal mass ejections. Ground level enhancement (GLE) is a sudden increase in the count rate of a ground neutron monitor. When GLE occurs, the associated SEP event shows a large peak intensity and fluence in the proton intensity of the high energy channels in the Geostationary Operational Environmental Satellite (GOES). This study examined the chemical composition ratio at the moment of SEP events to determine what is occurring at the SEP event origin site on the solar surface. This study used the data of the Solar Isotope Spectrometer (SIS) onboard the Advanced Composition Explorer (ACE) satellite for SEP events, which was confirmed by proton intensity data from the GOES satellite. The chemical compositions during the SEP events with and without GLE related to the solar flares in M5 class were compared. In addition, the solar wind composition in a normal quiet time and the solar photosphere abundance observed by spectroscopy were compared with the selected SEP events. As expected, all elements except helium showed less than a hundredfold increase in intensity at the SEP event periods than on quiet-day events. The helium intensity surged more than a thousandfold increase for SEP events with and without GLE. The abundance of the heavy elements at the periods of the SEP event accompanied by GLE was greater than that of the solar photosphere. Although it is generally believed that the erupted emission of electromagnetic radiation, including gamma and x-rays, called a flare, escapes from the deep undersurface core, the relatively higher abundance of helium compared to other elements at the moment of the flare blowing out the SEP events suggests that nuclear fusion by the magnetic confinement is occurring near the solar surface. [ABSTRACT FROM AUTHOR]

The M1.5-class flare and associated coronal mass ejection (CME) of 16 February 2011 was observed with the Extreme ultraviolet Imaging Spectrometer on board the Hinode spacecraft. Spray plasma associated with the CME is found to exhibit a Doppler blue-shift of 850 km s−1 – one of the largest values reported from spectroscopy of the solar disk and inner corona. The observation is unusual in that the emission line (Fe xii 193.51 Å) is not observed directly, but the Doppler shift is so large that the blue-shifted component appears in a wavelength window at 192.82 Å, intended to observe lines of O v , Fe xi and Ca xvii. The Fe xii 195.12 Å emission line is used as a proxy for the rest component of 193.51 Å. The observation highlights the risks of using narrow wavelength windows for spectrometer observations when observing highly-dynamic solar phenomena. The consequences of large Doppler shifts for ultraviolet solar spectrometers, including the upcoming Multi-slit Solar Explorer (MUSE) mission, are discussed. [ABSTRACT FROM AUTHOR]

Solar flares, along with other sun-originated events such as Coronal Mass Ejections, fast solar wind streams, and solar energetic particles are among the most relevant events in Space Weather. Moreover, solar flares are the most energetic processes that occur in our solar system. The in-depth study of their occurrence statistics, both over extended periods or during individual solar cycles, allows us to improve and constrain the basic physical models of their origin. Increasing the number of detected events, especially those of lower intensity, and the number of physical parameters that describe the detected flares is, therefore, a mandatory goal. In this paper, we present a computationally efficient algorithm for the detection of solar flares in the soft-X solar flux provided by the GOES (NASA/NOAA) satellite constellation. Our code produces a new flare catalogue increasing the number of events with respect to the official GOES list. In addition to increasing the number of identified events, the catalogue contains information such as: an estimate of the total energy released, start and end time of the event, possible overlap with other events, background level of the GOES X-ray emission close to the revealed event. After a detailed description of the detection algorithm, we carry out a preliminary analysis of the flares reported in our catalogue and compare our results with the official list of GOES for the period from 1998 to 2020. [ABSTRACT FROM AUTHOR]

Solar flares and coronal mass ejections (CMEs) cause immediate and adverse effects on the interplanetary space and geospace. In an era of space-based technical civilization, the deeper understanding of the mechanisms that produce them and the construction of efficient prediction schemes are of paramount importance. The source regions of flares and CMEs exhibit some common morphological characteristics, such as δ -spots, filaments and sigmoids, which are associated with strongly sheared magnetic polarity inversion lines, indicative of the complex magnetic configurations that store huge amounts of free magnetic energy and helicity. The challenge is to transform this empirical knowledge into parameters/predictors that can help us distinguish efficiently between quiet, flare-, and CME-productive (eruptive) active regions. This paper reviews these efforts to parameterize the characteristics of eruptive active regions as well as the importance of transforming new knowledge into more efficient predictors and including new types of data. Magnetic properties of active regions were first introduced when systematic ground-based observations of the photospheric magnetic field became possible and the relevant research was boosted by the provision of near real time, uninterrupted, high-quality observations from space, which allowed the study of large, statistically significant samples. Nonetheless, flare and CME prediction still faces a number of challenges. The magnetic field information is still constrained at the photospheric level and accessed only from one vantage point of observation, thus there is always need for better predictors; the dynamic behavior of active regions is still not fully incorporated into predictions; the inherent stochasticity of flares and CMEs renders their prediction probabilistic, thus benchmark sets are necessary to optimize and validate predictions. To meet these challenges, researchers have put forward new magnetic properties, which describe different aspects of magnetic energy storage mechanisms in active regions and offer the opportunity of parametric studies for over an entire solar cycle. This inventory of features/predictors is now expanded to include information from flow fields, transition region and coronal spectroscopy, data-driven modeling of the coronal magnetic field, as well as parameterizations of dynamic effects from time series. Further work towards these directions may help alleviate the current limitations in observing the magnetic field of higher atmospheric layers. In this task, fundamental and operational research converge, with promising results which could stimulate the development of new missions and lay the ground for future exploratory studies, also profiting from and utilizing the long anticipated observations of the new generation of instruments. [ABSTRACT FROM AUTHOR]

The Sun cubE onE (SEE) is a 12U CubeSat mission proposed for a phase A/B study to the Italian Space Agency that will investigate Gamma and X-ray fluxes and ultraviolet (UV) solar emission to support studies in Sun-Earth interaction and Space Weather from LEO. More in detail, SEE's primary goals are to measure the flares emission from soft-X to Gamma ray energy range and to monitor the solar activity in the Fraunhofer Mg II doublet at 280 nm, taking advantage of a full disk imager payload. The Gamma and X-ray fluxes will be studied with unprecedented temporal resolution and with a multi-wavelength approach thanks to the combined use of silicon photodiode and silicon photomultiplier (SiPM) -based detectors. The flare spectrum will be explored from the keV to the MeV range of energies by the same payload, and with a cadence up to 10 kHz and with single-photon detection capabilities to unveil the sources of the solar flares. The energy range covers the same bands used by GOES satellites, which are the standard bands for flare magnitude definition. At the same time SiPM detectors combined with scintillators allow to cover the non-thermal bremsstrahlung emission in the gamma energy range. Given its UV imaging capabilities, SEE will be a key space asset to support detailed studies on solar activity, especially in relation to ultraviolet radiation which strongly interacts with the upper layers of the Earth's atmosphere, and in relation to space safety, included in the field of human space exploration. The main goal for the UV payload is to study the evolution of the solar UV emission in the Mg II band at two different time scales: yearly variations along the solar cycle and transient variations during flare events. The Mg II index is commonly used as a proxy of the solar activity in the Sun-as-a-star paradigm, in which solar irradiance variations in the UV correlate with the variations in stratospheric ozone concentrations and other physical parameters of the Earth high atmosphere. SEE data will be used together with space and ground-based observatories that provide Solar data (e.g. Solar Orbiter, IRIS, GONG, TSST), high energy particle fluxes (e.g. GOES, MAXI, CSES) and geomagnetic data in a multi-instrument/multi-wavelength/multi-messenger approach. [ABSTRACT FROM AUTHOR]

Magnetic reconnection is a fundamental process for changing the magnetic topology and converting magnetic energy into other forms on the Sun, such as heat, flow energy and fast particle energy. In two dimensions it is fairly well understood, although some aspects still need to be developed. In three dimensions, it behaves very differently and a substantial body of theory and numerical experiment has now been built up, including reconnection at null points, separators and quasi-separators. Some aspects of solar flares can be understood with 2D reconnection models, but other aspects such as the shapes of flare ribbons, the acceleration of particles and the creation of twist in erupting flux ropes need a 3D understanding. A paradigm shift in our understanding of coronal heating by reconnection has been stimulated by dramatic new observations of photospheric flux cancellation from SUNRISE and from SST together with the realisation that it may well be driving nanoflare heating events and possibly campfires. [ABSTRACT FROM AUTHOR]

Coronal spectroscopy has pushed forward the understanding of physical processes in all phenomena on the Sun. In this review we concentrate specifically on plasma parameters measured in sources of the slow solar wind in active regions and the early phases of solar flares. These topics are a key part of the science goals of the Solar Orbiter mission (Müller et al., 2020) which has been designed to probe what drives the solar wind and solar transients that fill the heliosphere. Active regions, outside of flaring, have general characteristics that include closed loops showing red-shifted (down-flowing plasma), and the edges of the active regions showing blue-shifted (upflowing plasma). Constraining and understanding the evolution, behaviour and cause of the flows has been developed in the past years and are summarised. Of particular importance is the upflowing plasma which, in some cases, can contribute to the slow solar wind, and this review concentrates on recent results on this topic. The early phases of solar flares and their energy sources are not yet fully understood. For decades, there has been a huge interest in pin-pointing the trigger of a solar flare. Coronal spectroscopy has revealed small-scale dynamics that occurs tens of minutes before the flare begins. The understanding of the trigger is key to improving flare predictions in the future, as well as understanding the physical processes. Finally we look to the future of coronal spectroscopy, with new instruments and methodologies being developed that build on the current knowledge, and will improve significantly our physical understanding of processes at all scales on the Sun. [ABSTRACT FROM AUTHOR]

We present an analysis of the time-intensity profiles of 25 solar energetic proton events at 18.2 MeV, modelled by fitting an analytical function form (a modified Weibull function) to the observed intensities. Additionally relying on previous work that characterized the magnetic connectivity between the event-related solar flare and the observer in these events with three angular parameters, we investigate the fit function parameters, the connectivity parameters, and the iron-to-carbon ratio of the events for dependencies and correlations. We find that the fit parameter controlling the basic shape of the profile (parameter a) is not clearly dependent on the connectivity parameters or the Fe/C ratio, suggesting that the profile shapes of neither well and weakly connected nor generally "impulsive" and "gradual" events differ systematically during the early stages of the event at 1 AU. In contrast, the time scaling of the fit function (parameter b) is at least moderately correlated with both the magnetic connectivity parameters and the Fe/C ratio, in that well-connected and iron-rich events are typically shorter in relative duration than weakly connected and nominal-abundance events; intensity rise times display a similar correlation with the connectivity parameters. We interpret the former result as following from the combined effect of various transport processes acting on the particles in interplanetary space, while the latter is essentially consistent with established knowledge regarding the observed dependence of the time-intensity profile shapes of solar energetic particle events on their magnetic connectivity and heavy ion abundances. The desirability of modelling the particle transport effects in detail and extending the analysis to cover higher energies is indicated. [ABSTRACT FROM AUTHOR]

We report Forbush decreases (FD) in cosmic ray intensity from January 1996 to December 2008, the whole Solar Cycle 23rd. Statistical analysis is done for only 152 events for which associated solar flare position, flare classes, and Coronal Mass Ejections (CME) speed are given. We applied FD parameters taken from the Forbush Effects and Interplanetary Disturbances databases maintained by the Pushkov Institute of Terrestrial Magnetism, Ionosphere, and Radiowave Propagation (IZMIRAN), obtained by processing the data of the worldwide neutron monitor network using the global survey method (GSM) (A. Belov et al., 2018). For the said number of events, we examine their effect on interplanetary space and the decrease of the galactic cosmic rays (GCR) near Earth. We found that the 11–20° latitudinal belt shows more FD- associated flare events than the other latitudinal belts, and on this belt, the Southern hemisphere is more active. The results reveal that FDs and solar flares are well correlated. Statistical analysis is carried out for the magnitude of the CR decrease with solar and geomagnetic parameters. [ABSTRACT FROM AUTHOR]

Solar flares are a kind of violent solar eruptive activity phenomenon and an important warning device of space weather disturbance. In space weather forecasting, flare forecasting is an important forecast content. This paper proposes a flare prediction model based on long and short-term memory neural network, which uses the time sequence of magnetic field changes in the solar active region in the past 24 h to construct samples, and analyzes the time series evolution of magnetic field characteristics through the long and short-term memory neural network to predict whether ≥ M-level flares will occur in the next 48 h. This paper uses a data set for all active region samples from May 2010 to May 2017, and selects 10 magnetic field characteristic parameters of SDO/HMI SHARP. In the modeling process, six feature parameters with high weight, gain rate, and coverage rate were selected as input parameters through XGBoost method. Through test comparison, the false report rate and accuracy rate of the model are similar to the traditional machine learning model, and the accuracy rate and critical success index are better than the traditional machine learning model, which are 0.7483 and 0.7402, respectively. The overall effect of the model is better than that of the traditional machine learning model. [ABSTRACT FROM AUTHOR]

Onboard Chandrayaan-2 Orbiter, an X-ray Solar Monitor (XSM) instrument was flown for the measurement of intensity of solar X-rays within energy band of 1–15 keV. To achieve this, an active filter wheel drive mechanism is used to control the energy of the solar flares falling onto the detector by flipping the filter wheel. During normal flares, the filter wheel is steered to open position whereas during very large solar flares, a beryllium filter is positioned below the detector to reduce the incident solar energy. An in-built flare detection logic operates the mechanism in real-time when the threshold value of solar flares is crossed. The mechanism also has an additional calibration source which regularly calibrates the instrument. The filter wheel drive mechanism is developed as a compact, miniaturized system without requiring any hold-down thereby reducing the mass and design complications. The self-balanced filter wheel is designed by the ingenious usage of dead weights such that center of gravity of the wheel passes through the rotation axis. Together with the back-driving torque of the motor, the tendency of the wheel to jitter during launch is reduced, thus avoiding a separate hold down mechanism. An additional gripping force is ensured between the filter wheel and the motor shaft by using a grub screw. One end of the filter wheel shaft is supported at the base plate through a DU bush to reduce friction during filter wheel's rotation and the other end is connected to the motor shaft. A novel Optical Sensor based wheel position feedback system is also developed for the position indication during pre and post dynamic tests. In this paper, the design details of the XSM Filter wheel mechanism along with its analysis and hardware performance evaluation during theintegrated tests with the Chandrayaan-2 Orbiter spacecraft is presented. [ABSTRACT FROM AUTHOR]

• Designed a thick-panel curved origami-based protective shield. • Demonstrated the complete process of thickening space curved surface. • Resolved the compatibility issue of conical apex points during the thickening process. • Proposed a method for determining whether motion interference based on spatial vector. • Proposed the multifunctional integration of the protective shield with solar arrays. In recent years, as space is being explored more frequently, various spacecraft have been launched into space. Space debris and radiation in the universe as well as the irregular activities of the sun, such as solar flares and solar storms, can have serious effects on spacecraft. Protective shields are a favorable measure to protect spacecraft from space debris, radiation, and other damage. In this study, a protective shield for spacecraft is first proposed inspired by the behavior of mollusks. The concept of origami is then introduced for the folding and unfolding scheme design. The protective shield has a certain thickness, although its thickness is not significant and can be considered a thin-walled structure, it cannot be treated as zero-thickness origami since even a small thickness can cause issues such as motion interference. This study proposes three guidelines for thickening panels. Through the derivation of spatial geometry, a method to make the spatial curved surface thickening is presented. This method perfectly solves the compatibility problem of vertices in thickening, while making each panel manufacturable. After that, based on space vectors, a computational method for determining whether motion interference occurs in thick-panel curved origami is proposed, and the conditions for preventing motion interference are given. The accuracy and effectiveness of the proposed methods are verified by numerical simulations, and the complete unfolding and folding process of the deployable protective shield is also demonstrated. The methods proposed in this paper are all general and can be easily generalized to further and more complex situations. Finally, a case is shown where the deployable protective shield can be applied to a spacecraft like the Spitzer Space Telescope. [Display omitted] [ABSTRACT FROM AUTHOR]

• In the Galaxy active dwarf stars are the sources of cosmic rays. • These particles are produced in stellar flares. • The power of these stellar flares is enough to provide the density of energy of galactic cosmic rays observed in Galaxy. • In stellar flares positrons are also produced. • This production explains the positron excess recorded in space experiments. There are approximately (2–4)·1011 stars in the Galaxy. Many of these stars produce stellar flares, that is, they are active stars. It is known that our Sun accelerates charged particles during powerful solar flares. If solar and stellar flares are compared, one can find many common features in these phenomena, and it is generally assumed that the underlying mechanism in solar and stellar flares is the same. To explain the experimental data on cosmic rays obtained recently using balloons and space experiments, the existence of cosmic ray sources near the solar system is required. In the present article, we discuss briefly some cosmic ray experimental data that can be explained if sources of cosmic rays exist near the solar system. We consider active dwarf stars as cosmic ray sources (in addition to supernova remnants). These stars constitute the main stellar population in the Galaxy and generate powerful stellar flares, which are much more powerful than solar ones (up to 107 times). This suggestion enables to understand many features observed in cosmic rays over the past 20 years. In particular, the explanation of the positron excess is given in the frame of the known mechanisms without attracting dark matter. [ABSTRACT FROM AUTHOR]

Asymmetric behavior of the solar hemispheres is an essential aspect of the activity. This paper uses a complex network approach to study the solar flare asymmetric activity in two hemispheres. We construct a network based on the locations and flare flux (GOES flux classification) from 2008 December to 2019 December for 4033 and 4725 flares on the north and south hemispheres, respectively. We apply the visibility graph analysis to construct the networks for different spatial (HEALPix pixelization) constraints. The HEALPix Mollweide projection maps show the nodes with a considerable degree and clustering coefficients in low latitudes in the southern hemisphere. The northern hemisphere network exhibits more hubs (the nodes with the highest connectivity, closeness, betweenness, and Pagerank) than the south. The locations of identified hubs can indicate regions with high magnetic activity. Identifying active areas of the sun is one of the essential issues in space weather science. We explore the small-world and scale-free characteristic of the flare complex network that indicates the flares form a system of self-organized criticality and each flare has an influential role in occurring subsequent flares on the solar surface. [ABSTRACT FROM AUTHOR]

Despite strong indications that flares subjected to crosswinds can undergo fuel stripping mechanisms that reduce efficiency and lead to emission of unburned fuel, most published flare experiments have not considered the impact of a crosswind. Knowledge of flare performance in turbulent crosswinds representative of atmospheric wind is especially lacking. Accurate experiments to fill this gap can only be achieved in an environment where the wind conditions can be controlled. This work presents a methodology to determine the carbon conversion efficiency and species emission rates of a flare burning in a closed-loop wind tunnel. The developed methodology is based on solving an unsteady mass balance to relate measured accumulation rates in a closed-loop wind tunnel to emission rates, while extending the applicability and correcting errors of an earlier method. The developed methodology considers complicating factors such as infiltration and exfiltration of gases into and out of the wind tunnel, potential for reburning of products within the wind tunnel, and presence of inert species in the fuel stream. The methodology is assessed with a comprehensive Monte Carlo uncertainty and sensitivity analysis. Results suggest that carbon conversion efficiency can be measured with a systematic bias uncertainty of ≲ ±0.5%, ranging from 0.04% for a 99% efficient flare to 0.55% for a 70% efficient flare at 95% confidence, and methane emission rates can be measured within ±3.25% at 95% confidence. Demonstration experiments in a large closed-loop wind tunnel show that precision (repeatability) uncertainties will be larger but that overall (combined bias and precision) uncertainties of <10% are readily achievable. • Robust approach to quantify efficiency and emission rates of flares in crosswind. • Mathematical formulations correct a key error in previous work. • Method proven in Monte Carlo simulation and demonstrated in wind tunnel experiments. • Flare combustion efficiency and methane emissions quantified with low uncertainty. • New method is a cornerstone of ongoing experiments measuring emissions from flares. [ABSTRACT FROM AUTHOR]

• Spectroscopy of UV jets observed by IRIS show bidirectional flows, tilt n the spectra Mg II Si IV at the reconnection site of the jets. Solar jets are impulsive, collimated plasma ejections that are triggered by magnetic reconnection. They are observed for many decades in various temperatures and wavelengths, therefore their kinematic characteristics, such as velocity and recurrence, have been extensively studied. Nevertheless, the high spatial resolution of the Interface Region Imaging Spectrograph (IRIS) launched in 2013 allowed us to make a step forward in the understanding of the relationship between surges and hot jets. In this paper we report on several results of recent studies of jets observed by IRIS. Cool and hot plasma have been detected with ejections of cool blobs having a speed reaching 300 km s−1 during the impulsive phase of jet formation and slow velocity surges surrounding hot jets after the reconnection phase. Plasma characteristics of solar jets, such as the emission measure, temperature, and density have been quantified. A multi-layer atmosphere at the reconnection site based on observed IRIS spectra has been proposed. IRIS evidenced bidirectional flows at reconnection sites, and tilt along the spectra which were interpreted as the signature of twist in jets. The search of possible sites for reconnection could be achieved by the analysis of magnetic topology. Combining Solar Dynamics Observatory/Helioseismic Magnetic Imager (SDO/HMI) vector magnetograms and IRIS observations, it was found that reconnection site could be located at null points in the corona as well as in bald patch regions low in the photosphere. In one case study a magnetic sketch could explain the initiation of a jet starting in a bald patch transformed to a current sheet in a dynamical way, and the transfer of twist from a flux rope to the jet during the magnetic reconnection process. [ABSTRACT FROM AUTHOR]

Solar flares and coronal mass ejections are among the most prominent manifestations of the magnetic activity of the Sun. The strongest events of them tend to occur in active regions (ARs) that are large, complex, and dynamically evolving. However, it is not clear what the key observational features of such ARs are, and how these features are produced. This article answers these fundamental questions based on morphological and magnetic characteristics of flare-productive ARs and their evolutionary processes, i.e., large-scale flux emergence and subsequent AR formation, which have been revealed in observational and theoretical studies. We also present the latest modeling of flare-productive ARs achieved using the most realistic flux emergence simulations in a very deep computational domain. Finally, this review discusses the future perspective pertaining to relationships of flaring solar ARs with the global-scale dynamo and stellar superflares. [ABSTRACT FROM AUTHOR]

The lunar soils evolution over time is mainly caused by space weathering that includes the impacts of varying-sized meteoroids and charged particles implantation of solar/cosmic winds as well. It has long been established that space weathering leads to the formation of outmost amorphous layers (50–200 nm in thickness) embedded nanophase iron (npFe0) around the mineral fragments, albeit the origin of the npFe0 remains controversial. The Chang'e-5 (CE-5) mission returned samples feature the youngest mare basalt and the highest latitude sampling site , providing an opportunity to seek the critical clues for understanding the evolution of soils under space weathering. Here, we report the surface microstructures of the major minerals including olivine, pyroxene, anorthite, and glassy beads in the lunar soil of CE-5. Unlike the previous observations, only olivine in all crystals is surrounded by a thinner outmost amorphous SiO 2 layer (∼10 nm thick) and embedded wüstite nanoparticles FeO (np-FeO, 3–12 nm in size) instead of npFe0. No foreign volatile elements deposition layer and solar flare tracks can be found on the surface or inside the olivine and other minerals. This unique rim structure has not been reported for any other lunar, terrestrial, Martian, or meteorite samples so far. The observation of wüstite FeO and the microstructures support the existence of an intermediate stage in space weathering for lunar minerals by thermal decomposition. [ABSTRACT FROM AUTHOR]

Active region (AR) flux is released in the form of flares and Coronal Mass Ejections and a host of several other energetic events. The development of an AR is an indication of the accumulation of flux which reflects the non-potentiality of the region. Hence, the total flux released by all the flares associated with a given AR may be indicative of the total magnetic energy although not exhaustive. In this context, we report the good association between the number of flares occurring in a given AR and the cumulative flare duration in that AR. Hence, the number of flares occurring in an AR and consequently the cumulative flare duration therein can be regarded as a good measure of the underlying mechanism of that AR. [ABSTRACT FROM AUTHOR]

We present signatures of the super-strong magnetic fields of almost 105 Gauss range in the limb solar flare of 14 July 2005 at the altitudes of 5 – 30 Mm during the post-peak phase of the flare. These features follow from the study of the Stokes V profile in the Hα line at large distances of 1.5 up to 4 Å from its center. A reliable circular polarization (till 1%) was found that changes its sign when crossing the line center. The profile of the polarization differs significantly from the intensity gradient profile dI/dλ, which indicates the strong magnetic field mode. If these features are interpreted as manifestations of the Zeeman effect, the corresponding magnetic field strength reaches ∼ 90 kG. Similar spectral manifestations were not found in another bright emission formation on the solar limb, namely in the active prominence of 24 July 1999. Theoretical analysis of the picture of the Zeeman effect for the case of such giant fields shows that the σ components of the Hα line should be quite narrow (∼0.2 Å) due to the Pashen-Back effect, despite the complex picture of the splitting of this line. Since the observed widths of the peaks of the Stokes V profiles are much wider, this may mean a certain dispersion of the magnetic field strengths in the flare, at which the maximum strengths can be even some greater than those indicated above. [ABSTRACT FROM AUTHOR]

Using observations with XMM-Newton , we study the characteristics of a flare emanating from a solar analogous V895 Tau. At the peak of the flare, its luminosity reached 3. 3 × 1 0 30 erg s − 1 , which is ∼ 600 times more energetic than the X10 class flare on the Sun. The quiescent state corona of V895 Tau is depicted by a two-temperature plasma model with temperatures of 3.9 and 11 MK. The flare's evolution was carefully scrutinized through time-resolved X-ray spectroscopy, unveiling the variations in temperature, emission measure, abundance and luminosity during the flare. The temperature peaked at 36.1 MK, which is approximately four times higher than the pre-flare temperature. Employing a hydrodynamic loop model, we have estimated the half length of the flaring loop to be 5. 9 × 1 0 10 cm. Using the loop scaling laws, other loop parameters like density, pressure, volume, and minimum magnetic field are also estimated, and are found to be similar to those of other flares from similar type of stars. • Strongest X-ray superflare on solar analogue V895 Tau detected • Energy release during flare is 1. 6 × 1 0 34 erg • The quiescent corona is explained by a two-temperature plasma at 3.9 and 11 MK • The loop length of flaring plasma is 0.7 times the stellar radius • The coronal abundances increase by three times during the flare peak [ABSTRACT FROM AUTHOR]

The Radio Neutrino Observatory – Greenland (RNO-G) seeks discovery of ultra-high energy neutrinos from the cosmos through their interactions in ice. The science program extends beyond particle astrophysics to include radioglaciology and, as we show herein, solar observations, as well. Currently seven of 35 planned radio-receiver stations (24 antennas/station) are operational. These stations are sensitive to impulsive radio signals with frequencies between 80 and 700 MHz and feature a neutrino trigger threshold for recording data close to the thermal floor. RNO-G can also trigger on elevated signals from the Sun, resulting in nanosecond resolution time-domain flare data; such temporal resolution is significantly shorter than from most dedicated solar observatories. In addition to possible RNO-G solar flare polarization measurements, the Sun also represents an extremely useful above-surface calibration source. Using RNO-G data recorded during the summers of 2022 and 2023, we find signal excesses during solar flares reported by the solar-observing Callisto network and also in coincidence with ∼ 2/3 of the brightest excesses recorded by the SWAVES satellite. These observed flares are characterized by significant time-domain impulsivity. Using the known position of the Sun, the flare sample is used to calibrate the RNO-G absolute pointing on the radio signal arrival direction to sub-degree resolution. We thus establish the Sun as a regularly observed astronomical calibration source to provide the accurate absolute pointing required for neutrino astronomy. [ABSTRACT FROM AUTHOR]

The Radiation protection is of paramount importance in the planning of human exploration activities in space. The related risks must be considered with respect to two aspects: devising a proper shielding and providing answers to the requirement of an effective dosimetry evaluation in astronaut's activities. Both aspects have been considered using the Monte Carlo (MC) code MCNP 6.2 as the reference tool. As case study an application devised for the National Aeronautics and Space Administration (NASA) Artemis program has been chosen. The project aims to establish a sustainable human presence on the Moon, envisioning the realization of an outpost that will serve as a steppingstone for space exploration endeavors. A Class III shelter, in situ resource utilization (ISRU) built habitat for the Moon, has been designed through computational methods and topology optimization techniques, and analyzed in terms of radiation shielding performances and the strictly related structural behavior. The outpost must be able to withstand temperature variations, micrometeorite impacts, and the absence of a substantial atmosphere. Any solution studied to respect the constraints must devise robust and innovative materials and techniques to create habitats that have as goal the shielding from the Galactic Cosmic Rays (GCR) and from the solar flares to provide a safe and habitable environment at the time scales scheduled for the missions. Moreover, the outpost design must incorporate strategies for extracting and utilizing local resources. Overcoming such challenges will pave the way for the establishment of a sustainable human presence on the Moon and serve as a crucial leap for future space exploration missions. • Radiation protection's crucial role in space exploration planning. • Integration of radiation protection by design in lunar habitat design. • MCNP 6.2 and topology optimization coupling. • Design challenges for a sustainable lunar outpost in Artemis. • Innovative materials for shielding cosmic rays and solar flares. [ABSTRACT FROM AUTHOR]

Solar radio bursts are sudden peaks in the low-frequency radio emissions originating from the sun. These emissions, while revealing important insights into underlying physical mechanisms in solar physics, can also help predict space weather events that could have adverse effects on satellite communications and the global energy grid. A thorough understanding of this phenomena demands the collection and analysis of solar emission data over vast geographical and time scales. In this regard, the e-CALLISTO network plays a major role through having already archived more than 20 years worth of solar radio burst data. Leveraging on the advances in data analysis techniques, this data can be used to review the statistical significance of burst properties of type II and type III solar radio bursts and hence more importantly the magnetic field measurements of the active regions. In order to process the e-CALLISTO data, a software containing several data reduction processes is introduced to optimize the data analysis via a graphical user interface (GUI). The program is capable of reading out data from any CALLISTO receiving station, while offering visualization capabilities such as the color-corrected spectrum view, the plot of frequencies of the highest intensity, the individual frequency spectrum, the solar burst isolation portal, the fitting model for the radio burst, and the drift rate curve of the burst. These are achieved through using the raw "fits" files of spectra to perform background RFI reduction, identify and isolate solar radio burst regions, model the peak frequency variation using curve fitting, and thereby determine the frequency drift rates. The method can be directly applied to Type II and III solar bursts while providing space for tailoring and modification. In this work, the slow drift type II radio bursts were fitted by exponential decay and the fast drift type III radio bursts were approximated as linear decay. Hence, the frequency drift rates were computed for type II and type III radio bursts. The application is used to analyze several Type II and Type III solar radio bursts and depending on the bust type shock speed and electron velocity were determined. The GUI interface eliminates the time-consuming subjective manual analysis of e-CALLISTO data thereby making the analysis of solar radio bursts a routine and rapid process. • In this research a new software/python code has been introduced and tested for several Solar radio bursts data available in e-Callisto network. • Instead of finding the drift rates of solar radio bursts with image processing tools, analyzing intensity matrix of the solar radio bursts is used. • A new GUI is introduced for find the drift rates of the type II and type III solar radio bursts. • Using the new GUI, not only a graphical model can be illustrated for the bursts but some model statistics also can be obtained. [ABSTRACT FROM AUTHOR]

A new VLF (Very low Frequency) receiver has been developed by the Peruvian Space Agency (CONIDA) for space weather studies. The receiver has been designed based on a Red Pitaya board which performs an SDR (Software Defined Radio) to digitize, process and store the signal. The receiver is composed of a vertical antenna, a preamplifier to filter and amplify the incoming VLF signals from several transmitters located around the world. The receiver is able to cover a bandwidth from 1 up to 50 kHz and it has been developed in such a way as to be cost-effective, autonomous and solar-powered, making it suitable for installation in multiple locations with different geographic conditions. We show the performance of the receiver, the typical daily pattern of the lower ionosphere for the NAA VLF signal, as observed in Peru, and the first solar flares observed. The VLF amplitude curves recorded are validated by comparing them with data from SAVNET (The South American VLF Network) receiver installed in Peru. In a first effort to investigate the impact of solar flares on the lower ionosphere, we conducted a statistical analysis between VLF amplitude perturbations and 1–8 Å solar X-rays flux provided by GOES satellites, resulting in a linear relationship. • Software Defined Radio implemented on FPGA. • A cost-effective, autonomous and solar-powered VLF receiver has been designed. • Ionospheric disturbances related to solar flares are detected as VLF amplitude enhancement. • A significant correlation between VLF amplitude enhancement and C- and M-class solar flares was found. [ABSTRACT FROM AUTHOR]

• Finding solar release times of SEP events using velocity dispersion analysis. • For low CME speeds, difference between SEP and CME origin times is larger. • Proton peak flux - SF peak flux correlation falls with rise in particle energy. Properties and association of Solar Energetic Particle (SEP) events with their solar sources during the 24th solar cycle were examined. SEPs observed by SOHO ERNE were used. SEP properties include solar release time, peak proton flux and total fluence in different energy channels. Solar release times of SEP events were found out using Velocity Dispersion Analysis (VDA). It is observed that for low Coronal Mass Ejection (CME) velocities, the difference between SEP and CME release times is larger compared to that for high velocities. For SEPs associated with C class Solar Flares (SF), the average time difference in the release times is around 78 min, whereas in M and X class flares the time differences are 38 and 31 min respectively. Correlation analysis of proton peak flux with the CME speed and SF peak flux reveals that the coefficients decrease with increase in particle energy in both the cases. The correlation coefficient between total proton fluence of SEP and the peak flux of SF is moderate and decrease with increase in energy and tends to increase beyond 60 MeV. The correlation between total proton fluence and CME speed is high and it increases initially and then decrease with increase in energy. The analysis of H/He ratio of SEP events shows that the average value of the ratio extends from 16 to 837. [ABSTRACT FROM AUTHOR]

We perform a comparative spectro-temporal analysis on the variability classes of GRS 1915+105 and IGR J17091-3624 to draw inferences regarding the underlying accretion flow mechanism. The ν , as well as C2 class Rossi X-ray Timing Explorer observation, have been considered for analysis. We investigate the intensity variation of the source in different energy domains that correspond to different components of the accretion flow and infer the relative dominance of these flow components during the dip/flare events. We correlate the dependence of the dynamic photon index (Θ) with intensities in different energy bands and comment on the transition of the source to hard/soft phases during soft dips/flares. We also report the presence of sharp QPOs at ∼ 7.1 Hz corresponding to both softer and harder domain in the case of ν variability class of GRS 1915+105 and discuss the possible accretion flow configuration it suggests. Sharp QPO around ∼ 20 mHz is observed in ν and C2 classes of IGR J17091-3624 in low and mid energy band (2.0–6.0 keV and 6.0–15.0 keV), but remains undetected in high energy (15.0–60.0 keV). The 2.5–25.0 keV background-subtracted spectra have also been fitted with TCAF along with a Compton reflection component. A plausible accretion flow mechanism in order to explain the observed variability has been proposed. [ABSTRACT FROM AUTHOR]