Search

A novel method was developed based on the amplitude data of the EM waves measured by Digisondes to calculate and investigate the relative ionospheric absorption changes. The effect of 13 solar flares (>C8) that occurred from 4 to 10 September 2017 were studied at three European Digisonde stations (Juliusruh (54.63°N, 13.37°E), Průhonice (49.98°N, 14.55°E) and San Vito (40.6°N, 17.8°E)). The present study compares the results of the amplitude method with the absorption changes measured by the Finnish Riometer Network and determined by the NOAA D-RAP model during the same events. The X-class flares caused 1.5–2.5 dB of attenuation at 30–32.5 MHz based on the riometer data, while the absorption changes were between 10 and 15 dB in the 2.5–4.5 MHz frequency range according to the amplitude data. The impact caused by energetic particles after the solar flares are clearly seen in the riometer data, while among the Digisonde stations it can be observed only at Juliusruh in some certain cases. Comparing the results of the amplitude method with the D-RAP model it seems evident that the observed absorption values almost always exceed the values given by the model both at 2.5 MHz and at 4 MHz during the investigated period. According to the comparison between the riometer data with the D-RAP, generally, the model underestimates the absorption values obtained from the riometers during solar flares except at the highest latitude stations, while D-RAP overestimates the impact during the particle events. [ABSTRACT FROM AUTHOR]

On May 21, 2023, the Macao Science Satellite-1B (MSS-1B), a low-inclination, low-latitude, and high-precision scientific exploration satellite for geomagnetic fields and space environments, was successfully launched. The solar X-ray detector (SXD), one of the two major scientific payloads onboard the MSS-1B, has obtained a large amount of solar X-ray radiation data, which reveals the distribution law of the magnetic field in the low Earth orbit, as well as the coupling law of the Earth's magnetic field and the solar radiation and energy particle distributions. First, the overall design of the multi-detection-unit, broad-energy-range, small-volume, and low-power SXD was implemented to achieve the scientific objectives of the mission. Second, the technical indicators of the instrument were decomposed into various components, and the key technologies, such as collimator, processing circuit, thermal, and payload dataset designs, were reviewed. Third, the backgrounds, including electronic noise, cosmic diffuse X-ray background, and high-energy background in the Earth's radiation belts in and out of the field of view, were analyzed for the instrument. Then, the ground calibrations of the energy response, detection efficiency, and temperature-dependent peak drift of the SXD flight model were conducted. Finally, the in-orbit temperature, energy spectrum data, background, and solar flare process observation of the instrument in the in-orbit test stage are presented, verifying the instrument design, analysis, and ground calibration, providing a foundation for obtaining accurate solar X-ray radiation data, and achieving the scientific objectives of the satellite. [ABSTRACT FROM AUTHOR]

In this research paper we investigated the halo coronal mass ejections and sunspot number during the period December 2019 to December 2023 for the rising phase of solar cycle 25. The SOHO/LASCO instrument observed 145 HCMEs during this period. We selected 145 halo CMEs and the associated flares, SSN and Dst. The HCME is found to be significantly faster and more energetic than the other CME. During solar maximum, HCME occur more frequently. Here we have considered all the frontside disk halos, frontside limb halos and the backside halos of the sun. These halos are classified according to their source location. Mostly the frontside disk halos are more geoeffective. For 70% (7/10) of the halo CMEs associated with X class flares have a speed greater than 1000 km/s. The daily sunspot number (SSN) and the yearly mean total sunspot number are taken into consideration for our study. The study of sunspot numbers is essential for planning space-related activities, particularly for low Earth orbiting spacecraft. Geoeffectiveness is the capacity of HCMEs to induce geomagnetic storms. The "Dst (Disturbance storm time) index" is one geomagnetic metric that is used to measure this. We categorized geoeffective halos into three groups: strongly geoeffective (Strong-GE, Dst < −100 nT), moderately geoeffective (Moderate-GE, −100 < Dst ≤ −50 nT), and weakly geoeffective (Weak-GE, Dst > −50 nT). Only 3.44% of halo CMEs were strongly geoeffective, and all of these were disk halos. The NW quadrant has the highest number of events throughout the research period of December 2019–December 2023. In this paper, we illustrate how the parameters of halo coronal mass ejections, sunspots and Dst can be used for space weather effects, evaluating geoeffectiveness, and auroras. [ABSTRACT FROM AUTHOR]

The response of the thermosphere ionosphere system to an X1.3 class solar flare is studied using observations of the total electron content (TEC) and the Global Ionosphere Thermosphere Model (GITM) simulations. The solar flare erupted from the active region AR12975 on 30 March 2022. Owing to the absence of accompanying severe geomagnetic activity, it was possible to isolate the effects of the flare on the upper atmosphere. TEC data are processed for Continental USA (CONUS), employing filtering and binning techniques to create 2D variation maps. The spectral content of the TEC variations is analyzed using a wavelet coherence method. The immediate response of the solar flare exhibited broad similarities, while notable differences were observed during the recovery period between the East and West sides of the CONUS. GITM is used to explore the East–West asymmetry of the key T‐I parameters. Simulation results reveal that the coinciding interplanetary magnetic field southward turning had a greater influence on these parameters compared to the solar flare, while their nonlinear interaction introduced complex variations. Additional investigation reveals gravity wave damping also contributes to the asymmetric solar flare response. Plain Language Summary: This study examines how a solar flare, which erupted on 30 March 2022, affected the Earth's upper atmosphere. We used satellite data to measure changes in the amount of charged particles in the atmosphere above the United States (specifically the area known as CONUS) and ran computer simulations to better understand these changes. We found that while the immediate reaction of the atmosphere to the flare was similar across the CONUS, differences emerged between the East and West during the recovery phase. The simulations showed that these differences were influenced by local time differences between the East and West, as well as by variations in the Earth's magnetic field geometry above these regions. Additionally, the study identified that the damping of gravity waves also played a role in these regional differences. Overall, the research highlights how complex interactions between various factors can lead to different responses to solar events in different parts of the CONUS. Key Points: Spectral content and temporal variation of total electron content perturbations associated with an X1.3 Solar Flare are analyzedThe thermosphere‐ionosphere exhibits a longitudinal flare response during the recovery phaseThe nonlinear interaction of the solar flare with the southward turning of the interplanetary magnetic field Bz ${\mathrm{B}}_{z}$ introduces significant variability [ABSTRACT FROM AUTHOR]

A comprehensive modeling study has been conducted to investigate space weather effects at Mars during the 10 September 2017 solar flare, utilizing an integrated framework that combines the global magnetohydrodynamic (MHD) model and Mars Global Ionosphere‐Thermosphere Model (MGITM). This is the first time the thermosphere‐ionosphere‐magnetosphere system is self‐consistently simulated under realistic, time‐varying conditions. Our simulations align well with observations from the Mars Atmosphere and Volatile EvolutioN (MAVEN). Recognizing that complexities due to highly disturbed upstream conditions and rotating crustal fields obscure solar flare effects in orbit‐to‐orbit comparisons, we perform controlled simulations of nonflare and flare cases and exploit their contrast to quantify spatiotemporal variations in flare impact. Our results highlight pronounced and rapid dayside ionospheric perturbations, contrasting with weaker and delayed nightside responses. Notably, in the topside ionosphere, O2+ ${\mathrm{O}}_{2}^{+}$ and CO2+ ${\mathrm{O}}_{2}^{+}$ densities increase primarily on the dayside below ∼ ${\sim} $300 km altitude, peaking with an increase of 20%–30%. The O+ ${\mathrm{O}}^{+}$ density shows a more significant increase of up to ∼ ${\sim} $50%, extending into the magnetosphere and nightside via plasma transport, increasing its total loss rate by 14%. We observe distinct altitude‐dependent patterns in dayside electron density enhancements in percent, characterized by a weakening with altitude and a rapid decay below ∼ ${\sim} $150 km in line with the flare development, and a gradual intensification between ∼ ${\sim} $150–300 km due to plasma transport and flare‐induced atmospheric upwelling. Earlier Mars Global Surveyor observations were limited to the low‐altitude pattern due to atmospheric expansion and missed the higher altitude variations observed by MAVEN. Plain Language Summary: This study investigates the impact of a powerful X8.2‐class solar flare on 10 September 2017 at Mars. Using an integrated modeling framework that combines two state‐of‐the‐art global models, our simulations provide insights into distinct altitude‐dependent patterns of flare‐induced ionospheric density enhancements, pronounced day‐night asymmetry, and a moderate increase in ion escape. Key findings include rapid variations in ionospheric density enhancements at lower altitudes, with a gradual intensification at higher altitudes due to plasma transport and atmospheric upwelling. These findings contribute to a better understanding of how solar flares impact the space environment of unmagnetized or weakly‐magnetized planets like Mars. Key Points: The solar flare causes pronounced and rapid dayside ionospheric perturbations and weaker and delayed effects on the nightsideO2+ and CO2+ densities increase by 20%–30% above 150 km on the dayside, while O+ increases by up to 50% and over larger spacePercentage increase of dayside e− densities decreases with altitude and decays fast below ∼150 km, and rises and decays slowly above that [ABSTRACT FROM AUTHOR]

The results of the analysis of changes in electrotelluric potentials (ETP) during the observation of intense solar flare events and intense magnetic storms on Sakhalin are presented. The data were studied in the period from July 20 to October 12, 2023. The absence of characteristic changes in the ETP (integral amplification or attenuation of noise in the low-frequency region) depending on the presence or absence of a solar flare event is shown. At the same time, in some cases, the strongest flashes were found to coincide with the appearance of signals of the GUV type (Geyser type ULF Variation). For almost three months of observations, five cases of quasi-periodic GUV series have been identified, four of which coincide completely or partially with the times of solar flares and magnetic storms. It should be noted that earlier in the literature, the appearance of these signals was not correlated with any physical process. At the same time, the identification of such patterns is an integral part of extensive work on identifying predictive signs of earthquake preparation in the ETP

This work presents the development and testing of an experimental web-based SDR (software-defined radio) monitoring system for indirect solar activity detection, which has the ability to estimate and potentially predict various events in space and on earth, including solar flares, coronal mass ejections, and geomagnetic storms. The proposed system can be used to investigate the effect of solar activity on the propagation of very-low-frequency (VLF) signals. The advantages and benefits of the given approach are as follows: increasing measurement accuracy and eventual solar activity identification by combining measurements from multiple spatially distributed SDRs. The verification process involves carrying out several experiments comparing data from the GOES satellite system and the Dunksin SuperSID system with information received by the SDR monitoring system. Then, utilizing Pearson correlation coefficients, the measured data from the SDRs, along with those from the GOES satellite system and the Dunsing monitoring station, are investigated. At the time of a solar flare, the correlation value is above 90% for most of the stations used. Combining the signal-to-noise ratio via summation also shows an improvement in the results, with a correlation above 98%. [ABSTRACT FROM AUTHOR]

There are growing concerns about the effect of solar flares on the ionosphere, mainly due to possible deterioration or damage to our communication and navigation satellite systems. On 3 July 2021, and 28 October 2021, there were solar flares (SFs) classified as X1.59 and X1.0, respectively. These two SFs were the only ones of X‐class that occurred during the last low solar activity (LSA:2018–2021). Data from magnetometers and Global Positioning System (GPS)—Total Electron Content (TEC) are used to investigate the spatial‐temporal electrodynamics of the ionosphere from pole‐to‐pole in the American sector. Employing ∆H and vertical TEC, along with the ROT (rate of change of VTEC) parameter. Rapidly ∆H disturbances closely follow the X‐ray variation and the ∆H valleys and peaks are well‐synchronized during the SFs, indicating that they are linked. Major disturbances in the ∆H are noticed in the mid‐low‐equatorial latitudes. However, minor disturbances were seen at high latitudes. Also, |ROT| is a good indicator of the electron density changes during the SFs, especially when the X‐ray intensity rises to the peak. Plain Language Summary: There are growing concerns about the effect of solar flares on the ionosphere, mainly due to possible deterioration or damage to our communication and navigation satellite systems. This kind of space weather event known as solar flare, releases energy in the form of radiation in the entire electromagnetic spectrum. However, the UV, EUV, and X‐ray radiation burst penetrates deeper into the Earth's atmosphere and is absorbed in the D and E regions (lower ionosphere) and F‐region. In this investigation the ionospheric disturbances are investigated, from pole‐to‐pole, using a magnetometer and GPS‐TEC networks. Key Points: The primary objective of this paper is to investigate the ionospheric response to solar flares across the entire latitudinal rangeThe ∆H exhibited synchronized peaks and valleys, during SF. The ROT is the most effective parameter to study electron density disturbancesThe methodology employed in this study involves the calculation and analysis of ∆H, VTEC, and ROT (Rate of TEC change) [ABSTRACT FROM AUTHOR]

Measurements of Very-Low-Frequency (VLF) transmitter signals have been widely used to investigate the effects of various space weather events on the D-region ionosphere, including nowcasting solar flares. Previous studies have established a method to nowcast solar flares using VLF measurements, but only using measurements from dayside propagation paths, and there remains limited focus on day–night mixed paths, which are important for method applicability. Between March and May of 2022, the Sun erupted a total of 56 M-class and 6 X-class solar flares, all of which were well captured by our VLF receiver in Antarctica. Using these VLF measurements, we reexamine the capability of the VLF technique to nowcast solar flares by including day–night mixed propagation paths and expanding the path coverage in longitude compared to that in previous studies. The amplitude and phase maximum changes are generally positively correlated with X-ray fluxes, whereas the time delay is negatively correlated. The curve-fitting parameters that we obtain for the X-ray fluxes and VLF signal maximum changes are consistent with those in previous studies for dayside paths, even though different instruments are used, supporting the flare-nowcasting method. Moreover, the present results show that, for day–night mixed paths, the amplitude and phase maximum changes also scale linearly with the logarithm of the flare X-ray fluxes, but the level of change is notably different from that for dayside paths. The coefficients used in the flare-nowcasting method need to be updated for mixed propagation paths. [ABSTRACT FROM AUTHOR]

Measurements of magnetic fields near seismic sources during solar flares are vital for understanding the dynamics of solar activity. We used spectropolarimetric observations of the X17.2/4B solar flare on 28 October 2003, over a wavelength interval of 43 Å, including the D3, D2, D1, and Ni I 5892.88 Å lines, to analyze the Stokes I ± V profiles. Effective magnetic fields within 0.5–1.5 kG were measured in the D1, D2, and D3 lines at different flare locations, with the photospheric Ni I 5892.88 Å line showing a weaker field of below 0.5 kG. The D3 line showed rapid plasma descents of up to 11 km/s, in contrast to the slower velocities within 2.3 km/s observed in other lines. The differing amplitudes in the I + V and I − V profiles indicated potential non-Zeeman polarization effects. Secondary Stokes V peaks were also detected up to 8 Å from the D3 emission core. Significant altitudinal inhomogeneity in the magnetic field strengths was detected, possibly indicating the local magnetic collapse, facilitating the Lorentz-force driven mechanism of the seismic source excitation. [ABSTRACT FROM AUTHOR]

Solar flares are characterized by sudden bursts of electromagnetic radiation from the Sun's surface, and are caused by the changes in magnetic field states in active solar regions. Earth and its surrounding space environment can suffer from various negative impacts caused by solar flares, ranging from electronic communication disruption to radiation exposure-based health risks to astronauts. In this paper, we address the solar flare prediction problem from magnetic field parameter-based multivariate time series (MVTS) data using multiple state-of-the-art machine learning classifiers that include MINImally RandOm Convolutional KErnel Transform (MiniRocket), Support Vector Machine (SVM), Canonical Interval Forest (CIF), Multiple Representations Sequence Learner (Mr-SEQL), and a Long Short-Term Memory (LSTM)-based deep learning model. Our experiment is conducted on the Space Weather Analytics for Solar Flares (SWAN-SF) benchmark data set, which is a partitioned collection of MVTS data of active region magnetic field parameters spanning over nine years of operation of the Solar Dynamics Observatory (SDO). The MVTS instances of the SWAN-SF dataset are labeled by GOES X-ray flux-based flare class labels, and attributed to extreme class imbalance because of the rarity of the major flaring events (e.g., X and M). As a performance validation metric in this class-imbalanced dataset, we used the True Skill Statistic ( T S S ) score. Finally, we demonstrate the advantages of the MVTS learning algorithm MiniRocket, which outperformed the aforementioned classifiers without the need for essential data preprocessing steps such as normalization, statistical summarization, and class imbalance handling heuristics. [ABSTRACT FROM AUTHOR]

A new model of a force-free magnetic flux rope with a high concentration of electric current on the axis is presented. The general property of axisymmetric force-free magnetic ropes is that with the exit of the top of the magnetic loop-rope into the corona, the external pressure that keeps it from lateral expansion steadily decreases, and with some critical decrease in this pressure, the longitudinal magnetic field of the rope becomes zero on the surface where the electric current changes its sign (it is current inversion surface—CIS). In this case, the force-free parameter and the azimuthal electric current jϕ(r) experience a second-order discontinuity on this surface, so that in the vicinity of CIS their values begin to increase without limit. The current (drift) speed of electrons here will inevitably exceed the speed of ion sound. This serves as a trigger for the heating of non-isothermal plasma (so it turns out Te Ti) and the excitation of plasma ion-acoustic instability of the plasma not only near the CIS, but also in the central region of the rope, on its axis, where the current density is especially high. The appearance of anomalous resistance leads to rapid dissipation of the magnetic field and the generation of a super-Dreicer electric field. The Parker effect, associated with the equalization (with some delay) of the torque along the axis of the rope due to the transfer of the azimuthal field to the region of energy release, leads to quasiperiodic pulsations of hard flare radiation and, ultimately, ensures the flare release of the most part of free magnetic energy accumulated in the rope. [ABSTRACT FROM AUTHOR]

The paper presents the results of a numerical assessment of the contribution of the ionospheric D region to the total electron content during six powerful X‐ray flares that occurred in September 2017. The calculation of the electron concentration in the lower ionosphere was carried out using a plasma‐chemical model of the ionospheric D region. This model was verified using the data of ground‐based radiophysical measurements in the VLF (very low frequency) range and data of the incoherent scattering radar. To calculate the ionization rate at the D region heights, we used real data on the radiation flux measured by the GOES and SDO satellites during the considered flares. The total electron content was estimated using GNSS data. As a result of the analysis, it was found that the contribution of the lower ionosphere to the TEC change varied from 7% to 23% for flares with different spectra. A functional dependency has been obtained that can be used to estimate the contribution of the D region to the TEC increment depending on the spectrum of the flare. Key Points: A technique for estimating the redistribution of the electron concentration in the ionosphere during solar flares is presentedIt was found that the contribution of the D region to the TEC change varied from 7% to 23% during the flares in September 2017A functional dependency of the D region contribution to the TEC change on the fraction of X‐rays in the flare spectrum is obtained Plain Language Summary: Changes in solar radiation fluxes are observed in a wide range of wavelengths during solar flares. The variations of total electron content in the ionosphere occurs due to an increase in radiation in the UV and X‐ray wavelength ranges. The main increase in ionization caused by flares occurs in the F region (h > 120 km), so the electron concentration increment in the lower part of the ionosphere (h < 90 km) is often neglected. The existing experimental measurement methods do not allow us to estimate the redistribution of the electron concentration in the ionosphere during disturbances; therefore, to estimate the contribution of the lower ionosphere to the total electron content during flares, we used GNSS data and theoretical plasma‐chemical model of the D region. In this work, it is shown that the contribution of the D region to the change of the total electron content can reach 23% during X‐ray flares. [ABSTRACT FROM AUTHOR]

We present an automated solar flare detection software tool to automatically process solar observed images, detect and track solar flares, and finally compile an event catalog. It can identify and track flares that happen simultaneously or temporally close together. The method to identify a flare is based on the local intensity changes in macropixels. The basic characteristics, such as the time and location information of a flare, are determined with a triple-threshold scheme, with the first threshold (global threshold) to determine the occurrence (location) of the flare and the second and third thresholds (local thresholds) to determine the real start and end times of the flare. We have applied this tool to one month of continuous solar ultraviolet (UV) images obtained by the Solar Disk Imager (SDI) onboard the Advanced Space-based Solar Observatory (ASO-S), which show active phenomena such as flares, filaments or prominences, and solar jets. Our automated tool efficiently detected a total number of 226 solar events. After a visual inspection, we found that only one event was misidentified (unrelated to an active event). We compared the detected events with the GOES X-ray flare list and found that our tool can detect 81% of GOES M-class and above flares (29 out of 36), from which we conclude that the intensity increase in SDI UV images can be considered as a good indicator of a solar flare. [ABSTRACT FROM AUTHOR]

In this paper, we use the key parameters data set of the Neutral Gas and Ion Mass Spectrometer from the Mars Atmosphere and Volatile Evolution (MAVEN) mission. The particle density profiles of electrons, CO 2 + / N 2 + , CO + , O 2 + , O + , NO + , O 2 and O from 90 to 500 km have been deduced by adopting the Chapman modeling methodology. The correlation of the peak density/altitude with the solar zenith angle, the changes in the profile of the Martian ionosphere during solar flares, and the effects of Martian dust storms are analyzed. The results exhibit a positive/negative correlation between the peak density/altitude of the M2 layer and the solar zenith angle. Within the MAVEN observational record available, only three C-Class flares occurred on 26 August 2016, 29 November 2020, and 26 August 2021. The analysis reveals during these solar flare events, the electron density of the M2 layer above 200 km increases obviously. The peak density of M1 increases by 33.4%, 13.2% and 7.4%, while the peak height decreases by 0.1%, 10.2% and 4.4%, respectively. The Martian dust storm causes the peak height of the M2 layer to increase by 19.5 km, and the peak density to decrease by 4.2 ×   10 9   m − 3 . Our study shows that the Martian ionosphere is similar to the Earth's, which is of great significance for understanding the planetary ionosphere. [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 statistical analysis of the impact of the top 50 X-class solar flares (1997–2024) on global seismic activity as well as on the earthquake preparation zones located in the illuminated part of the globe and in an area of 5000 km around the subsolar point was carried out. It is shown by a method of epoch superposition that for all cases, an increase in seismicity is observed, especially in the region around the subsolar point (up to 33%) during the 10 days after the solar flare in comparison with the preceding 10 days. The case study of the aftershock sequence of a strong Mw = 9.1 earthquake (Sumatra–Andaman Islands, 26 December 2004) after the solar flare of X10.16 class (20 January 2005) demonstrated that the number of aftershocks with a magnitude of Mw ≥ 2.5 increases more than 17 times after the solar flare with a delay of 7–8 days. For the case of the Darfield earthquake (Mw = 7.1, 3 September 2010, New Zealand), it was shown that X-class solar flares and M probably triggered two strong aftershocks (Mw = 6.1 and Mw = 5.9) with the same delay of 6 days on the Port Hills fault, which is the most sensitive to external electromagnetic impact from the point of view of the fault electrical conductivity and orientation. Based on the obtained results, the possible application of natural electromagnetic triggering of earthquakes is discussed for the earthquake forecast using confidently recorded strong external electromagnetic triggering impacts on the specific earthquake preparation zones, as well as ionospheric perturbations due to aerosol emission from the earthquake sources recorded by satellites. [ABSTRACT FROM AUTHOR]

Space weather profoundly impacts Earth and its surrounding space environment, necessitating improved prediction to safeguard critical infrastructure such as communication and satellites. Solar flares can disrupt communications and pose radiation risks to airline passengers. While traditional methods offer rough estimates of solar activity trends, the potential of artificial intelligence in this domain warrants exploration. This study addresses this research gap by evaluating the performance of recurrent neural networks (RNNs) for sunspot forecasting and assessing the suitability of extreme gradient boosting (XGBoost) for solar event classification. Two publicly available datasets serve as the foundation for this research. To enhance algorithm performance through optimal hyperparameter selection, metaheuristic optimizers are employed. A unique contribution is the introduction of a modified particle swarm optimization algorithm, specifically tailored to the study's needs. Two experiments were conducted: In the first, RNNs predicted sunspot occurrence up to three steps ahead. The best-performing model, optimized using the introduced modified metaheuristic, achieved an impressive R 2 value of 0.840448, surpassing competing algorithms. In the second experiment, XGBoost models assessed solar flare severity, with the top model again optimized by the modified metaheuristic, achieving an accuracy of 0.981565. This novel approach highlights the potential for enhancing solar activity forecasting techniques and offers valuable insights into feature impacts on model decisions, thereby advancing our understanding of space weather. [ABSTRACT FROM AUTHOR]

The Ionospheric Total Electron Content (TEC) measured in the ray path of the signals directly contributes to the Range Error (RE) of the satellite signals, which affects positioning and navigation. Employing the Co-Kriging-based Surrogate Model (COKSM) to predict TEC and RE correction has proven prolific. This research attempted to test and compare the prediction capability of COKSM with an Artificial Intelligence-based Feed Forward Neural Network model (FFNN) during five X-Class Solar Flares of 2021–22. Also, the results are validated by comparing them with the IRI PLAS 2017 model. TEC, solar, and geomagnetic parameters data for Hyderabad GPS station located at 17.31° N latitude and 78.55° E longitude were collected from IONOLAB & OMNIWEB servers. The COKSM uses six days of input data to predict the 7th day TEC, whereas prediction using the FFNN model is done using 45 days of data before the prediction date. The performance evaluation is done using RMSE, NRMSE, Correlation Coefficient, and sMAPE. The average RMSE for COKSM varied from 1.9 to 9.05, for FFNN it varied from 2.72 to 7.69, and for IRI PLAS 2017 it varied from 7.39 to 11.24. Likewise, evaluation done for three different models over five different X-class solar flare events showed that the COKSM performed well during the high-intensity solar flare conditions. On the other hand, the FFNN model performed well during high-resolution input data conditions. Also, it is notable that both models performed better than the IRI PLAS 2017 model and are suitable for navigational applications. [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]

The angular distance of the solar flares to the projective point of the center of the solar disk on the solar spherical surface has been studied by the heliographical or helioprojective coordinates, during the periods 1975–2021 for GOES events and 2002–2021 for RHESSI events, hereafter “distance.” It gives a specific distribution curvature. It has also been noted that when using the number of solar flare events in each satellite, GOES or RHESSI, or even using the sum of the flux (class) or importance parameter, it obtains the same result, which is that the shape of the distribution curve remains in its shape without any significant change. In addition, it has been shown that the distribution curve contains a specific number of peaks. These peaks have a specific distance from the center of the solar disk that is very similar to the projection of the solar interior layers on the solar disk. For this reason, the names of these four main peaks have been given as follows: (1) the core circle (0–15°): it is a projection of the solar core onto the solar disk, (2) radiative ring (15–45°), and (3) the convection ring (45–55°). The limb ring is 80–90°. This result makes us wonder why the number of events in the middle of the solar disk is few, and also small at the solar limb, while many in the other parts in the solar disk. This suggests that we need to understand the sun better than before, and it also suggests that solar flares are connected to each other through the solar interior layers, the extent of which may reach the convection zone or perhaps beyond that, or the opacity of the convection zone may be less than the currently estimated value. [ABSTRACT FROM AUTHOR]

In this study, a statistical study between three solar activity features (sunspot numbers (SN), solar flare (SF), and solar active prominence (SAP)) and total column ozone over five sites of India namely Srinagar (34° 5' N, 74° 47' E) (Jammu & Kashmir) from North, Kolkata (22° 34' N, 88° 21' E) (West Bengal) from East, Nagpur (21° 8' N, 79° 05' E) (Maharashtra) from centre, Ahmedabad (23° 2' N, 72° 35' E) (Gujrat) from west and Trivandrum (8° 31' N, 76° 56' E) (Kerla) from south for a duration of 33 years from 1986 to 2019 containing solar cycle 22, 23 and 24 are attempted. The TCO of considered sites are significantly correlated with different Solar activity features. The TCO's correlation coefficient is positive with SF for both the annual and seasonal periods and is negative with SN and SAP for the yearly and all-seasonal periods. According to this study the TCO concentration is dependent on sun intensity during the entire season. This statistical study enhanced understanding of the importance of solar activity features for the production of TCO in the Earth's atmosphere. [ABSTRACT FROM AUTHOR]

Abstract The angular distance of the solar flares to the projective point of the center of the solar disk on the solar spherical surface has been studied by the heliographical or helioprojective coordinates, during the periods 1975–2021 for GOES events and 2002–2021 for RHESSI events, hereafter “distance.” It gives a specific distribution curvature. It has also been noted that when using the number of solar flare events in each satellite, GOES or RHESSI, or even using the sum of the flux (class) or importance parameter, it obtains the same result, which is that the shape of the distribution curve remains in its shape without any significant change. In addition, it has been shown that the distribution curve contains a specific number of peaks. These peaks have a specific distance from the center of the solar disk that is very similar to the projection of the solar interior layers on the solar disk. For this reason, the names of these four main peaks have been given as follows: (1) the core circle (0–15°): it is a projection of the solar core onto the solar disk, (2) radiative ring (15–45°), and (3) the convection ring (45–55°). The limb ring is 80–90°. This result makes us wonder why the number of events in the middle of the solar disk is few, and also small at the solar limb, while many in the other parts in the solar disk. This suggests that we need to understand the sun better than before, and it also suggests that solar flares are connected to each other through the solar interior layers, the extent of which may reach the convection zone or perhaps beyond that, or the opacity of the convection zone may be less than the currently estimated value.

Solar winds result from the eruption of plasma streams from the solar corona. This plasma, which consists of proton particles, electrons, X-rays, and radio waves, penetrates the heliosphere and accelerates from the interplanetary space toward the Earth with high kinetic energy and thermal energy. In addition, if it collides with the Earth's atmosphere, it disrupts human life. But despite the Earth's magnetic field and the magnetic reconnection process in this area, the Earth's magnetosphere acts like a shield and prevents these substances from affecting the Earth. To obtain the necessary information to investigate all kinds of phenomena that happen around the Sun, the use of satellite data is the best and most reliable method in terms of accuracy and up-to-date data. The data from the Goes meteorological satellite, LASCO spacecraft, and the Solar Dynamic Observatory are the information that we use in this article to advance our goals. To check the correlation between solar eruptions and changes in the Earth's magnetosphere layer, we use the wavelet analysis method with Morlet's fundamental wave, which is an important tool for processing fluctuations. The results of accurate numerical calculations of this research showed that there is a strong correlation between the magnetic activities of the Sun and the characteristic indices of the Earth's magnetosphere layer, which can affect the Earth's atmosphere as well.

A novel method was developed based on the amplitude data of the EM waves measured by Digisondes to calculate and investigate the relative ionospheric absorption changes. The effect of 13 solar flares (>C8) that occurred from 4 to 10 September 2017 were studied at three European Digisonde stations (Juliusruh (54.63°N, 13.37°E), Průhonice (49.98°N, 14.55°E) and San Vito (40.6°N, 17.8°E)). The present study compares the results of the amplitude method with the absorption changes measured by the Finnish Riometer Network and determined by the NOAA D-RAP model during the same events. The X-class flares caused 1.5–2.5 dB of attenuation at 30–32.5 MHz based on the riometer data, while the absorption changes were between 10 and 15 dB in the 2.5–4.5 MHz frequency range according to the amplitude data. The impact caused by energetic particles after the solar flares are clearly seen in the riometer data, while among the Digisonde stations it can be observed only at Juliusruh in some certain cases. Comparing the results of the amplitude method with the D-RAP model it seems evident that the observed absorption values almost always exceed the values given by the model both at 2.5 MHz and at 4 MHz during the investigated period. According to the comparison between the riometer data with the D-RAP, generally, the model underestimates the absorption values obtained from the riometers during solar flares except at the highest latitude stations, while D-RAP overestimates the impact during the particle events.

We show using superposed epoch analysis (SEA) that the most energetic protons (> 60 MeV ) in the near-Earth interplanetary magnetic field (IMF) have a peak almost immediately (less than a day) after the peak in solar-flare index (SFI), while protons greater than 10 MeV peak one day after the SFI and protons greater than 1 MeV peak two days after the SFI. The geomagnetic indices AU, -AL, PC, Ap, and -Dst peak after two to three days in SEAs after the peak in SFI. The auroral electrojet indices AU and -AL, however, have only low peaks. In particular, the response of the eastward electrojet, AU, to SFI is negligible compared to other geomagnetic indices. The SEAs of the SFI and cosmic-ray counts (CR) show that the deepest decline in the CR intensity also follows with a 2 – 3-day lag the maximum of the SFI for Solar Cycles 20 – 24. The depths of the declines are related to the SFI strength of each cycle, i.e., the average decline is about 5% for Cycles 21 and 22, but only 3% for Cycle 24. The strongest Cycle 19, however, differs from the other cycles such that it has a double-peaked decline and lasts longer than the decline of the other cycles. The double-superposed epoch analyses show that the response of IMF Bv2, which is about two days, and CR to SFI are quite simultaneous, but sometimes Bv2 may peak somewhat earlier than the decline existing in CR. [ABSTRACT FROM AUTHOR]

Self-organization in continuous systems is associated with dissipative processes. In particular, for magnetized plasmas, it is known as magnetic relaxation, where the magnetic energy is converted into heat and kinetic energy of flow through the process of magnetic reconnection. An example of such a system is the solar corona, where reconnection manifests as solar transients like flares and jets. Consequently, toward investigation of plasma relaxation in solar transients, we utilize a novel approach of data-constrained MHD simulation for an observed solar flare. The selected active region NOAA 12253 hosts a GOES M1.3 class flare. The investigation of extrapolated coronal magnetic field in conjunction with the spatiotemporal evolution of the flare reveals a hyperbolic flux tube (HFT), overlying the observed brightenings. MHD simulation is carried out with the EULAG-MHD numerical model to explore the corresponding reconnection dynamics. The overall simulation shows signatures of relaxation. For a detailed analysis, we consider three distinct subvolumes. We analyze the magnetic field line dynamics along with time evolution of physically relevant quantities like magnetic energy, current density, twist, and gradients in magnetic field. In the terminal state, none of the subvolumes is seen to reach a force-free state, thus remaining in nonequilibrium, suggesting the possibility of further relaxation. We conclude that the extent of relaxation depends on the efficacy and duration of reconnection, and hence on the energetics and time span of the flare. [ABSTRACT FROM AUTHOR]

On 3 July 2021, an X1.5 solar flare from the National Oceanic and Atmospheric Administration solar Active Region AR12838 (24°N, 88°W) occurred at 14:18 UT, peaked at 14:29 UT, and decayed at 14:34 UT. The study of this X1.5 solar flare is significant due to its unique geomagnetic crochet feature at high latitudes and its effective signature on Earth. The study examined X‐rays, the extreme ultraviolet spectrum, ionospheric equivalent current (IEC), and geomagnetic field components. The study reveals a sudden increase in IEC during the X1.5 flare episode, forming a zonal current region and producing a geomagnetic crochet signature in geomagnetic field components at high latitudes (50°–80°N) along the 11°–26°E longitude sector during the flare peak time. All three geomagnetic field components show different sensitivity to the solar flare effect (sfe), and the amplitude and phase of the geomagnetic crochet across latitudes (for a given longitude) are consistent with the variations in the IEC. The present study is the first to appraise geomagnetic crochets of low magnitude (8–40 nT) and short duration (10–15 min) at high latitudes, particularly in the polar cusp region, during the X‐class limb flare. Plain Language Summary: The X1.5 solar flare at 14:18 UT on 3 July 2021, occurred in a newly formed solar active region AR12838 (24°N, 88°W) on the sun. The current study analyses the solar flare effect (sfe) signature at high latitude induced by an X1.5 flare, and compares the results from previous paper of Yamauchi et al. (2020, https://doi.org/10.5194/angeo-38-1159-2020). However, while that paper reported geomagnetic crochet of high amplitude (200 nT) and long duration (∼2 hr), the present work reports geomagnetic crochet of small amplitude (40 nT) and short duration (∼15 min). The current study is unique regarding observations of geomagnetic crochet in the polar cusp region. Key Points: An X1.5‐class solar flare was recorded on 3 July 2021, from the newly emerged solar active region NOAA AR12838 over the solar limbThe current study examines the solar flare effect at high latitude magnetometer stations, an aspect that has not been extensively studiedUnique signatures of Cusp geomagnetic crochet of small amplitude and short duration are observed [ABSTRACT FROM AUTHOR]

Space weather phenomena, including solar flares and coronal mass ejections, have significant influence on Earth. These events can cause satellite orbital decay due to heat-induced atmospheric expansion, disruption of GPS navigation and telecommunications systems, damage to satellites, and widespread power blackouts. The potential of flares and associated events to damage technology and disrupt human activities motivates prediction development. We use Transformer networks to predict whether an active region (AR) will release a flare of a specific class within the next 24 h. Two cases are considered: ≥Cclass and ≥M-class. For each prediction case, separate models are developed. We train the Transformer to use time-series data to classify 24- or 48-h sequences of data. The sequences consist of 18 physical parameters that characterize an AR from the Space-weather HMI Active Region Patches data product. Flare event information is obtained from the Geostationary Operational Environmental Satellite flare catalog. Our model outperforms a prior study that similarly used only 24 h of data for the ≥C-class case and performs slightly worse for the ≥M-class case. When compared to studies that used a larger time window or additional data such as flare history, results are comparable. Using less data is conducive to platforms with limited storage, on which we plan to eventually deploy this algorithm. [ABSTRACT FROM AUTHOR]

Solar flares are broadly classified as impulsive or gradual. Ions accelerated in a gradual flare are thought to be accelerated through a shock acceleration mechanism, but the particle acceleration process in an impulsive flare is still largely unexplored. To understand the acceleration process, it is necessary to measure the high-energy gamma rays and neutrons produced by the impulsive flare. Under such circumstances, on 7 November 2004, a huge X2.0 flare occurred on the solar surface, where ions were accelerated to energies greater than 10 GeV. The accelerated primary protons collided with the solar atmosphere and produced line gamma rays and neutrons. These particles were received as neutrons and line gamma rays, respectively. Neutrons of a few GeV, on the other hand, decay to produce secondary protons while traveling 0.06 au in the solar–terrestrial space. These secondary protons arrive at the magnetopause. Although the flux of secondary protons is very low, the effect of collecting secondary protons arriving in a wide region of the magnetosphere (the Funnel or Horn effect) has resulted in significant signals being received by the solar neutron telescope at Mt. Sierra Negra (4600 m). This information suggests that ions on the solar surface are accelerated to over 10 GeV with an impulsive flare. [ABSTRACT FROM AUTHOR]

We first report that the solar flare time sequence exhibits a fluctuation characterized by its power spectral density being inversely proportional to the signal frequency. This is the 1/f fluctuation, or pink noise, observed ubiquitously in nature. Using GOES16 data, we found that low-energy flares ( E ≤ E m e a n ) display 1/f fluctuations, whereas high-energy flares ( E > E m e a n ) show a flat spectrum. Furthermore, we found that the timing sequence of the flares reveals clearer 1/f fluctuations. These observations suggest that the solar flare 1/f fluctuations are associated with low-energy phenomena. We investigated the origin of these 1/f fluctuations based on our recent hypothesis: 1/f fluctuations arise from amplitude modulation and demodulation. We propose that this amplitude modulation is encoded by the resonance with the solar five-minute oscillation (SFO) and demodulated by magnetic reconnections. We partially demonstrate this scenario by analyzing the SFO eigenmodes resolving the frequency degeneration in the azimuthal order number m using the solar rotation and resonance. Given the robust nature of 1/f fluctuations, we speculated that the solar flare 1/f fluctuations may be inherited by the various phenomena around the Sun, such as the sunspot numbers and cosmic rays. In addition, we draw parallels between solar flares and earthquakes, both exhibiting 1/f fluctuations. Interestingly, the analysis applied to solar flares can also be adapted to earthquakes if we read the SFO as Earth's free oscillation and magnetic reconnections as fault ruptures. Moreover, we point out the possibility that the same analysis also applies to the activity of a black hole/disk system if we read the SFO as the quasi-periodic oscillation of a black hole. [ABSTRACT FROM AUTHOR]

This work presents the development and testing of an experimental web-based SDR (software-defined radio) monitoring system for indirect solar activity detection, which has the ability to estimate and potentially predict various events in space and on earth, including solar flares, coronal mass ejections, and geomagnetic storms. The proposed system can be used to investigate the effect of solar activity on the propagation of very-low-frequency (VLF) signals. The advantages and benefits of the given approach are as follows: increasing measurement accuracy and eventual solar activity identification by combining measurements from multiple spatially distributed SDRs. The verification process involves carrying out several experiments comparing data from the GOES satellite system and the Dunksin SuperSID system with information received by the SDR monitoring system. Then, utilizing Pearson correlation coefficients, the measured data from the SDRs, along with those from the GOES satellite system and the Dunsing monitoring station, are investigated. At the time of a solar flare, the correlation value is above 90% for most of the stations used. Combining the signal-to-noise ratio via summation also shows an improvement in the results, with a correlation above 98%.

Measurements of Very-Low-Frequency (VLF) transmitter signals have been widely used to investigate the effects of various space weather events on the D-region ionosphere, including nowcasting solar flares. Previous studies have established a method to nowcast solar flares using VLF measurements, but only using measurements from dayside propagation paths, and there remains limited focus on day–night mixed paths, which are important for method applicability. Between March and May of 2022, the Sun erupted a total of 56 M-class and 6 X-class solar flares, all of which were well captured by our VLF receiver in Antarctica. Using these VLF measurements, we reexamine the capability of the VLF technique to nowcast solar flares by including day–night mixed propagation paths and expanding the path coverage in longitude compared to that in previous studies. The amplitude and phase maximum changes are generally positively correlated with X-ray fluxes, whereas the time delay is negatively correlated. The curve-fitting parameters that we obtain for the X-ray fluxes and VLF signal maximum changes are consistent with those in previous studies for dayside paths, even though different instruments are used, supporting the flare-nowcasting method. Moreover, the present results show that, for day–night mixed paths, the amplitude and phase maximum changes also scale linearly with the logarithm of the flare X-ray fluxes, but the level of change is notably different from that for dayside paths. The coefficients used in the flare-nowcasting method need to be updated for mixed propagation paths.

Measurements of magnetic fields near seismic sources during solar flares are vital for understanding the dynamics of solar activity. We used spectropolarimetric observations of the X17.2/4B solar flare on 28 October 2003, over a wavelength interval of 43 Å, including the D3, D2, D1, and Ni I 5892.88 Å lines, to analyze the Stokes I ± V profiles. Effective magnetic fields within 0.5–1.5 kG were measured in the D1, D2, and D3 lines at different flare locations, with the photospheric Ni I 5892.88 Å line showing a weaker field of below 0.5 kG. The D3 line showed rapid plasma descents of up to 11 km/s, in contrast to the slower velocities within 2.3 km/s observed in other lines. The differing amplitudes in the I + V and I − V profiles indicated potential non-Zeeman polarization effects. Secondary Stokes V peaks were also detected up to 8 Å from the D3 emission core. Significant altitudinal inhomogeneity in the magnetic field strengths was detected, possibly indicating the local magnetic collapse, facilitating the Lorentz-force driven mechanism of the seismic source excitation.

Solar cosmic rays (SCRs) are generated during the primordial energy release in solar flares. This explosive process takes place in the solar corona above the active region. It represents the fast release of the magnetic field energy of the current sheet, which is formed near a singular magnetic field line. Solar cosmic rays appear as a result of the acceleration of charged particles, mainly protons, by an inductive electric field in the current sheet equal to the field E = V × B/c (with V the speed of plasma and B the magnetic field near the current sheet, and c the speed of light). To study the mechanism of solar flares and obtain conditions for studying SCR acceleration, it is necessary to carry out magnetohydrodynamic (MHD) simulations of flare situations in the solar corona above a real active region. Methods of stabilization were developed which made it possible to partially solve the problem of numerical instabilities. MHD simulations shows complicated configurations near the singular line. Comparison of the results of the MHD simulations with observations showed the general agreement of the positions of the current sheets with regions of intense flare radiation. However, there are some problems with the details of such coincidences. The results obtained in this paper show the possibility of improving the methods of MHD simulation in order to solve the problems that arise during solving of MHD equations.

The paper presents the results of estimation of the effects of September 5–12, 2017 solar flares on the regional disturbance of Earth's ionosphere according to data from a distributed network of GNSS stations located mostly in the Volga Federal District of the Russian Federation. The GNSS data processing software package we have developed is used to analyze recorded signal power and daily two-frequency phase measurements, as well as to calculate the total electron content and map the data. The results of the study show that during powerful solar flares X2.2 and X9.3 on September 6 the median value of the total electron content, calculated for the Volga Federal District, increased up to 0.25 TECU and 0.6 TECU respectively. At that time, the region of interest (40°–55° E) was sunlit. The prolonged magnetic storms on September 8 also generated noticeable ionospheric disturbances up to 0.2 TECU. At the same time, neither the solar flares nor the magnetic storms had a significant effect on the power characteristics of the recorded signals from navigation satellites in the region under study. The median carrier-to-noise ratio calculated for the region considered over the entire observation period did not differ from the values recorded under undisturbed ionospheric conditions and varied between 47–53 dBHz and 38–49 dBHz for frequencies L1 and L2 respectively.

Space weather phenomena, including solar flares and coronal mass ejections, have significant influence on Earth. These events can cause satellite orbital decay due to heat-induced atmospheric expansion, disruption of GPS navigation and telecommunications systems, damage to satellites, and widespread power blackouts. The potential of flares and associated events to damage technology and disrupt human activities motivates prediction development. We use Transformer networks to predict whether an active region (AR) will release a flare of a specific class within the next 24 h. Two cases are considered: ≥C-class and ≥M-class. For each prediction case, separate models are developed. We train the Transformer to use time-series data to classify 24- or 48-h sequences of data. The sequences consist of 18 physical parameters that characterize an AR from the Space-weather HMI Active Region Patches data product. Flare event information is obtained from the Geostationary Operational Environmental Satellite flare catalog. Our model outperforms a prior study that similarly used only 24 h of data for the ≥C-class case and performs slightly worse for the ≥M-class case. When compared to studies that used a larger time window or additional data such as flare history, results are comparable. Using less data is conducive to platforms with limited storage, on which we plan to eventually deploy this algorithm.

We examine the Forbush decreases (FDs) associated with solar flares and coronal mass ejections (CMEs) from January 2008 to December 2019, covering the whole of Solar Cycle 24, and we compare them to our earlier study of Solar Cycle 23 (Bhatt and Chandra, Adv. Space Res. 71, 1098, 2023). On a sample of 56 events, we conducted a statistical analysis using solar and geomagnetic parameters to examine their effect on interplanetary space and the decrease in the galactic cosmic rays (GCR). Our research concentrated on an in-depth analysis of the two most significant events. The first event with an FD magnitude of 11.2% on 8 March 2012 and the second with an FD magnitude of 7.7% on 7 September 2017, respectively. We discovered that compared to other latitude bands, the northern 11 – 20° latitude band had the highest number of FD-associated flare events. We conducted a statistical analysis of FD magnitude, geomagnetic Dst-index, solar and interplanetary parameters. [ABSTRACT FROM AUTHOR]

Solar flares are among the most severe space-weather phenomena, and they have the capacity to generate radiation storms and radio disruptions on Earth. The accurate prediction of solar-flare events remains a significant challenge, requiring continuous monitoring and identification of specific features that can aid in forecasting this phenomenon, particularly for different classes of solar flares. In this study, we aim to forecast C- and M-Class solar flares utilising a machine-learning algorithm, namely the Light Gradient Boosting Machine. We have utilised a dataset spanning nine years, obtained from the Space-weather Helioseismic and Magnetic Imager Active Region Patches (SHARP), with a temporal resolution of 1 h. A total of 37 flare features were considered in our analysis, comprising of 25 active-region parameters and 12 flare-history features. To address the issue of class imbalance in solar-flare data, we employed the Synthetic Minority Over-sampling Technique (SMOTE). We used two labelling approaches in our study: a fixed 24-h window label and a varying window that considers the changing nature of solar activity. Then, the developed machine-learning algorithm was trained and tested using forecast-verification metrics, with an emphasis on evaluating the true skill statistic (TSS). Furthermore, we implemented a feature-selection algorithm to determine the most significant features from the pool of 37 features that could distinguish between flaring and non-flaring active regions. We found that utilising a limited set of useful features resulted in improved prediction performance. For the 24-h prediction window, we achieved a TSS of 0.63 (0.69) and an accuracy of 0.90 (0.97) for ≥C- (≥M)-Class solar flares. [ABSTRACT FROM AUTHOR]