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Solar eruptive activities, mainly including solar flares, coronal mass ejections (CME), and solar proton events (SPE), have an important impact on space weather and our technosphere. The short-term solar eruptive activity prediction is an active field of research in the space weather prediction. Numerical, statistical, and machine learning methods are proposed to build prediction models of the solar eruptive activities. With the development of space-based and ground-based facilities, a large amount of observational data of the Sun is accumulated, and data-driven prediction models of solar eruptive activities have made a significant progress. In this review, we briefly introduce the machine learning algorithms applied in solar eruptive activity prediction, summarize the prediction modeling process, overview the progress made in the field of solar eruptive activity prediction model, and look forward to the possible directions in the future.

We analyzed 58 high-energy proton events that occurred during the years 1996 – 2022. In 32 out of the 58 (55%) events, the proton energies extended up to ∼ 68  MeV but did not reach 100 MeV. In the remaining 26 events, the proton energies exceeded 100 MeV. We studied the differences in the characteristics of these proton events and their associations with solar and interplanetary phenomena to improve understanding proton sources and acceleration processes. The coronal mass ejections (CMEs) associated with > 100  MeV proton events appeared to be, on average, more energetic than those associated with < 100  MeV proton events. The peak and integrated fluxes (fluence) of the soft X-ray (SXR) flares were higher in > 100 MeV proton events, but there was almost no difference in the rise times of the flares. In a major part of the > 100  MeV proton events, protons were released over the rise phase of the SXR flares, whereas in most of the < 100  MeV events the proton releases occurred after the peak of the SXR flares. We established limits for the CME speed V CME and SXR peak flux F pk or total fluence F i , which helped us to distinguish the events in the two groups. Solar eruptions with V CME > 1000  km s −1 and F > pk 5 ⋅ 10 − 5  W m −2 had a high probability to produce proton events of > 100  MeV. On the other hand, eruptions with V > CME 900  km s −1 and F < i 5 ⋅ 10 − 4  J m −2 and eruptions with V < CME 900  km s −1 irrespective of the SXR total fluence were very likely to produce proton events of < 100  MeV. All proton events were associated with decametric Type III radio bursts, and most of them had Type II bursts associations either in metric or decametric–hectometric (DH) wavelengths or both. Both metric- and DH-Type II emissions were observed in 50% of < 100  MeV proton events while they were observed in 88% of > 100  MeV events. Our analysis showed that protons in most of the > 100  MeV events were released low in the corona ( ≤ 3.0 R ⊙ ) before the onsets of the DH-Type II radio bursts. Conversely, protons in most of the < 100  MeV events were released higher in the corona ( > 3 R ⊙ ) and after the DH-Type II onsets. We conclude that protons in most of the > 100  MeV events are accelerated either by the flare reconnection processes or by shocks low in the corona and could undergo reacceleration higher in the corona in CME shocks manifested in DH-Type II radio emission. In the < 100  MeV events, protons are mainly accelerated in CME shocks at coronal heights > 3 R ⊙ .

Recently, it has been confirmed that extreme solar proton events can lead to significantly increased atmospheric production rates of cosmogenic radionuclides. Evidence of such events is recorded in annually resolved natural archives, such as tree rings [carbon-14 (14C)] and ice cores [beryllium-10 (10Be), chlorine-36 (36Cl)]. Here, we show evidence for an extreme solar event around 2,610 years B.P. (∼660 BC) based on high-resolution 10Be data from two Greenland ice cores. Our conclusions are supported by modeled 14C production rates for the same period. Using existing 36Cl ice core data in conjunction with 10Be, we further show that this solar event was characterized by a very hard energy spectrum. These results indicate that the 2,610-years B.P. event was an order of magnitude stronger than any solar event recorded during the instrumental period and comparable with the solar proton event of AD 774/775, the largest solar event known to date. The results illustrate the importance of multiple ice core radionuclide measurements for the reliable identification of short-term production rate increases and the assessment of their origins.

Among the coronal mass ejections (CMEs) and solar proton events (SPEs) frequently observed by near-Earth spacecraft, the SPE that occurred on 28 October 2021 stands out as a remarkable research event. This is due to the infrequency of reported ground-level enhancements it induced. The CSES (China seismo-electromagnetic satellite) is equipped with high-energy particle detectors, namely, HEPP and HEPD, capable of measuring protons within an energy range of 2 MeV to 143 MeV. These detectors provide valuable opportunities for studying solar activity. By utilizing the Monte Carlo method to simulate the pile-up effect and accounting for the detector’s dead time, with the assistance of real-time incident counting rates, we successfully corrected the spectra in the 10–50 MeV range. The energy spectrum is important for understanding solar proton events. We used the data from the HEPP (high-energy particle package) and HEPD (high-energy particle detector) to obtain the total event-integrated spectrum, which possessed good continuity. Additionally, we compared the observations from the CSES with those from the NOAA satellite and achieved reasonable agreement. We also searched for ground-based responses to this solar activity in China and discovered Forbush decreases detected by the Yang Ba Jing Muon Telescope experiment. In conclusion, the HEPP and HEPD can effectively combine to study solar activity and obtain a smooth and consistent energy spectrum of protons across a very wide energy range.

The results of radiocarbon variation studies observed in annual tree rings from the NW Pacific (USA Northwest) (Stuiver and Braziunas 1993) and Europe (England, Brehm et al. 2021; Slovakia, Povinec 1977, 1987) are reviewed with the aim of better understanding the 11-year radiocarbon cycle and possible impacts of solar proton events on 14C levels in the atmosphere and biosphere. The average Δ14C amplitude in tree rings for the period of 1798–1944 was 1.3 ± 0.3‰, the average periodicity was 11 ± 1 years, and the average time shift between the sunspot numbers and Δ14C records was 3 ± 1 years. A new solar activity minimum (Gleissberg minimum, 1878–1933) has been identified in the Δ14C data sets from the NW Pacific and England, showing Δ14C excess of 7‰, comparable to the Dalton minimum (1797–1823). No significant changes in Δ14C levels were identified that could be associated with solar proton events during 1800–1950.

The article presents the results of a comparative analysis of the solar proton event on March 30, 2022, which has an unusual time profile of solar proton fluxes, and the previous and subsequent solar proton events (March 28, 2022, and April 02, 2022). Increases in energetic proton fluxes in the interplanetary and near-Earth space are associated with successive solar X-ray flares M4.0, X1.3, and M3.9 and three halo-type coronal mass ejections. The study was based on experimental data obtained from spacecraft located in the interplanetary space (ACE, WIND, STEREO A, and DSCOVR), in a circular polar orbit at an altitude of 850 km (Meteor-M2) and in geostationary orbit (GOES-16, Electro-L2). An explanation has been proposed for the specific features of the energetic proton flux profile in the solar proton event on March 30, 2022: protons accelerated in the flare on March 30, 2022 were partially screened by an interplanetary coronal mass ejection, the source of which was the explosive processes on the Sun on March 28, 2022; late detection of maximum proton fluxes, simultaneous for particles of different energies, is due to the arrival of particle fluxes inside an interplanetary coronal mass ejection. The spatial distribution of solar protons in near-Earth orbit was similar to the distribution at the Lagrange point L1 but with a delay of ~50 min.

During a few solar energetic particle (SEP) events, solar protons were trapped within the geomagnetic field and reached the outer edge of the inner radiation belt. We reproduced this phenomenon by modeling the proton flux distribution at the Low‐Earth Orbit (LEO) for different geomagnetic conditions during solar particle events. We developed a three‐dimensional relativistic test particle simulation code to compute the 70–180 MeV solar proton Lorentz trajectories in low L‐shell range from 1 to 3. The Tsyganenko model (T01) generated the background static magnetic field with the IGRF (v12) model. We have selected three Dst index values: −7, −150, and −210 nT, to define quiet time, strong, and severe geomagnetic storms and to generate the corresponding inner magnetic field configurations. Our results showed that the simulated solar proton flux was more enhanced in the high‐latitude regions and more expanded toward the lower latitude range as long as the geomagnetic storm was intensified. Satellite observations and geomagnetic cutoff rigidities confirmed the numerical results. Furthermore, the LEO proton flux distribution was deformed, so the structure of the proton flux inside the South Atlantic Anomaly (SAA) became longitudinally extended as the Dst index decreased. Moreover, we have assessed the corresponding radiation environment of the LEO mission. We realized that, for a higher inclined LEO mission during an intense geomagnetic storm (Dst = −210 nT), the probability of the occurrence of the Single Event Upset (SEU) rates increased by 19% and the estimated accumulated absorbed radiation doses increased by 17% in comparison with quiet conditions.

High energy protons from solar energetic particle (SEP) events are a hazard to spacecraft systems and instruments. For interplanetary and geosynchronous‐Earth‐orbiting spacecraft, a mission's cumulative SEP fluence is an important consideration for hardware design. The total solar proton fluence for a mission can be dominated by a small number of very high‐fluence events. Because of the sporadic and unpredictable nature of these large events, data sets collected over multiple solar cycles are needed to construct a statistical model that can predict a mission's risk of seeing a given fluence exposure during its mission. Several statistical models have been developed, including the JPL model and the Emission of Solar Protons (ESP) model. The models produce somewhat different results, which could be due in part to the different data sets from which they were derived. To understand the sensitivity of predicted mission fluence to the choice of data set and to the statistical distribution to which that data set is fit, we present a comparison of the JPL and ESP cumulative fluence models as reformulated from the same SEP data set, a background‐subtracted version of the Reference Data Set Version 2.0 (RDSv2.0) based on data from IMP‐8 and GOES, covering 41 years of SEP events from 1974 to 2015 with proton energies between 5 and 289 MeV. The comparisons show that different modeling approaches can produce a factor of 2 or greater difference in the mission fluences even when the same data set is used for model development.

Solar proton events (SPEs) affect the Earth’s atmosphere, causing additional ionization in the high-latitude mesosphere and stratosphere. Ionization rates from such solar proton events maximize in the stratosphere, but the formation of ozone-depleting nitrogen and hydrogen oxides begins at mesospheric altitudes. The destruction of mesospheric ozone is associated with protons with energies of about 10 MeV and higher and will strongly depend on the intensity of the flux of these particles. Most studies investigating the impact of SPEs on the characteristics of the middle atmosphere have been based on either simulations or reanalysis datasets, and some studies have used satellite observations to validate model results. We study the impact of SPEs on cold-season ozone loss in both the northern and southern hemispheres using Aura MLS mesospheric ozone measurements over the 2004 to 2024 period. Here, we show how strongly SPEs can deplete polar mesospheric ozone in different hemispheres and attempt to evaluate this dependence on the intensity of solar proton events. We found that moderate SPEs consisting of protons with an energy of more than 10 MeV and a flux intensity of more than 100 pfu destroy mesospheric ozone in the northern hemisphere up to 47% and in the southern hemisphere up to 33%. For both hemispheres, the peak of winter ozone loss was observed at about 76 km. In the northern hemisphere, maximum winter ozone loss was observed on the second day after a solar proton event, but in the southern hemisphere, winter ozone depletion was already detected on the first day. In the southern hemisphere, mesospheric ozone concentrations return to pre-event levels on the ninth day after a solar proton event, but in the northern hemisphere, even on the tenth day after a solar proton event, the mesospheric ozone layer may not be fully recovered. The strong SPEs with a proton flux intensity of more than 1000 pfu lead to a maximum winter ozone loss of up to 85% in the northern hemisphere, and in the southern hemisphere winter, ozone loss reaches 73%.

We propose a mechanism for proton propagation from the Sun to Earth orbit in the electromagnetic field presented, in the simplest case, through the Parker model. Within this model, proton ingress on the Earth is shown possible in the case when the Earth is in the surroundings of the heliospheric current sheet neutral line (HCSNL), at the distance from the latter that is smaller than the Larmor radius of the protons drifting along the HCSNL. Based on that model, we analyzed the paths of the protons with energies characteristic of solar proton events. As a result of such an analysis, solar proton events on the Earth appear to be observed only in the case when energetic protons eject from an active region (AR) located in the northern (southern) hemisphere of the Sun, at the positive (negative) polarity of the solar global magnetic field in that AR. There is a minimal value for the proton energy below which solar proton events on the Earth are not observed. This energy value is proportional to the value for the angle of the latitude at which the flare AR is located.