We analyzed 58 high-energy proton events that occurred during the years 1996 – 2022. In 32 out of the 58 (55 ∼ 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 VCME and SXR peak flux Fpk or total fluence Fi, which helped us to distinguish the events in the two groups. Solar eruptions with VCME > 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 <100 MeV proton events while they were observed in 88 >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⊙.

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(-1)during 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 (VTR) 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) [IESPpeak]) 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 VTR(0.68 +/- 0.05 and 0.71 +/- 0.06), the CME space speed (VCMEspace) (0.59 +/- 0.05 and 0.68 +/- 0.07), and the logarithm of SEP peak intensity (log(10) [ISEPpeak]) (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) [DTII]).Using linear combinations of two or more variables improved the correlations. The best two-variable combination explaining log(10) [IESPpeak] was VTRcombined with log(10) [ISEPpeak] 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 VTR, VCMEspaceand log(10) [SXRF] are used. The correlation coefficients between the calculated and observed log(10) [IESPpeak] 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 VTR, log(10) [ISEPpeak], VCMEspace(or log(10) [SXRF]), and log(10) [DTII]. 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.

We have analysed energetic storm particle (ESP) events in 116 interplanetary (IP) shocks driven by front-side full and partial halo coronal mass ejections (CMEs) with speeds >400 kms-1during the years 1996-2015. We investigated the occurrence and relationships of ESP events with several parameters describing the IP shocks, and the associated CMEs, type II radio bursts, and solar energetic par-ticle (SEP) events. Most of the shocks (57%) were associated with an ESP event at proton energies >1 MeV. The shock transit speeds from the Sun to 1 AU of the shocks associated with an ESP event were significantly greater than those of the shocks without an ESP event, and best distinguished these two groups of shocks from each other. The occurrence and maximum intensity of the ESP events also had the strongest dependence on the shock transit speed compared to the other parameters investigated. The cor-relation coefficient between ESP peak intensities and shock transit speeds was highest (0.73 +/- 0.04) at 6.2 MeV. Weaker dependences were found on the shock speed at 1 AU, Alfve acute accent nic and magnetosonic Mach numbers, shock compression ratio, and CME speed. On aver-age all these parameters were significantly different for shocks capable to accelerate ESPs compared to shocks not associated with ESPs, while the differences in the shock normal angle and in the width and longitude of the CMEs were insignificant. The CME-driven shocks producing energetic decametric-hectometric (DH) type II radio bursts and high-intensity SEP events proved to produce also more frequently ESP events with larger particle flux enhancements than other shocks. Together with the shock transit speed, the characteristics of solar DH type II radio bursts and SEP events play an important role in the occurrence and maximum inten-sity of ESP events at 1 AU.(c) 2022 COSPAR. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

We have analysed 58 high-energy proton events and 36 temporally related near-relativistic electron events from the years 1997 – 2015 for which the velocity dispersion analysis of the first-arriving particles gave the apparent path lengths between 1 and 3 AU. We investigated the dependence of the characteristics of the proton events on the associations of type II, III, and IV radio bursts. We also examined the properties of the soft X-ray flares and coronal mass ejections associated with these events. All proton events were associated with decametric type III radio bursts, while type IV emission was observed only in the meter wavelengths in some of the events (32/58). Almost all proton events (56/58) were associated with radio type II bursts: 11 with metric (m) type II only, 11 with decametric–hectometric (DH) only, and 34 with type II radio bursts at both wavelength ranges. By examining several characteristics of the proton events, we discovered that the proton events can be divided into two categories. The characteristics of events belonging to the same category were similar, while they significantly differed between events in different categories. The distinctive factors between the categories were the wavelength range of the associated type II radio emission and the temporal relation of the proton release with respect to the type II onset. In Category 1 are the events which were associated with only metric type II emission or both m and DH type II and the release time of protons was before the DH type II onset (18/56 events). Category 2 consists of the events which were associated with only DH type II emission or both m and DH type II and the protons were released at or after the DH type II onset (31/56 events). For seven of the 56 events we were not able to determine a definite category due to timing uncertainties. The events in Category 1 had significantly higher intensity rise rates, shorter rise times, lower release heights, and harder energy spectra than Category 2 events. Category 1 events also originated from magnetically well-connected regions and had only small time differences between the proton release times and the type III onsets. The soft X-ray flares for these events had significantly shorter rise times and durations than for Category 2 events. We found 36 electron events temporally related to the proton events, which fulfilled the same path length criterion as the proton events. We compared the release times of protons and electrons at the Sun, and discovered that in 19 of the 36 events protons were released almost simultaneously (within ${\pm}\,7$ minutes) with the electrons, in 16 events protons were released later than the electrons, and in one event electrons were released after the protons. The simultaneous proton and electron events and the delayed proton events did not unambiguously fall in the two categories of proton events, although most of the events in which the protons were released after the electrons belonged to Category 2. We conclude that acceleration of protons in Category 1 events occurred low in the corona, either by CME-driven shocks or below the CMEs in solar flares or in CME initiation related processes. It seems plausible that protons in Category 2 events were accelerated by CME-driven shocks high in the solar corona. Large delays of protons with respect to type III onsets in the events where protons were released after the electrons suggest late acceleration or release of protons close to the Sun, but the exact mechanism causing the delay remained unclear.

We have searched for solar proton events consisting of both solar energetic particles (SEPs) accelerated near the Sun and energetic storm particles (ESPs) accelerated by interplanetary shocks driven by coronal mass ejections (CMEs) and observed near the time when the shock passes the observer. The purpose of this study is to investigate the possibilities and advantages of using energetic particle observations for mid-term (warning time several hours) forecasting of geomagnetic storms or as a support for longer-term forecasting methods based on solar observations. The study period extends from May 1996 to December 2017 covering the entire solar cycle 23 and the major part of solar cycle 24. Using two particle energies, 2 and 20 MeV, we found 95 SEP-ESP events of which 65 were associated with geomagnetic storms with Dst <= -50 nT caused by CMEs. We performed correlation analysis between log(10 vertical bar)Dst (nT)vertical bar and various parameters characterising the particle events or the associated CMEs. We found the best correlations for the single independent variables Delta t(Esp-sEp) (r = -0.47 +/- 0.08), which is the difference between the ESP peak time and SEP onset time, the CME direction parameter DP (r = 0.47 +/- 0.10), and the logarithm of the maximum ESP energy log(10)[E-ESP(max) (MeV)] (r = 0.44 +/- 0.11). Using a linear combination of these three variables improves the correlation (r = 0.68 +/- 0.07). We suggest that an empirical equation based on these three parameters and requiring only coronagraph observations of CMEs and energetic particle measurements in interplanetary space can be used for mid-term forecasting of geomagnetic storm strengths. We found that 74% of the strongest storms (Dst <= -200 nT) during the study period were associated with energetic particle events. The average warning time and its standard deviation for all geomagnetic storms associated with SEP-ESP events was (15 +/- 10) hours. (C) 2019 COSPAR. Published by Elsevier Ltd. All rights reserved.

We studied the occurrence and characteristics of geomagnetic storms associated with disk-centre full-halo coronal mass ejections (DC-FH-CMEs). Such coronal mass ejections (CMEs) can be considered as the most plausible cause of geomagnetic storms. We selected front-side full-halo coronal mass ejections detected by the Large Angle and Spectrometric Coronagraph onboard the Solar and Heliospheric Observatory (SOHO/LASCO) from the beginning of 1996 till the end of 2015 with source locations between solar longitudes E10 and W10 and latitudes N20 and S20. The number of selected CMEs was 66 of which 33 (50%) were deduced to be the cause of 30 geomagnetic storms with \(\mathrm{Dst} \leq- 50~\mbox{nT}\). Of the 30 geomagnetic storms, 26 were associated with single disk-centre full-halo CMEs, while four storms were associated, in addition to at least one disk-centre full-halo CME, also with other halo or wide CMEs from the same active region. Thirteen of the 66 CMEs (20%) were associated with 13 storms with \(-100~\mbox{nT} < \mbox{Dst} \leq- 50~\mbox{nT}\), and 20 (30%) were associated with 17 storms with \(\mbox{Dst}\leq- 100~\mbox{nT}\). We investigated the distributions and average values of parameters describing the DC-FH-CMEs and their interplanetary counterparts encountering Earth. These parameters included the CME sky-plane speed and direction parameter, associated solar soft X-ray flux, interplanetary magnetic field strength, \(B_{t}\), southward component of the interplanetary magnetic field, \(B_{s}\), solar wind speed, \(V_{sw}\), and the \(y\)-component of the solar wind electric field, \(E_{y}\). We found only a weak correlation between the Dst of the geomagnetic storms associated with DC-FH-CMEs and the CME sky-plane speed and the CME direction parameter, while the correlation was strong between the Dst and all the solar wind parameters (\(B_{t}\), \(B_{s}\), \(V_{sw}\), \(E_{y}\)) measured at 1 AU. We investigated the dependences of the properties of DC-FH-CMEs and the associated geomagnetic storms on different phases of solar cycles and the differences between Solar Cycles 23 and 24. In the rise phase of Solar Cycle 23 (SC23), five out of eight DC-FH-CMEs were geoeffective (\(\mbox{Dst} \leq- 50~\mbox{nT}\)). In the corresponding phase of SC24, only four DC-FH-CMEs were observed, three of which were nongeoeffective (\(\mbox{Dst} > - 50~\mbox{nT}\)). The largest number of DC-FH-CMEs occurred at the maximum phases of the cycles (21 and 17, respectively). Most of the storms with \(\mbox{Dst}\leq- 100~\mbox{nT}\) occurred at or close to the maximum phases of the cycles. When comparing the storms during epochs of corresponding lengths in Solar Cycles 23 and 24, we found that during the first 85 months of Cycle 23 the geoeffectiveness rate of the disk-centre full-halo CMEs was 58% with an average minimum value of the Dst index of \(- 146~\mbox{nT}\). During the corresponding epoch of Cycle 24, only 35% of the disk-centre full-halo CMEs were geoeffective with an average value of Dst of \(- 97~\mbox{nT}\).

We have investigated the occurrence and characteristics of solar energetic particle (SEP) events related to full halo coronal mass ejections (FHCMEs) from source locations close to the central meridian of the Sun. Halo CMEs detected by SOHO/LASCO between 1996 and end of 2014 originating from source locations between solar longitudes E10 and W10 were first identified. The CMEs were divided in three groups according to the latitude of the source region: 26 equatorial events in the latitude range [N10, S10], 16 northern events in the range (N10,N20], and 22 southern events in the range (S10, S20]. We then searched for associated solar proton events based on SOHO/ERNE observations. In altogether 25 cases (13 equatorial, 6 northern, and 6 southern events) an association was found. For these events, we found good correlations of the peak intensities of 2 MeV, 20 MeV, and 68 MeV protons with both the CME speed and the X-ray flare magnitude, as determined by the soft X-ray peak flux or the event integrated flux. The correlation coefficients ranged from 0.47 to 0.83 for the CME speed, from 0.63 to 0.88 for the X-ray peak flux and from 0.64 to 0.89 for the X-ray integrated flux depending on the proton energy.