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Type-II radio emission often accompanies events in solar cosmic rays and is an indicator of the propagation of a shock wave in the solar corona. Conversely, the shock wave associated with coronal mass ejections plays an important role in the acceleration of solar protons. Both of these phenomena can occur unaccompanied by solar cosmic rays, while not all solar cosmic ray events are accompanied by type-II radio emission. The statistical relationships between these phenomena are considered based on the catalogs of solar proton events for the 23rd and 24th solar-activity cycles. It is shown that the events of solar cosmic rays accompanied by type-II radio emissions are among the most powerful in terms of both particle characteristics and source characteristics.

Homogeneous series of solar cosmic-ray events for four solar-activity cycles against the background of decreased activity in cycles 23 and 24 are considered. The number of solar cosmic-ray events with energies above 10 MeV decreased insignificantly, while the number of ground-level enhancements in comparison between cycles 23 and 24 decreased by eight times. It is shown that the average contribution of flares to the generation of ground-level enhancements decreased from cycle 23 to cycle 24 by three times, and the average contribution of coronal mass ejections decreased by five times; the average contribution of flares to the generation of solar cosmic rays with energy >10 MeV decreased by 1.3 times, and the average contribution of coronal mass ejections increased by 1.4 times.

Solar proton events possess a wide variety of features that reflect the conditions of solar proton acceleration and propagation. Relevant investigations rely on statistical methods that make it possible to classify events with the aim of obtaining deeper insight into physical processes leading to the generation of solar cosmic rays. In classifying events in power, the intensity of particles with energy above 10MeV at the maximum of the event time profile or the fluence of particles throughout the event time is usually used. A new parameter, Eqm, that characterizes the proton event power and which is some kind of approximation of the maximum energy of accelerated particles is analyzed in the present study. Correlations of Eqm with properties of x-ray flares on the Sun and with the velocity of coronal mass ejections are examined.

Variations in the flux of Jovian electrons near the Earth in two synodic cycles of the Earth–Jupiter system, in 1974–1975 and 2007–2008, are considered. In the 1974–1975 cycle, Jovian electrons were observed by IMP-8 during 13 successive solar rotations; electrons were observed by SOHO during 14 solar rotations during the 2007–2008 cycle. The fluxes of these electrons in each solar revolution experienced variations with a characteristic time scale of ~27 d , with the maximum flux near the middle of the rotation. The mean period of the variations does not coincide with the synodic period for the Sun–Earth system, equal to 27.3 d . The mean variation periods for the electron fluxes were 26.8 d in 1974–1975 and 26.1 d in 2007–2008. The detected variations are interpreted as reflecting variations in the structure of the solar wind speed and associated magnetic traps, the confinement time of the electrons in thesemagnetic traps, and the influence of the relative positions of the Earth and Jupiter in space.

A comparative analysis has been carried out of the parameters of energetic electrons in the tail of the Earth’s magnetosphere that belong to three sources, i.e., electrons of solar origin, electrons generated in the magnetosphere of Jupiter, and electrons in the Earth’s magnetosphere. The differences in the time profiles of fluxes and energy spectra of the three electron sources, their relation to fluxes outside the magnetosphere, and periods of the occurrence of electron fluxes of each type are considered.

The energy spectra and relative abundances of 3He, 4He, C, O, and Fe ions with energies of ~0.04–2 MeV/nucleon are studied using data from the ULEIS instrument on board the ACE spacecraft obtained during quiescent periods in 2006–2012. During the unique, prolonged minimum between cycles 23 and 24, 35 quiescent periods were distnguished, during which solar-wind flows from near-equatorial coronal holes (CHs) were detected. It is shown that the C/O and Fe/O ratios for suprathermal ions correspond to the relative abundances of the corresponding thermal ions in the fast and slow (Maxwellian) solar wind (SWICS/ACE), while the 4He/O ratio exceeds the corresponding ratio in the solar wind by a factor of two. The intensities of the 3He, 4He, C, O, and Fe suprathermal ions in outflows from CHs grow with the speed of the solar wind. This indicates that, in periods ofminimumsolar activity, suprathermal ions from CHs represent a high-temperature “tail” of the solar wind. An additional flux of suprathermal helium ions may also be contributed by other external sources.

It is shown that the number of solar proton events (SPEs) with proton energies (E) higher than 10 and 100 MeV in the current solar cycle (cycle 24) differs slightly from the number of the same events in earlier cycles (cycles 21–23), even though solar activity was low during the growth and maximum phase in cycle 24. A deficit was in this case observed for the most powerful GLE events, which are characterized by high proton fluxes with E > 100 MeV. The ratio of the number of SPEs with E > 10 and 100 MeV to the number of sunspots in cycle 24 doubled, compared to the same ratio in cycles 21–23, and the relative number of GLEs fell by more than half. The characteristics of flares and coronal mass ejections associated with proton events with E > 100 MeV in cycle 24 were virtually the same as the analogous parameters in cycle 23.

The solar proton singularities in cycles 20–23 were compared. For such a comparison, it is of special importance to present information about solar proton events (SPEs) uniformly. The Katalog working group, including representatives of different institutions, created SPE catalogs for 1970–2010. These catalogs include solar events with E ≥ 10 MeV proton fluxes exceeding 1 cm−2 s−1 sr−1 near the Earth. The various conditions that accompany SPEs result in a considerable scatter of the flux parameters and energy spectra and in a difference in time profiles. Regularities in the distribution of these parameters during four solar activity cycles can be specifically revealed only based on a statistical approach that is used in this work. In this case a comparison can be successful only when the analyzed data series are homogeneous. Solar activity singularities during the entire period of SPE measurements (from cycle 19 to the end of cycle 23) are described. The methods for adjusting solar events in particles that are registered near the Earth to solar sources are of special importance. These statistical data suggest that the number of SPEs in the cycles and the event distribution within a solar cycle may indicate that the SPE generation character is different in cycles 20–21 and 22–23.

The relative abundances of suprathermal (with energies ∼0.04–2 MeV/nucleon) 3He, 4He, C, O, and Fe ions and the energy spectra of 3He and Fe ions in near-Earth space during quiescent periods of solar activity are studied. Measurements obtained with the ULEIS instrument onboard the ACE spacecraft during the 23rd and 24th solar cycles are used. Substantial differences in the energy spectra of suprathermal ions in the 23rd and 24th solar cycles are observed for the selected quiescent periods. Appreciable differences in the energy dependences of the relative ion abundances are also found. One possible explanation for the results obtained is that the background ions were accelerated to suprathrmal energies under different conditions in the solar corona in these two cycles.

Data from the ULEIS instrument aboard the ACE spacecraft are used to study the energy spectra of 3He and 4He ions produced during periods of the quiet Sun in the 23rd solar cycle in the energy range ∼0.08–2 MeV/nucleon. Differences in the spectra and 3He/4He relative abundances for three groups of quiet periods dominated by different sources of ions are demonstrated: weak impulsive solar flares, particles of the solar corona, and solar wind particles accelerated to energies of several MeV/nucleon.

The ion composition of fluxes of charged particles in interplanetary space with energies ∼0.03–10 MeV/nucleon are studied during quiet periods in the 23rd solar-activity cycle using data from the ACE spacecraft. Apart from the activity minimum, the Fe/O ratio during such periods corresponds to either the relative abundances of ions in particle fluxes accelerated in solar flares or the mean abundances of elements in the solar corona. At the cycle minimum, this ratio takes on values characteristic for the solar wind. These results indicate that the background fluxes of low-energy particles in the phases of the growth, maximum, and decay of the solar cycle include significant contributions from both coronal particles accelerated to suprathermal energies and particles accelerated in small impulsive solar flares. The particle fluxes from such flares are distinguished by an enhanced abundance of iron ions.

Combination of data on declined intensities of particles of different nature (e, p, and α) into a single dependence of characteristic decline time τ on particle rigidity in a wide range of R reveals the diversity of forms of τ(R) in different events: regular increase, decrease, and independence of R, as well as the presence in some events of maxima and minima. The problem of studying τ(R) has something in common with long standing problem of the rigidity dependence of mean free path λ(R). The considered set of forms of τ(R) allows one to conclude that at present there is no uniform dependence τ(R), as well as λ(R), and, therefore, no their common model interpretation in a wide range of rigidities exists.

The value of the radial gradient of low-energy (∼0.5–2 MeV) protons in the heliosphere at distances of 20–80 AU in the periods of solar activity minima in 1985–1987 and 1994–1997 was estimated using the data of the Voyager-1 and Voyager-2 spacecraft (s/c). Preliminary results on the dependence of the radial gradient on the distance were obtained for protons of these energies. The value of the radial gradient varies from −3% (AU)−1 to −1% (AU)−1 at distances from the Sun of ∼20–60 AU, reaching +0.7% (AU)−1 at maximum considered distances (∼80 AU). The sign reversal of the proton radial gradient at a distance of 60–70 AU is interpreted as the appearance of a new component: up to the point of inversion there are mainly particles of the solar origin and/or accelerated in the inner heliosphere, while after the reversal of the gradient’s sign the fluxes of particles prevail whose source is located far from the Sun (maybe in the vicinity of the heliosphere boundary in the region of existence of the termination shock).

The dynamics of the proton energy spectrum during the solar cycle is studied. The spectra were determined by 1–100 MeV particle fluxes measured by different instruments mounted aboard the Earth's IMP-8 satellite for more than one hundred quiet-time intervals in the period between 1974 and 1991. The galactic branch of the spectra (Ep > 10 MeV) constructed for every quiet interval was fitted by a power law function, J =CEν. The theory predicts that in the 1–100 MeV energy range, where the adiabatic cooling of particles is dominant, ν = 1, while we have derived a ν double-peak distribution. The main maximum has the mean value 〈ν〉 = 1.35. The mean value of the second, much weaker maximum, is 〈ν〉 = 0.95. Within the main maximum, ν values are distributed in accordance with the Gaussian law with a standard deviation 〈D/ν〉 = 0.12. The substantial difference of ν from unity requires the elaboration of a new model of modulation processes in the inner heliosphere. The ν values corresponding to the second maximum show that modulation processes correspond sometimes to theoretical conceptions. It is shown that ν correlates weakly with parameters A and γ describing the solar branch of the spectrum (J(E) = AE–γ). At the same time, a more significant correlation is observed between ν and the solar activity index, Rz , the counting rate of the Deep River neutron monitor, and the energy value in the minimum of the energy spectrum flux, Emin .

Time variations with a duration of ∼0.6–1.5 years are studied in the interplanetary space for protons and helium nuclei with energies of 0.3–10 MeV per nucleon at a quiescent time of solar activity. It is shown that at 1 AU in the periods 1978–1981 and 1988–1990, at the phases of growth of the 21st and 22nd solar cycles, the background fluxes of these particles determined as minimum intensity levels in every month increased demonstrating steplike variations. At the same time, the intensity of galactic cosmic rays (GCRs) decreased also with the formation of modulation steps. Each step of low-energy particles was finished by a deep minimum of intensity (“gap”) in both protons and helium nuclei and with a simultaneous short-term increase of the GCR intensity. We present the results of studying five such steps in the intensity of low-energy particles that were observed simultaneously and were opposite in phase with modulation steps of galactic particles. The lowest values of the H/He ratio were recorded at the end of every step, at the lowest intensities of these particles, i.e., in the “gap.” The true background population at 1 AU was detected precisely at these time intervals, when the contributions of flare particles and those accelerated in the international space were minimum. Various possibilities of the origination of the steplike variations of the background fluxes of protons and helium nuclei with energies of 0.3–10 MeV per nucleon, correlated with similar GCR variations, are discussed.

Variations of the proton spectra in the 0.3–100 MeV energy range based on the data of various instruments installed onboard the IMP-8 satellite are studied for “very quiet,” “quiet,” and “quasi-stable” solar activity periods during the years 1974–1991. As many as 118 spectra were approximated by two power laws: the left-hand and galactic branches of the spectrum were fitted by the AE–γ function and a dependence of the CE type, respectively, the sum J(E) = AE–γ + CE providing the total spectrum. It is shown that the spectra vary within a solar cycle with a shift of the minimum energy (Emin) to higher energies with increasing solar activity. It follows from the relations between the spectrum parameters thus obtained that, in particular periods of time, an increase (decrease) of the particle flux in the low-energy branch of the spectrum and an intensification (depression) of the GCR particle flux modulation take place simultaneously. This is manifested in a shift of the spectrum parallel to the energy axis. The study of the spectra in the most quiet time during three successive solar minima have shown that low-energy (0.3–10 MeV) protons, as well as GCR, are subject to the 22-year variation in the solar magnetic cycle.