Time-dependent energy spectra of galactic cosmic rays (GCRs) carry fundamental information regarding their origin and propagation. When observed at the Earth, these spectra are significantly affected by the solar wind and the embedded solar magnetic field that permeates the heliosphere, changing significantly over an 11 yr solar cycle. Energy spectra of GCRs measured during different epochs of solar activity provide crucial information for a thorough understanding of solar and heliospheric phenomena. The PAMELA experiment collected data for almost 10 years (2006 June 15–2016 January 23), including the minimum phase of solar cycle 23 and the maximum phase of solar cycle 24. In this paper, we present new spectra for helium nuclei measured by the PAMELA instrument from 2010 January to 2014 September over a three-Carrington-rotation time basis. These data are compared to the PAMELA spectra measured during the previous solar minimum, providing a picture of the time dependence of the helium-nuclei fluxes over a nearly full solar cycle. Time and rigidity dependencies are observed in the proton-to-helium flux ratios. The force-field approximation of the solar modulation was used to relate these dependencies to the shapes of the local interstellar proton and helium-nuclei spectra.

Using measurements from the PAMELA and ARINA spectrometers onboard the RESURS DK-1 satellite, we have examined the 27-day intensity variations in galactic cosmic ray (GCR) proton fluxes in 2007-2008. The PAMELA and ARINA data allow for the first time a study of time profiles and the rigidity dependence of the 27-day variations observed directly in space in a wide rigidity range from ~300 MV to several GV. We find that the rigidity dependence of the amplitude of the 27-day GCR variations cannot be described by the same power-law at both low and high energies. A flat interval occurs at rigidity R = <0.6-1.0> GV with a power-law index gamma = - 0.13+/-0.44 for PAMELA, whereas for R >= 1 GV the power-law dependence is evident with index gamma = - 0.51+/-0.11. We describe the rigidity dependence of the 27-day GCR variations for PAMELA and ARINA data in the framework of the modulation potential concept using the force-field approximation for GCR transport. For a physical interpretation, we have considered the relationship between the 27-day GCR variations and solar wind plasma and other heliospheric parameters. Moreover, we have discussed possible implications of MHD modeling of the solar wind plasma together with a stochastic GCR transport model concerning the effects of corotating interaction regions.

We present a study of the east–west anisotropy of trapped-proton fluxes in low-Earth orbit based on the measurements of the Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics (PAMELA) experiment. The differential intensities of eastward- and westward-traveling protons detected in the South Atlantic Anomaly region were estimated as a function of equatorial pitch angle and drift shell, for six energy bins between 80 MeV and 2 GeV. We found that, as a consequence of the strong atmospheric gradient coupled with the large gyroradius in this energy range, the intensities of eastward fluxes exceed those of westward fluxes by a factor of ∼10–20. However, the reported directional asymmetry also depends on the sign of the local flux gradient, resulting in more intense westward fluxes beyond the radial distances where the inner belt peaks. PAMELA observations can be used to improve the description of the near-Earth radiation environment at lowest altitudes and highest trapping energies, where current theoretical and empirical models are affected by the largest uncertainties.

We present a study of the solar-cycle variations of >80 MeV proton flux intensities in the lower edge of the inner radiation belt, based on the measurements of the Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics (PAMELA) mission. The analyzed data sample covers an 8 year interval from 2006 July to 2014 September, thus spanning from the decaying phase of the 23rd solar cycle to the maximum of the 24th cycle. We explored the intensity temporal variations as a function of drift shell and proton energy, also providing an explicit investigation of the solar-modulation effects at different equatorial pitch angles. PAMELA observations offer new important constraints for the modeling of low-altitude particle radiation environment at the highest trapping energies.

Precise time-dependent measurements of the Z = 2 component in the cosmic radiation provide crucial information about the propagation of charged particles through the heliosphere. The PAMELA experiment, with its long flight duration (15th June 2006 - 23rd January 2016) and the low energy threshold (80 MeV/n) is an ideal detector for cosmic ray solar modulation studies. In this paper, the helium nuclei spectra measured by the PAMELA instrument from July 2006 to December 2009 over a Carrington rotation time basis are presented. A state-of-the-art three-dimensional model for cosmic-ray propagation inside the heliosphere was used to interpret the time-dependent measured fluxes. Proton-to-helium flux ratio time profiles at various rigidities are also presented in order to study any features which could result from the different masses and local interstellar spectra shapes.

The energy spectra of galactic cosmic rays carry fundamental information regarding their origin and propagation, but, near Earth, cosmic rays are significantly affected by the solar magnetic field which changes over time. The time dependence of proton and electron spectra were measured from July 2006 to December 2009 by PAMELA experiment, that is a ballooon-borne experiment collecting data since 15 June 2006. These studies allowed to obtain a more complete description of the cosmic radiation, providing fundamental information about the transport and modulation of cosmic rays inside the heliosphere. The study of the time dependence of the cosmic-ray protons and helium nuclei from the unusual 23rd solar minimum through the following period of solar maximum activity is presented.

This report presents the results of analysis of proton flux variations in the inner radiation belt obtained by ARINA spectrometer. The ARINA satellite experiment was carried out on board the Russian low-orbit satellite Resurs-DK1 (altitude 350-600 km, inclination 70$^{o}$) from 2006 till 2016. The spectrometer registered high-energy protons (30-100 MeV) with energy resolution of 10 \% and angular resolution of 7$^{o}$. In this work proton flux variations in the inner radiation belt (L=1.14, B=0.20 G) were analyzed with solar index F10.7 in various phases of the 24th solar cycle. Proton flux anticorrelates with F10.7 index (coefficient correlation -0.95) and its value varies 5-7 times. Time lag between proton flux and F10.7 index was found to be 5-6 months for total period (2006-2016) and it can decrease to 2-3 months in some periods of the 24th solar cycle.

The phenomenon of a positron anomaly in cosmic rays at energies above 10 GeV can not be explained within the framework of secondary positron production mechanisms into interstellar media. One possible explanation can be that positron excess is generated by ∼ TeV dark matter particles annihilation or decay. Very high energies are not available for modern magnetic spectrometers because of their small size, but magnetic analysis with geomagnetic field extending for thousands of kilometres can be used. One approach to the high energy positron detection deals with allowed and forbidden trajectories Earth’s magnetic field. It was shown that at the equatorial position of the detector it is possible to separate positrons and electrons using only a position-sensitive electromagnetic calorimeter up to energies ∼ 250 GeV using detector with angular resolution of about 5 degrees. Second approach consists in the joint registration of an electron, or positron, and the synchrotron photons emitted by them into magnetosphere. It is shown that for space born detector at about ∼ 400 km orbit identification of positrons up to tens TeV is possible using synchrotron radiation detector and imaging calorimeter.

During the PAMELA satellite experiment started in 2006 onboard the Resurs-DK1 spacecraft (350–600 km, an inclination of 70°), cosmic ray charged particle fluxes in low near-Earth orbits were measured to the beginning of 2016. The data obtained during the experiment on high-energy proton (0.1–10 GeV) fluxes in the radiation belt made it possible to measure maximum proton trapping energies in various solar activity phases. The measurement results showed that the maximum proton trapping energy at L shells of 1.16–1.22 in the periods of both solar activity minimum (2009) and maximum (2014) was ∼2 GeV.

The PAMELA magnetic spectrometer was launched onboard the Resurs-DK1 satellite into a near-polar Earth orbit with an altitude of 350–600 km, in order to study fluxes of cosmic ray particles and antiparticles in the wide energy range of ~80 MeV to hundreds of GeV. The results from observations of electron and positron fluxes in 2006–2016 are presented.

Precision measurements of the Z = 2 component in cosmic radiation provide crucial information about the origin and propagation of the second most abundant cosmic ray species in the Galaxy (9% of the total). These measurements, acquired with the PAMELA space experiment orbiting Earth, allow to study solar modulation in details. Helium modulation is compared to the modulation of protons to study possible dependencies on charge and mass. The time dependence of helium fluxes on a monthly basis measured by PAMELA has been studied for the period between July 2006 to January 2016 in the energy range from 800 MeV/n to ~ 20 GeV/n.

The PAMELA experiment has measured cosmic ray particles and antiparticles fluxes at Earth orbit from June 2006 till January 2016 onboard the Resurs-DK1 satellite. Measurements were carried out during the solar minimum of 23 solar cycle with negative polarity A < 0 of heliospheric magnetic field till the beginning of 24 cycle with positive polarity A > 0. In this paper, the results of observations of electron and positron fluxes are presented in wide energy range from several hundreds MeVs till several TeVs These measurements provide important information to study cosmic ray sources and propagation in Galaxy and heliosphere.

The results are presented from an analysis of proton fluxes in the inner radiation belt (RB), obtained with the ARINA spectrometer. The ARINA satellite experiment was performed on board the Russian low-orbit spacecraft Resurs-DK1 (altitude 350–600 km; inclination 70°; duration, 2006–2016). The spectrometer registered high-energy protons (30–100 MeV) with an energy resolution of 10% and an angular resolution of 7°. The geographical and pitch-angle distribution of proton flux in the inner radiation belt (1.15 < L < 2.0) were analyzed during the waning phase of the 23rd solar cycle and main part of the 24th cycle. It is shown that the proton flux intensity depends on the phase of the solar cycle (the minimum intensity is observed in the period of the solar activity maximum and vice versa) and varies by 2–7 times for different L‑shells.

Protons detected by the PAMELA experiment in the period 2006-2014 have been analyzed in the energy range between 0.40 and 50 GV to explore possible periodicities besides the well known solar undecennial modulation. An unexpected clear and regular feature has been found at rigidities below 15 GV, with a quasi-periodicity of similar to 450 days. A possible Jovian origin of this periodicity has been investigated in different ways. The results seem to favor a small but not negligible contribution to cosmic rays from the Jovian magnetosphere, even if other explanations cannot be excluded.

New results on the short-term galactic cosmic-ray (GCR) intensity variation (Forbish decrease) in 2006 December measured by the PAMELA instrument are presented. Forbush decreases are sudden suppressions of the GCR intensities, which are associated with the passage of interplanetary transients such as shocks and interplanetary coronal mass ejections (ICMEs). Most of the past measurements of this phenomenon were carried out with ground-based detectors such as neutron monitors or muon telescopes. These techniques allow only the indirect detection of the overall GCR intensity over an integrated energy range. For the first time, thanks to the unique features of the PAMELA magnetic spectrometer, the Forbush decrease, commencing on 2006 December 14 and following a CME at the Sun on 2006 December 13, was studied in a wide rigidity range (0.4–20 GV) and for different species of GCRs detected directly in space. The daily averaged GCR proton intensity was used to investigate the rigidity dependence of the amplitude and the recovery time of the Forbush decrease. Additionally, for the first time, the temporal variations in the helium and electron intensities during a Forbush decrease were studied. Interestingly, the temporal evolutions of the helium and proton intensities during the Forbush decrease were found to be in good agreement, while the low rigidity electrons ( GV) displayed a faster recovery. This difference in the electron recovery is interpreted as a charge sign dependence introduced by drift motions experienced by the GCRs during their propagation through the heliosphere.

Despite the significant progress achieved in recent years, the physical mechanisms underlying the origin of solar energetic particles (SEPs) are still a matter of debate. The complex nature of both particle acceleration and transport poses challenges to developing a universal picture of SEP events that encompasses both the low-energy (from tens of keV to a few hundreds of MeV) observations made by space-based instruments and the GeV particles detected by the worldwide network of neutron monitors in ground-level enhancements (GLEs). The high-precision data collected by the Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics (PAMELA) satellite experiment offer a unique opportunity to study the SEP fluxes between ∼80 MeV and a few GeV, significantly improving the characterization of the most energetic events. In particular, PAMELA can measure for the first time with good accuracy the spectral features at moderate and high energies, providing important constraints for current SEP models. In addition, the PAMELA observations allow the relationship between low and high-energy particles to be investigated, enabling a clearer view of the SEP origin. No qualitative distinction between the spectral shapes of GLE, sub-GLE and non-GLE events is observed, suggesting that GLEs are not a separate class, but are the subset of a continuous distribution of SEP events that are more intense at high energies. While the spectral forms found are to be consistent with diffusive shock acceleration theory, which predicts spectral rollovers at high energies that are attributed to particles escaping the shock region during acceleration, further work is required to explore the relative influences of acceleration and transport processes on SEP spectra.

Measurements of secondary-electron and secondary-positron fluxes below the geomagnetic cutoff in near-Earth space were performed by means of the PAMELA magnetic spectrometer installed on board the Resurs-DK1 satellite launched on June 15, 2006, in an elliptical orbit of inclination 70° and altitude 350 to 600 km. This spectrometer permits measuring the fluxes of electrons and positrons over a wide energy range, as well as determining their spatial distributions to a precision of about 2°. A calculation of particle trajectories in the geomagnetic field makes it possible to separate electrons and positrons originating from cosmic-ray interactions in the Earth’s magnetosphere. The spatial distributions of quasitrapped, trapped, and short-lived albedo positrons and electrons of energy above 70 MeV in the radiation belt were analyzed. The ratio of the electron-to-positron fluxes and the energy spectra of the electrons and positrons in question are indicative of different productionmechanisms for stably trapped and quasitrapped secondary particles.