Galactic Cosmic Ray Transport Research Articles

A Comprehensive Comparison of Various Galactic Cosmic-Ray Models to the State-of-the-art Particle and Radiation Measurements

Galactic cosmic rays (GCRs) are the slowly varying background energetic particles that originate outside the solar system, are modulated by the heliospheric magnetic field, and pose ongoing radiation hazards to deep space exploration missions. To assess the potential radiation risk, various models have been developed to predict the GCR flux near Earth based on propagation theories and/or empirical functions. It is essential to benchmark these models by validating against the state-of-the-art measurements. In this work, a comprehensive model–observation comparison of the energy-dependent particle flux has been performed, by combining five typical GCR models and observational data from the Cosmic Ray Isotope Spectrometer on board the Advanced Composition Explorer spacecraft at relatively lower energies and data from the Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics and Alpha Magnetic Spectrometer at higher energies. The analysis shows that, out of the five models investigated in this study, the optimal model, characterized by minimal relative difference or reduced chi-square divergence from measurements, depends on the particle type, energy range, and epoch of interest. Furthermore, a silicon slab is applied to compute the absorbed dose rate using conversion factors applied to GCR model outputs, and the results are compared to measurements from the Cosmic Ray Telescope for the Effects of Radiation. The comparisons in this paper have implications for the strengths and limitations of individual GCR models, advance our comprehension of the underlying GCR transport mechanisms, and also have strong application aspects for mitigating space radiation risks.

Magnetic Trapping of Galactic Cosmic Rays in the Outer Heliosheath and Their Preferential Entry into the Heliosphere

This paper examines the geometry of interstellar magnetic field lines close to the boundary of the heliosphere in the direction of the unperturbed local interstellar magnetic field, where the field lines are spread apart by the heliopause (HP). Such field parting establishes a region of weaker magnetic field of about 300 au in size in the northern hemisphere that acts as a giant magnetic trap affecting the propagation of galactic cosmic rays (GCRs). The choice of an analytic model of the magnetic field in the very local interstellar medium allows us to qualitatively study the resulting magnetic field draping pattern while avoiding unphysical dissipation across the HP-impeding numerical magnetohydrodynamic (MHD) models. We investigate GCR transport in the region exterior to the heliosphere, including the magnetic trap, subject to guiding center drifts, pitch angle scattering, and perpendicular diffusion. The transport coefficients were derived from Voyager 1 observations of magnetic turbulence in the VLISM. Our results predict a ring current of energetic ions drifting around the interior of the magnetic trap. It is also demonstrated that GCRs cross the HP for the first time preferentially through a crescent-shaped region between the magnetic trap and the upwind direction. The paper includes results of MHD modeling of the heliosphere that provide the coordinates of the center of the magnetic trap in ecliptic coordinates. In addition to the heliosphere, we examine several extreme field draping configurations that could describe the astrospheres of other stars.

Galactic cosmic ray transport in the absence of resonant scattering

ABSTRACT Galactic cosmic ray transport relies on the existence of turbulence on scales comparable with the gyration radius of the particles and with wavenumber vector oriented along the local magnetic field. In the standard picture, in which turbulence is injected at large scales and cascades down to smaller scales, it is all but guaranteed that the turbulent fluctuations at the scales relevant for resonant scattering may be present, either because of anisotropic cascading or because of the onset of damping processes. This raises questions on the nature of cosmic ray scattering, especially at energies ≳1 TeV, where self-generation is hardly relevant. Here, by means of numerical simulations of charged test particles in a prescribed magnetic field, we perform a gedankenexperiment aimed at investigating particle diffusion in a situation in which turbulence is mainly present at large scales, and discuss possible implications of this set-up for cosmic ray transport phenomenology.

The Effect of Magnetic Field Line Topology on ICME-related GCR Modulation

The large-scale magnetic structure of interplanetary coronal mass ejections (ICMEs) has been shown to affect the galactic cosmic-ray (GCR) flux measured in situ by spacecraft, causing temporary decreases known as Forbush decreases (FDs). In some ICMEs, the magnetic ejecta exhibits a magnetic flux rope (FR) structure; the strong magnetic field strength and closed field line geometry of such ICME FRs have been proposed to act as a shield to GCR transport. In this study, we identify four ICMEs near Earth that drove FDs with similar mean magnetic field strengths (20–25 nT), two ICMEs with more typical mean speeds (∼400 km s−1), and two fast (∼750 km s−1) ICMEs. Within each speed pairing, we identify an ICME that exhibited an open magnetic field line topology and compare its effect on the GCR flux to that which exhibited a mostly closed topology. We investigate the different mechanisms that contribute to the resulting ICME-related FDs and their recovery and determine which properties, if any, play a more important role than others in driving FDs. We find that much of the GCR response to the ICME events in this study is independent of the open or closed magnetic field line topology of the FR and that features such as the fluctuations in speed, magnetic field structure, and expansion within the FR may play more of a role in determining the smaller-scale structure of the FD profile.

Comparison of Doses in Lunar Habitats Located at the Surface and in Crater

As humanity prepares for extended lunar exploration, understanding the radiation environment on the Moon is important for astronaut safety. This study utilized the Particle and Heavy-Ion Transport code System (PHITS), a stochastic Monte Carlo-based radiation transport code, to simulate the radiation environment inside a habitat, focusing on the impact of galactic cosmic rays (GCRs) interacting with local lunar and habitat material, and to calculate the effective dose equivalent. Placing a lunar base in a crater can provide additional shielding by reducing the GCR flux incident on the base. Furthermore, the secondary radiation field created by GCR interactions may be altered by the local topological features. GCR transport calculations were performed for a hypothetical base on a flat surface and in shallow and deep craters to determine the overall efficacy in dose reduction gained by placing a base in a 100 m diameter crater. Our findings indicate that the depth of lunar habitats significantly influences the effective dose equivalent, with deeper locations offering substantial protection. Specifically, alongside a crater wall at a deep depth (15 m), in solar minimum conditions, the total dose was reduced by approximately 44.9% compared to the dose at the surface. Similarly, at a shallow depth (5 m), a reduction of approximately 10.7% was observed. As the depth of the crater increased, the neutron contribution to the total dose also increased. Comparing the simulated doses to NASA’s lifetime exposure limits provides insights into mission planning and astronaut safety, emphasizing the importance of strategic habitat placement and design.

Charge-Sign Dependent Cosmic-Ray Modulation Observed with the Calorimetric Electron Telescope on the International Space Station.

We present the observation of a charge-sign dependent solar modulation of galactic cosmic rays (GCRs) with the Calorimetric Electron Telescope onboard the International Space Station over 6yr, corresponding to the positive polarity of the solar magnetic field. The observed variation of proton count rate is consistent with the neutron monitor count rate, validating our methods for determining the proton count rate. It is observed by the Calorimetric Electron Telescope that both GCR electron and proton count rates at the same average rigidity vary in anticorrelation with the tilt angle of the heliospheric current sheet, while the amplitude of the variation is significantly larger in the electron count rate than in the proton count rate. We show that this observed charge-sign dependence is reproduced by a numerical "drift model" of the GCR transport in the heliosphere. This is a clear signature of the drift effect on the long-term solar modulation observed with a single detector.

Analysis of Galactic Cosmic Ray Anisotropy During the Time Period from 1996 to 2020

We study the influence of drift effects on the galactic cosmic ray anisotropy (GCRA) in different periods of solar activity (from 1996 to 2020) using data from the global network of neutron monitors. We analyze the GCRA in 1996, the last year of Solar Cycle 22 with positive polarity (A>0), Solar Cycles 23 and 24 with both positive (A>0) and negative polarities (A<0), and the 2020 onset of Solar Cycle 25 with positive polarity (A>0). We show that in positive polarity periods, a diffusion model with noticeably manifested drift is acceptable, whereas the diffusion-dominated model of galactic cosmic ray (GCR) transport is more acceptable in negative polarity periods.We found that the average radial component of the drift vector for A>0 practically points to 12 h, and for the A<0 polarity to 24 h, respectively. These results are consistent with the drift theory of modulation of GCRs. According to theory, during positive or negative polarity periods, a drift stream of GCRs is directed away from or toward the Sun, respectively, thus giving rise to long-term changes of the radial component of the GCRA.The calculated magnitudes of the radial and tangential components of the GCRA in different sectors of the heliospheric magnetic field were used to calculate the parameters that characterize the GCR modulation in interplanetary space.

Simulation of Solar Wind Turbulence near Corotating Interaction Regions: Superposed Epoch Analysis of Simulations and Observations

The effect of the turbulence that is associated with solar wind corotating interaction regions (CIRs) on transport of galactic cosmic rays remains an outstanding problem in space science. Observations show that the intensities of the plasma and magnetic fluctuations are enhanced within a CIR. The velocity shear layer between the slow and fast wind embedded in a CIR is thought to be responsible for this enhancement in turbulent energy. We perform physics-based magnetohydrodynamic simulations of the plasma background and turbulent fluctuations in the solar wind dominated by CIRs for radial distances between 0.3 and 5 au. A simple but effective approach is used to incorporate the inner boundary conditions for the solar wind and magnetic field for the periods 2007–2008 and 2017–2018. Legendre coefficients at the source surface obtained from the Wilcox Solar Observatory library are utilized for dynamic reconstructions of the current sheet and the fast and slow streams at the inner boundary. The dynamic inner boundary enables our simulations to generate CIRs that are reasonably comparable with observations near Earth. While the magnetic field structure is reasonably well reproduced, the enhancements in the turbulent energy at the stream interfaces are smaller than observed. A superposed epoch analysis is performed over several CIRs from the simulation and compared to the superposed epoch analysis of the observed CIRs. The results for the turbulent energy and correlation length are used to estimate the diffusion tensor of galactic cosmic rays. The derived diffusion coefficients could be used for more realistic modeling of cosmic rays in a dynamically evolving inner heliosphere.

The importance of Fe fragmentation for LiBeB analyses

Context. High-precision data from AMS-02 on Li, Be, and B provide the best constraints on Galactic cosmic-ray transport parameters. Aims. We re-evaluate the impact of Fe fragmentation on the Li, Be, and B modelling. We discuss the consequences on the transport parameter determination and reassess whether a primary source of Li is needed to match AMS-02 data. Methods. We renormalised several cross-section parametrisations to existing data for the most important reactions producing Li, Be, and B. We used the USINE code with these new cross-section sets to re-analyse Li/C, Be/C, and B/C AMS-02 data. Results. We built three equally plausible cross-section sets. Compared to the initial cross-section sets, they lead to an average enhanced production of Li (∼20 − 50%) and Be (∼5 − 15%), while leaving the B flux mostly unchanged. In particular, Fe fragmentation is found to contribute to up to 10% of the Li and Be fluxes. Used in the combined analysis of AMS-02 Li/C, Be/C, and B/C data, the fit is significantly improved, with an enhanced diffusion coefficient (∼20%). The three updated cross-section sets are found to either slightly undershoot or overshoot the Li/C and B/C ratios: this strongly disfavours evidence for a primary source of Li in cosmic rays. We stress that isotopic cosmic-ray ratios of Li (and to a lesser extent Be), soon to be released by AMS-02, are also impacted by the use of these updated sets. Conclusions. Almost no nuclear data exist for the production of Li and B isotopes from Ne, Mg, Si, and Fe, whereas these reactions are estimated to account for ∼20% of the total production. New nuclear measurements would be appreciated and help to better exploit the high-precision AMS-02 cosmic-ray data.

Prospects for detection of a galactic diffuse neutrino flux

A Galactic cosmic-ray transport model featuring non-homogeneous transport has been developed over the latest years. This setup is aimed at reproducing γ-ray observations in different regions of the Galaxy (with particular focus on the progressive hardening of the hadronic spectrum in the inner Galaxy) and was shown to be compatible with the very-high-energy γ-ray diffuse emission recently detected up to PeV energies. In this work, we extend the results previously presented to test the reliability of that model throughout the whole sky. To this aim, we compare our predictions with detailed longitude and latitude profiles of the diffuse γ-ray emission measured by Fermi-LAT for different energies and compute the expected Galactic ν diffuse emission, comparing it with current limits from the ANTARES collaboration. We emphasize that the possible detection of a Galactic ν component will allow us to break the degeneracy between our model and other scenarios featuring prominent contributions from unresolved sources and TeV halos.

Galactic cosmic rays above the Earth’s atmosphere

AbstractGalactic cosmic rays (GCRs) originate from sources outside the solar system and reach the Earth’s environment from all directions. More than 100 years after the first detection of cosmic rays, the origin of high-energy cosmic rays is still a mystery. Although our knowledge of the origin and propagation of cosmic rays is relatively limited, we can study the radiation conditions in the near-Earth space environment in more detail. The origin, composition, and energy spectra of cosmic rays are briefly discussed in this paper. A brief review of the transport of galactic cosmic rays in the heliosphere is given. The geomagnetic effects on galactic cosmic rays and the atmospheric interactions of primary particles are also discussed in the paper.

The transport of galactic cosmic rays in heliosphere: The HelMod model compared with other commonly employed solar modulation models

HelMod model allows one to describe how solar modulation affects the propagation of galactic cosmic rays (GCRs) through the heliosphere by solving the Parker transport equation. HelMod provides modulated spectra for protons and nuclei during high and low solar activity periods, in the inner and outer heliosphere, at Earth location and outside the ecliptic plane, as well as at different distances from Sun in the inner and outer heliosphere. The GCRs mainly constitute the high-energy population of the so-called space radiation environment. Modulated cosmic-ray spectra of protons and nuclei, obtained from HelMod and other solar modulation codes were compared to the AMS–02 spectra ranging from GeV up to TeV energies. Concerning other commonly used solar modulation models, HelMod modulated spectra are available over the entire rigidity range and observation period of AMS–02 mission. A quantitative comparison among models was carried out using ΔΦ, i.e., the relative difference between the experimental and simulated fluences, and ηRMS, i.e., the error-weighted root mean square of the relative difference between AMS–02 experimental data and simulated differential intensities. HelMod was found to achieve a good agreement over the full set of experimental data with, typically, ΔΦ within ±2.5% and ηRMS within 5%. Usually larger or, in a few cases, much larger values for ΔΦ and ηRMS were found for the other models.

A detailed comparison of techniques used to model drift in numerical cosmic ray modulation models

Drifts have long been known to play a significant role in the transport and modulation of galactic cosmic rays (GCRs), occurring due to gradients in, as well as the curvature of, the heliospheric magnetic field (HMF). GCRs also drift along the wavy current sheet, a structure separating regions of opposite HMF polarity. Furthermore, the influence of drift effects is solar cycle dependent, as can, for example, be seen in the 22-year cycle observed in neutron monitor observations, corresponding to the 22-year HMF polarity cycle. As such, over the previous decades several techniques have been proposed to incorporate these effects into numerical cosmic ray modulation models. The present study compares the effects of employing these techniques, using a 3D, stochastic, ab initio GCR modulation model with a simulated solar cycle dependence. It is found that, for solar minimum conditions, all methods considered yield similar GCR intensities, but that the choice of method becomes significant when heliospheric conditions approaching solar maximum are to be modelled.

INCREASE: An updated model suite to study the INfluence of Cosmic Rays on Exoplanetary AtmoSpherEs

AbstractExoplanets are as diverse as they are fascinating. They vary from ultrahot Jupiter‐like low‐density planets to presumed gas‐ice‐rock mixture worlds such as GJ 1214b or worlds as LHS 1140b, which features twice the Earth's bulk density. Regarding the great diversity of exoplanetary atmospheres, much remains to be explored. For a few selected objects such as GJ1214b, Proxima Centauri b, and the TRAPPIST‐1 planets, the first observations of their atmospheres have already been achieved or are expected in the near future with the launch of the James Webb Space Telescope envisaged in October 2021. However, in order to interpret these observations, model studies of planetary atmospheres that account for various processes—such as atmospheric escape, outgassing, climate, photochemistry, as well as the physics of air showers and the transport of stellar energetic particles and galactic cosmic rays through the stellar astrospheres and planetary magnetic fields—are necessary. Here, we present our model suite INCREASE, a planned extension of the model suite discussed in Herbst, Grenfell, et al. (2019).

Galactic cosmic ray transport in inner heliosphere: Study with ion chamber and neutron monitor data for 1936–2006

Galactic cosmic ray (GCR) solar diurnal variation data recorded by shielded ion chambers at Cheltenham/Fredericksburg (CH-IC) and Yakutsk (Yak-IC) are corrected for diurnal temperature variation in upper atmosphere and used to calculate the ratio α of GCR free paths normal (λ⊥) and parallel (λ||) to mean interplanetary magnetic field (IMF) B for 1936–2006; α is an important parameter in theories for GCR modulations in heliosphere including anisotropies. Also, neutron monitor (NM) data at low latitudes (Huancayo / Haleakala) are analyzed for 1953–2006; they are not affected by temperature variation in upper atmosphere. Calculations assume negligible symmetric latitude GCR density gradient (Gθs) based on observational evidence. Results support Ahluwalia and Modzelewska (2020) inference for global network of NMs and Nagoya vertical muon telescope (NagV-MT) that α depends on polarity of B at Earth orbit. GCR modulation theories quote α values much smaller than those computed by us. Flat heliosphere current sheet (HCS) and Master equations derived by Ahluwalia and Dorman (1997) are used for computing α and study its correlation with solar activity for positive (p) and negative (n) polarity intervals of B at 1 AU; B points outward/ inward from the Sun during p/n interval in northern hemisphere, IMF polarity changes sign near sunspot number (SSN) maximum. The results challenge validity of the conceptual understanding of GCR modulation processes in the heliosphere, pointing to a need for an acceptable theory to explain empirical results reported in this paper. We propose two Ulysses-like spacecrafts be put in a fast scan mode, making complimentary observations in solar north and south hemispheres for at least a complete solar cycle to obtain more precise information about temporal variations of GCR latitude gradients with solar activity and its dependence on GCR rigidity, facilitating a physically meaningful computation of α.

Galactic cosmic ray transport in the heliosphere: Forbush ion chamber data analysis

The study of ratio α (=λ⊥/λ||) of galactic cosmic ray (GCR) free paths normal (λ⊥) and parallel (λ||) to the mean interplanetary magnetic field (IMF) B is continued with annual mean GCR solar diurnal anisotropy (SDA) data of the Cheltenham/Fredericksburg shielded ion chamber (CH-IC) for 1936–1977 previously analyzed by Bieber and Chen (1991) but not corrected for atmospheric temperature effect. This study uses CH-IC data corrected for temperature effect to calculate α for the first time assuming negligible latitudinal density gradient. Solar activity dependence of α shown by Bieber and Chen (BC) remains qualitatively unchanged. Present GCR modulation theories do not provide guidance for α, its rigidity or solar cycle dependence. Flat heliosphere current sheet (HCS) and Master equations derived by Ahluwalia and Dorman (1997) are used for computing α and study its rigidity dependence and correlation with solar activity for positive (p) and negative (n) polarity intervals of B at 1 AU; B points outward/ inward from the Sun during p/n interval in Northern hemisphere, IMF polarity changes sign near sunspot number (SSN) maximum. CH-IC median rigidity of response (Rm) for GCR differential spectrum is 67 GV. We show that computed α is high for p- and low for n-intervals, also α is low near SSN maximum and high near SSN minimum when effective limiting GCR rigidity (Rc) for SDA is known to be <100 GV. The results are consistent with those reported earlier by Ahluwalia and Modzelewska (2020) for NagV-MT (Rm = 60 GV) for 1971–2017; they challenge validity of present conceptual understanding of GCR modulation processes in the heliosphere, pointing to a great need to develop an acceptable modulation theory to explain empirical results reported in this paper.

Superposed Epoch Analysis of Galactic Cosmic Rays and Solar Wind based on ACE Observations During Two Recent Solar Minima

Abstract Based on galactic cosmic ray (GCR) and plasma observations from the ACE spacecraft, in this work, we analyze the relation between the GCR counts and the solar wind parameters during two recent two solar minima (for the years 2007.0–2009.0, and 2016.5–2018.5) by means of the superposed epoch analysis (SEA) method. The results indicate that GCRs are strongly modulated by the co-rotating interaction regions (CIRs) in the solar wind, and that the occurrences of stream interfaces (SIs) between fast and slow solar wind are correlated with a depression in GCR counts. The so-called “snow plow” effect of GCR variation prior to SI crossing appears during the first solar minimum, and the GCR counts decrease after the crossing, corresponding to a sudden drop in the diffusion coefficient at the SIs. The gradient of GCR counts shows that the transport efficiency of GCRs is low (high), relative to slow (fast) solar wind. However, during the second solar minimum, we see a completely opposite scenario; the “snow plow” effect is not observed, and GCR transport becomes faster in slow solar wind, and slower in fast solar wind. In addition, heliospheric current-sheet crossings also correlate with GCR counts. Particles drift along the current sheet, then accumulate in a pileup structure, where diffusion and drift effects may be balanced. It is found that the drift effect rivals the diffusion and convection on the GCR transport at 1 au during the two solar minima.

The impact of astrophysical dust grains on the confinement of cosmic rays

ABSTRACT We argue that charged dust grains could significantly impact the confinement and transport of galactic cosmic rays. For sub-GeV to ∼103 GeV cosmic rays, small-scale parallel Alfvén waves, which isotropize cosmic rays through gyro-resonant interactions, are also gyro-resonant with charged grains. If the dust is nearly stationary, as in the bulk of the interstellar medium, Alfvén waves are damped by dust. This will reduce the amplitude of Alfvén waves produced by the cosmic rays through the streaming instability, thus enhancing cosmic ray transport. In well-ionized regions, the dust damping rate is larger by a factor of ∼10 than other mechanisms that damp parallel Alfvén waves at the scales relevant for ∼GeV cosmic rays, suggesting that dust could play a key role in regulating cosmic ray transport. In astrophysical situations in which the dust moves through the gas with super-Alfvénic velocities, Alfvén waves are rendered unstable, which could directly scatter cosmic rays. This interaction has the potential to create a strong feedback mechanism where dust, driven through the gas by radiation pressure, then strongly enhances the confinement of cosmic rays, increasing their capacity to drive outflows. This mechanism may act in the circumgalactic medium around star-forming galaxies and active galactic nuclei.

Influence of Solar Disturbances on Galactic Cosmic Rays in the Solar Wind, Heliosheath, and Local Interstellar Medium: Advanced Composition Explorer, New Horizons, and Voyager Observations

Abstract We augment the heliospheric network of galactic cosmic ray (GCR) monitors using 2012–2017 penetrating radiation measurements from the New Horizons (NH) Pluto Energetic Particle Spectrometer Science Investigation (PEPSSI), obtaining intensities of ≳75 MeV particles. The new, predominantly GCR observations provide critical links between the Sun and Voyager 2 and Voyager 1 (V2 and V1), in the heliosheath and local interstellar medium (LISM), respectively. We provide NH, Advanced Composition Explorer (ACE), V2, and V1 GCR observations, using them to track solar cycle variations and short-term Forbush decreases from the Sun to the LISM, and to examine the interaction that results in the surprising, previously reported V1 LISM anisotropy episodes. To investigate these episodes and the hitherto unexplained lagging of associated in situ shock features at V1, propagating disturbances seen at ACE, NH, and V2 were compared to V1. We conclude that the region where LISM magnetic field lines drape around the heliopause is likely critical for communicating solar disturbance signals upstream of the heliosheath to V1. We propose that the anisotropy-causing physical process that suppresses intensities at ∼90° pitch angles relies on GCRs escaping from a single compression in the draping region, not on GCRs trapped between two compressions. We also show that NH suprathermal and energetic particle data from PEPSSI are consistent with the interpretation that traveling shocks and corotating interaction region (CIR) remnants can be distinguished by the existence or lack of Forbush decreases, respectively, because turbulent magnetic fields at local shocks inhibit GCR transport while older CIR structures reaching the outer heliosphere do not.

Study of the 27 Day Variations in GCR Fluxes during 2007–2008 Based on PAMELA and ARINA Observations

Abstract Using measurements from the PAMELA and ARINA spectrometers on board the Resurs-DK1 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 gigavolts. 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 GV with a power-law index γ = −0.13 ± 0.44 for PAMELA, whereas for R ≥ 1 GV, the power-law dependence is evident with index γ = −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.