Cosmic Ray Intensity Research Articles

Evolution of planar magnetic structure within the stream interaction region and its connection with a recurrent Forbush decrease

ABSTRACT In general, stream interaction region (SIR)-induced Forbush decreases are recurrent and low magnitude in nature. The diffusion–convection associated with the SIR plays an important role in their modulation. Here, we study the evolution of planar magnetic structure (PMS) within the SIR and its contribution to cosmic ray modulation. Interestingly, we found the presence of PMS structures within the SIR from the leading part of the SIR to the minimum of the cosmic ray intensity in two events. The PMS may have originated due to the high compression caused by the fast solar wind, which amplifies and aligns the pre-existing discontinuities in the ambient slow solar wind. The study also suggests that the existence of PMS, enhanced initial mass function (IMF) strength, and associated turbulent regions decreases the perpendicular diffusion coefficient and causes a decrease in the cosmic ray intensity observed on Earth. Moreover, a slow decrease in IMF magnitude concurs with the recovery phase of cosmic ray intensity.

Ring of Stations Method in Cosmic Rays Variations Research

For over 60 years, neutron monitors have been the main standard and high precision detectors for measuring cosmic rays with energy from 400 MeV to hundreds GeV. In order to obtain sufficiently complete information about the distribution of cosmic rays outside the magnetosphere, it is necessary to have a network of detectors spaced evenly enough around the globe. The ring of stations method is one of the most useful methods for studying the properties of the angular distribution of cosmic rays without expressing the cosmic ray intensity in terms of spherical harmonics. The method allows one to get the hourly longitude distribution of the cosmic ray intensity without modeling. The main objective of this work is to expand the use of the ring of stations method, as it is a convenient and useful method of studying cosmic ray variation. Using the ring of stations method, it is possible to study specific angular distributions of cosmic ray variation that are described poorly by the sum of the first spherical harmonics. The ring of stations method is primarily used to study Forbush decreases. Detailed descriptions of Forbush decrease investigation by the ring of stations method are presented in this study. The application of the method to the study of the precursors of Forbush decreases and cosmic rays behavior inside the solar wind disturbances is shown.

Modulation of Galactic Cosmic Rays by Plasma Disturbances Propagating Through the Local Interstellar Medium in the Outer Heliosheath

Abstract The modulation of cosmic rays by a propagating plasma disturbance, a global merged interaction region (GMIR), in the heliosheath is simulated using a Vlasov–Fokker–Planck equation for the transport of energetic particles with significant anisotropy. The prescribed plasma structure of the GMIR contains a shock front and plasma rarefaction region behind the shock, which propagate through a simplified paramagnetic shielding model of the heliosheath. When a GMIR goes through the heliospheric magnetic field in the inner heliosheath, its modulation effects on cosmic rays are consistent with typical Forbush decreases. When a GMIR goes through the interstellar magnetic field in the outer heliosheath, only cosmic rays with large pitch angles with respect to the magnetic field vector (cosine values close to zero) are modulated by it. The difference is due to the very weak scattering of particles by the interstellar turbulence. Particles trapped in the rarefied magnetic field inside a GMIR suffer a significant amount of adiabatic cooling, which results in a considerable intensity decrease and a bidirectional anisotropy. The simulation result can be used to explain what Voyager 1 observed in the very local interstellar medium. Depending on the strength of plasma compression inside a GMIR, some cosmic rays may be accelerated, but the GMIR effect on the cosmic-ray intensity is much weaker than that due to adiabatic cooling because particles have only a brief interaction with a GMIR without trapping.

Effects of solar activity on production rates of short‐lived cosmogenic radionuclides

AbstractThe solar activity can be quantified by solar modulation parameter Φ that affects the heliospheric magnetic field. This activity influences the intensity of the galactic cosmic ray (GCR) particle flux within the solar system, and consequently, the differential primary particle spectra depend on the solar modulation parameter Φ (MeV). The modulation parameter Φ shows spatial and temporal variations (Leya and Masarik 2009). Some of the solar activity variations are cyclic and result in measurable effects as for example the 11‐year solar cycle. Variations in solar activity only induce small effects on the production of long‐lived cosmogenic radionuclides. This is due to the fact that activities measured in meteorites usually correspond to saturation values and represent long‐term average values. Long‐lived radionuclides often require millions of years of irradiation by GCR to reach saturation and therefore activity cycles average out. In contrast, one can expect strongly pronounced variations for saturation values caused by primary flux intensity variations, if short‐lived radionuclides with half‐lives ranging from days to a few years are investigated. Short‐lived cosmogenic nuclides were the subject of many experimental and theoretical investigations (e.g., Evans et al. 1982; Spergel et al. 1986; Neumann et al. 1997; Komura et al. 2002; Laubenstein et al. 2012). The aim of this work is to develop formulae for calculating production rates of radionuclides with short half‐life, taking into account temporal variations in the primary cosmic ray intensity. The developed formulae were applied to the Kosice and Chelyabinsk meteorites. The results for the Košice meteorite were already published (Povinec et al. 2015). Here, we give a full explanation of underlying model.

The Distribution Function of Cosmic Rays at the Initial Stage of a Solar Proton Event

The propagation of solar cosmic rays in the interplanetary medium is considered on the basis of the kinetic equation describing the small-angle multiple scattering of charged particles. Energetic particles are assumed to be injected into the interplanetary medium by an instantaneous point-like source. The spatial-temporal distribution of the density and anisotropy of high-velocity particles during the anisotropic phase of a burst of solar cosmic rays is studied. An analytical expression for the distribution function of cosmic rays in the small-angle approximation is derived; the evolution of the angular distribution of energetic particles is investigated. It has been shown that, under weak scattering of charged energetic particles on fluctuations of the interplanetary magnetic field, the intensity of solar cosmic rays impulsively increases at the initial stage of their enhancement. The anisotropy in the angular distribution of solar cosmic rays monotonously decreases with time and exhibits the highest value at the moment of the first particles' arrival to a given point of space.

Modeling the Time Delay Problem of Galactic Cosmic Ray Flux in Solar Cycles 21 and 23

We present a 2-dimensional time-dependent simulation based on Parker’s transport equation (PTE) describing the propagation of energetic astroparticles – cosmic rays (CR) in the heliosphere. PTE is a second order partial differential equation containing four major processes: diffusion, convection, drift, and adiabatic cooling responsible for modulation of the CR flux in the heliosphere. We implement in the numerical simulation, a few physical parameters as the tilt angle, delta , of the heliospheric current sheet (HCS), module, B, of the interplanetary magnetic field (IMF), and variations of drift effect of the CR particles with solar activity (SA). Our approach is the implementation of two independent parameters (proxies), gamma and nu . The parameters gamma and nu are calculated from various independent sources, gamma , from neutron monitors (NM) daily data, and nu , using the IMF hourly data. The solutions of PTE obtained from our numerical model are compared with the variations of the CR flux recorded by NMs. We prove the existence of a varying delay time (DT) between the changes of galactic cosmic ray (GCR) intensity and the parameters characterizing SA. Based on our investigation, we obtained different DTs in Solar Cycles 21 and 23. We conclude that the calculated DTs, after comparison with the observed DTs, are useful parameters for the study of GCR transport in the heliosphere.

A Fully Time-dependent Ab Initio Cosmic-Ray Modulation Model Applied to Historical Cosmic-Ray Modulation

Abstract Cosmogenic nuclide records can in principle allow for the estimation of the behavior of the heliospheric magnetic field (HMF) in the distant past. This requires careful modeling of cosmic-ray transport in a manner that is as realistic as possible, taking into account as many of the factors affecting the transport of cosmic-rays (CRs) as possible. The present study presents a 3D time-dependent ab initio CR modulation code that utilizes as inputs simple theoretically and observationally motivated temporal profiles to model large-scale (such as the tilt angle) and small-scale (such as the magnetic variance) parameters relevant to CR transport. Galactic CR proton differential intensities computed using this model for the period 1977–2001 are in reasonable to good agreement with spacecraft observations, reproducing the major salient features of the observed CR intensity temporal profile. To investigate pre-space-age cosmic-ray modulation, and to test conclusions previously drawn regarding the relative importance of drift effects on said modulation, historic estimates of the past HMF presented by McCracken & Beer were used as inputs for the model. The resulting CR temporal intensity profile displays clear evidence of drift effects, with a sharp peak in intensities during the Dalton Minimum.

Electron-positron annihilation ray deduction for airborne gamma-ray spectrometry

In nuclear accidents, airborne gamma-ray spectrometry is used to monitor the radioactive cloud. As the radioactive cloud diffused at the height of 750 m–2500 m, the airborne gamma-ray spectrum is affected by electron-positron annihilation. This study established the relationship between electron-positron annihilation ray and cosmic ray by analyzing and processing the experimental data. Therefore, based on the cosmic ray intensity, the contribution of electron-positron annihilation can be estimated and removed. The correction method can improve the accuracy of radioactive cloud monitoring in the early stage of the nuclear power station accidents and nuclear explosion for airborne gamma spectrometer.

Cosmic-ray interactions with the Sun using the fluka code

The interactions of cosmic rays with the solar atmosphere produce secondary particle which can reach the Earth. In this work we present a comprehensive calculation of the yields of secondary particles as gamma-rays, electrons, positrons, neutrons and neutrinos performed with the FLUKA code. We also estimate the intensity at the Sun and the fluxes at the Earth of these secondary particles by folding their yields with the intensities of cosmic rays impinging on the solar surface. The results are sensitive on the assumptions on the magnetic field nearby the Sun and to the cosmic-ray transport in the magnetic field in the inner solar system.

Solar Rotational Oscillation and Its Subharmonics in Solar Wind Plasma Field, Geomagnetic, and Cosmic Ray Intensity Indicator in the Solar Cycle 24/25 Minimum

AbstractTo study synodic period and its subharmonics, we have utilized hourly average data of solar wind plasma field, geomagnetic index, and galactic cosmic ray intensity along with 5 min average data of selected solar wind field parameters during the recent minimum of Solar Cycle 24. Wavelet analyses of hourly average data reveal 28.1, 13.1, and 6.8 day of sigma in interplanetary magnetic field; 27.1, 13.1, and 9.0 day of plasma speed; 27.1, 13.6, 3.9, and 2.2 day of interplanetary electric field; 27.1, 13.6, 3.8, and 2.2 day of southward component of magnetic field; 26.2, 13.6, 8.6, and 3.0 day of geomagnetic Ap index; and 28.1, 11.0, 9.3, 7.0, and 1.6 day periods of galactic cosmic ray intensity. In addition to these prominent short‐term periods, we have significantly observed 6.6, 3.3, and 1.7 day periods of sigma in interplanetary magnetic field (σB); 5.6, 4.2, and 2.2 day of electric field (Ey) and 5.6, 3.3, and 2.4 day of southward component of magnetic field (Bz) in the 5 min average data. During the recent solar minimum, we have observed one solar rotational period and its second, third, fourth, fifth, sixth, seventh, eighth, tenth, eleventh, and twelfth subharmonics. The observed subharmonics of solar rotational period make the current solar minimum very special and noteworthy to study.

INVESTIGATING THE INFLUENCE OF GEOMETRY OF THE HELIOSPHERIC NEUTRAL CURRENT SHEET AND SOLAR ACTIVITY ON MODULATION OF GALACTIC COSMIC RAYS WITH A METHOD OF MAIN COMPONENTS

The work studies the cumulative modulating effect of the geometry of the interplanetary magnetic field's neutral current sheet and solar activity on propagation of galactic cosmic rays in the heliosphere. The role of each factor on the modulation of cosmic rays is estimated using a method of main components. The application of the method to experimental data on solar activity, to the tilt angle of the neutral sheet, and cosmic ray intensity for a long period from 1980 to 2018 allows us to reveal the temporal dynamics of roles of these factors in the modulation. The modulation character is shown to strongly depend on the polarity of the Sun’s general magnetic field. Results of the study confirm the existing theoretical concepts of the heliospheric modulation of cosmic rays and reflect its peculiarities for almost four full cycles of solar activity.

Effect of Thunderstorm Electric Field on the Cosmic Ray Secondary Particle Energy at LHAASO

The Large High Altitude Air Shower Observatory (LHAASO) is located in Daocheng, Sichuan. Featured with frequent thunderstorms in summer seasons, it is beneficial to study the influence of atmospheric electric field on cosmic rays during thunderstorms. In this paper, Monte-Carlo simulations are performed to study the effect of thunderstorm electric field on the cosmic ray secondary electron energy at LHAASO. The energy distribution of electrons changes under the action of electric field. In the low energy region, the total number of electrons increases significantly, while at high energies, it does not change obviously. In the electric field of 1700V·cm−1 (above the critical field of the Relativistic Runaway Electron Avalanche (RREA) process), the electrons with an energy less than 120MeV can be accelerated. When the energy is below 60MeV, the number of electrons increases exponentially with an amplitude up to about 2252%. It is consistent with the theory of RREA. When the electric field strength is 1000V·cm−1 (below the threshold of the RREA process), the electrons with an energy less than 70MeV are accelerated, and their number increases significantly, but the increase (about 86%) is far lower than that of the critical field of the RREA process. The physical mechanism for accelerating the cosmic ray secondary particles by the thunderstorm electric field is discussed in the case when the electric field is less than the runaway electric field. These results may provide important information for studying the variations of cosmic ray intensity on the LHAASO detection surface during thunderstorms.

Исследование методом главных компонент влияния геометрии нейтрального токового слоя гелиосферы и солнечной активности на модуляцию галактических космических лучей

The work studies the cumulative modulating effect of the geometry of the interplanetary magnetic field's neutral current sheet and solar activity on propagation of galactic cosmic rays in the heliosphere. The role of each factor on the modulation of cosmic rays is estimated using a method of main components. The application of the method to experimental data on solar activity, to the tilt angle of the neutral sheet, and cosmic ray intensity for a long period from 1980 to 2018 allows us to reveal the temporal dynamics of roles of these factors in the modulation. The modulation character is shown to strongly depend on the polarity of the Sun’s general magnetic field. Results of the study confirm the existing theoretical concepts of the heliospheric modulation of cosmic rays and reflect its peculiarities for almost four full cycles of solar activity.

Responses and Periodic Variations of Cosmic Ray Intensity and Solar Wind Speed to Sunspot Numbers

To investigate the periodic behaviour and relationship of sunspot numbers with cosmic ray intensity and solar wind speed, we present analysis from daily data generated from 1995 January to 2018 December. Cross-correlation and wavelet transform tools were employed to carry out the investigation. The analyses confirmed that the cosmic ray intensity correlates negatively with the sunspot numbers, exhibiting an asynchronous phase relationship with a strong negative correlation. The trend in cosmic ray intensity indicates that it undergoes the 11-year modulation that mainly depends on the solar activity in the heliosphere. On the other hand, the solar wind speed neither shows a clear phase relationship nor correlates with the sunspot numbers but shows a wide range of periodicities that could possibly be connected to the pattern of coronal hole configuration. A number of short and midterm variations were also observed from the wavelet analysis, i.e., 64–128 and 128–256 days for the cosmic ray intensity, 4–8, 32–64, 128–256, and 256–512 days for the solar wind speed, and 16–32, 32–64, 128–256, and 256–512 days for the sunspot numbers.

Study of the Cosmic Rays and Interstellar Medium in Local H i Clouds Using Fermi-LAT Gamma-Ray Observations

Abstract An accurate estimate of the interstellar gas density distribution is crucial to understanding the interstellar medium (ISM) and Galactic cosmic rays (CRs). To comprehend the ISM and CRs in a local environment, a study of the diffuse γ-ray emission in a midlatitude region of the third quadrant was performed. The γ-ray data in the 0.1–25.6 GeV energy range of the Fermi Large Area Telescope (LAT) and other interstellar gas tracers such as the HI4PI survey data and the Planck dust thermal emission model were used, and the northern and southern regions were analyzed separately. The variation of the dust emission with the total neutral gas column density was studied in high dust temperature areas, and the / ratio was calibrated using γ-ray data under the assumption of a uniform CR intensity in the studied regions. The measured integrated γ-ray emissivities above 100 MeV are and in the northern and southern regions, respectively, supporting the existence of a uniform CR intensity in the vicinity of the solar system. While most of the gas can be interpreted to be with a spin temperature of or higher, an area dominated by optically thick with was identified.

Delineation of possible influence of solar variability and galactic cosmic rays on terrestrial climate parameters

The present paper has investigated the associations of solar activity (SA), represented by total solar irradiance (TSI), galactic cosmic rays (GCR) and terrestrial climate parameters in particular the global cloudiness and global surface temperature. To that end, we have analysed thirty five years (1983–2018) data of these parameters and have applied the Granger-causality test in order to assess whether there is any potential predictability power of one indicator to the other. The correlations among the involved parameters are tested using Vector Auto Regression (VAR) model and variance decomposition method. As a result of the above analysis, we have found that the TSI is an important factor and has contributed about 8.77 ± 0.42% in the cosmic ray intensity variations. In case of cloud cover variations, the other three parameters (TSI, cosmic ray and global surface temperature) have played a significant role. Further, the TSI changes have contributed 1.68 ± 0.03% fluctuations in the variance of the cloud cover while the cosmic ray intensity and global surface temperature have contributed about 4.89 ± 0.08% and 10.87 ± 1.41% respectively. In case of the global surface temperature anomaly both TSI and cloud covers have contributed about 5.07 ± 0.47% and 14.42 ± 2.13% fluctuations respectively. Additionally, we have also assessed the impact of internal climate oscillations like multivariate ENSO index (MEI), north Atlantic oscillations (NAO) and quasi biennial oscillations (QBO) on cloud cover variations. The contribution of these internal oscillations e.g. ENSO, NAO and QBO in cloud cover variation were reported as 7.48 ± 1.02%, 5.51 ± 0.16% and 1.36 ± 0.43% respectively.

Prolonged production of 14C during the ~660 BCE solar proton event from Japanese tree rings

Annual rings record the intensity of cosmic rays (CRs) that had entered into the Earth’s atmosphere. Several rapid 14C increases in the past, such as the 775 CE and 994CE 14C spikes, have been reported to originate from extreme solar proton events (SPEs). Another rapid 14C increase, also known as the ca. 660 BCE event in German oak tree rings as well as increases of 10Be and 36Cl in ice cores, was presumed similar to the 775 CE event; however, as the 14C increase of approximately 10‰ in 660 BCE had taken a rather longer rise time of 3–4 years as compared to that of the 775 CE event, the occurrence could not be simply associated to an extreme SPE. In this study, to elucidate the rapid increase in 14C concentrations in tree rings around 660 BCE, we have precisely measured the 14C concentrations of earlywoods and latewoods inside the annual rings of Japanese cedar for the period 669–633 BCE. Based on the feature of 14C production rate calculated from the fine measured profile of the 14C concentrations, we found that the 14C rapid increase occurred within 665–663.5 BCE, and that duration of 14C production describing the event is distributed from one month to 41 months. The possibility of occurrence of consecutive SPEs over up to three years is offered.

Forbush-storm classification of the events as a device for the solar wind diagnostics

The geoeffectiveness of the solar wind is usually determined on Earth by such phenomena in the geomagnetic field as storms and substorms. The second, no less significant effect is a sharp decrease in the intensity of galactic cosmic rays (GCR) Forbush effects. A joint examination of these effects in the geomagnetic field and in the GCR makes it possible to obtain additional diagnostic features, since they carry different information. The behavior of the geomagnetic field reflects changes in the magnetosphere, while the GCR intensity depends on the spatial configuration of the magnetic field in the heliosphere. To carry out such work, it is proposed to use the Forbush-Storm classification — a catalog of geophysical events in the geomagnetic field and cosmic rays. The catalog shows the dates and time of the beginning of the events of a decrease in the Dst geomagnetic field index and in GCR intensity from 1996 to 2017, for 2 cycles of solar activity. It is shown that these two types of terrestrial manifestations of interplanetary disturbances can occur simultaneously or separately.

Ring of Station Method in Research of Cosmic Ray Variations: 1. General Description

For over 60 years, neutron monitors have remained the main standard, stable instrument for the measurement of cosmic rays with energies from 400 MeV to hundreds of GeV. In order to obtain sufficiently complete information about the distribution of cosmic rays outside the magnetosphere, it is necessary to have a network of detectors that are fairly evenly spaced around the globe. One of the most useful methods to obtain the properties of the angular distribution of cosmic rays without decomposition into harmonics is the ring of station method. It allows one to obtain the instantaneous (more precisely, hourly) longitudinal distribution of the intensity of cosmic rays without its modeling. The main goal of this work is to expand the use of the ring of station method, a convenient and useful method for the study of cosmic ray variations.

Temporal and Spatial Variations of Cosmogenic Radionuclide Production Rates in Chondrites During Their Passage Through the Inner Heliosphere

To study radiation environment in the interplanetary space, cosmogenic radionuclides in meteorites, the production rates of which are in direct proportionality to the intensity of cosmic rays, are used. The contents of cosmogenic radionuclides of different half-lives T1/2, measured in 42 stony meteorites (chondrites) having sequentially fallen onto the Earth during the period of 1959–2016, are analyzed. They are accumulated by the galactic cosmic rays (GCRs) along the orbits of the chondrites before their falls onto the Earth at some average heliocentric distances, depending on the size of the chondrite orbit and on T1/2 of the radionuclide. The comparison with the calculated production rates of radionuclides in the identical chondrites for isotropic irradiation by the GCRs at ~ 1 AU is demonstrated. The calculations are based on the stratospheric balloon monthly data on the GCR intensity [1] for the periods of accumulation of each radionuclide in each chondrite. The dependence of production rates of the radionuclides of different half-lives upon the GCR variations in the heliosphere is studied. The obtained long set of homogeneous data on cosmogenic radionuclide production rates in consecutively fallen chondrites provides the unique information on the space-time continuum of the cosmogenic radionuclide production rates and their variations over a long-time scale, which could be useful in the correlative analyses of processes in the inner heliosphere and, thus, in the forecast of radiation situation, which is important for the predicted manned flights.