Angular Distribution Of Cosmic Rays Research Articles

Small-scale Anisotropies of Cosmic Rays from Turbulent Flow

Within the classical convection–diffusion approximation, we show that the angular distribution of cosmic rays (CRs) in a highly turbulent flow may exhibit significant small-scale anisotropies. The CR intensity angular power spectrum C ℓ is then a direct reflection of interstellar turbulence, from which one expects C ℓ ∝ ℓ −γ−1 for ℓ ≫ 1, where γ is the power-law turbulence spectral index. Observations by IceCube and HAWC at TeV energies can be explained approximately with the Kolmogorov law γ = 5/3 with a convection velocity dispersion of 20 km s−1 on the scale of 10 pc.

Peculiarities of sporadic variations in density and anisotropy of galactic cosmic rays in solar cycle 24

In this work, we have processed data from the global network of neutron monitors and muon telescopes by the global survey method to study variations in the density and anisotropy of galactic cosmic rays during Forbush decreases observed in solar cycle 24. The simultaneous use of two different type detectors made it possible to examine the temporal dynamics of the angular distribution of cosmic rays in two different energy intervals. Besides, we have used measurements of the Yakutsk cosmic ray spectrograph after A.I. Kuzmin to assess the energy spectrum index during large disturbances of the interplanetary medium in this cycle. Analysis of the results obtained confirms our early statements that solar activity cycle 24 features an increased level of turbulence in the interplanetary magnetic field.

Особенности спорадических вариаций плотности и анизотропии галактических космических лучей в 24-м цикле солнечной активности

In this work, we have processed data from the global network of neutron monitors and muon telescopes by the global survey method to study variations in the density and anisotropy of galactic cosmic rays during Forbush decreases observed in solar cycle 24. The simultaneous use of two different type detectors made it possible to examine the temporal dynamics of the angular distribution of cosmic rays in two different energy intervals. Besides, we have used measurements of the Yakutsk cosmic ray spectrograph after A.I. Kuzmin to assess the energy spectrum index during large disturbances of the interplanetary medium in this cycle. Analysis of the results obtained confirms our early statements that solar activity cycle 24 features an increased level of turbulence in the interplanetary magnetic field.

Method of global survey involving data of muon telescope network

In 1967, the Yu.G. Shafer Institute of Cosmophysical Research and Aeronomy developed a global survey method that allowed application of the global network of neutron monitors as a single device, simultaneously oriented to various directions and providing information on distribution of cosmic rays per each measured moment. By analogy with this approach, a method for calculation of anisotropy parameters of high-energy cosmic rays has been proposed, involving measurement data from the Global Muon Detector Network and Yakutsk stations. To implement the method, receiving vectors of the stations have been calculated, making it possible to consider associations between cosmic ray variations in the interplanetary medium and those observed at Earth. The paper also discusses some methodological issues related to correct determination of angular distribution of cosmic rays in the interplanetary space. Based on the modified method of global survey, parameters of the first two moments of the angular distribution of cosmic rays for 2012–2018 have been calculated.

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.

GALACTIC COSMIC RAY ANISOTROPY MODELLING

We calculate the angular distribution of cosmic rays at a given point of the heliosphere under the assumption that the incoming flux from outer space is isotropic. The static magnetic field is shown to cause no anisotropy provided that the observation point is situated out of the trapped particle area. We consider a coronal ejection model in the form of a static cylinder with an axial homogeneous magnetic field inside. We calculate angular distribution samples in the trapped particle area (inside the cylinder) and show that there is a certain cone of directions with a reduced flux. For the same model with the moving cylinder, the angular distribution samples are calculated for different positions of the observation point outside the cylinder. Anisotropy of order of the ejection to light velocity ratio is shown to arise. The calculated samples are in qualitative agreement with URAGAN muon hodoscope data.

Моделирование анизотропии галактических космических лучей

We calculate the angular distribution of cosmic rays at a given point of the heliosphere under the assumption that the incoming flux from outer space is isotropic. The static magnetic field is shown to cause no anisotropy provided that the observation point is situated out of the trapped particle area. We consider a coronal ejection model in the form of a static cylinder with an axial homogeneous magnetic field inside. We calculate angular distribution samples in the trapped particle area (inside the cylinder) and show that there is a certain cone of directions with a reduced flux. For the same model with the moving cylinder, the angular distribution samples are calculated for different positions of the observation point outside the cylinder. Anisotropy of order of the ejection to light velocity ratio is shown to arise. The calculated samples are in qualitative agreement with URAGAN muon hodoscope data.

Investigation of the cosmic ray angular distribution and the East–West effect near the top of Etna volcano with the MEV telescope

An experimental investigation of cosmic muons has been carried out with the Muography of Etna Volcano (MEV) tracking telescope, installed at an altitude of about 3100 m a.s.l. in front of the North-East Etna crater. The analysis of a statistically significant data sample ($$\sim 10^7$$ events), taken during a period of approximately 2 months, has been carried out to investigate the angular distribution of cosmic muons originating both from the open sky side and from a large solid rock thickness (Etna side). Due to the geographical orientation of the MEV telescope, anisotropies caused by the East–West effect could also be observed, extracting the asymmetry factor in small steps of the zenithal angle.

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.

Monitoring of geomagnetic disturbances using the global survey method in real time

A method for forecasting geomagnetic storms using the realization of the global survey method in real time is presented. The method is based on data from the worldwide network of neutron monitors NMDB. Using this method, we analyze the behavior of components of three-dimensional angular distribution of cosmic rays in the interplanetary medium, which were due to the first two spherical harmonics, over the period from 2013 to 2018. We have established that the main parameters that respond to the arrival of geoeffective disturbances of the interplanetary medium at Earth are changes in amplitudes of zonal (north-south) components of cosmic ray distribution. In order to select effective criteria for identifying predictors of geomagnetic disturbances and their possible temporal variations, we have made a retrospective analysis of the relationship between behaviors of the above components and geomagnetic disturbances occurring during the period of interest.

Мониторинг геомагнитных возмущений на основе метода глобальной съемки в реальном времени

A method for forecasting geomagnetic storms using the realization of the global survey method in real time is presented. The method is based on data from the worldwide network of neutron monitors NMDB. Using this method, we analyze the behavior of components of three-dimensional angular distribution of cosmic rays in the interplanetary medium, which were due to the first two spherical harmonics, over the period from 2013 to 2018. We have established that the main parameters that respond to the arrival of geoeffective disturbances of the interplanetary medium at Earth are changes in amplitudes of zonal (north-south) components of cosmic ray distribution. In order to select effective criteria for identifying predictors of geomagnetic disturbances and their possible temporal variations, we have made a retrospective analysis of the relationship between behaviors of the above components and geomagnetic disturbances occurring during the period of interest.

The Distribution Function of Solar Cosmic Rays under Prolonged Particle Injection

Abstract—The propagation of solar cosmic rays (SCR) in the interplanetary medium is considered on the basis of the Fokker–Planck kinetic equation. It is known that the SCR distribution function averaged over a solar proton event contains valuable data on the scattering process for energetic charged particles by interplanetary magnetic fields. A steady-state solution for the kinetic equation in the small-angle approximation is obtained, and the dependence of the angular distribution function of cosmic rays on the distance to the particle source is examined. This solution is applicable if the distance to the particle source is short compared to the mean free path of cosmic rays and if particles are moving primarily in the radial direction. The angular distribution of particles at large (compared to the mean free path of cosmic rays) distances to the particle source is also analyzed. An analytical expression for the distribution function of cosmic rays in the form of a sum of an isotropic component and a small anisotropic one is derived. It is demonstrated that the angular distribution of cosmic rays depends to a considerable extent on the anisotropy of their scattering. The scattering characteristics of energetic charged particles by fluctuations of interplanetary magnetic fields are estimated based on observational data for several SCR flares.

Investigation of mechanisms of formation of the second spherical harmonics of the galactic cosmic ray angular distribution

Mechanisms of formation of a second spherical harmonic of an angular distribution of galactic cosmic rays in the heliosphere are investigated. On the basis of data of Nagoya multidirectional muon telescope using a method of tensor anisotropy of cosmic rays time courses of symmetric diurnal, antisymmetric diurnal and semidiurnal variations of cosmic rays were obtained for the period 1971-2017. An abrupt offset of a phase of the semidiurnal variation to the earlier time during a positive polarity of the general magnetic field of the Sun, which closely correlates with the temporal change of a phase of the symmetric diurnal variations. It was shown the existence of annual variations of the tensor anisotropy components, which can be satisfactorely described by a single modulation factor - a screening of cosmic rays by the sector-structured interplanetary magnetic field. Moreover, the theory indicates on the existense of a stable north-south asymmetry of the interplanetary magnetic field - shift of the neutral current sheet to the south of solar equator.

Angular distribution of cosmic rays from an individual source in a turbulent magnetic field

We obtain the angular distribution of the cosmic rays reaching an observer from an individual source and after propagation through a turbulent magnetic field, for different ratios between the source distance and the diffusion length. We study both the high-energy quasi-rectilinear regime as well as the transition towards the diffusive regime at lower energies where the deflections become large. We consider the impact of energy losses, showing that they tend to enhance the anisotropy of the source at a given energy. We also discuss lensing effects, in particular those that could result from the regular galactic magnetic field component, and show that the effect of the turbulent extragalactic magnetic fields can smooth out the divergent magnification peaks that would result for point-like sources in the limit of no turbulent deflections.

Features of cosmic ray modulation in October and November 2003

Using data from the worldwide network of cosmic ray stations, Forbush decreases on October 29–31 and November 20–21, 2003 were studied using method of spectrographic global survey. The indices of the variation spectrum for the power representation of the particle magnetic rigidity over the range of 10–50 GV are given for different stages of the development of Forbush decreases, which proved to be greater for the event on November 20–21 than for the one on October 29–31, 2003. A high degree of anisotropy in the angular distribution of cosmic rays in the Forbush decrease periods and its phase variability indicate the dispersal of magnetic clouds and the high degree of regularity of the interplanetary magnetic field (IMF) in these structures; the presence of bidirectional anisotropy suggests a loop structure of the IMF during the events of October 29, 2003.

Cosmic ray angular distribution employing plastic scintillation detectors and flash-ADC/FPGA-based readout systems

Abstract It is known that secondary cosmic rays are high energetic particles which are products of shower particles, when primary cosmic rays from outer space hit the atmosphere molecules. Many studies of cosmic rays show that cosmic flux depends on the depth of atmosphere. At ground level, most secondary cosmic rays are muons, a type of charged particle, and have angular dependence. The purpose of this article was to develop the telescope with two plastic scintillation detectors to investigate the angular distribution of cosmic rays at ground level. Directions of investigation were carried out vertical, 45-degree oblique and horizontal directions with respect to earth surface, approximately from North to South. Electronic readout system was developed from Flash Analog Digital Converter (Flash-ADC) of 8 bits-250Ms/sec, and Embedded Field Programmable Gate Array (FPGA)-based trigger. LabVIEWTM interface was written for controlling trigger system and taking data. For each direction measurement, the deposited energy spectra in the scintillators were obtained. The interest of cosmic-ray events was analyzed for counting. Angular distribution was obtained quantitatively. The experiment has been done at University of Science-HCMC.

Cosmic ray anisotropy based on Yakutsk station in real time

The method has been developed to calculate galactic cosmic ray anisotropy parameters by using on-line data of the neutron monitor 24-NM-64 and muon telescope at the Yakutsk station. The preliminary analysis shows that characteristic changes in the anisotropy parameters caused by the first spherical harmonics of cosmic ray angular distribution are observed 1–2 days before the onset of the most part of large-scale geophysical disturbances on the Earth. There is reason to believe that the attraction of data of geophysical observations of other kinds will allow to develop the forecast methods for the arrival of large-scale interplanetary disturbances at the Earth.

Generalised 3D-reconstruction method of a dipole anisotropy in cosmic-ray distributions

We develop a method to study the anisotropy of a cosmic-ray angular distribution, using both the right ascension and the declination of the arrival directions. It generalises the full-sky coverage method of Sommers (2001) to partial-sky coverage experiments. When the angular distribution consists of a dipolar modulation of an otherwise isotropic flux, the method allows one to reconstruct the dipole amplitude and the dipole orientation in 3D space. We analyse in detail the statistical properties of the method, introducing the concept of reconstruction power, and show that it is generally more powerful than the standard Rayleigh analysis in right ascension. We clarify the link between the traditionally-used first harmonic amplitude and the true, physical dipole amplitude, and we investigate the variation of the reconstruction powers as a function of the dipole orientation. We illustrate the method by computing the amplitude and angular reconstruction powers of the Pierre Auger Observatory, with the Southern site alone and with both Southern and Northern sites. In this particular case, we find that the building of a similar site in the Northern hemisphere would decrease the time needed for the method to reveal a significant departure from an isotropic cosmic-ray distribution by a factor of about eight.

Monte Carlo calculation of the angular distribution of cosmic rays at flight altitudes

The angular distribution of the secondary radiation produced by the galactic component of cosmic rays has been determined by simulating the penetration of the primary spectra in the Earth's atmosphere. The simulations have been carried out with the latest version of the FLUKA code. Particles have been scored at various altitudes according to their angle of incidence for some significant values of vertical cut-off rigidity and solar modulation parameter. The calculated results at typical cruise altitudes for a civil aircraft are presented. The data at 10.7 km have been fitted with simple mathematical equations. It has been demonstrated that the major contribution to the doses at aviation altitudes arises from downward-directed particles. The isotropic irradiation usually assumed for the evaluation of aircrew exposure could be a very poor approximation.

Background components of Ge detectors in Ogoya underground laboratory

Ogoya underground laboratory, (OUL; 270 m water equivalent), has 5 well, 4 planar, and 1 coaxial-type ultra-low background Ge detectors with passive shield of old lead. An anticoincidence system with a plastic scintillator (PS) has been tested to reduce cosmic-ray-induced background. Energy spectra of PSs, coincidence counting rate, and angular distribution of cosmic rays were studied. Based on this study, we propose a new index of Ge surface area-normalized background counting rate (d −1 cm −2) to compare shielding efficiency between different types of Ge detectors.