Cutoff Rigidity Research Articles

Simulation of cosmic rays inside an aircraft: spectral perturbation and dose reduction due to aircraft structures and contents.

In this study, an intricate combinatorial geometry model of a Boeing 777-300ER aircraft was constructed for Monte Carlo transport simulations. The aircraft-induced perturbations of the energy spectra and effective doses of secondary cosmic rays at a typical civil aviation altitude (10km) were investigated on a component-by-component basis, which included neutrons, protons, photons, electrons, positrons, muons and charged pions. Two geomagnetic cutoff rigidities (1.35 and 15.53 GV) and two solar modulation parameters (430 and 1360 MV) were considered in the aforementioned simulations. The characteristics of various cosmic-ray components at six locations along the fuselage were assessed and compared with those of an unperturbed radiation field in the atmosphere. Aircraft structures and contents reduced the effective doses of personnel inside the aircraft to varying degrees, up to an ~32% reduction in the middle section of the passenger cabin. On average, the dose reduction was ~12-16% depending on geomagnetic and solar conditions. Quantifying the aircraft's self-shielding effects can further improve the estimation accuracy of aircrew and passengers' exposure to cosmic radiation. Information regarding the perturbed energy spectra of cosmic rays may be useful for designing onboard experiments or analyzing onboard measurement data.

Constraining the sources of ultra-high-energy cosmic rays across and above the ankle with the spectrum and composition data measured at the Pierre Auger Observatory

In this work we present the interpretation of the energy spectrum and mass composition data as measured by the Pierre Auger Collaboration above 6 × 1017 eV. We use an astrophysical model with two extragalactic source populations to model the hardening of the cosmic-ray flux at around 5 × 1018 eV (the so-called “ankle” feature) as a transition between these two components. We find our data to be well reproduced if sources above the ankle emit a mixed composition with a hard spectrum and a low rigidity cutoff. The component below the ankle is required to have a very soft spectrum and a mix of protons and intermediate-mass nuclei. The origin of this intermediate-mass component is not well constrained and it could originate from either Galactic or extragalactic sources.To the aim of evaluating our capability to constrain astrophysical models, we discuss the impact on the fit results of the main experimental systematic uncertainties and of the assumptions about quantities affecting the air shower development as well as the propagation and redshift distribution of injected ultra-high-energy cosmic rays (UHECRs).

Cosmic ray cutoff rigidity governing by solar wind and magnetosphere parameters during the 2017 Sep 6–9 solar-terrestrial event

For the 2017 Sep 6–9 geomagnetic disturbance, we calculated (within the Tsyganenko magnetospheric magnetic field model Ts01) the cosmic ray (CR) geomagnetic cutoff threshold rigidities. We also compared those values with the calculation results obtained from ground-based observations at the global network of neutron monitors (GNNM) through the spectrographic global survey (SGS). Shown is a satisfactory correlation between the geomagnetic cutoff threshold rigidity variations obtained based on the Ts01 model and those obtained from the GNNM ground-based observations. An intercorrelation of the CR geomagnetic threshold variations with the parameters for geomagnetic activity, for solar wind, and for the interplanetary magnetic field (IMF) was established to be different at different stages of the magnetospheric-geomagnetic disturbance. This is because such an intercorrelation is caused by the dynamics of current systems, whose intensifying and damping occur differently over different time intervals. During the storm main phase, the geomagnetic cutoff rigidity threshold variation is shown to be governed, mainly, by the Dst and by the solar wind velocity, as well as by the IMF southern component and by the electric field azimuth component.

Active radiation measurements over one solar cycle with two DOSTEL instruments in the Columbus laboratory of the International Space Station

Two DOSimetry TELescopes (DOSTELs) have been measuring the radiation environment in the Columbus module of the International Space Station (ISS) since 2009 in the frame of the DOSIS and DOSIS 3D projects. Both instruments have measured the charged particle flux rate and dose rates in a telescope geometry of two planar silicon detectors. The radiation environment in the ISS orbit is mostly composed by galactic cosmic radiation (GCR) and its secondary radiation and protons from the inner radiation belt in the South Atlantic Anomaly (SAA) with sporadic contributions of solar energetic particles at high latitudes. The data presented in this work cover two solar activity minima and corresponding GCR intensity maxima in 2009 and 2020 and the solar activity maximum and corresponding GCR intensity minimum in 2014/2015. Average dose rates measured in the Columbus laboratory in the ISS orbit from GCR and SAA are presented separately. The data is analyzed with respect to the effective magnetic shielding and grouped into different cut-off rigidity intervals. Using only measurements in magnetically unshielded regions at low cut-off rigidity and applying a factor for the geometrical shielding of the Earth, absorbed dose rates and dose equivalent rates in near-Earth interplanetary space are estimated for the years 2009 to 2022.

Angular distribution of low momentum atmospheric muons at ground level

We report measurements of the angular distributions of low momentum atmospheric muons at 38 m above sea level for zenith angles θ between -60 and 60 degrees in the south-north direction. The muon detection was performed with two NaI(Tl) scintillation detectors mounted in coincidence. An adjustable lead thickness placed between the detectors allowed to select muons with a minimal momentum ranging from 0.3 to 0.9 GeV/c. The integrated and the differential muon flux were determined by analyzing the deposited energy spectra in the scintillators backed up by a Geant4 simulation of the experimental setup. The results are consistent with the cos n (θ) distribution in good agreement with the literature. These data contribute to fill the gap in the geomagnetic cutoff rigidity interval 8 GV < Pc < 14 GV where no similar measurements were performed before. We found that n = 1.88 - 0.12 Pμ c in this domain of muon momenta cutoff Pμ c < 1 GeV/c. The present measurements are useful for many muon studies requiring an accurate integrated flux.

Transferring Tsyganenko 1989 magnetospheric modulation for cosmic radiation cutoff rigidity values to different epochs of the International geomagnetic reference field

A technique has been developed that will transfer the Tsyganenko 1989 modulation for cutoff rigidity values to different epochs of the International Geomagnetic Reference Field (IGRF). The technique separates the effect of the Tsyganenko external currents on cutoff rigidity values previously calculated at 450 km using the 1995 IGRF such that these effects can be applied to other models of the IGRF. The Tsyganenko modulation effects were then applied to the 2020 internal field model. Two improvements to the original set of calculations include a three-point longitudinal smoothing to reduce the unevenness of the penumbral effects and a replacement of the original −100 Dst values for Kp values > 5 to −50 Dst increments. These changes have extended the original library of 88 world grids to a total of 128 world grids of cutoff rigidity values that are applicable for all Kp values (0–9 + ) and Dst values to −500 nT.

The Relationship of Magnetospheric Parameters with Cosmic-Ray Cutoff Rigidities Depending on Latitude

The Relationship of Magnetospheric Parameters with Cosmic-Ray Cutoff Rigidities Depending on Latitude

Probing solar storms with GRAPES-3 scintillator detectors

The GRAPES-3 muon telescope in Ooty, India detected a 2-h burst of cosmic ray muons (Eμ⩾1GeV) on 22 June 2015 upon the arrival of a strong coronal mass ejection which triggered a G4 class geomagnetic storm. A detailed study of this event with the aid of Monte Carlo simulations suggests that the observed excess muons are due to a weakening of Earth’s magnetic field caused by reconnection of the strong Bz component of interplanetary magnetic field with that of Earth (Mohanty, 2016). This caused a lowering of the geomagnetic cutoff rigidity and led to the entering of excess threshold cosmic rays into the Earth’s atmosphere. The event was also analyzed with the data recorded by the GRAPES-3 scintillator detector array. These detectors record cosmic ray shower particles above a few MeV energy in contrast to GeV threshold of the muon telescope, but they lack directional information. Here, we will present these results and compare them with the results from the muon telescope. We will discuss the relevance of these results to the space weather prediction.

Cosmic ray measurements at high cutoff rigidity site - Preliminary results

In January 2007, King Abdulaziz University, Jeddah (21.5o N; 39.2o E; 14.8 GV), Saudi Arabia, installed a single channel muon detector for monitoring and studying the variations of the cosmic ray (CR) muons. Brief description of the developed detector will be presented. A few results obtained by the detector so far will be given and discussed. These include the impact of the atmospheric pressure and temperature, the daily variations, the responses of the detector to transit and long term of the solar disturbances. Performances of the detector were compared with the King Abdulaziz city for science and technology (KACST) muon detector installed in Riyadh Saudi Arabia and with the Oulu neutron monitor at Oulu and showed comparable results.

The Relationship of Magnetospheric Parameters with Cosmic-Ray Cutoff Rigidities Depending on Latitude

We have studied the features of the latitudinal behavior of geomagnetic thresholds of cosmic rays R, as well as their sensitivity to the interplanetary medium and magnetospheric parameters during three phases of the magnetic storm on September 7–8, 2017, in the initial, main, and recovery phases. For this purpose, values of R were calculated in two different ways—by the method of spectrographic global survey (Rsgs) and by the method of tracing the trajectories of cosmic-ray (CR) particles in the model magnetic field (Ref). The maximum lowering of thresholds is observed at the storm maximum (Dst = –142 nT), reaching the values of ΔRsgs = –0.52 GV and ΔRef = –0.66 GV. The curve of ΔRsgs variations, depending on the observation station (latitude) cutoff rigidity, assumes a classical form with a maximum dropping the thresholds at midlatitudinal stations. ΔR correlates most strongly with the Dst index, which indicates that the ring current plays a main part in the dependence of variations of CR cutoff rigidities. The significant influence of solar-wind velocity V and interplanetary magnetic field (IMF) parameters on ΔRsgs and ΔRef is also seen. In the main phase, ΔRef depends on B and Bz of the IMF, and ΔRsgs depends on B and By. For ΔRsgs, the correlation with electromagnetic parameters varies, depending on the observation station, in a regular manner. There is no such tendency for ΔRef.

Unidirectional gradient of galactic cosmic ray intensity at different cut-off rigidities and solar magnetic polarities

Energetic charged particles known as Galactic cosmic rays (GCRs) are mostly protons originating from supernova remnants. The solar wind modulates the GCR intensity near-Earth along the solar cycles (SCs) in association with the heliospheric magnetic field (HMF). GCR intensity as observed by the neutron monitor at low, medium, high cut-off rigidities (Pc ) is employed to calculate the South-North (SN) asymmetry of GCR densities (n) of different magnetic polarity states (A) of the HMF. The study covered SCs 22/23, 23/24 and 24/25, during negative and positive states (A < 0 and A > 0). We used the modified correction for secular changes in n to determine the SN asymmetry of n (δnS−N /n) with respect to the heliospheric current sheet (HCS), a wavy structure dividing the northern and southern HMFs. We found anti-correlation of corrected tilt angle of HCS [α] for Earth’s excursions in helio-latitude with the corrected δnS−N/n, particularly during A < 0 epoch (2004-2008) and A > 0 epoch (2015-2019 not 1996-1998). The results indicate that HCS drift is crucial for asymmetric modulation and latitude gradient of GCR in both epochs. The asymmetric latitudinal gradient [G ⊥] shows strong positive correlation to the consistency between the corrected δnS−N/n and for all epochs and Pc .

The Asymptotic Directions of Approach and the Magnetic Rigidity Cutoff of Cosmic Ray Particles for Airports at Different Latitudes and Longitudes

The Asymptotic Directions of Approach and the Magnetic Rigidity Cutoff of Cosmic Ray Particles for Airports at Different Latitudes and Longitudes

Extended Cosmic Ray Decreases with Strong Anisotropy after Passage of Interplanetary Shocks

The passage of an interplanetary shock and/or interplanetary coronal mass ejection often causes a rapid decrease in the Galactic cosmic-ray (GCR) flux, known as a Forbush decrease, followed by a recovery of the flux over some days. These local effects are of short duration and strongly rigidity dependent, with higher-rigidity particles exhibiting much weaker effects. In contrast, we present data for two events in which the cosmic-ray flux gradually decreased for about 1 week after shock passage, then recovering over the following week, with the highest anisotropy levels observed throughout Solar Cycle 24. These extended decreases have a weak rigidity dependence and are much more prominent in observations at higher cutoff rigidity, where the initial Forbush decrease is not clearly detected and other variations are generally weak, as we demonstrate using data from the Princess Sirindhorn Neutron Monitor at Doi Inthanon, Thailand with a cutoff rigidity of about 17 GV. We propose that these extended decrease events were initiated upon the passage of an interplanetary shock that inhibited the inflow of GCRs along the interplanetary magnetic field, possibly due to magnetic mirroring at the shock. We also discuss the general behavior of GCR anisotropy as observed at this high cutoff rigidity.

The asymptotic directions of approach and the magnetic rigidity cutoff of cosmic ray particles for airports at different latitudes and longitudes

The asymptotic directions of approach and the magnetic rigidity cutoff of cosmic ray particles for airports at different latitudes and longitudes

Linking cosmic ray intensities to cutoff rigidity through multifractal detrented fluctuation analysis

We use multifractal detrented fluctuation analysis (MFDFA) to investigate the relationship between magnetic rigidity or ”cutoff rigidity” and the variability and multifractal behavior in the time series of the cosmic ray flux on Earth, which is detected by neutron monitors on the Earth’s surface. Because the cutoff rigidity depends strongly on the geographical latitude of the detectors, not all detectors produce equal cosmic ray counts. Our results indicate that there is some bias in the chaotic nature of the cosmic ray series associated with the latitude of the monitoring stations. We obtain an important relationship between the cutoff rigidity (R) for different behaviors and the Hurst exponent of the series corresponding to the counts at the neutron monitor stations. In particular, an inverse relationship is observed with higher rigidity corresponding to a lower Hurst exponent (H(q=a)=maR+Ba). In particular, for q=−10, considering all time series, the correlation coefficient is approximately 0.80, whereas the R-squared is 0.638, and the coefficients of the linear regression for this case are m=−0.0425±0.006 and b=0.8703±0.025.

COR system: A tool to evaluate cosmic ray trajectories in the Earth’s magnetosphere

We present a tool for simulations of cosmic ray trajectories in the magnetosphere called COR (Cut-Off Rigidity). The COR tool provides a framework offering a wide range of functionalities and the possibility to realize extensive simulations at scalable multicore/multinode systems. COR is available at https://cor.crmodels.org.Code used by COR for simulations of cosmic ray trajectories was validated by simulations and results published in a series of articles in the last three decades. In the article, we additionally validated the results of the code by comparison with other available codes. The code for simulations of trajectories is published at GitHub from https://github.com/COR-Cut-off-rigidity/Trajectories_IGRF_T04_C.

The Southern African neutron monitor program: A regional network to study global cosmic ray modulation

Neutron monitor (NM) observations provide a unique, long-term record of galactic cosmic ray intensities, from which many valuable insights have been drawn as to the transport and modulation of these particles. In this paper, the African Neutron Monitor Network, which provides NM observations for broad range of cutoff rigidities, and spanning an exceptional period of time, is introduced. Aspects of these NM observations from this network are discussed, followed by a demonstration of time-dependent numerical cosmic ray modulation modelling done at the North-West University in South Africa, which hosts this network.

A proposal to extend the spectrographic global survey method

We present a modified spectrographic global survey method to split the cosmic ray variations into components of the interplanetary, geomagnetospheric, and atmospheric origin from ground-based observations of the cosmic ray intensity. We show a possibility to use all the available suite of ground-based instrumentation recording cosmic rays (global network of the neutron monitors located at different locations and altitudes, ground- and underground-based muon telescopes, etc.) for such studies without involving the data from aerologic atmospheric sounding. As a demonstration of the method functionality, we provide the calculation results for the variations in the isotropic flux, pitch angle anisotropy of primary cosmic rays in the interplanetary space, changes in the planetary system of geomagnetic cutoff rigidities for every observational hour, as well as the atmosphere temperature above the point of observation of cosmic ray charged components for selected time intervals.

Study of the Ground Level Enhancements effect on atmospheric electric properties and mineral dust particle charging

The effect of Ground Level Enhancements (GLEs) on the atmospheric and dust particles electrical properties is studied. It has been found that in the case of fair weather conditions, GLE events enhance the atmospheric electrical conductivity, reduce the columnar resistance, and modify the fair weather electric field, air–earth conduction current, and possibly the Ionospheric Potential (IP) in a way that depends on the geomagnetic cut-off rigidity of the location and the altitude. If a dust particle layer is present, GLE events tend to cancel its electrical effects in the ambient atmosphere. This means that the enhancement of the electric field and the reduction of atmospheric electrical conductivity, caused by the ion attachment to dust particles, not only tend to return to their ambient fair weather values, but they can be further modified as if the dust layer was not present. Finally, in terms of dust particles’ electrical properties, GLE events tend to modify the ion attachment mechanism, and in principle, the particle net charge, and the electric field “sensed” by them, increase. Nevertheless, since the electrical force magnitude is up to six orders of magnitude less than gravity, the increase of the particles’ electrical properties is not sufficient to modify the particle settling dynamics and settling velocities.

Study on Long-Term Variation Characteristics of Geomagnetic Cutoff Rigidities of Energetic Protons Caused by Long-Term Variation of Geomagnetic Field

As a parameter that quantitatively measures the shielding effect of the Earth’s magnetic field on energetic particles, the geomagnetic cutoff rigidities will change significantly with the long-term change of geomagnetic field. In this article, by using the numerical simulation method, combined with the variation trend of the Earth’s main field International Geomagnetic Reference Field (IGRF) model and the energetic particles’ windows (EPWs), the variation characteristics of the cutoff rigidities of geomagnetic energetic particles in the vertical direction from 1965 to 2025 were studied. The study found that there is a close relationship between the cutoff latitude corresponding to the cutoff rigidities and the background magnetic field intensity, but they are not in a simple linear relationship. The changes of the cutoff rigidities and geomagnetic field in the northern and southern hemispheres are asymmetric. The weakening of the geomagnetic field will push the cutoff latitudes toward the near equatorial region in the southern hemisphere, but for northern hemisphere the phenomenon is not always credible. In the northern hemisphere, the areas of EPWs will decrease at a relative rate of 0.03%/yr, but in the southern hemisphere, it will increase at a rate of about 0.05%/yr to 0.12%/yr. The long-term trajectory of the positions of the EPWs’ central points do not correspond to geomagnetic poles, nor the magnetic dip poles, relatively speaking, its position is closer to the geomagnetic poles. The study can be used for a long-term forecasting of cutoff rigidities caused by background geomagnetic field variations.