Galactic Cosmic Ray Variations Research Articles

Variations in the Inferred Cosmic-Ray Spectral Index as Measured by Neutron Monitors in Antarctica

A technique has recently been developed for tracking short-term spectral variations in Galactic cosmic rays (GCRs) using data from a single neutron monitor (NM), by collecting histograms of the time delay between successive neutron counts and extracting the leader fraction L as a proxy of the spectral index. Here we analyze L from four Antarctic NMs from 2015 March to 2023 September. We have calibrated L from the South Pole NM with respect to a daily spectral index determined from published data of GCR proton fluxes during 2015–2019 from the Alpha Magnetic Spectrometer (AMS-02) on board the International Space Station. Our results demonstrate a robust correlation between the leader fraction and the spectral index fit over the rigidity range 2.97–16.6 GV for AMS-02 data, with uncertainty of 0.018 in the daily spectral index as inferred from L. In addition to the 11 yr solar activity cycle, a wavelet analysis confirms a 27 day periodicity in the GCR flux and spectral index corresponding to solar rotation, especially near sunspot minimum, while the flux occasionally exhibits a strong harmonic at 13.5 days. The magnetic field component along a nominal Parker spiral (i.e., the magnetic sector structure) is a strong determinant of such spectral and flux variations, with the solar wind speed exerting an additional, nearly rigidity-independent influence on flux variations. Our investigation affirms the capability of ground-based NM stations to accurately and continuously monitor cosmic-ray spectral variations over the long-term future.

Measurements of Cosmic Rays by a Mini‐Neutron Monitor at Neumayer III From 2014 to 2017

AbstractA mini‐neutron monitor (MNM) was installed at the German Antarctic Neumayer III station, measuring the variation of galactic cosmic rays and searching for Forbush Decreases (FDs) caused by solar activities. Running continuously from 2014 until the end of 2017, the long‐term stability of the detector could be investigated. After correcting the air pressure and normalization to the 27 days running mean averages of the SANAE and TERA Neutron Monitors (NMs), the daily running mean count rates are compared with the SANAE and TERA NMs also installed in Antarctica. For most of the 14 FDs with magnitudes greater than 3, taken from the list compiled by the IZMIRAN group (http://spaceweather.izmiran.ru/eng/dbs.html), the three detectors show consistent particle flux variation, although the average rate of the MNM is more than a hundred times smaller. The light and low‐cost MNM is an ideal alternative to heavy and old NMs, especially at high altitudes and remote environments.

Analysis of the spectrum of 27-day GCR variations in 2015–2016

This work presents the results of the analysis of 27-day variations in the flux of galactic protons registered by STEREO, SOHO, and AMS-02 in 2015–2016. We calculate variations’ amplitude using several different approaches and propose a description of its energy dependence in the range of magnetic rigidity from approximately 0.3 to 100 GV. We also analyse variations of the solar modulation potential, which is the only parameter of force-field model, and consider the possibility of describing the 27-day variations of galactic cosmic rays within the framework of this model. It is shown that rigidity dependence of the 27-day variations amplitude cannot be properly described using this simple approximation.

Bridging machine learning and diagnostics of the ESA LISA space mission with equation discovery via explainable artificial intelligence

The Laser Interferometer Space Antenna (LISA) of the European Space Agency will be the first interferometer for low-frequency (10-4–10-1 Hz) gravitational wave detection in space. LISA will detect spurious accelerations of the test masses, the end mirrors of the interferometer, of the order of femto-g. Amongst spurious signals, Coulomb forces due to stray electric fields coupling with charge deposited on the test masses by galactic and solar particles and the noise associated to the charging process must be monitored during the mission lifetime. Precious clues on spurious forces acting on the test masses have been studied with the LISA Pathfinder mission, meant for the testing of the instrumentation that will be placed on board LISA, in 2016–2017. In this work we present the design and implementation of a workflow leading to equation discovery for the relationship between solar wind speed, galactic cosmic-ray variations and interplanetary magnetic field intensity observations for the diagnostics of LISA. The workflow exploits explainable artificial intelligence tools to build a bridge between the opaque predictions obtained with machine learning (ML) models and data analysis performed by humans with space mission observations. The core step of the workflow is the implementation, tuning and optimisation of an opaque ML regressor explicitly designed for the future LISA mission, based on input observations of the galactic cosmic-ray flux and of the interplanetary magnetic field intensity. The regressor is aimed at reconstructing the solar wind speed, a parameter of fundamental importance, but not available, for the mission environment monitoring. The workflow ends with the application of explainable clustering techniques to the opaque model in order to (i) obtain human-interpretable outputs instead of opaque ones without any noticeable loss in the predictive performance and (ii) discover an equation describing the quantitative relationship between the involved variables, currently missing in the literature. The correlation amongst the transit of interplanetary structures, galactic cosmic-ray variations and LISA test-mass charging is illustrated here.

A Numerical Study of the Effects of a Corotating Interaction Region on Cosmic-Ray Transport. II. Features of Cosmic-Ray Composition and Rigidity

We continue the numerical modeling of a corotating interaction region (CIR) and the effects it has on solar-rotational recurrent variations of galactic cosmic rays (GCRs). A magnetohydrodynamic model is adapted to simulate the background solar wind plasma with a CIR structure in the inner heliosphere, which is incorporated into a comprehensive Parker-type transport model. The focus is on the simulation of the effects of a CIR on GCR protons and the two helium isotopes as a function of heliolongitude. This is to establish whether the difference in composition affects how they are modulated by the CIR in terms of their distribution in longitude. It is demonstrated that particle diffusion and drift influence the effects of the CIR with increasing rigidity from 100 MV up to 15 GV. It is found that protons and helium isotopes are modulated differently with longitude by the CIR and that particle drift influences the modulation effects in longitude. These differences dissipate with increasing rigidity. The final results are focused on the simulated amplitude of these GCR flux variations as a function of rigidity. The amplitude displays a power-law behavior above ∼1 GV with an index similar to the power index of the rigidity dependence of the assumed diffusion coefficients. The simulations further show that below this rigidity, the amplitude at first flattens off, displaying a plateau-like profile, but it then increases systematically with decreasing rigidity below ∼0.3 GV. Again, a power-law behavior is displayed, but it is completely different from that above 1 GV.

Possible Influence of Solar Cyclicity on Extratropical Cyclone Trajectories in the North Atlantic

In this work, we study long-term changes in the main directions of movement (storm tracks) of extratropical cyclones in the North Atlantic for the period 1873–2021, based on the data of the MSLP (Mean Sea Level Pressure) archives from the Climatic Research Unit and NCEP/DOE AMIP-II reanalysis. It was found that in the cold half of the year, the mean latitudes of storm tracks undergo oscillations with the periods ~80–100, ~40–45, and ~22 years, which indicates their possible association with solar cyclicity. Cyclone trajectories were found to shift northward at the minimum of the Gleissberg secular cycle (~1900–1930) and southward at its maximum (~1940–1960). The secular variations are the most pronounced in the western part of the North Atlantic, with the peak-to-peak amplitude reaching ~3–5°, and disappear at longitudes east of Greenwich. On the bidecadal timescale, cyclone tracks were found to shift noticeably to the north in even solar cycles and weakly to the south in odd ones. The most significant northward shifts (~1–2°) were detected during the descending phase and the minimum of the solar cycle (from the second to the sixth year after the solar maximum) in the eastern part of the North Atlantic (longitudes 30–10° W). The detected oscillations of cyclone trajectories may be caused by long-term changes in the intensity of the stratospheric polar vortex associated with galactic cosmic ray variations and geomagnetic activity.

Estimating the Effective Energy of Neutron Monitors from 27-Day Variations in Galactic Cosmic Rays

Estimating the Effective Energy of Neutron Monitors from 27-Day Variations in Galactic Cosmic Rays

Estimation of the neutron monitors’ effective energies based on the 27-day galactic cosmic rays variations

We presented a new method of the neutron monitors’ (NM’s) effective energy estimation based on the 27‑day galactic cosmic rays (GCR) variations: using AMS-02 measurements we study rigidity dependance of 27-day variations’ amplitude and calculate the energy value so that the variability of the GCR particles at this energy is equal to that of the NM’s count rate. We examined how NM’s effective energy depends on the geomagnetic cutoff rigidity using data of several NM.

Influence of Solar Activity and Galactic Cosmic Ray Variations on Trajectories of Extratropical Cyclones in the North Atlantic

Influence of Solar Activity and Galactic Cosmic Ray Variations on Trajectories of Extratropical Cyclones in the North Atlantic

Cosmic ray fluctuations and MHD waves in the solar wind

During large-scale solar wind disturbances, variations in galactic cosmic rays with periods from several minutes to 2–3 hours, which are called cosmic ray fluctuations in the scientific literature, often occur. Such fluctuations are not observed in the absence of disturbances. Since cosmic rays are charged particles, their modulation in the heliosphere occurs mainly under the influence of the interplanetary magnetic field, or rather its turbulent part — MHD waves. In order to adequately describe the relationship between their fluctuation spectra, it is necessary to be able to isolate a certain type of MHD waves from direct measurements of the interplanetary medium parameters. In this paper, we consider some methods for determining the contribution of three solar wind MHD turbulence branches, namely, Alfvén, fast, and slow magnetosonic waves corresponding to the turbulence spectrum inertial region frequencies 10⁻⁴<ν<10⁻¹ Hz, at which cosmic ray fluctuations are observed, to the observed power spectra of interplanetary magnetic field modulus fluctuations. To do this, we apply the methods of spectral and polarization analysis. In the absence of measurement data on SW parameters, to identify the type of MHD turbulence we use the known wave polarization properties that Alfvén and magnetosonic waves are polarized in different planes relative to the plane containing the average IMF vector and wave vector.
 Our results show that with the correct determination of the spectra of three MHD wave types, their sum, within the limits of errors, agrees well with the observed spectra of the interplanetary magnetic field modulus, and a small difference can be attributed to static inhomogeneities and oscillations frozen into plasma, as well as to various discontinuities that are always inevitably present in the solar wind.

Флуктуации космических лучей и МГД-волны в солнечном ветре

During large-scale solar wind disturbances, variations in galactic cosmic rays with periods from several minutes to 2–3 hours, which are called cosmic ray fluctuations in the scientific literature, often occur. Such fluctuations are not observed in the absence of disturbances. Since cosmic rays are charged particles, their modulation in the heliosphere occurs mainly under the influence of the interplanetary magnetic field, or rather its turbulent part — MHD waves. In order to adequately describe the relationship between their fluctuation spectra, it is necessary to be able to isolate a certain type of MHD waves from direct measurements of the interplanetary medium parameters. In this paper, we consider some methods for determining the contribution of three solar wind MHD turbulence branches, namely, Alfvén, fast, and slow magnetosonic waves corresponding to the turbulence spectrum inertial region frequencies 10⁻⁴<ν<10⁻¹ Hz, at which cosmic ray fluctuations are observed, to the observed power spectra of interplanetary magnetic field modulus fluctuations. To do this, we apply the methods of spectral and polarization analysis. In the absence of measurement data on SW parameters, to identify the type of MHD turbulence we use the known wave polarization properties that Alfvén and magnetosonic waves are polarized in different planes relative to the plane containing the average IMF vector and wave vector. 
 Our results show that with the correct determination of the spectra of three MHD wave types, their sum, within the limits of errors, agrees well with the observed spectra of the interplanetary magnetic field modulus, and a small difference can be attributed to static inhomogeneities and oscillations frozen into plasma, as well as to various discontinuities that are always inevitably present in the solar wind.

Interplanetarymedium monitoring with LISA: Lessons from LISA Pathfinder

The Laser Interferometer Space Antenna (LISA) of the European Space Agency (ESA) will be the first low-frequency gravitational-wave observatory orbiting the Sun at 1 AU. The LISA Pathfinder (LPF) mission, aiming at testing the instruments to be located on board the LISA spacecraft (S/C), hosted, among the others, fluxgate magnetometers and a particle detector as parts of a diagnostics subsystem. These instruments allowed us to estimate the magnetic and Coulomb spurious forces acting on the test masses that constitute the mirrors of the interferometer. With these instruments, we also had the possibility to study the galactic cosmic-ray short term-term variations as a function of the particle energy and the associated interplanetary disturbances. Platform magnetometers and particle detectors will also be placed on board each LISA S/C. This work reports on an empirical method that allowed us to disentangle the interplanetary and onboard-generated components of the magnetic field by using the LPF magnetometer measurements. Moreover, we estimate the number and fluence of solar energetic particle events expected to be observed with the ESA Next Generation Radiation Monitor during the mission lifetime. An additional cosmic-ray detector, similar to that designed for LPF, in combination with magnetometers, would permit to observe the evolution of recurrent and non-recurrent galactic cosmic-ray variations and associated increases of the Interplanetary Magnetic Field at the transit of high-speed solar wind streams and interplanetary counterparts of coronal mass ejections. The diagnostics subsystem of LISA makes this mission also a natural multi-point observatory for space weather science investigations.

Solar Activity, Galactic Cosmic Ray Variations, and the Global Seismicity of the Earth

Solar Activity, Galactic Cosmic Ray Variations, and the Global Seismicity of the Earth

Influence of Interacting Solar Wind Disturbances on the Variations in Galactic Cosmic Rays

Influence of Interacting Solar Wind Disturbances on the Variations in Galactic Cosmic Rays

Scaling Features of Diurnal Variation of Galactic Cosmic Rays

We analyze the scaling properties of the diurnal variation of galactic cosmic rays (GCRs) in Solar Cycle 24 and the solar minima between Solar Cycles 23/24 and 24/25 for 2007 – 2019 based on the count rates of the Oulu, Newark, Hermanus, and Potchefstroom neutron monitors. The scaling features of the GCR diurnal variation are studied by evaluating the Hurst exponent, a quantitative parameter used as an indicator of the state of the randomness of a time series. We estimate the Hurst exponents for GCR diurnal-variation parameters amplitude and phase using structure-function and detrended-fluctuation-analysis methods. Results show that the Hurst exponents for the GCR diurnal variation vary in the range from approx0.3 to approx0.9, with a general tendency of being systematically above 0.5. It suggests that the GCR diurnal variation reveals a more persistent structure than Brownian motion. However, the time series of GCR diurnal-variation amplitude and phase evolve from a more persistent structure in the solar minimum between Solar Cycles 23/24 in 2007 – 2009 to a more random character in and near the solar maximum 2012 – 2014. This observation seems to be in agreement with the general configuration of the heliosphere through the 11-year solar-activity cycle. Moreover, the temporal profile of the Hurst exponent for GCR diurnal amplitude and phase around the beginning of the solar minimum between Solar Cycles 24/25 (2018 – 2019) differs from the solar minimum between Solar Cycles 23/24 in 2007 – 2009, suggesting a dependence on solar-magnetic polarity. These findings could shed more light on GCR particle transport in the turbulent heliosphere over the solar cycle.

Galactic cosmic ray modulation at Mars and beyond measured with EDACs on Mars Express and Rosetta

Galactic cosmic rays (GCRs) are an intrinsic part of the heliospheric radiation environment and an inevitable challenge to long-term space exploration. Here we show solar-cycle-induced GCR modulation at Mars in the period 2005–2020, along with GCR radial gradients, by comparing Mars Express and Rosetta engineering parameters to sunspot number time series. The engineering parameters used are the error detection and correction (EDAC) counters, cumulative counters that are triggered by charged energetic particles that cause memory errors in onboard computers. EDAC data provide a new way of gaining insight into the field of particle transport in the heliosphere; these data also allow us to complement dedicated radiation instrumentation as EDAC software is present on all spacecraft. This dataset was used to capture variations in GCRs in both space and time, yielding the same qualitative information as ground-based neutron monitors. Our analysis of the Mars Express EDAC parameter reveals a strong solar cycle GCR modulation, with a time lag of ∼5.5 months. By combining Mars Express with Rosetta data, we calculate a 4.7 ± 0.8% increase in EDAC count rates per astronomical unit, which we attribute to a radial gradient in GCR fluxes in accordance with established literature. The potential of engineering data for scientific purposes remains mostly unexplored. The results obtained from this work demonstrate, for the first time for heliophysics purposes, the usefulness of the EDAC engineering parameter, the usefulness of data mining, and the utility of keeping missions operational for many years, all of which provide complimentary data to nominal science instruments.

Variations of the Galactic Cosmic Rays in the Recent Solar Cycles

Abstract In this paper, we study the Galactic cosmic-ray (GCR) variations over the solar cycles 23 and 24, with measurements from NASA’s Advanced Composition Explorer/Cosmic Ray Isotope Spectrometer instrument and the ground-based neutron monitors (NMs). The results show that the maximum GCR intensities of heavy nuclei (5 ≤ Z ≤ 28, 50∼500 MeV nuc−1) at 1 au during the solar minimum in 2019–2020 break their previous records, exceeding those recorded in 1997 and 2009 by ∼25% and ∼6%, respectively, and are at the highest levels since the space age. However, the peak NM count rates are lower than those in late 2009. The difference between GCR intensities and NM count rates still remains to be explained. Furthermore, we find that the GCR modulation environment during the solar minimum P 24/25 are significantly different from previous solar minima in several aspects, including remarkably low sunspot numbers, extremely low inclination of the heliospheric current sheet, rare coronal mass ejections, weak interplanetary magnetic field and turbulence. These changes are conducive to reduce the level of solar modulation, providing a plausible explanation for the record-breaking GCR intensities in interplanetary space.

Galactic Cosmic Rays, Cosmic-Ray Variations, and Cosmogenic Nuclides in Meteorites

Abstract We present a new generation of model calculations for cosmogenic production rates in various types of solar system bodies. The model is based on the spectra for primary and secondary particles calculated using the INCL++6 code, which is the most reliable and most sophisticated code available for spallation reactions. Thanks to the recent improvements (extending the code to lower and higher energies and considering light charged particles as ejectiles and projectiles), we can for the first time directly consider primary and secondary Galactic α particles. We calculate production rates for 22Na, 10Be, and 26Al in an L-chondrite with a radius of 45 cm and in the Apollo 15 drill core, and we determine the long-term average Galactic cosmic-ray (GCR) spectrum (represented by the solar modulation potential Φ) in the meteoroid orbits at ∼3 au of Φ = 600 MV and at 1 au, i.e., for Earth and Moon of Φ = 660 MV. From this, we calculate a long-term average GCR gradient in the inner solar system of ∼5% au−1. Finally, we discuss the possibility of studying temporal GCR variations and meteoroid orbits using production rate ratios of short- and long-lived radionuclides.

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.

Recurrence of galactic cosmic-ray intensity and anisotropy in solar minima 23/24 and 24/25 observed by ACE/CRIS, STEREO, SOHO/EPHIN and neutron monitors

Aims.We studied the 27-day variations of galactic cosmic rays (GCRs) based on neutron monitor (NM), ACE/CRIS, STEREO, and SOHO/EPHIN measurements in the solar minima 23/24 and 24/25, which are characterized by the opposite polarities of solar magnetic cycle. We used the opportunity to reanalyze the polarity dependence of the amplitudes of the recurrent GCR variations in 2007–2009 for the negativeA < 0 solar magnetic polarity and to compared it with the clear periodic variations related to solar rotation in 2017–2019 for positiveA > 0.Methods.We used the Fourier analysis method to study the periodicity in the GCR fluxes. Because the GCR recurrence is a consequence of solar rotation, we analyzed not only GCR fluxes, but also solar and heliospheric parameters to examine the relations of the 27-day GCR variations and heliospheric as well as solar wind parameters.Results.We find that the polarity dependence of the amplitudes of the 27-day variations of the GCR intensity and anisotropy for NMs data is kept for the last two solar minima: 23/24 (2007–2009) and 24/25 (2017–2019), with greater amplitudes in the positiveA > 0 solar magnetic polarity. ACE/CRIS, SOHO/EPHIN, and STEREO measurements are not governed by this principle of greater amplitudes in the positiveA > 0 polarity. The GCR recurrence caused by the solar rotation for low-energy (< 1 GeV) cosmic rays is more sensitive to the enhanced diffusion effects, resulting in the same level in 27-day amplitudes for the positive and negative polarities. In contrast, the high-energy (> 1 GeV) cosmic rays that are registered by NMs are more sensitive to the large-scale drift effect, which leads to the 22-year Hale cycle in the 27-day GCR variation, with the larger amplitudes in theA > 0 polarity than inA < 0.