Galactic Cosmic Ray Intensity Research Articles

The galactic cosmic ray intensity fluctuations during perturbations of the solar wind in early November 2021

In order to develop methods for predicting negative manifestations of space weather, the dynamics of fluctuations in the intensity of galactic cosmic rays during geophysical disturbances in early November 2021 is studied. The obtained results point to the possibility of real-time short-term space weather forecasting based on the measurement data of the Russian national ground-based network of cosmic ray stations.

Global Analysis of the Extended Decreases in Cosmic Rays Observed with Worldwide Networks of Neutron Monitors and Muon Detectors: Temporal Variation of the Rigidity Spectrum and Its Implication

This paper presents the global analysis of two extended decreases in the galactic cosmic-ray intensity observed by worldwide networks of ground-based detectors in 2012. This analysis is capable of separately deriving the cosmic-ray density (or omnidirectional intensity) and anisotropy, each as a function of time and rigidity. A simple diffusion model along the spiral field line between Earth and a cosmic-ray barrier indicates the long duration of these events, resulting from about 190° eastern extent of a barrier such as an interplanetary shock followed by the sheath region and/or the corotating interaction region (CIR). It is suggested that the coronal mass ejection merging with and compressing the preexisting CIR at its flank can produce such an extended barrier. The derived rigidity spectra of the density and anisotropy both vary in time during each event period. In particular we find that the temporal feature of the “phantom Forbush decrease (FD)” reported in an analyzed period is dependent on rigidity, and looks quite different at different rigidities. From these rigidity spectra of the density and anisotropy, we derive the rigidity spectrum of the average parallel mean free path of pitch angle scattering along the spiral field line and infer the power spectrum of the magnetic fluctuation and its temporal variation. The possible physical cause of the strong rigidity dependence of the phantom FD is also discussed. These results demonstrate the high-energy cosmic rays observed at Earth responding to remote space weather.

Fifty years of studying the GCR intensity during inversion of the heliospheric magnetic fields. II. HMF inversion on the inner heliospheric boundary

Phenomena in the outer layer of the solar atmosphere, the heliosphere, including the supersonic solar wind, the heliospheric magnetic field (HMF) carried by it, and cosmic rays propagating in the heliosphere are important for many processes occurring in this layer. For some of these processes such as geomagnetic activity or propagation of cosmic rays, not only the strength, but also the direction of the field is significant. Nonetheless, if in this regard the situation during periods of low sunspot activity is quite clear — the heliosphere is divided into two hemispheres with opposite polarity (toward the Sun/away from the Sun), — during periods of high sunspot activity when the HMF inversion occurs, there is no simple model of this phenomenon. The paper is a sequel to the study of the HMF inversion phenomenon and associated effects in the intensity of galactic cosmic rays (GCR). Previously, general ideas about the 22-year cyclicity in the characteristics of the Sun, heliosphere, and cosmic rays have been formulated, and the effects observed in the GCR intensity, which we associate with the HMF inversion, have been discussed in detail. This paper deals with a model of HMF inversion, associated only with the evolution of the magnetic field in the layer between the photosphere and the base of the heliosphere due to changes in the distribution of photospheric fields from one solar rotation to the next one, and shows that this is not enough to explain the main effects in the GCR intensity. In this layer, the magnetic field is the main energy factor. A more complete model of HMF inversion, including the transformation of its characteristics due to the interaction of different-speed solar wind streams in the heliosphere itself, where the solar wind is the main energy factor, will be discussed in the next paper.

Пятьдесят лет исследования поведения интенсивности ГКЛ в периоды инверсии гелиосферного магнитного поля. II. Инверсия ГМП на внутренней границе гелиосферы

Phenomena in the outer layer of the solar atmosphere, the heliosphere, including the supersonic solar wind, the heliospheric magnetic field (HMF) carried by it, and cosmic rays propagating in the heliosphere are important for many processes occurring in this layer. For some of these processes such as geomagnetic activity or propagation of cosmic rays, not only the strength, but also the direction of the field is significant. Nonetheless, if in this regard the situation during periods of low sunspot activity is quite clear — the heliosphere is divided into two hemispheres with opposite polarity (toward the Sun/away from the Sun), — during periods of high sunspot activity when the HMF inversion occurs, there is no simple model of this phenomenon. The paper is a sequel to the study of the HMF inversion phenomenon and associated effects in the intensity of galactic cosmic rays (GCR). Previously, general ideas about the 22-year cyclicity in the characteristics of the Sun, heliosphere, and cosmic rays have been formulated, and the effects observed in the GCR intensity, which we associate with the HMF inversion, have been discussed in detail. This paper deals with a model of HMF inversion, associated only with the evolution of the magnetic field in the layer between the photosphere and the base of the heliosphere due to changes in the distribution of photospheric fields from one solar rotation to the next one, and shows that this is not enough to explain the main effects in the GCR intensity. In this layer, the magnetic field is the main energy factor. A more complete model of HMF inversion, including the transformation of its characteristics due to the interaction of different-speed solar wind streams in the heliosphere itself, where the solar wind is the main energy factor, will be discussed in the next paper.

Unusual Forbush Decreases and Geomagnetic Storms on 24 March, 2024 and 11 May, 2024

As the current solar cycle 25 progresses and moves towards solar maxima, solar activity is increasing and extreme space weather events are taking place. Two severe geomagnetic storms accompanied by two large Forbush decreases in galactic cosmic ray intensity were recorded in March and May, 2024. More precisely, on 24 March 2024, a G4 (according to the NOAA Space Weather Scale for Geomagnetic Storms) geomagnetic storm was registered, with the corresponding geomagnetic indices Kp and Dst equal to 8 and −130 nT, respectively. On the same day, the majority of ground-based neutron monitor stations recorded an unusual Forbush decrease. This event stands out from a typical Forbush decrease because of its high amplitude decrease phase and rapid recovery phase, i.e., 15% decrease and an extremely rapid recovery of 10% within 1.5 h, as recorded at the Oulu neutron monitor station. Furthermore, on 10–13 May 2024, an unusual G5 geomagnetic storm (geomagnetic indices Kp = 9 and Dst = −412 nT) was registered (the last G5 storm had been observed in 2003). In addition, the polar neutron monitor stations recorded a Ground Level Enhancement (GLE74) during the recovery phase of a large Forbush decrease of 15%, which started on 10 May 2024. In this study, a detailed analysis of these two severe events in regard to the accompanying solar activity, interplanetary conditions and solar energetic particle events is provided. Moreover, the results of the NKUA “GLE Alert++ system”, the NKUA/IZMIRAN “FD Precursory Signals” method and the NKUA “ap Prediction tool” concerning these events are presented.

The Algorithm of the Two Neutron Monitors for the Analysis of the Rigidity Spectrum Variations of Galactic Cosmic Ray Intensity Flux in Solar Cycle 24

The method of the two neutron monitors was used to analyze the parameters of the rigidity spectrum variations (RSV) of galactic cosmic ray intensity (GCR) flux in solar cycle 24 based on the data from the global network of neutron monitors. This method is an alternative to the least squares method when there are few monitors working stably in a given period, and their use in the least squares method is impossible. Analyses of the changes in exponent γ in the RSV of GCR flux from 2009 to 2019 were studied. The soft RSV (γ = 1.2–1.3) of the GCR flux around the maximum epoch and the hard RSV (γ = 0.6–0.9) around the minimum epoch of solar activity (SA) is the general feature of GCR modulation in the GeV energy scale (5, 50), to which neutron monitors were found to correspond. Therefore, various values of the RSV γ in the considered period show that during the decrease and increase period of SA, the essential changes in the large-scale structure of the heliospheric magnetic field (HMF) fluctuations/turbulence take place. The exponent γ of the RSV of the GCR flux can be considered a significant parameter to investigate the long-period changes in the GCR flux.

Cosmic-Ray Transport in the Presence of a Fisk-type Heliospheric Magnetic Field: Investigating the Influence of Drift

Drifts due to the gradients in, and curvatures of, the heliospheric magnetic field (HMF) play a significant role in the transport of galactic cosmic rays (GCRs) in the heliosphere. Although this has been well studied for the Parker HMF, the influence of Fisk-type fields, with their unique geometry, has hitherto received less attention. Here, drift velocity profiles computed for a Schwadron–Parker hybrid field are compared with those for a purely Parkerian field. Furthermore, the influence of this field on GCR modulation, as computed with a 3D, ab initio, modulation model, is investigated. Globally, the differences between the computed intensities are small. Nevertheless, local measures, such as azimuthal variations in the GCR intensities, show a significant influence of the Schwadron–Parker hybrid field on GCR transport.

Dynamics of the energy spectrum of solar-diural variations in the intensity of cosmic rays in 22–25 cycles of solar activity

Periodic 24-hour variations in the intensity of galactic cosmic rays, continuously observed by ground-based detectors, are called solar diurnal variations. The nature of these variations lies in the existence in the interplanetary medium of an anisotropic spatial distribution of galactic cosmic rays, which arises during the interaction of these particles with the heliosphere. It is believed that the physical factors responsible for the observed anisotropy of galactic cosmic rays are the processes of convection, diffusion and their drift. The combination of these factors determines the main parameters of solar diurnal variations, such as amplitude, phase and energy spectrum. To study the energy spectrum of solar-diurnal variations, we used measurement data from muon telescopes of the Yakutsk Cosmic Ray Spectrograph after A.I. Kuzmin and Nagoya stations (Japan). The research approach is based on the idea of the crossed telescope method, originally designed to take into account the temperature effect. Due to the difference in the receiving characteristics of the crossed northern and southern directions of the above muon telescopes, the intensity variations recorded by them are sensitive to changes in the energy spectrum of solar-diurnal variations. This property was used to assess the dynamics of the energy spectrum of solar-diurnal variations for 22–25 cycles of solar activity. Analysis of the data obtained showed that in the last minimum of solar activity in 2018-2021. An anomalously early phase of solar-diurnal variations was observed. To study this phenomenon, we simulated the ratio and phase difference of a pair of northern and southern crossed directions for both muon telescopes for different types and values of the energy spectrum of solar-diurnal variations. A comparison of model calculations and observational data has made it possible to establish that during periods of minimum solar activity in the positive polarity of the general magnetic field of the Sun, a significant softening of the energy spectrum of solar-diurnal variations is observed. The reasons for the discovered phenomenon are discussed.

Catalogues of Forbush Decreases for the Period of 1957 - 1967

This work presents catalogues of Forbush Deceraeses (FDs) between the periods of 1957 – 1967. Forbush Decrease is a short-time decrease in the intensity of galactic cosmic rays. Such decreases are traced to solar wind disturbances. This work aims to study the catalogues of FDs. To achieve this aim, two approaches will be adopted namely; (1) downloading and presenting the IZMIRAN FDs from their website (2) applying the automated methods of FD identification developed by Okike and Umahi (2019) to identify and present FDs. The IZMIRAN catalog which applied the global survey method, identified a total of 450 FDs while the automated generated FDs (FD1 and FD2) which applied Fourier transformation, identified 500 and 458 FDs respectively. A close study on the three catalogues, pinpointed some differences and similarities. These were attributed to the differences in their methods of identification.

Cosmic Radiation Reliability Analysis for Aircraft Power Electronics

Cosmic Ray induced failures are a major concern for the electronic system reliability of airborne and space systems. Power system voltages on aerospace platforms are on a steady upward trend. High voltage power converters suffer from Single Event Burnout failures caused by cosmic rays. The established standards propose a scaling factor based on measured background galactic cosmic rays intensity at operating altitude to apply de-rating factors. The radiation environment in the atmosphere can be increased due to the cascading of primary solar energetic particles during solar eruptions. In this work, the altitude profile of the radiation environment is simulated using a GEANT4 Monte-Carlo code. The failure rates due to both background Galactic Cosmic Rays and Solar Energetic Particles are quantitatively evaluated. Further to the known influence of geomagnetic shielding of cosmic rays, the geographical distribution of cosmic rays at flight altitudes of 10 km are also presented. The estimated cosmic ray intensity can then be combined with experimentally measured failure rate data to predict the impact on the reliability of power converters, giving a new level of accuracy in the modeling of such failure mode in more electric aircraft applications. It is shown for the first time in the scientific literature by using experimental data and state-of-the-art models, that the solar energetic particles storms fluxes vastly exceed the recommended standard and constitute a risk for the power electronics reliability.

Galactic cosmic rays at 0.7 A.U. with Venus Express housekeeping data

We apply a previously developed procedure to characterize galactic cosmic rays (GCRs) at 0.7 A.U. with engineering data coming from the Venus Express mission. The engineering parameters are the Error Detection and Correction EDAC cumulative counters, used for detection and correction of memory errors induced by highly energetic particles. It has already been demonstrated that the slope of this counter measures GCR fluxes using data from Mars Express (1.5 A.U.) and Rosetta (up to 4 A.U.) data. Here, we reproduce these methods using Venus Express EDAC data in order to understand the behavior of GCRs closer to the Sun. We again witness the anti-correlation of EDAC slope with the solar activity and further investigate this procedure. The resulting time-lag between maximum sunspot number and minimum GCRs intensity at Venus is close to one day instead of the expected several months. This work represents one of the first characterization of galactic cosmic rays at small distances to the Sun over a long period of time and further cements the value of using EDAC counters as scientific information.

Fluctuations in the Intensity of Galactic Cosmic Rays during Perturbations of the Solar Wind in Early November 2021

Fluctuations in the Intensity of Galactic Cosmic Rays during Perturbations of the Solar Wind in Early November 2021

Reconstructing Sunspot Number by Forward-Modelling Open Solar Flux

The open solar flux (OSF) is the integrated unsigned magnetic flux leaving the top of the solar atmosphere to form the heliospheric magnetic field. As the OSF modulates the intensity of galactic cosmic rays at Earth, the production rate of cosmogenic isotopes – such as 14C and 10Be stored in tree rings and ice sheets – is closely related to the OSF. Thus on the basis of cosmogenic isotope data, OSF can be reconstructed over millennia. As sunspots are related to the production of OSF, this provides the possibility of reconstructing sunspot number (SSN) and hence properties of the solar cycles prior to the first sunspot telescopic observations in 1610. However, while models exist for estimating OSF on the basis of SSN, the hysteresis present in OSF and the lack of a priori knowledge of the start/end dates of individual solar cycles means that directly inverting these models is not possible. We here describe a new method that uses a forward model of OSF to estimate SSN and solar cycle start/end dates through a Monte Carlo approach. The method is tested by application to geomagnetic reconstructions of OSF over the period 1845-present, and compared to the known SSN record for this period. There is a substantial improvement in reconstruction of both the SSN time series and the solar cycle start/end dates compared with existing OSF-SSN regression methods. This suggests that more accurate solar-cycle information can be extracted from cosmogenic isotope records by forward modelling, and also provides a means to assess the level of agreement between independent SSN and OSF reconstructions. We find the geomagnetic OSF and observed SSN agree very well after 1875, but do differ during the early part of the geomagnetic record, though still agree within the larger observational uncertainties.

Fifty years of studying the GCR intensity during inversion of heliospheric magnetic fields I. Observations

The effects of the 22-year variation of solar magnetic fields in the galactic cosmic ray (GCR) intensity were first observed and interpreted as manifestations of inversion of the high-latitude solar magnetic field in properties of heliospheric magnetic fields by the Lebedev Physical Institute team in 1973. Since then, these effects have been studied already for 50 years.
 The situation with the heliospheric magnetic field is clear for periods of medium and low sunspot activity — the heliosphere consists of two unipolar “hemispheres” separated by a wavy global heliospheric current sheet and characterized by a general polarity A (unit quantity with the sign of the radial component of the heliospheric magnetic field in the northern hemisphere). Yet there is no consensus on what the inversion of the heliospheric magnetic field is and which effects in the GCR intensity are connected with this phenomenon.
 In this article, we briefly formulate general concepts of the 22-year variation in characteristics of the Sun, heliosphere, and GCR intensity and discuss the observed effects in the GCR intensity, which we attribute to the heliospheric magnetic field reversal. Models for this phenomenon and the results of GCR intensity calculations with these models will be discussed in the next article.

Пятьдесят лет исследования поведения интенсивности ГКЛ в периоды инверсии гелиосферного магнитного поля. I. Наблюдаемые эффекты

The effects of the 22-year variation of solar magnetic fields in the galactic cosmic ray (GCR) intensity were first observed and interpreted as manifestations of inversion of the high-latitude solar magnetic field in properties of heliospheric magnetic fields by the Lebedev Physical Institute team in 1973. Since then, these effects have been studied already for 50 years.
 The situation with the heliospheric magnetic field is clear for periods of medium and low sunspot activity — the heliosphere consists of two unipolar “hemispheres” separated by a wavy global heliospheric current sheet and characterized by a general polarity A (unit quantity with the sign of the radial component of the heliospheric magnetic field in the northern hemisphere). Yet there is no consensus on what the inversion of the heliospheric magnetic field is and which effects in the GCR intensity are connected with this phenomenon.
 In this article, we briefly formulate general concepts of the 22-year variation in characteristics of the Sun, heliosphere, and GCR intensity and discuss the observed effects in the GCR intensity, which we attribute to the heliospheric magnetic field reversal. Models for this phenomenon and the results of GCR intensity calculations with these models will be discussed in the next article.

Forecast of Intense Geomagnetic Storms in February-March 2023, Based on Measurements of Galactic Cosmic Ray Intensity Fluctuations

Forecast of Intense Geomagnetic Storms in February-March 2023, Based on Measurements of Galactic Cosmic Ray Intensity Fluctuations

Temporal variability of galactic cosmic ray intensity and its dependence on various solar parameters observed during solar cycles 23 and 24

Temporal variability of galactic cosmic ray intensity and its dependence on various solar parameters observed during solar cycles 23 and 24

The Influence of Corotating Regions of Interaction of the Solar Wind on Long-Term Variations in the Intensity of Galactic Cosmic Rays

An analysis of the data of spacecraft that scanned large areas of the heliosphere, as well as the resultsof magnetohydrodynamic calculations, indicates that the corotating interaction regions of solar wind (SW),which are almost always present in the low- and mid-latitude heliosphere, sometimes strongly change thelarge-scale characteristics of the heliosphere that are important for long-term variations in the intensity ofgalactic cosmic rays (GCRs). In particular, for Carrington rotation no. 2066 (January–February 2008), theseregions enhance magnetic fields in the inner (r 3–5 AU) heliosphere and weaken them in the middle andfar heliosphere, as well as significantly changing the polarity distribution of heliospheric magnetic fields. Theassumption is made that in this situation the influence of the corotating interaction regions should lead to anincrease in the GCR intensity in many regions of the heliosphere. This paper discusses the process of changingthe polarity distribution of heliospheric magnetic fields due to the interaction of SW streams for Carringtonrotation no. 2066 of different speeds, the simple model of the heliospheric magnetic field without aninteraction between the SW streams of different speeds, as well as the results of numerical two-dimensionalfinite-difference calculations of longitude-averaged GCR intensity with the use of this model in comparisonwith a three-dimensional Monte Carlo calculation based on three-dimensional magnetohydrodynamic simulationof the heliosphere.

The Influence of Corotating Regions of Interaction of the Solar Wind on Long-Term Variations in the Intensity of Galactic Cosmic Rays

The Influence of Corotating Regions of Interaction of the Solar Wind on Long-Term Variations in the Intensity of Galactic Cosmic Rays

Флуктуации интенсивности галактических космических лучей перед геомагнитной бурей 25-26 августа 2018 года

В данной работе с целью создания методов прогноза негативных проявлений космической погоды исследуется динамика флуктуаций интенсивности галактических космических лучей во время сильной геомагнитной бури 25-26 августа 2018 года. Флуктуации интенсивности космических лучей - это квазипериодические вариации с периодами менее 3-х часов, которые эпизодически возникают в межпланетном пространстве во время крупномасштабных возмущений солнечного ветра. Эти возмущения обусловлены распространением межпланетных ударных волн, выбросов корональной массы, высокоскоростных потоков, которые во многом и определяют космическую погоду. Для анализа привлекались 1-минутные исправленные на давление данные измерений нейтронных мониторов станций космических лучей Бухта Тикси и Якутск, а также 1-минутные данные прямых измерений межпланетного магнитного поля, плотности и скорости солнечного ветра на космическом аппарате WIND. В результате установлено, что перед началом бури на инерционном участке спектров турбулентности солнечного ветра в области частот ~10-4 ÷ 8.33·10-3 Гц наблюдались быстрые магнитозвуковые волны значительной амплитуды. Предполагается, что эти волны были сгенерированы в области взаимодействия медленного и быстрого потоков солнечного ветра, вызвавшего эту геомагнитную бурю. При этом поток галактических космических лучей был подвержен модуляции со стороны быстрых магнитозвуковых волн. Это проявилось в измерениях нейтронных мониторов как регистрация значимых когерентных флуктуаций интенсивности галактических космических лучей более чем за сутки до начала геомагнитной бури. Полученные результаты указывают на возможность осуществления кратковременного прогноза начала сильных геомагнитных бурь в режиме реального времени на основе использования данных измерений станций космических лучей. This paper investigates the dynamics of galactic cosmic ray intensity fluctuations during a strong geomagnetic storm on 25-26 August 2018 in order to establish methods for predicting negative space weather manifestations. Cosmic ray intensity fluctuations are quasi-periodic variations with periods of less than 3 hours, which occur episodically in interplanetary space during large-scale disturbances of the solar wind. These disturbances are due to the propagation in space of interplanetary shock waves, coronal mass ejections and high-speed solar wind flows, which largely determine space weather. The analysis involved 1-minute pressure-corrected measurement data from neutron monitors at the Tiksi Bay and Yakutsk cosmic ray stations, as well as 1-minute data from direct measurements of the interplanetary magnetic field, solar wind density and speed onboard the WIND spacecraft. As a result, it was found that immediately before the start of the storm, fast magnetosonic waves of significant amplitude were observed in the inertial section of the solar wind turbulence spectra in the frequency range ~10-4 ÷ 8.33·10-3 Hz. It is assumed that these waves were generated in the region of interaction between slow and fast solar wind streams, which caused this geomagnetic storm. At the same time, the galactic cosmic ray flux was subject to modulation by fast magnetosonic waves. This manifested in measurements of neutron monitors as the registration of significant coherent galactic cosmic ray intensity fluctuations more than a day before the onset of a geomagnetic storm. The obtained results indicate the possibility of real-time short-term prediction of the onset of strong geomagnetic storms using data measured by cosmic ray stations.