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Solar Modulation of Cosmic Rays
Abstract and Figures
This is an overview of the solar modulation of cosmic rays in the
heliosphere. It is a broad topic with numerous intriguing aspects so that a
research framework has to be chosen to concentrate on. The review focuses on
the basic paradigms and departure points without presenting advanced
theoretical or observational details for which there exists a large number of
comprehensive reviews. Instead, emphasis is placed on numerical modeling which
has played an increasingly signi?cant role as computational resources have
become more abundant. A main theme is the progress that has been made over the
years. The emphasis is on the global features of CR modulation and on the
causes of the observed 11-year and 22-year cycles and charge-sign dependent
modulation. Illustrative examples of some of the theoretical and observational
milestones are presented, without attempting to review all details or every
contribution made in this ?eld of research. Controversial aspects are discussed
where appro- priate, with accompanying challenges and future prospects. The
year 2012 was the centennial celebration of the discovery of cosmic rays so
that several general reviews were dedicated to historical aspects so that such
developments are brie y presented only in a few cases.
Figures - available via license: Creative Commons Attribution-NonCommercial 4.0 International
Content may be subject to copyright.
... Therefore, continuous monitoring of the GCR flux anisotropies and variabilities at individual ground stations is relevant for Space Weather (SW) research as it may serve as a tool for remote sensing of the IMF (e.g. Kudela et al., 2000;Potgieter, 2013). ...
... The solar-controlled modulation of the GCR flux observed at Earth is generally divided into different types according to the timescale of the variation: the 22-yr, the 11-yr, the 27-day, the diurnal variation (DV) and the Forbush-type (Grieder, 2001). In addition to the aforementioned variations, there are several long-term periodicities (Potgieter, 2013) as well as a recently observed anomalous anisotropy specifically in the polar region (e.g. Gil et al., 2018). ...
A new water-Cherenkov radiation detector, located at the Argentine Marambio Antarctic Base (64.24S-56.62W), has been monitoring the variability of galactic cosmic ray (GCR) flux since 2019. One of the main aims is to provide experimental data necessary to study interplanetary transport of GCRs during transient events at different space/time scales. In this paper we present the detector and analyze observations made during one full year. After the analysis and correction of the GCR flux variability due to the atmospheric conditions (pressure and temperature), a study of the periodicities is performed in order to analyze modulations due to heliospheric phenomena. We can observe two periods: (a) 1 day, associated with the Earth's rotation combined with the spatial anisotropy of the GCR flux; and (b) $\sim$ 30 days due to solar impact of stable solar structures combined with the rotation of the Sun. From a superposed epoch analysis, and considering the geomagnetic effects, the mean diurnal amplitude is $\sim$ 0.08% and the maximum flux is observed in $\sim$ 15 hr local time (LT) direction in the interplanetary space. In such a way, we determine the capability of Neurus to observe anisotropies and other interplanetary modulations on the GCR flux arriving at the Earth.
... troposphere in the past. The flux of galactic cosmic rays near Earth is modulated by solar magnetic activity (Potgieter, 2013;Cliver, Richardson, and Ling, 2013) that is often quantified via the modulation potential of the solar wind and heliospheric magnetic field (Caballero-Lopez and Moraal, 2004;Usoskin et al., 2005), after accounting for the effect of Earth's slowly changing geomagnetic field, which provides additional shielding from cosmic rays (Usoskin, Solanki, and Korte, 2006;Snowball and Muscheler, 2007). Production tables for individual isotopes have been computed by Webber and Higbie (2003), Usoskin andKovaltsov (2008), Webber, Higbie, andMcCracken (2007), and Kovaltsov, Mishev, and Usoskin (2012). ...
We report progress on the ongoing recalibration of the Wolf sunspot number (SN\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$S_{\mathrm{N}}$\end{document}) and group-sunspot number (GN\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$G_{\mathrm{N}}$\end{document}) following the release of version 2.0 of SN\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$S_{\mathrm{N}}$\end{document} in 2015. This report constitutes both an update of the efforts reported in the 2016 Topical Issue of Solar Physics and a summary of work by the International Space Science Institute (ISSI) International Team formed in 2017 to develop optimal SN\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$S_{\mathrm{N}}$\end{document} and GN\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$G_{\mathrm{N}}$\end{document} reconstruction methods while continuing to expand the historical sunspot-number database. Significant progress has been made on the database side while more work is needed to bring the various proposed SN\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$S_{\mathrm{N}}$\end{document} and (primarily) GN\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$G_{\mathrm{N}}$\end{document} reconstruction methods closer to maturity, after which the new reconstructions (or combinations thereof) can be compared with (a) “benchmark” expectations for any normalization scheme (e.g., a general increase in observer normalization factors going back in time), and (b) independent proxy data series such as F10.7 and the daily range of variations of Earth’s undisturbed magnetic field. New versions of the underlying databases for SN\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$S_{\mathrm{N}}$\end{document} and GN\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$G_{\mathrm{N}}$\end{document} will shortly become available for years through 2022 and we anticipate the release of the next versions of these two time series in 2024.
... We observe a dispersion of the fluxes below 10 GeV because the lower energetic particles (<10 GeV) interact more with the heliosphere, the magnetosphere, the atmosphere and even the vehicle itself. Therefore, depending on the location (and the presence of an atmosphere or not) and the solar modulation [34,35], the particle flux obviously varies. Above 10 GeV, data are very similar whatever the measurement system, since the particles are too energetic to be affected enough to change the results. ...
The device downscaling of electronic components has given rise to the need to consider specific failures in onboard airplane electronics. Single Event Effects (SEE) are a kind of failures that occur due to radiation in the atmosphere. For the purpose of ensuring onboard electronic reliability, there is a clear need for new tools to predict the SEE rate, at both avionic altitudes and at ground level. In this work, we develop a new tool: RAMSEES (Radiation Atmospheric Model for SEE Simulation), which simulates the atmospheric radiative environment induced by cosmic rays. This multiscale and multi-physics phenomenon is simulated using the Geant4 toolkit, allowing the creation of a database to characterize the radiation environment in the atmosphere as a function of altitude. We show the need to simulate very high-energy particles such as 100 TeV space protons, because they are the main contributor of radiation at avionic altitudes as well as at ground level. Our approach shows a good agreement with the experimental data, the standards, and other models, and it also points out some discrepancies, especially below 18 km of altitude. RAMSEES can be the basis of the estimation of the SEE rate from ground level to the stratosphere, at any given position and time.
... scattering and diffusion on magnetic irregularities, convection by expanding solar wind, adiabatic cooling, and large-scale drifts. All these processes are ultimately driven by solar activity leading to the solar modulation of cosmic-ray flux near Earth so that the cosmic-ray flux is stronger when solar activity is weak and vice-versa (e.g., Potgieter, 2013). Thus, knowing the modulated flux of GCRs at a moment in time, one can assess the level of solar activity slightly before that (within one year - Koldobskiy et al, 2022). ...
Solar activity has a cyclic nature with the ~11-year Schwabe cycle dominating its variability on the interannual timescale. However, solar cycles are significantly modulated in length, shape and magnitude, from near-spotless grand minima to very active grand maxima. The ~400-year-long direct sunspot-number series is inhomogeneous in quality and too short to study robust parameters of long-term solar variability. The cosmogenic-isotope proxy extends the timescale to twelve millennia and provides crucial observational constraints of the long-term solar dynamo modulation. Here, we present a brief up-to-date overview of the long-term variability of solar activity at centennial--millennial timescales. The occurrence of grand minima and maxima is discussed as well as the existing quasi-periodicities such as centennial Gleissberg, 210-year Suess/de Vries and 2400-year Hallstatt cycles. It is shown that the solar cycles contain an important random component and have no clock-like phase locking implying a lack of long-term memory. A brief yet comprehensive review of the theoretical perspectives to explain the observed features in the framework of the dynamo models is presented, including the nonlinearity and stochastic fluctuations in the dynamo. We keep gaining knowledge of the processes driving solar variability with the new data acquainted and new models developed.
... Because of the particular needs in sport such as increased energy requirements, sports players have been in search for a diversity of food, utilizing different types of diets, and taking supplements in able to increase their sporting performance. Such situations demonstrate the importance of having a good nutritional knowledge for both a general healthy life, and for long-term sport life of athletes (Calella, iacullo, Valerio, 2017;Potgieter, 2013). ...
the aim of the present study was to validate and implement a nutrition questionnaire to measure nutrition knowledge of university students, and athletes. Male, and female students (N = 476) voluntarily participated in the survey in 2019. Non-health related (n = 156), nutrition students (n = 163), and varsity athletes (n = 157) responded to the questionnaire, twice with 15 days' interval between. in this study, new "general and Sport Nutrition Knowledge" (gSNK) and, two other "Short general Nutrition Knowledge" (SgNK) and, "Short Sport Nutrition Knowledge" (SSNK) questionnaires were used to determine the validation of the survey. one-way ANovA, t Test, Pearson correlation coefficient, and cronbach's α statistics were used to evaluate validity and reliability (p < 0.05). the internal consistency, test-retest reliability, concurrent validity with two similar tools, and construct validity among the groups of students for nutrition knowledge were employed throughout the data analysis. Nutrition students outperformed in all nutrition knowledge sections. respectively, athletes were the second, and non-nutrition related students were the third in sport nutrition (p < 0.05). With regard to general and total nutrition knowledge scores, female students performed significantly better than males (p < 0.01). Modified questionnaire was found to be valid, reliable, and suitable tool for Eurasian university students, and athletes. results also illustrated that the intermittently nutrition educations are required for athletes, as it is recommended in related literature.
... The effect of SW in the observed CR properties is called the solar modulation. One of the well-known effects is the 11 and 22 year period time variation of the observed GCR intensity (e.g., McDonald 1998;Potgieter 2013). The intensity of GCRs anticorrelates with a sunspot number. ...
Solar activity has a cyclic nature with the ≈11-year Schwabe cycle dominating its variability on the interannual timescale. However, solar cycles are significantly modulated in length, shape and magnitude, from near-spotless grand minima to very active grand maxima. The ≈400-year-long direct sunspot-number series is inhomogeneous in quality and too short to study robust parameters of long-term solar variability. The cosmogenic-isotope proxy extends the timescale to twelve millennia and provides crucial observational constraints of the long-term solar dynamo modulation. Here, we present a brief up-to-date overview of the long-term variability of solar activity at centennial – millennial timescales. The occurrence of grand minima and maxima is discussed as well as the existing quasi-periodicities such as centennial Gleissberg, 210-year Suess/de Vries and 2400-year Hallstatt cycles. It is shown that the solar cycles contain an important random component and have no clock-like phase locking implying a lack of long-term memory. A brief yet comprehensive review of the theoretical perspectives to explain the observed features in the framework of the dynamo models is presented, including the nonlinearity and stochastic fluctuations in the dynamo. We keep gaining knowledge of the processes driving solar variability with the new data acquainted and new models developed.
A key first step to constrain the impact of energetic particles in exoplanet atmospheres is to detect the chemical signature of ionisation due to stellar energetic particles and Galactic cosmic rays. We focus on GJ$\,$436, a well-studied M dwarf with a warm Neptune-like exoplanet. We demonstrate how the maximum stellar energetic particle momentum can be estimated from the stellar X-ray luminosity. We model energetic particle transport through the atmosphere of a hypothetical exoplanet at orbital distances between $a=0.01-0.2\,$au from GJ$\,$436, including GJ$\,$436$\,$b's orbital distance (0.028$\,$au). For these distances we find that, at top-of-atmosphere, stellar energetic particles ionise molecular hydrogen at a rate of $\zeta_{\rm StEP,H_2} \sim 4\times10^{-10}-2\times10^{-13}\,\mathrm{s^{-1}}$. In comparison, Galactic cosmic rays alone lead to $\zeta_{\rm GCR, H_2}\sim2\times 10^{-20}-10^{-18} \,\mathrm{s^{-1}}$. At 10au we find that ionisation due to Galactic cosmic rays equals that of stellar energetic particles: $\zeta_{\rm GCR,H_2} = \zeta_{\rm StEP,H_2} \sim 7\times10^{-18}\,\rm{s^{-1}}$ for the top-of-atmosphere ionisation rate. At GJ$\,$436$\,$b's orbital distance, the maximum ion-pair production rate due to stellar energetic particles occurs at pressure $P\sim 10^{-3}\,$bar while Galactic cosmic rays dominate for $P>10^2\,$bar. These high pressures are similar to what is expected for a post-impact early Earth atmosphere. The results presented here will be used to quantify the chemical signatures of energetic particles in warm Neptune-like atmospheres.
During the crossings of the Voyager 1 and 2 spacecraft of the solar wind termination shock (TS), the power-law spectra expected from diffusive shock acceleration of anomalous cosmic rays (ACRs) at the TS were not observed. The spectra seem to be modulated, but unfolding to the expected form as the spacecraft move away from the TS into the heliosheath. We use a comprehensive numerical model to study these new observations in order to gain understanding as to what acceleration processes may be involved. The model is applied to computing the features of ACR Oxygen spectra in the inner and outer heliosphere. It incorporates diffusive shock acceleration at the TS, a latitude dependent compres-sion ratio and injection efficiency based on the results of hydrodynamic models. In addition, it incorporates adiabatic heating and stochastic acceleration (diffu-sion in momentum space) in the heliosheath.
We show that the variations of the interplanetary magnetic field strength (B) over a 22-year period are tracked by the inverted profile of the cosmic ray density measured by neutron monitors. We suggest that global changes in the Sun's magnetic field are more important for long-term modulation than magnetic field enhancements resulting from the merging of high-speed flows and coronal mass ejections in the outer heliosphere. The unexpectedly close relationship that we find between the “tilt angle” of the heliospheric current sheet and the cosmic ray density away from solar minimum for both polarity states of the solar magnetic field may be accounted for by the anticorrelation between the cosmic ray density and field strength variations.
Magnetic effects are ubiquitous and known to be crucial in space physics and astrophysical media. We have now the opportunity to probe these effects in the outer heliosphere with the two spacecraft Voyager 1 and 2. Voyager 1 crossed, in December 2004, the termination shock and is now in the heliosheath. On August 30, 2007 Voyager 2 crossed the termination shock, providing us for the first time in-situ measurements of the subsonic solar wind in the heliosheath. With the recent in-situ data from Voyager 1 and 2 the numerical models are forced to confront their models with observational data. Our recent results indicate that magnetic effects, in particular the interstellar magnetic field, are very important in the interaction between the solar system and the interstellar medium. We summarize here our recent work that shows that the interstellar magnetic field affects the symmetry of the heliosphere that can be detected by different measurements. We combined radio emission and energetic particle streaming measurements from Voyager 1 and 2 with extensive state-of-the art 3D MHD modeling, to constrain the direction of the local interstellar magnetic field. The orientation derived is a plane ∼60°–90° from the galactic plane. This indicates that the field orientation differs from that of a larger scale interstellar magnetic field, thought to parallel the galactic plane. Although it may take 7–12 years for Voyager 2 to leave the heliosheath and enter the pristine interstellar medium, the subsonic flows are immediately sensitive to the shape of the heliopause. The flows measured by Voyager 2 in the heliosheath indicate that the heliopause is being distorted by local interstellar magnetic field with the same orientation as derived previously. As a result of the interstellar magnetic field the solar system is asymmetric being pushed in the southern direction. The presence of hydrogen atoms tend to symmetrize the solutions. We show that with a strong interstellar magnetic field with our most current model that includes hydrogen atoms, the asymmetries are recovered. It remains a challenge for future works with a more complete model, to explain all the observed asymmetries by V1 and V2. We comment on these results and implications of other factors not included in our present model.
The theory of the acceleration, ionization, and transport of anomalous cosmic ray oxygen, including all eight nonzero charge states, is discussed in the framework of a model in which the primary acceleration occurs at the termination shock of the solar wind. This generalizes previous work that considered only singly charged anomalous cosmic rays. The ratio of multiply charged to singly charged anomalous cosmic rays in the inner heliosphere is found in simulations to increase rapidly above a characteristic energy Tc of ∼20 MeV nucleon-1. The value of Tc is not very sensitive to variations in the parameters, but it does increase somewhat as the particles' characteristic acceleration time is decreased. Tc is close to the electrostatic potential between the heliospheric pole and equator, suggesting that singly charged particles cannot be readily accelerated beyond this potential energy whereas those with higher charge can. These simulation results are found to be in good agreement with recent SAMPEX observations, reported in a companion Letter. © 1996. The American Astronomical Society. All rights reserved.
The heliospheric current sheet (HCS) is the boundary between open oppositely directed magnetic field lines which commonly originate as the outward extension of the solar magnetic dipole. The dipole tilt, the rotation of the Sun, and the outward propagation of the solar wind cause peaks and valleys in the current sheet which spiral outward. The HCS extends throughout the heliosphere to the greatest distances reached by Pioneer and Voyager. It serves as a magnetic equator, and solar wind parameters including speed, temperature, density, and composition vary with distance from the HCS. Extrapolated back to the Sun, especially near solar minimum, the HCS corresponds to the low-latitude streamer belt. Both features are closely related to a neutral line obtained by extrapolating photospheric magnetic fields to a source surface at several solar radii. The current sheet and sector structure persist throughout the solar cycle including solar maximum. At 1 AU the width of the HCS is approximately 10,000 km while a surrounding plasma sheet is thicker by a factor of ∼30. The field inside the HCS does not simply decrease to a null and then reappear with the opposite sense. Instead, the field rotates at nearly constant magnitude from one polarity to the other. In spite of theoretical expectations that fields on opposite sides of the HCS will merge or reconnect, there is little evidence that such is occurring. Many scientific questions remain unanswered. What are the global properties of the HCS near solar maximum, and how faithfully are they reproduced by source surface models? Are multiple HCS crossings caused by waves on the current sheet or by multiple current sheets? What is the effect of coronal mass ejections on the HCS and vice versa?
[1] A nonlinear guiding center (NLGC) theory for diffusion of charged particles perpendicular to the mean magnetic field was recently proposed. Here, we draw attention to a number of attractive features of this theory: (1) The theory provides a natural mechanism to connect the perpendicular mean free path with the parallel mean free path. In fact, the parallel mean free path is the only particle property required to determine uniquely the perpendicular mean free path. (2) Under a broad range of conditions, the theory predicts that the perpendicular mean free path will be of order one percent or a few percent of the parallel mean free path, in agreement with numerical simulations of particle transport. (3) For conditions representative of the inner heliosphere, the theory predicts values of the perpendicular mean free path in agreement with observational determinations from Jovian electrons and from modeling Ulysses observations of Galactic protons.
The centennial anniversary of the discovery of cosmic rays was in 2012. Since this discovery considerable progress has been made on several aspects related to galactic cosmic rays in the heliosphere. It is known that they encounter a turbulent solar wind with an imbedded heliospheric magnetic field when entering the Sun’s domain. This leads to significant global and temporal changes in their intensity inside the heliosphere, a process known as the solar modulation of cosmic rays. The prediction of a charge-sign dependent effect in solar modulation in the late 1970s and the confirmatory observational discoveries can also be considered as a milestone. A short review is given of these predictions based on theoretical and numerical modelling work, the observational confirmation and related issues.
A latitude survey of the cosmic ray intensity at sea level was conducted during the 1986/1987 solar minimum period on commercial vessels of the South African Marine Corporation (SAFMARINE). The results show that the differential response function for the 1986/1987 solar minimum agrees well with that measured in 1965. Both these response functions are significantly lower than those for 1976 and 1954. This result supports the 22-year modulation cycle as predicted, for example, by models including drift effects of the charged cosmic ray particles in the large-scale interplanetary magnetic field. A cross-over of the spectra at rigidities of about 7 GV was also observed. Such a crossover is necessary to explain both the stationary neutron monitor counting rates and the lower-energy balloon and space observations in consecutive solar cycles.