Variation Of Cosmic Ray Intensity Research Articles

Effects of solar activity on production rates of short‐lived cosmogenic radionuclides

AbstractThe solar activity can be quantified by solar modulation parameter Φ that affects the heliospheric magnetic field. This activity influences the intensity of the galactic cosmic ray (GCR) particle flux within the solar system, and consequently, the differential primary particle spectra depend on the solar modulation parameter Φ (MeV). The modulation parameter Φ shows spatial and temporal variations (Leya and Masarik 2009). Some of the solar activity variations are cyclic and result in measurable effects as for example the 11‐year solar cycle. Variations in solar activity only induce small effects on the production of long‐lived cosmogenic radionuclides. This is due to the fact that activities measured in meteorites usually correspond to saturation values and represent long‐term average values. Long‐lived radionuclides often require millions of years of irradiation by GCR to reach saturation and therefore activity cycles average out. In contrast, one can expect strongly pronounced variations for saturation values caused by primary flux intensity variations, if short‐lived radionuclides with half‐lives ranging from days to a few years are investigated. Short‐lived cosmogenic nuclides were the subject of many experimental and theoretical investigations (e.g., Evans et al. 1982; Spergel et al. 1986; Neumann et al. 1997; Komura et al. 2002; Laubenstein et al. 2012). The aim of this work is to develop formulae for calculating production rates of radionuclides with short half‐life, taking into account temporal variations in the primary cosmic ray intensity. The developed formulae were applied to the Kosice and Chelyabinsk meteorites. The results for the Košice meteorite were already published (Povinec et al. 2015). Here, we give a full explanation of underlying model.

Effect of Thunderstorm Electric Field on the Cosmic Ray Secondary Particle Energy at LHAASO

The Large High Altitude Air Shower Observatory (LHAASO) is located in Daocheng, Sichuan. Featured with frequent thunderstorms in summer seasons, it is beneficial to study the influence of atmospheric electric field on cosmic rays during thunderstorms. In this paper, Monte-Carlo simulations are performed to study the effect of thunderstorm electric field on the cosmic ray secondary electron energy at LHAASO. The energy distribution of electrons changes under the action of electric field. In the low energy region, the total number of electrons increases significantly, while at high energies, it does not change obviously. In the electric field of 1700V·cm−1 (above the critical field of the Relativistic Runaway Electron Avalanche (RREA) process), the electrons with an energy less than 120MeV can be accelerated. When the energy is below 60MeV, the number of electrons increases exponentially with an amplitude up to about 2252%. It is consistent with the theory of RREA. When the electric field strength is 1000V·cm−1 (below the threshold of the RREA process), the electrons with an energy less than 70MeV are accelerated, and their number increases significantly, but the increase (about 86%) is far lower than that of the critical field of the RREA process. The physical mechanism for accelerating the cosmic ray secondary particles by the thunderstorm electric field is discussed in the case when the electric field is less than the runaway electric field. These results may provide important information for studying the variations of cosmic ray intensity on the LHAASO detection surface during thunderstorms.

Responses and Periodic Variations of Cosmic Ray Intensity and Solar Wind Speed to Sunspot Numbers

To investigate the periodic behaviour and relationship of sunspot numbers with cosmic ray intensity and solar wind speed, we present analysis from daily data generated from 1995 January to 2018 December. Cross-correlation and wavelet transform tools were employed to carry out the investigation. The analyses confirmed that the cosmic ray intensity correlates negatively with the sunspot numbers, exhibiting an asynchronous phase relationship with a strong negative correlation. The trend in cosmic ray intensity indicates that it undergoes the 11-year modulation that mainly depends on the solar activity in the heliosphere. On the other hand, the solar wind speed neither shows a clear phase relationship nor correlates with the sunspot numbers but shows a wide range of periodicities that could possibly be connected to the pattern of coronal hole configuration. A number of short and midterm variations were also observed from the wavelet analysis, i.e., 64–128 and 128–256 days for the cosmic ray intensity, 4–8, 32–64, 128–256, and 256–512 days for the solar wind speed, and 16–32, 32–64, 128–256, and 256–512 days for the sunspot numbers.

Delineation of possible influence of solar variability and galactic cosmic rays on terrestrial climate parameters

The present paper has investigated the associations of solar activity (SA), represented by total solar irradiance (TSI), galactic cosmic rays (GCR) and terrestrial climate parameters in particular the global cloudiness and global surface temperature. To that end, we have analysed thirty five years (1983–2018) data of these parameters and have applied the Granger-causality test in order to assess whether there is any potential predictability power of one indicator to the other. The correlations among the involved parameters are tested using Vector Auto Regression (VAR) model and variance decomposition method. As a result of the above analysis, we have found that the TSI is an important factor and has contributed about 8.77 ± 0.42% in the cosmic ray intensity variations. In case of cloud cover variations, the other three parameters (TSI, cosmic ray and global surface temperature) have played a significant role. Further, the TSI changes have contributed 1.68 ± 0.03% fluctuations in the variance of the cloud cover while the cosmic ray intensity and global surface temperature have contributed about 4.89 ± 0.08% and 10.87 ± 1.41% respectively. In case of the global surface temperature anomaly both TSI and cloud covers have contributed about 5.07 ± 0.47% and 14.42 ± 2.13% fluctuations respectively. Additionally, we have also assessed the impact of internal climate oscillations like multivariate ENSO index (MEI), north Atlantic oscillations (NAO) and quasi biennial oscillations (QBO) on cloud cover variations. The contribution of these internal oscillations e.g. ENSO, NAO and QBO in cloud cover variation were reported as 7.48 ± 1.02%, 5.51 ± 0.16% and 1.36 ± 0.43% respectively.

The Origin of Short-Time Variations in Cosmic-Ray Intensity

It is well known today that a continuous stream of highly ionized plasma is emitted from the Sun’s surface. This plasma is called the solar wind and consists of protons, electrons, and light nuclei. The solar wind pushes the solar magnetic field into interplanetary space to form the interplanetary magnetic field. The interplanetary magnetic field is a dynamical system that depends on the solar cycle and the Sun’s rotation phase. Thus, the Solar System is a natural plasma physics laboratory with an enormous multitude of different effects showing the current state of the system. By recording cosmic-ray fluxes, one can study the behavior of the interplanetary magnetic field and obtain information about processes that occur both on the Sun’s surface and throughout the Solar System. The main short-time variations in cosmic-ray intensity include the 27-day variations and the Forbush decreases. These variations are caused by complex solar plasma structures, which are generated by different processes on the Sun’s surface and propagate through space in a wide range of velocities. Cosmic-ray fluxes recorded with the PAMELA magnetic spectrometer on board the Resurs DK1 satellite in 2006–2016 are used to show some examples of cosmic-ray variations.

Solar activity imprints in tree ring-data from northwestern Russia

The Sun's role in climate variability is now a subject of debates, especially in the context of understanding contribution of solar forcing to modern global warming. Besides, there are some evidences of the approaching new Grand Solar Minimum with Little Ice Age climatic conditions. This expectation is based on the occurrence of the extended solar minimum of 2006–2009. To investigate the possible Sun-climate connection the regional tree-ring chronology covering the period from 1445 to 2005 was analyzed. A total of 36 timber cores of pine Pinus sylvestris L. were sampled near the northern tree-line at Loparskaya station (68.6 N, 33.3 E), including the oldest living pine with more than 560 years of age. The data were processed using modern methods adopted in dendrochronology (cross-dating and standardization) with the help of COFECHA and ARSTAN programs. The analysis revealed significant cooling events, coinciding with the Spoerer (1400–1540), Maunder (1645–1715), Dalton (1790–1830), and Gleissberg (1880–1910) Grand Solar Minima. The application of MTM-spectrum and wavelet decomposition analysis identified the existence of the main cycles of solar activity (5.4, 11.7 and 22 years) in tree-ring width variations. As possible extraterrestrial forcings of climate change we consider here variations in solar irradiance and cosmic ray intensity modulated by the interplanetary magnetic field. As solar and cosmic ray activity indicators we used the annual sunspot number, geomagnetic aa index and Be^10 cosmogenic isotope records. To examine the relationship in time-frequency scale between tree-ring growth and solar activity, the cross wavelet transform and wavelet coherence analysis were applied to the time series. The wavelet coherence analysis identified that the 11 yr and 22 yr periodicities were clearly manifested in the all solar-tree rings connections during and around the Grand Minima of solar activity including the Maunder minimum, when, as is known, sunspots were practically absent. These results confirm the existence of solar activity effect on climate and tree growth above the Arctic Circle and are important for understanding the modern climatic processes.

Modulation effect of magnetic corotating trap on 27-day cosmic ray variation in November–December 2014

We study the 27-day cosmic-ray (CR) intensity variation occurring in November–December 2014, using ground-based measurements from the worldwide network of neutron monitors and GOES-15 satellites. A determining factor in the considerable difference between amplitudes of the 27-day CR variation in November–December 2014 is shown to be significant changes in energy losses taking place when particles move in regular heliospheric electromagnetic fields. In this period, there was a long-living corotating trap produced by a vast coronal hole in the south of the Sun in interplanetary space. Configuration of this trap induced the energy loss of ~3–20 GeV CRs, due to which ground-based neutron monitors recorded an abnormally large amplitude of the 27-day variation.

Модуляционное влияние коротирующей магнитной ловушки на 27-дневные вариации космических лучей в ноябре–декабре 2014 г.

We study the 27-day cosmic-ray (CR) intensity variation occurring in November–December 2014, using ground-based measurements from the worldwide network of neutron monitors and GOES-15 satellites. A determining factor in the considerable difference between amplitudes of the 27-day CR variation in November–December 2014 is shown to be significant changes in energy losses taking place when particles move in regular heliospheric electromagnetic fields. In this period, there was a long-living corotating trap produced by a vast coronal hole in the south of the Sun in interplanetary space. Configuration of this trap induced the energy loss of ~3–20 GeV CRs, due to which ground-based neutron monitors recorded an abnormally large amplitude of the 27-day variation.

Galactic Cosmic-Ray Anisotropies: Voyager 1 in the Local Interstellar Medium

Abstract Since crossing the heliopause on 2012 August 25, Voyager 1 observed reductions in galactic cosmic ray count rates caused by a time-varying depletion of particles with pitch angles near 90°, while intensities of particles with other pitch angles remain unchanged. Between late 2012 and mid-2017, three large-scale events occurred, lasting from ∼100 to ∼630 days. Omnidirectional and directional high-energy data from Voyager 1’s Cosmic Ray Subsystem are used to report cosmic ray intensity variations. Omnidirectional (≳20 MeV) proton-dominated measurements show up to a 3.8% intensity reduction. Bidirectional (≳70 MeV) proton-dominated measurements taken from various spacecraft orientations provide insight about the depletion region’s spatial properties. We characterize the anisotropy as a “notch” in an otherwise uniform pitch angle distribution of varying depth and width centered about 90° in pitch angle space. The notch averages 22° wide and 15% deep, signifying a depletion region that is broad and shallow. There are indications that the anisotropy is formed by a combination of magnetic trapping and cooling downstream of solar-induced transient disturbances in a region that is also likely influenced by the highly compressed fields near the heliopause.

27-day variation of galactic cosmic ray intensity by PAMELA experiment. Relationship with heliospheric parameters

We analyzed the dynamics of the 27-day variation of galactic cosmic rays (GCR) using PAMELA data in the solar cycle 24 covering the period of 2006-2015. We studied the time line of the proton and helium spectra for different rigidities measured by PAMELA and compared with neutron monitor (NM) observations. We studied the relationship between the 27-day variations of GCR and heliospheric parameters: solar wind velocity and heliospheric magnetic field (HMF). We found that the 27-day variation observed by PAMELA was changing over the solar cycle 24. Near the solar minimum in the 2007-2008 it was observed the stationary 27-day variation with stable amplitude and time of maximum for almost ∼8 solar rotations. Solar wind velocity and Bx component of the HMF also showed the same clear 27-day periodicity. The recurrent changes of solar wind velocity were in strong antiphase with changes of GCR. In contrary in the rising phase of the solar cycle 24 the period of quasi-recurrent GCR variations was much more variable in time and in duration, in average 27-days, but also with the strong contamination of the higher harmonics. The antiphase relation between GCR and solar wind is not so clearly pronounced. Moreover, in the rising phase of the solar cycle 24 we established in all analyzed parameters some wave packages, periodically enhanced, taking place averagely each 1.5-2 years, suggesting the occurrence of the quasi biannual oscillations (QBOs).

The Behaviour of Galactic Cosmic-Ray Intensity During Solar Activity Cycle 24

We have studied long-term variations of galactic cosmic-ray (GCR) intensity in relation to the sunspot number (SSN) during the most recent solar cycles. This study analyses the time lag between the GCR intensity and SSN, and hysteresis plots of the GCR count rate against SSN for Solar Cycles 20 – 23, to validate a methodology against previous results in the literature, before applying the method to provide a timely update on the behaviour of Cycle 24. Plots of SSN versus GCR show a clear difference between the odd- and even-numbered cycles. Linear and elliptical models have been fit to the data, with the linear fit and elliptical model proving the more suitable model for even- and odd-numbered solar-activity cycles, respectively, in agreement with previous literature. Through the application of these methods for Solar Cycle 24, it has been shown that Cycle 24 experienced a lag of two to four months between the GCR intensity and SSN, and this follows the trend of the preceding activity cycles, albeit with a slightly longer lag than previous even-numbered cycles. It has been shown through the hysteresis analysis that the linear fit is a better representative model for Cycle 24, as the ellipse model does not show a significant improvement, which is also in agreement with previous even-numbered cycles.

Solar Cyclic Modulation of Diurnal Variation in Cosmic Ray Intensity

Cosmic rays are ions that move at relativistic speeds. They generate secondary cosmic rays by successive collisions with atmospheric particles, and then, the secondary particles reach the ground. The secondary particles are mainly neutrons and muons, and the neutrons are observed by the ground neutron monitor. This study compared the diurnal variation in cosmic ray intensity obtained via harmonic analysis and that obtained through the pile-up method, which was examined in a previous study. In addition, we analyzed the maximum phase of the diurnal variation using four neutron monitors with a cutoff rigidity below approximately 6 GV, located at similar longitudes to the Oulu and Rome neutron monitors. Expanding the data of solar cycles 20–24, we examined the time of the maximum cosmic ray intensity, that is, the maximum phase regarding the solar cyclic modulation. During solar cycles 20–24, the maximum phase derived by harmonic analysis showed no significant difference with that derived by the pile-up method. Thus, the pile-up method, a relatively straightforward process to analyze diurnal variation, could replace the complex harmonic analysis. In addition, the maximum phase at six neutron monitors shows the 22-year cyclic variation very clearly. The maximum phase tends to appear earlier and increase the width of the variation in solar cycles as the cutoff rigidity increases.

Evidence of Energy and Charge Sign Dependence of the Recovery Time for the 2006 December Forbush Event Measured by the PAMELA Experiment

Abstract New results on the short-term galactic cosmic-ray (GCR) intensity variation (Forbish decrease) in 2006 December measured by the PAMELA instrument are presented. Forbush decreases are sudden suppressions of the GCR intensities, which are associated with the passage of interplanetary transients such as shocks and interplanetary coronal mass ejections (ICMEs). Most of the past measurements of this phenomenon were carried out with ground-based detectors such as neutron monitors or muon telescopes. These techniques allow only the indirect detection of the overall GCR intensity over an integrated energy range. For the first time, thanks to the unique features of the PAMELA magnetic spectrometer, the Forbush decrease, commencing on 2006 December 14 and following a CME at the Sun on 2006 December 13, was studied in a wide rigidity range (0.4–20 GV) and for different species of GCRs detected directly in space. The daily averaged GCR proton intensity was used to investigate the rigidity dependence of the amplitude and the recovery time of the Forbush decrease. Additionally, for the first time, the temporal variations in the helium and electron intensities during a Forbush decrease were studied. Interestingly, the temporal evolutions of the helium and proton intensities during the Forbush decrease were found to be in good agreement, while the low rigidity electrons ( GV) displayed a faster recovery. This difference in the electron recovery is interpreted as a charge sign dependence introduced by drift motions experienced by the GCRs during their propagation through the heliosphere.

Distribution of temperature coefficient density for muons in the atmosphere

To date, several dozens of new muon detectors have been built. When studying cosmic-ray intensity variations with these detectors, located deep in the atmosphere, it is necessary to calculate all character-istics, including the distribution of temperature coeffi-cient density for muons in the atmosphere, taking into account their specific geometry. For this purpose, we calculate the density of temperature coefficients of muon intensity in the atmosphere at various zenith angles of detection at sea level and at various depths underground for different absorption ranges of primary protons and pions in the atmosphere.

Распределение плотности температурных коэффициентов для мюонов в атмосфере

To date, several dozens of new muon detectors have been built. When studying variations in cosmic-ray intensity with these detectors, located deep in the atmosphere, it is necessary to calculate all characteristics, including the distribution of temperature coefficient density for muons in the atmosphere, taking into account their specific geometry. For this purpose, we calculate the density of temperature coefficients of muon intensity in the atmosphere at various zenith angles of detection at sea level and at various depths underground for different absorption ranges of primary protons and pions in the atmosphere.

Heliospheric modulation of cosmic rays: model and observation

This paper presents the basic model of cosmic ray modulation in the heliosphere, developed in Yu.G. Shafer Institute of Cosmophysical Research and Aeronomy of the Siberian Branch of RAS. The model has only one free modulation parameter: the ratio of the regular magnetic field to the turbulent one. It may also be applied to the description of cosmic ray intensity variations in a wide energy range from 100 MeV to 100 GeV. Possible mechanisms of generation of the mentioned turbulence field are considered. The primary assumption about the electrical neutrality of the heliosphere appears to be wrong, and the zero potential needed to match the model with observations in the plane of the solar equator can be achieved if the frontal point of the heliosphere, which is flowed around by interstellar gas, lies near the mentioned plane. We have revealed that the abnormal rise of cosmic ray intensity at the end of solar cycle 23 is related to the residual modulation produced by the subsonic solar wind behind the front of a standing shock wave. The model is used to describe features of cosmic ray intensity variations in several solar activity cycles.

A model of possible variations of the galactic cosmic ray intensity over the recent billion years

Based on the analysis of published data on exposure ages of iron meteorites determined with the 40K/K method (T K) and ages calculated using short-lived cosmogenic radionuclides (with the half-life T 1/2 < 1 Myr) in combination with stable cosmogenic isotopes of noble gases (TRS), the following results have been obtained. (1) The distribution of T RS ages (106 values) has an exponential shape, similar to that for ordinary chondrites, but different from the distribution of T K ages (80 values). The difference is most likely due to small amounts of data for meteorites with low T K ages (less than ~200–300 Myr). The latter can be ascribed to the difficulty of measurement of small concentrations of cosmogenic potassium isotopes. This circumstance makes the selection of meteorites with 40K/K ages nonrepresentative and casts doubt on the correctness of conclusions about the variations of the intensity of galactic cosmic rays (GCR) based on the analysis of distribution of these ages. (2) The magnitude of the known effect (systematic overestimation of T K ages in comparison with T RS ages) has been refined. The value k = T K/T RS = 1.51 ± 0.03 is acquired for the whole population of data. We have shown the inefficiency of the explanation of this effect on account of an exponential change in the GCR intensity (I T ) with time (T) according to the relation I T = I 0exp(–γT) over the whole range of ages of iron meteorites. (3) In order to explain the overestimation of T K ages in comparison with T RS ages, a model has been proposed, according to which the GCR intensity has exponentially increased in the interval of 0–1500 Myr governed by the relation: I T = I T = 1500 (1 + αexp(–βT)). For one of the variants of this model, the GCR intensity has exponentially increased by a factor of two only over the recent ~300 Myr, remaining approximately constant for the rest of the time. The data acquired with the use of this model indicate that the measured T K ages are close to the actual time that the meteorites existed in space; the data are in agreement with the observed exponential distribution of T RS ages.

Гелиосферная модуляция космических лучей: модель и наблюдения

This paper presents the basic model of cosmic ray modulation in the heliosphere, developed in Yu.G. Shafer Institute of Cosmophysical Research and Aeronomy of the Siberian Branch of RAS. The model has only one free modulation parameter: the ratio of the regular magnetic field to the turbulent one. It may also be applied to the description of cosmic ray intensity variations in a wide energy range from 100 MeV to 100 GeV. Possible mechanisms of generation of the mentioned turbulence field are considered. The primary assumption about the electrical neutrality of the heliosphere appears to be wrong, and the zero potential needed to match the model with observations in the plane of the solar equator can be achieved if the frontal point of the heliosphere, which is flowed around by interstellar gas, lies near the mentioned plane. We have revealed that the abnormal rise of cosmic ray intensity at the end of solar cycle 23 is related to the residual modulation produced by the subsonic solar wind behind the front of a standing shock wave. The model is used to describe features of cosmic ray intensity variations in several solar activity cycles.

Causes of long-term variations in galactic cosmic ray intensity in the inner heliosphere

Alternative points of view on the main reasons for the long-term (11- and 22-year) variations in the galactic cosmic ray intensity observed at the Earth’s orbit are discussed. Arguments are given in support of the opinion that the influence of the poloidal branch of solar activity on the 11-year variation in GCR intensity is important. Approaches toward a phenomenological description of the behavior of GCR intensity are discussed.

Diurnal Variation of Cosmic Ray Intensity at Different Group of Geomagnetic Index (Ap)

The solar modulation of Galactic Cosmic Rays (GCR) is revealed in the record of neutron monitors in terms of daily variation. Day-to-day and long term basis daily variations have been investigated for the recent period from 1965 to 2015 along with geomagnetic disruption index Ap on twelve-monthly average basis. Here Ap index has been used as a placeholder for the solar bring on interplanetary disturbances. It is create that, in general on an annual average basis, both the diurnal amplitude as well as the diurnal phase is considerably lower in the years of low Ap values, through the period 1965 to 2015. Such as a result was also informed for the earlier periods. However, anomalous and determined results for the diurnal variations have been received when the daily values of Ap are diffused in five groups with the first group demonstrating low Ap condition (i.e. quite periods) and the last group naturally representing the disturbed conditions.