GCR Modulation Research Articles

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.

О проявлении коротирующих областей взаимодействия солнечного ветра в вариациях интенсивности ГКЛ

The regions of interaction between solar wind streams of different speed, known as corotating interaction regions, form an almost constantly existing structure of the inner heliosphere. Using observational data on the main characteristics of the heliosphere, important for GCR modulation, and the results of 3D MHD modeling of corotating interaction regions, and Monte Carlo simulation of recurrent GCR variations, we analyze the importance of the corotating interaction regions for longitude-averaged characteristics of the heliosphere and GCR propagation, and possible ways for simulating long-term GCR intensity variations with respect to the corotating interaction regions.

О проявлении коротирующих областей взаимодействия солнечного ветра в вариациях интенсивности ГКЛ

The regions of interaction between solar wind streams of different speed, known as corotating interaction regions, form an almost constantly existing structure of the inner heliosphere. Using observational data on the main characteristics of the heliosphere, important for GCR modulation, and the results of 3D MHD modeling of corotating interaction regions, and Monte Carlo simulation of recurrent GCR variations, we analyze the importance of the corotating interaction regions for longitude-averaged characteristics of the heliosphere and GCR propagation, and possible ways for simulating long-term GCR intensity variations with respect to the corotating interaction regions.

Aspects of the Influence of the Global Heliospheric Current Sheet on GCR Propagation

The influence of the global heliospheric current sheet on the heliospheric characteristics important for GCR propagation is considered, particularly the strong dependence of the solar wind velocity on the distance from the current sheet. A simple model of the solar wind velocity is proposed that, after estimating the parameters from observations, can be used for theoretical studies of GCR modulation. The choice of the GCR propagation model to be used for periods of low and medium sunspot activity is discussed.

On Contribution of Poloidal Branch of Solar Activity to Heliosphere and GCR Modulation

The point of view is substantiated that during periods of low sunspot activity many heliospheric characteristics (the solar wind velocity, the form of the heliospheric current sheet, the strength of the heliospheric magnetic field) can be considered as the manifestations in the heliosphere of the poloidal branch of solar activity. As these characteristics strongly influence the process of the GCR transport through the heliosphere the contribution of the poloidal branch of solar activity to the GCR solar modulation should also be substantial. This conclusion is at odds with the wide-spread belief that the modulated GCR intensity is mainly determined by the sunspot cycle.

Overview of galactic cosmic ray solar modulation in the AMS-02 era

A new era in cosmic rays physics has started thanks to the precise and continuous observations from space experiments such as PAMELA and AMS-02. Invaluable results are coming out from these new data that are rewriting the theory of acceleration and propagation of cosmic rays. Both at high energies, where several new behaviors have been measured, challenging the accuracy of theoretical models, and also at low energies, in the region affected by the solar modulation. Precise measurements are increasing our knowledge of the effects of solar modulation on low energy cosmic rays, allowing a detailed study of propagation and composition as it has never been done before. These measurements will serve as a high-precision baseline for continued studies of GCR composition, GCR modulation over the solar cycle, space radiation hazards, and other topics.In this review paper, the status of the latest measurements of the cosmic rays in the context of solar modulation are presented together with the current open questions and the future prospects. How new measurements from the AMS-02 experiment will address these questions is also discussed.

Cosmogenic radionuclides in Chelyabinsk and Kosice chondrites and features of solar cycles 23 and 24

Based on the example of the measured and calculated contents of cosmogenic radionuclides in freshly fallen Chelyabinsk and Kosice chondrites, an indirect approach to studying variations in galactic cosmic rays is presented that uses variations in the rates of production of radionuclides with different half-lives in the meteorites that continuously fall to Earth from orbits of different sizes and inclinations. The advantages of monitoring these data over a long time scale to establish the main regularities of solar modulation processes in the heliosphere are demonstrated. The possible effect of stochastic factors in the operation of the solar dynamo had on the peculiarities of GCR modulation in solar cycles 23 and 24 is discussed.

Energetic particles in the heliosphere and GCR modulation: Reviewing of SH-posters

This rapporteur paper addresses the SH poster session titled "Energetic particles in the heliosphere (solar and anomalous CRs, GCR modulation)" of the 23rd European Cosmic Ray Symposium (ECRS) and the 32nd Russian Cosmic Ray Conference (RCRC). The 65 posters presented are tentatively divided into five sections: Instruments and Methods; Solar Energetic Particles; Short Term Variations; Long Term Variations; Heliosphere.

Monitoring of GCR temporal and spatial variations in the inner heliosphere according to cosmogenic radionuclides in fresh-fallen meteorites

The meteorite data on monitoring of the GCR gradient variations at 2-4 AU from the Sun in 1957-2010 testify to the influence of the character of the solar magnetic field inversions during the maximum of the solar cycles on depth of the GCR modulation in the heliosphere.

Two-dimensional transport equation for GCR in three-dimensional models of the heliosphere

An axisymmetric transport equation for galactic cosmic rays is proposed, which is a consequence of an equation three-dimensional in spatial coordinates. In this equation, the three-dimensionality is caused by the heliospheric current sheet of arbitrary shape. The feature of the proposed equation consists in the consideration of the source associated with variations of the three-dimensional GCR intensity. The equation can be used to describe GCR modulation processes in the GCR heliosphere.

Heliospheric current sheet and GCR modulation in 1976–2007

The correlation between the GCR intensity and the tilt of the heliospheric current sheet (HCS) during three solar cycles is considered. The correlation coefficients for the periods of decreasing and increasing intensity have been calculated, and the time lag of the GCR variations delay relative to changes in the HCS tilt has been determined. It has been shown that the correlation coefficients are independent of the heliospheric magnetic field (HMF) direction. The possible diffusive mechanism, by which the current sheet tilt is related to the GCR intensity, is briefly discussed.

MODELLING COSMIC RAY ELEMENT SPECTRA AND IONIZATION IN THE IONOSPHERES AND ATMOSPHERES OF TERRESTRIAL AND JOVIAN PLANETS

The galactic (GCRs) and anomalous (ACRs) cosmic rays form the lower parts of the planetary ionospheres. For this purpose analytical and numerical spectra for cosmic particles are necessary. Our knowledge of GCR modulation in the solar system was greatly enhanced thanks to the heliospheric missions, Voyagers 1 and 2, Pioneer 10 and Ulysses. In this paper, a new model for the calculation of the GCR and ACR element differential spectra D(E) on the basis of satellite measurements is created. This computed analytical model gives a practical possibility for investigation of experimental data from measurements of GCR and ACR component. The contribution of GCRs and ACRs to the ionization of the atmospheres of outer planets Uranus, Neptune and Pluto increases drastically.

Modeling spectra of cosmic rays influencing on the ionospheres of the earth and outer planets during solar maximum and minimum

The galactic (GCRs) and anomalous (ACRs) cosmic rays form the lower parts of the planetary ionospheres. For this purpose analytical and numerical spectra for cosmic particles are necessary. The spectra of GCRs and ACRs observed in the Solar system are modulated by the Sun. Our knowledge of GCR modulation in the solar system was greatly enhanced thanks to the heliospheric missions, Voyager 1 and 2 that covered the outer Solar system up to ∼75 AU radial distance from the Sun. In this paper, a new model for the calculation of the GCR and ACR differential spectra D( E) on the basis of satellite and balloon measurements is created. This computed analytical model gives a practical possibility for investigation of experimental data from measurements of galactic cosmic rays and their anomalous component. The integral spectra D(> E) are computed and also obtained. The average radial gradient of GCR is accepted 4%/AU [F. Mcdonald, Z. Fujii, et al. The cosmic ray radial and latitudinal intensity gradient in the inner and outer heliosphere, in: Proceedings of 27th International Cosmic Ray Conference, Copernicus Gesellschaft, p. 3906, 2001]. The contribution of GCRs and ACRs to the ionization of the ionospheres of outer planets will be increased with increase of the planetary distances from the Sun.

Daily values of the solar SXR background and modulation of GCRs (1987, 1988, 1990 and 1992)

We present here the results of the intercorrelation analysis between the daily Calgary Galactic Cosmic Ray intensity values (CNI) and daily solar SXR background (XBG - unresolved full-sun SXR GOES flux). The anticorrelation between CNI and XBG is statistically significant for 1987, 1988 and 1992 sequences. In 1990, no anticorrelation between CNI and XBG was found. The latter fact gives evidence for the Global Merged Interaction Region (GMIR) being the most dominant GCR modulation structure of the 1990's outer heliospherical system, while local heliospherical structures seemed to play the secondary role.