Proxies for long-term cosmic ray variability

Abstract The thesis is focused on the reconstruction of long-term cosmic ray variability using proxy data. The 11-year solar cycle in production/deposition rates of cosmogenic nuclides ¹⁰Be and ¹⁴C has been modelled for the conditions of grand minima and maxima of solar activity (namely, Maunder Minimum and Grand Modern Maximum). The result shows that contrary to the observed strongly suppressed amplitude of the solar cycle in sunspots during Maunder Minimum relatively to Grand Modern Maximum, the cosmic ray proxies have the comparable amplitudes during the two periods. This phenomenon is caused by the nonlinear relation between solar activity and production of cosmogenic nuclides. In addition to well-established proxies of cosmic rays, nitrate in polar ice has been recently proposed as a new proxy for the long-term variability of galactic cosmic rays. The thesis contains two tests of its applicability for this purpose with TALDICE and EPICA-Dome C ice core data from Central Antarctica. The results support the proposal for the multimillennial time scales. Lunar samples acquired during the Apollo missions are important data for estimating the averaged energy spectra of galactic cosmic rays and solar energetic particles at the Earth’s orbit. The development in modelling of the interaction between energetic particles and matter makes it necessary to revise the earlier results. Because of that, new production rates of ¹⁰Be and ¹⁴C in lunar samples by galactic cosmic rays and solar energetic particles have been computed. New accurate cosmic ray reconstructions from natural archives containing cosmogenic nuclides use sophisticated climatic models requiring yield functions of the nuclides with high altitude resolution. These functions have been computed for ⁷Be, ¹⁰Be, ¹⁴C, ²²Na, and ³⁶Cl in the Earth’s atmosphere. Overall, the major purpose of the studies presented in the thesis is to increase the quality of reconstructions of the long-term cosmic ray variability for better understanding of the solar and heliospheric physics

Spectra of solar energetic particles and galactic cosmic rays over a million years reconstructed using aluminium-26 data from lunar rocks

Abstract Direct measurements of solar energetic particles (SEP) cover the space era of several decades, but indirectly they can be studied for thousands and millions of years backward using cosmogenic nuclides in lunar rocks and soil. With a proper nuclide production model, it is possible to estimate the mean energy spectrum of SEP, as well as of galactic cosmic rays (GCR) from a depth profile of the measured nuclide content. Here we used aluminium-26 (lifetime 1.03 Myr) measurements in Apollo-mission lunar samples. Previous estimates of the SEP spectrum from lunar data were based on the assumed specific shape and only provided reconstructed spectral parameters. We report a different approach to use a lunar rock as an integral spectrometer within 20–80 MeV. With that, one can reconstruct the particle spectrum directly without any a-priori assumptions on its exact shape. For each studied lunar sample, we have developed an accurate Geant4 model. We estimated the average GCR spectrum over the last million years (the modulation potential 496±40 MV), which is consistent with that for the Holocene (449±70 MV), but significantly lower than that for the modern epoch (660±20MV).We also made a true reconstruction of the mean SEP spectrum over the last million years. The integral flux >30 MeV was estimated as 37.4 particles/(cm² s), which is consistent with that for the modern epoch. The estimated occurrence probability of SEP events shows no expected events with fluence >30 MeV over 5×10¹⁰ and 1×10¹¹ particles/cm² on millennial and Mega-year time scales, respectively

An anisotropic cosmic-ray enhancement event on 07-June-2015:a possible origin

Abstract A usual event, called anisotropic cosmic-ray enhancement (ACRE), was observed as a small increase (≤5%) in the count rates of polar neutron monitors during 12–9 UT on 07 June 2015. The enhancement was highly anisotropic, as detected only by neutron monitors with asymptotic directions in the southwest quadrant in geocentric solar ecliptic (GSE) coordinates. The estimated rigidity of the corresponding particles is ≤1 GV. No associated detectable increase was found in the space-borne data from the Geostationary Operational Environmental Satellite (GOES), the Energetic and Relativistic Nuclei and Electron (ERNE) on board the Solar and Heliospheric Observatory (SOHO), or the Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics (PAMELA) instruments, whose sensitivity was not sufficient to detect the event. No solar energetic particles were present during that time interval. The heliospheric conditions were slightly disturbed, so that the interplanetary magnetic field strength gradually increased during the event, followed by an increase of the solar wind speed after the event. It is proposed that the event was related to a crossing of the boundary layer between two regions with different heliospheric parameters, with a strong gradient of low-rigidity (<1 GV) particles. It was apparently similar to another cosmic-ray enhancement (e.g., on 22 June 2015) that is thought to have been caused by the local anisotropy of Forbush decreases, with the difference that in our case, the interplanetary disturbance was not observed at Earth, but passed by southward for this event

Properties of cosmic-ray sulfur and determination of the composition of primary cosmic-ray carbon, neon, magnesium, and sulfur:ten-year results from the Alpha Magnetic Spectrometer

Abstract We report the properties of primary cosmic-ray sulfur (S) in the rigidity range 2.15 GV to 3.0 TV based on 0.38 x 10⁶ sulfur nuclei collected by the Alpha Magnetic Spectrometer experiment (AMS). We observed that above 90 GV the rigidity dependence of the S flux is identical to the rigidity dependence of Ne-Mg-Si fluxes, which is different from the rigidity dependence of the He-C-O-Fe fluxes. We found that, similar to N, Na, and Al cosmic rays, over the entire rigidity range, the traditional primary cosmic rays S, Ne, Mg, and C all have sizeable secondary components, and the S, Ne, and Mg fluxes are well described by the weighted sum of the primary silicon flux and the secondary fluorine flux, and the C flux is well described by the weighted sum of the primary oxygen flux and the secondary boron flux. The primary and secondary contributions of the traditional primary cosmic-ray fluxes of C, Ne, Mg, and S (even Z elements) are distinctly different from the primary and secondary contributions of the N, Na, and Al (odd Z elements) fluxes. The abundance ratio at the source for S/Si is 0.167 ± 0.006, for Ne/Si is 0.833 ± 0.025, for Mg/Si is 0.994 ± 0.029, and for C/O is 0.836 ± 0.025. These values are determined independent of cosmic-ray propagation