Connections between neutron monitor count rate and solar modulation strength

We suggest a new approach to the normalisation of neutron monitor response to galactic cosmic rays. The reference normalisation count rate is the neutron monitor response to the model unmodulated flux of galactic cosmic rays. A comparison of the actually recorded neutron monitor count rate with the calculated normalisation count rate can provide one with an observationally obtained true-of-date integral measure of the current level of solar modulation of galactic cosmic rays. The Slovak VEGA grant agency is acknowledged for the grant 2-5137.     

临近空间大气中子环境的仿真研究

以大气模型、宇宙线模型和地磁截止刚度模型为基础,利用蒙特卡罗方法在国内首次建立了临近空间大气中子环境的计算机仿真模型,分别研究了银河宇宙线、太阳宇宙线诱发的大气中子环境分布规律以及地磁场屏蔽作用对大气中子环境的影响.通过与国外相关模型对比,证明本仿真模型是准确、可靠的,对太阳质子事件的详细分析,弥补了国外已有模型中的不足.该模型可用于临近空间大气中子诱发的元器件单粒子效应评估,以及航空机组人员飞行期间所接受的辐射剂量分析. 关键词： 临近空间 大气中子 单粒子效应 蒙特卡罗     

Terrestrial Seismic Activity and Neutrons from the Surface of the Earth Associated with Lunar and Solar Tides

drastic increase in the flux of thermal neutrons of secondary cosmic radiation coming from the Earth was observed in the Pamir Mountains during the solar eclipse of July 22, 1990. In the following years, such phenomena were observed on each new moon and each full moon, when lunar and solar tides combine to produce an exceptionally high resultant tide. Tidal forces may serve as a trigger for the release of the deepearth seismic energy in a certain region. This directed our attention to the search for a temporal correlation between earthquakes and new and full moons, which may help identify a new type of seismic activity precursor. Such a correlation was found in the circum-Pacific belt and the adjacent regions at latitudes above 40° N and 10° S. The results of daytime measurements of the thermal neutron flux from the surface of the Earth in the Western Pamirs (Moskvin Glade, 4200 m above sea level) on August 1–14, 1994, are reported in the present study. Since these days were quiet in terms of weather and heliophysical and geophysical activity, the intensity of neutrons of secondary cosmic radiation was expected to remain almost constant. However, twofold (or even larger) intraday variations of the neutron count rate were observed on August 1–14, 1994. These quiet measurement conditions rule out the possibility that these bursts were associated with certain known extraterrestrial factors. It has been demonstrated that the observed neutron-intensity peaks were produced by lunar and solar tides. These results confirm that tidal forces play a prominent part in the generation of neutron fluxes from the surface of the Earth. The Astronomical Yearbook for 1994 published by the Russian Academy of Sciences was used in the present study.     

Features of cosmic ray variation at the phase of the minimum between the 23rd and 24th solar cycles

The minimum between the 23rd and 24th cycles of solar activity was unusually deep and extended. The modulation of cosmic rays was minimal for the more than 70-year-long period of direct measurements. The data from stratospheric measurements by the Lebedev Physical Institute suggest that the flux of cosmic rays with more than 100 MeV/nucleon of energy exceeded the highest ever observed level (May 1965) by almost 12%. However, the ground-based neutron monitors sensitive to relatively high energies indicated that the flux of cosmic rays increased by less than 3%. This work compares the variations in the cosmic rays over periods of five minima of solar activity (the 20th to the 24th cycle). It is shown that in late 2008, an extra flux of particles with energies less than several GeV/nucleon was detected in the Earth’s orbit. A similar (though far smaller in scale) phenomenon was also observed in 1987 at the same orientation of the Sun’s magnetic field A < 0, but was not observed in epochs where A > 0.     

太阳大耀斑期间甚高能粒子流强增加的一种机制

近年来,在太阳大耀班期间,由地面中子记录装置及地下不同深度μ子记录器记录到宇宙线粒子的短期增长(GLE)现象,其能量范围已达几百GeV,甚至可达TeV能区.本文讨论了TeV能区的增长现象可能是银河宇宙线部分粒子获得再加速,由于宇宙线粒子能谱很陡,几百GeV的再加速能量能使TeV以上能区宇宙线流强有明显增长.     

Cosmic Ray Flux Variation due to Solar Flares during January 16—20, 2005 with YBJ-ARGO Experiment

The YBJ-ARGO experiment is located in Tibet at 4300m a.s.l.. The data of this experiment under scalar mode can be used to study the solar modulation of cosmic ray flux at E>10GeV. The data during January 15—17, 2005 are analyzed, and a cosmic ray flux Forbush decrease after several X class solar flares has been observed. All detailed structures of the flux curves are similar to the results from neutron monitors. The maximum amplitudes of FD are about －6%, －6%, －4% and －3% with multiplicity greater than 1, 2, 3 and 4, respectively, i.e. the maximum amplitude of FD decreases as the energy of cosmic ray increases. These are the results about a FD measured at the same site (Yangbajing) with different cosmic ray energies for the first time.     

New method for estimating the absolute flux and energy spectrum of solar cosmic rays based on neutron-monitor data

A new method is described for estimating the absolute flux of solar cosmic rays based on the data from a single neutron monitor. The method is capable of yielding the energy spectrum at the isotropic phase of a solar flare using the available data from the currently operable worldwide network of cosmic-ray stations. The method is based on the determination of the effective momentum or energy for which the particle flux derived from the neutron-monitor count rate is weakly sensitive to small variations in the exponent of the power-law spectrum. A comparison of the calculations with direct space-borne measurements and calculations by other authors based on the data from the neutron-monitor network shows their satisfactory agreement for the last ground-level enhancement of solar cosmic rays observed on December 13, 2006.     

宇宙线福布什下降期间羊八井云量的变化

进入地球大气中的宇宙线强度发生变化,可能导致气候,比如云量的变化. 利用羊八井中子监测器在2003—2004年观测到3次宇宙线福布什下降,在这期间同时记录了观测站点上空的云量变化. 通过对宇宙线福布什下降期间羊八井上空云量的统计分析发现,宇宙线福布什下降期间云量增加,即云量对宇宙线福布什下降表现出明显的负响应. 这表明,宇宙线福布什下降期间,低纬度薄云层地区云量增加,与其他观测结果相一致.     

Ultimate ground level enhancements of solar cosmic ray intensity

Possible values of ground level enhancements (GLEs) of the intensity of solar cosmic rays (SCRs) that can be recorded by neutron monitors (NMs) are estimated in two different ways for the ultimate spectra of solar protons. The first approach uses the statistical dependence between the maximum values of the integral proton flux >100 МeV and the GLE recorded by an NM. The second is to calculate the expected effect for the ultimate spectrum at a particular NM with known couple coefficients, atmospheric depth, and the threshold of the geomagnetic cutoff. Estimates using the first method vary from 9600 to 160000% for high-latitude NMs; estimates using the second method, from 1200 to 750000%. The obtained lower limits approximately correspond to GLE values observed earlier, and the upper limits are two orders of magnitude higher. Studies of the possible impact of solar proton events with spectra close to ultimate on the Earth’s atmosphere and biosphere should be continued.     

Application of student’s criterion for detecting ground level enhancements of solar cosmic ray intensity

Student’s criterion is used to detect ground level enhancements of solar cosmic ray intensity at middle latitudes. Application of this test to the data recorded by Alma-Ata high-altitude neutron monitor made it possible to detect the arrival of solar-origin relativistic particles on November 6, 1997 and August 24, 1998.     

Temporal changes in the energy spectrum of Forbush decreases in 20–23 solar activity cycles

Variations in the energy spectrum of galactic cosmic rays during Forbush decreases registered in the 20–23 solar activity cycles are studied, using the data from neutron monitors and the Yakutsk cosmic ray spectrograph. It is shown that the Forbush decreases in the 23rd cycle of solar activity had a harder energy spectrum than in the three previous cycles, due to the relatively low level of turbulence of the interplanetary magnetic field during the 23rd solar activity cycle.     

Quasiperiodic Variations of Solar Activity and Cosmic Rays

Quasiperiodic variations of various manifestations of solar activity, parameters of the interplanetary medium, and the flux of galactic cosmic rays (GCRs) are studied using the data of stratospheric sounding and measurements with neutron monitors. Groups of spectral components with periods of ~2, 1.3, and ~1 year are identified in the range of periods shorter than 5 years. Particular attention is paid to quasi-2-year GCR variations that are induced by similar variations of the mean magnetic field of the Sun and are integral to the processes of solar activity.     

Energy spectrum and flows of solar cosmic rays during periods of their ground level enhancement

Events of the ground level enhancement of relativistic solar cosmic rays are studied using data from the world network of neutron monitor stations. The energy spectrum index and the absolute flow of solar cosmic rays for 15 GLE events observed between 1977 and 2012 are estimated from their effective energies [1]. The dynamics of changes in the index of the power energy spectrum γ in the range from 3 to 7 is observed.     

Heliospheric modulation of high-energy cosmic rays: II. Deformation of the neutral surface

Analysis of neutron monitor data in the periods of negative and positive polarities of the general solar magnetic field has revealed a dependence of the long-term cosmic-ray modulation on both deformation of the neutral surface of the interplanetary magnetic field and solar activity level. The effects of solar activity and neutral surface deformation dominate at positive and negative polarities, respectively. The magnetic drift of cosmic rays with different trajectories in the epochs of positive and negative polarities is responsible for this behavior of the 11-year and annual density modulations.     

Effect of solar eclipses on neutron flux variations at the Earth’s surface

The results of the investigation of the neutron flux variations at the Tien Shan high-altitude scientific station during solar eclipses on September 23, 1987; August 11, 1999; and March 29, 2006 are reported. It is established that, during these periods, the dynamics of neutron intensity variations in the frequency range 10^?5–10^?3 Hz is due to geophysical sources of disturbances. An increase in the thermal neutron flux from the Earth’s Crust is observed.     

Monitoring of the thermal neutron flux in the EDELWEISS II dark matter direct search experiment

The results from measurements of thermal neutron flux in the EDELWEISS II experiment aimed at the direct detection of WIMPs (weakly interacting massive particles) by means of cryogenic germanium bolometers are described. Detailed knowledge of the neutron background is of crucial importance for the experiment, since neutrons with the MeV energy range of scattering seem to be hard to distinguish from the expected WIMP signal within the bolometers. Monitoring of the thermal neutron flux is performed using a mobile detection system with a low background proportional ³He counter. The neutron flux measurements were performed both outside and inside the device’s shielding, in the direct proximity of a cryostat with built-in germanium detectors. The sensitivity of the created thermal neutron detection system is on the level of 10⁻⁹ neutron (cm² s)⁻¹.     

Plasmoid impacts on neutron stars and highest energy cosmic rays

Particle acceleration by electrostatic polarization fields that arise in plasmas streaming across magnetic fields is discussed as a possible acceleration mechanism of highest energy ( greater, similar10(20) eV) cosmic rays. Specifically, plasmoids arising in planetoid impacts onto neutron star magnetospheres are considered. We find that such impacts at plausible rates may account for the observed flux and energy spectrum of the highest energy cosmic rays.     

Observation of heliospheric disturbances in the muon component of cosmic rays

The possibilities of using ground-based muon hodoscopes to study heliospheric disturbances are discussed. Mapping of the matrices of muon flux angular distributions recorded at the ground level in geocentric solar ecliptic coordinates with allowance for the asymptotic directions of primary protons of galactic cosmic rays makes it possible to observe the dynamics of heliospheric disturbances in the near-Earth space. Variations in some other characteristics of muon flux angular distributions are also analyzed.     

On the possible contribution of solar-cosmic factors to the global warming of XX century

The effect of changes in the total solar irradiance and intensity of galactic cosmic rays on the increase in the global temperature of the Earth over the last 120 years was investigated using a one-dimensional energy-balance climate model. It is shown that the joint effect of solar and cosmic factors during this periodcan lead to an increase in the average temperature of the northern hemisphere by 0.25–0.35°C. It is concluded that the solar luminosity and the cosmic-ray flux can make a significant contribution to the global warming of the last century.     

Efficiency of detection for neutron detectors with different geometries

The response of neutron detectors to the flux of secondary cosmic radiation particles incident on the detectors is simulated mathematically and detection efficiencies are found for neutron detectors of various designs.