首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 875 毫秒
1.
A series of yearly data on the concentration of radioactive carbon 14C in tree rings measured at the Tbilisi State University in 1983–1986 and covering the time interval 1600–1940 is statistically analyzed. We find evidence for a 22-year cyclicity in the intensity of Galactic cosmic rays (GCRs) during the Maunder minimum of the solar activity (1645–1715), testifying that the solar dynamo mechanism continued to operate during this epoch. Variations of Δ14C on timescales of tens and hundreds of years correlate well with the corresponding variations of the GCR intensity and solar activity, making radiocarbon a reliable source of information on long-timescale variations of solar activity in the past. Short-timescale (<30 years) fluctuations of Δ14C may be appreciably distorted by time variations not associated directly with solar activity; probable origins of this distortion are discussed.  相似文献   

2.
Production rates of15N by both solar cosmic rays (SCR) and galactic cosmic rays (GCR) have been calculated for moon, as well as meteorites of various sizes. Our production rates of15N which considered both the reaction channels16O(p, pn)15O and16O(p, 2p)15N separately are about 30% higher than those by Reedy (1981) who considered only the channel16O(p, pn)15O and used an empirical scaling factor to estimate the contribution from16O(p, 2p)15N. Production ratio15N21 Ne is composition dependent and hence is different for various silicate minerals. Additionally the ratio15N/21Ne is very sensitive to the energy spectrum of the cosmic rays. This fact can be made use of in characterizing as well as in decoupling the SCR and GCR effects in extraterrestrial samples.  相似文献   

3.
The rates of production of21Ne and22Ne in spallation reactions, both due to solar as well as galactic cosmic rays, in some major meteoritic minerals, e.g. olivines, feldspars and pyroxenes, are calculated using their energy spectra and excitation functions. The production profiles of21Ne and22Ne due to galactic cosmic rays, and the22Ne/21Ne ratio depend upon the size of the meteoroid. The22Ne/21Ne ratio is very sensitive to the abundance of sodium and consequently its depth profile is distinctly different in feldspars, the ratio increasing with depth rather than decreasing as in pyroxenes and olivines. In the near-surface regions, up to a depth of 2cm, production due to solar flare protons dominates, giving rise to a steep gradient in isotopic production as well as in the22Ne/21Ne ratio. Composite production profiles are given and compared with measurements in some meteorites.  相似文献   

4.
Study of several cosmic ray effects, such as VH track density, spallogenic26Al and53Mn activity,21Ne and22Ne/21Ne ratio, made in the same sample or in cores taken from different meteorites can identify parameters related to the exposure history of meteorites and cosmic ray flux variations. Meteorites with single or multiple exposure can be distinguished from a track production rate —22Ne/21Ne correlation diagram and cosmic ray flux variations over 106–107 years can be deduced from a three-isotope correlation diagram of26Al,53Mn and21Ne. Isotopic data based on chondrites with simple, one-stage exposure are consistent with the same average galactic cosmic ray intensity over the past 2 million years as that during the past 107 years.  相似文献   

5.
Role of solar activity on modern climate change, particularly in the decadal scale is an important scientific issue. This paper reviews the recent observation of decadal solar signal in earth’s climate, with focus on the mechanism of solar radiation, ultraviolet radiation and cosmic rays on climate system ,and its validation. The paper points out that the assessment of uncertainty in observations, amplification process of the climate system, as well as possible future impact of solar extreme events are challenges in the present study. Finally, the keys of breakthrough are pointed, to provide a reference for future research.  相似文献   

6.
An analysis of the dynamics of the electron temperature of the solar atmosphere in regions where solar flares appear is presented. The temperatures are estimated from the emission in spectral lines of ions with various degrees of ionization. The emission of ionized helium and highly ionized iron was used. Images of preflare states and of flares from the archive of the American SDO spacecraft are analyzed. A solar flare is usually preceded by the registration of a bright glowing structure above the action region, with a temperature exceeding that of the corona. This preflare structure (~1010 cm) is identified with the development of a system of currents, which, according to numerical simulations, is responsible for the accumulation of energy above the active region before the flare. After several tens of hours of a slow increase in the brightness of the preflare glow in the 94 Å iron (FeXVIII) line, the emission in the 193 Å line of FeXXIV increases sharply, indicating a flare-like growth of the temperature up to at least 20 MK. This growth of the emission coincides with the onset of the solar flare. The observed dynamics of the emission in spectral lines of highly ionized ions is consistent with an electrodynamic model of a solar flare based on the accumulation of magnetic energy in a current sheet above the active region and the explosive release of the stored energy. Studies of mechanisms for solar flares are of special importance in connection with the discovery of solar cosmic rays. Information from the worldwide network of neutron monitors and from the GOES spacecraft has made it possible to firmly state that the source of solar rays is solar flares, not shocks generated by such flares. It cannot be ruled out that a similar mechanism, not shocks, is also responsible for the acceleration of cosmic rays in the Galaxy.  相似文献   

7.
《Quaternary Science Reviews》2007,26(11-12):1547-1556
A new method of permafrost dating with the cosmogenic radionuclide 36Cl is presented. In the first application, syngenetic ice wedges are dated using the ratio of 36Cl and Cl concentrations in ice as the signal. 36Cl is produced in the atmosphere by nuclear reactions of cosmic rays on argon. Stable chlorine enters the atmosphere from the oceans. Their ratio does not depend on chloride concentration in precipitations and on sublimation of snow. In situ production of 36Cl in permafrost ice via cosmic ray-induced reactions and neutron capture are calculated and the dating age limit is estimated as 3 million years. 36Cl/Cl ratios in permafrost samples from cape Svyatoy Nos (Laptev Sea coast), North-Eastern Siberia, are measured by accelerator mass spectrometry. Analysis of the first results and the calculated dates support the feasibility of the 36Cl permafrost dating method  相似文献   

8.
月壤颗粒微观环带的太空风化成因   总被引：2，自引：0，他引：2  
太空风化是迄今31亿年以来影响月球表面物质演化过程的主要因素,主要包括陨石、微陨石的轰击,太阳风粒子的注入,太阳/银河宇宙射线的辐射以及周期性的加热作用等。通过深入剖析太阳风粒子的注入与溅射、微陨石轰击的蒸发与沉积、宇宙射线辐射的辐射损伤等过程的作用机理,探讨了不同太空风化过程对矿物颗粒环带厚度、化学组成、晶体结构等特征的影响,认为微陨石轰击与太阳风注入是形成月壤颗粒微观环带的主导因素,宇宙射线辐射与周期性加热的影响可忽略不计。进一步结合非晶质环带、富内含物环带、多环环带以及小泡环带等月壤颗粒主要环带的基本特征,在总结和对比分析各类型环带的厚度、结构以及化学组成特征基础上,对不同类型环带的成因进行初步推断,认为非晶质环带、小泡环带以及多环环带的内层环带具有太阳风作用特征,而富内含物环带、多环环带的外层环带则具有微陨石轰击的成因特征。根据目前单纯依靠环带的化学组成分析解释环带成因存在的不足,指出了通过补充分析矿物晶体结构在模拟太空风化实验过程中的变化特征来研究环带成因的新思路。  相似文献   

9.
Volcanoes with silica-rich and highly viscous magma tend to produce violent explosive eruptions that result in disasters in local communities and that strongly affect the global environment. We examined the timing of 11 eruptive events that produced silica-rich magma from four volcanoes in Japan (Mt. Fuji, Mt. Usu, Myojin-sho, and Satsuma-Iwo-jima) over the past 306 years (from AD 1700 to AD 2005). Nine of the 11 events occurred during inactive phases of solar magnetic activity (solar minimum), which is well indexed by the group sunspot number. This strong association between eruption timing and the solar minimum is statistically significant to a confidence level of 96.7%. This relationship is not observed for eruptions from volcanoes with relatively silica-poor magma, such as Izu-Ohshima. It is well known that the cosmic-ray flux is negatively correlated with solar magnetic activity, as the strong magnetic field in the solar wind repels charged particles such as galactic cosmic rays that originate from outside of the solar system. The strong negative correlation observed between the timing of silica-rich eruptions and solar activity can be explained by variations in cosmic-ray flux arising from solar modulation. Because silica-rich magma has relatively high surface tension (~ 0.1 Nm?1), the homogeneous nucleation rate is so low that such magma exists in a highly supersaturated state without considerable exsolution, even when located relatively close to the surface, within the penetration range of cosmic-ray muons (1–10 GeV). These muons can contribute to nucleation in supersaturated magma, as documented by many authors studying a bubble chamber, via ionization loss. This radiation-induced nucleation can lead to the pre-eruptive exsolution of H2O in the silica-rich magma. We note the possibility that the 1991 Mt. Pinatubo eruption was triggered by the same mechanism: an increase in cosmic-ray flux triggered by Typhoon Yunya, as a decrease in atmospheric pressure results in an increase in cosmic-ray flux. We also speculate that the snowball Earth event was triggered by successive large-scale volcanic eruptions triggered by increased cosmic-ray flux due to nearby supernova explosions.  相似文献   

10.
Galactic cosmic rays and solar protons ionize the present terrestrial atmosphere,and the air showers are simulated by well-tested Monte-Carlo simulations,such as PHITS code.We use the latest version of PHITS to evaluate the possible ionization of protoplanetary disks by galactic cosmic rays(GCRs),solar protons,and by supernova remnants.The attenuation length of GCR ionization is updated as 118 g cm~(-2),which is approximately 20% larger than the popular value.Hard and soft possible spectra of solar protons give comparable and 20% smaller attenuation lengths compared with those from standard GCR spectra,respectively,while the attenuation length is approximately 10% larger for supernova remnants.Further,all of the attenuation lengths become 10% larger in the compound gas of cosmic abundance,e.g.128 g cm~(-2) for GCRs,which can affect the minimum estimate of the size of dead zones in protoplanetary disks when the incident flux is unusually high.  相似文献   

11.
太阳变化驱动气候变化研究进展   总被引：19，自引：4，他引：19  
从5个方面综述了近20年来太阳变化驱动气候变化研究的进展,重点在机制方面,即对全球变暖原因看法的分歧、太阳总辐射量的卫星测量结果、树轮14C记录与太阳变化代用指标、太阳变化影响的模拟研究,以及太阳—宇宙射线—云量的关系。强调这是一个有重大经济和科学意义的前沿课题。  相似文献   

12.
Cosmic ray produced isotopes in terrestrial systems   总被引：2，自引：0，他引：2  
Continuing improvements in the sensitivity of measurement of cosmic ray produced isotopes in environmental samples have progressively broadened the scope of their applications to characterise and quantify a wide variety of processes in earth and planetary sciences. In this article, I will concentrate on the new developments in the field of nuclear geophysics, based on isotopic changes produced by cosmic rays in the terrestrial systems. This field, which is best described as cosmic ray geophysics, caught roots with the discovery of cosmogenic14C on the Earth by Willard Libby in 1948, and grew rapidly at first, but slowed down during the ’60s and ’70s. In the ’80s, there was arenaissance in cosmic ray produced isotope studies, thanks mainly to the developments of the accelerator mass spectrometry technique capable of measuring minute amounts of radioactivity in terrestrial samples. This technological advance has considerably enhanced the applications of cosmic ray produced isotopes and today we find them being used to address diverse problems in earth and planetary sciences I discuss the present scope of the field of cosmic ray geophysics with an emphasis ongeomorphology. I must stress here that this is the decade in which this field, which has been studied passionately by geographers, geomorphologists and geochemists for more than five decades, has at its service nuclear methods to introduce numeric time controls in the range of centuries to millions of years.  相似文献   

13.
The model of stellar origin of the anomalous component in the low energy cosmic rays for He to Fe ions observed in space vehicles is studied in the light of recent results. The model of heliospheric origin by Fisket al which has several attractive features cannot explain the long-term variations of intensity observed during 1974 to 1978 as pointed out by Nagashima and Morishita. The stellar origin model of Durgaprasad and Biswas, on the other hand, can easily account for the sudden appearance of the anomalous component in 1972 and its large decrease in intensity in 1978 on the basis of polarity reversal of the solar magnetic field as discussed by Nagashima and Morishita (1980). In this work, we show that in the stellar model energetic ions of He, C, N, O, etc. could originate in O-type stars which manifest very strong stellar wind with mass loss rate of 3·10?6 M⊙ per year. These have terminal velocities of about 1200 to 4000 km/sec and are typically a few times their escape velocity. These velocities correspond to ion energies of 10 to 100 keV/amu. These ions are in partly ionised state and are accelerated in the interstellar shock fronts to about 1 to 50 MeV/amu and thus account for the observed anomalous component of low energy cosmic rays.  相似文献   

14.
大量研究表明，从数小时到十年、百年时间尺度上的天气、气候变化受太阳活动影响显著。近年来，全球云量、北大西洋冬季气旋等气候、气象要素与银河宇宙射线通量变化、太阳能量粒子事件等空间天气事件显著的统计相关被陆续发现。在此基础上，提出太阳活动驱动气候变化空间天气机制，其基本观点是：空间天气事件通过改变云物理特性影响气象、气候，其核心是：太阳活动造成的空间天气事件与云微物理过程的联系，目前空间天气理论分化为离子诱导成核机制和全球大气电路—静电云微物理机制（简称Tinsley机制）。主要回顾和总结了近年来空间天气机制研究的发展，包括观测与理论，取得的成果，并对其未来的发展提出展望。   相似文献   

15.
Recent results on cosmic ray interactions in lunar samples and meteorites resulting in production of stable and radionuclides, particle tracks and thermoluminescence are reviewed. A critical examination of26A1 depth profiles in lunar rocks and soil cores, together with particle track data, enables us to determine the long term average fluxes of energetic solar protons (>10 MeV) which can be represented by (J s,R o)=(125, 125). The lunar rock data indicate that this flux has remained constant for 5×105 to 2×106 years. Production rates of stable and radionuclides produced by galactic cosmic rays is given as a function of size and depth of the meteoroid. Radionuclide (53Mn,28Al) depth profiles in meteorite cores, whose preatmospheric depths are deduced from track density profiles are used to develop a general procedure for calculating isotope production rates as a function of meteoroid size. Based on the track density and22Ne/21Ne production rates, a criterion is developed to identify meteorites with multiple exposure history.22Ne/21Ne ratio <1·06 is usually indicative of deep shielded exposure. An examination of the available data suggests that the frequency of meteorites with multiple exposure history is high, at least 15% for LL, 27% for L and 31% for H chondrites. The epi-thermal and the thermal neutron density profiles in different meteorites are deduced from60Co and track density data in Dhajala, Kirin and Allende chondrites. The data show that the production profile depends sensitively on the size and the chemical composition of the meteoroid. Cosmic ray-induced thermoluminescence in meteorites of known preatmospheric sizes has been measured which indicates that its production profile is nearly flat and insensitive to the size of the meteoroid. Some new possibilities in studying cosmic ray implanted radionuclides in meteorites and lunar samples using resonance ionisation spectroscopy are discussed.  相似文献   

16.
The dominant component of nuclear tracks observed in meteoritic minerals poor in uranium is produced by cosmic ray very heavy (vh:Z>20) nuclei. Studies of cosmic ray tracks and other cosmogenic effects in meteorites give us information on the irradiation history of these meteorites and enable us to estimate the extent of ablation during their atmospheric transit, and hence their pre-atmospheric masses. In a specific type of meteorite, known asgas-rich meteorite, one finds individual grains and xenoliths that have received solar flare and galactic cosmic ray irradiation prior to the formation of these meteorites. Detailed studies of these exotic components give insight into the accretionary processes occurring in the early history of the solar system. Some of the important results obtained from such studies and their implications to meteoritics are summarized.  相似文献   

17.
Arguments are presented in support of the idea that the total energy losses of cosmic rays passing through molecular clouds can exceed the energy production due to the action of shocks in supernovae. Galactic cosmic rays interacting with the surface layers of molecular clouds can be efficiently reflected, so that they do not penetrate into the depths of the clouds. Low-energy cosmic rays (E < 1 GeV) that can produce the primary ionization of the molecular-cloud gas can be generated inside such clouds by numerous shocks arising due to supersonic turbulence.  相似文献   

18.
Studies of the extreme solar proton event of January 20, 2005 intensified the contest over of a long-standing problem: are solar cosmic rays arriving at the Earth accelerated by solar flares or by shocks preceding rapidly moving coronal mass ejections? Among the most important questions is the relationship between the energy spectra of the solar cosmic rays and the frequency spectra of flare microwave bursts. Some studies of previous solar-activity cycles have shown that such a relationship does exist, in particular, for protons with energies of tens of MeV. The present work analyzes this relation using data for 1987–2008. For flare events observed in the western half of the disk, there is a significant correlation between the index δ, which is equivalent to the power-law index of the integrated energy spectrum of 10–100 MeV protons detected near the Earth’s orbit, and radio burst parameters such as a ratio of peak fluxes S at two frequencies (for example, at 9 and 15 GHz) and a microwave peak frequency f m . Proton fluxes with hard (flat) energy spectra (δ ≤ 1.5) correspond to hard microwave frequency spectra (S 9/S 15 ≤ 1 and f m ≥ 15 GHz), while flares with soft radio spectra (S 9/S 15 ≥ 1.5 and f m ≤ 5 GHz) result in proton fluxes with soft (steep) energy spectra (δ ≥ 1.5–2). It is also shown that powerful high-frequency bursts with the hardest radio spectra (f m ≈ 30 GHz) can point at acceleration of significant proton fluxes in flares occurring in strong magnetic fields. These results argue that solar cosmic rays (or at least their initial impulses) are mainly accelerated in flares associated with impulsive and post-eruptive energy release, rather than in shocks driven by coronal mass ejections.  相似文献   

19.
Cosmogenic radionuclides with distinctive half-lives from chondritic falls were used as natural detectors of galactic cosmic rays (GCR). A unique series of uniform data was obtained for variations in the integral gradients of GCR with a rigidity of R > 0.5 GV in 1955–2000 on heliocentric distances of 1.5–3.3 AU and heliographic latitudes between 23° S and 16° N. Correlation analysis was performed for the variations in GCR gradients and variations in solar activity (number of sunspots, SS, and intensity of the green coronal line, GCL), the intensity of the interplanetary magnetic field (IMF), and the inclination of the heliospheric current sheet (HCS). Distribution and variations of GCR were analyzed in 11-year solar cycles and during a change in 22-year magnetic cycles. The detected dependencies of GCR gradients on the intensity of IMF and HCS inclination provided insight into the differences in the processes of structural transformation of IMF during changes between various phases of solar and magnetic cycles. The investigated relationships lead to the conclusion that a change of secular solar cycles occurred during solar cycle 20; moreover, there is probably still an increase in the 600-year solar cycle, which can be among the major reasons for the observed global warming.  相似文献   

20.
The flare source of thermal X-rays above a magnetic arch in the corona arises from the dissipation of the magnetic energy of the current sheet formed at the reconnection of magnetic-field lines. The sources of hard X-rays emitted from the footpoints of the magnetic arch are beams of electrons accelerated in field-aligned currents induced by the Hall electric field generated in the current sheet. Both the hard X-rays detected above the active region and the type III radio emission are radiated by electrons accelerated in the field-aligned currents induced by Alfven waves. The solar cosmic rays are emitted promptly at the instant of the flare. It is important that the Lorentz electric field accelerates protons along the singular magnetic X line. The relativistic protons propagate along the interplanetary magnetic field. These protons have exponential spectra, typical for acceleration occurring in current sheets. A mechanism that is relevant for the generation of delayed cosmic rays, which demonstrate significant anisotropy and a power-law spectrum with γ ∼5, is also discussed.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号