Cosmogenic radioisotopes in the Dhajala chondrite: implications to variations of cosmic ray fluxes in the interplanetary space

Activities of a suite of radioisotopes ranging in half-life from 5.6 days (⁵²Mn) to 3.7 m.y. (⁵³Mn) have been measured in the Dhajala chondrite. The results show that all the radioactivities are close to the expected levels except⁵⁴Mn and ²²Na. Their activities are higher than those based on the interplanetary fluxes at 1 A.U. near the ecliptic, expected immediately before the fall of Dhajala, corresponding to the time of solar minimum. Furthermore, activity ratios of ⁵⁴Mn/⁵³Mn and ²²Na/²⁶Al are higher by 30–50% than expected. The departure from the expected values is discussed in terms of spatial variations of cosmic rays based on the computed orbital parameters of the meteoroid. If the galactic cosmic ray fluxes in the equatorial region (±15°) are assumed to be the same as in the ecliptic plane then these results suggest higher fluxes by 33 ± 7% at heliographic latitudes 15–40°S, during solar minimum.     

Fe/O ratio variations during the disturbed stage in the development of the solar cosmic ray fluxes: Manifestations of the first ionization potential effect in the solar cosmic ray composition

The accelerated particle energy spectra in different energy intervals (from 0.06 to 75.69 MeV n^–1) have been constructed for various powerful flare events (1997–2006) with the appearance of solar cosmic rays (SCRs) based on the processing of data from the Advanced Composition Explorer (ACE) and WIND spacecraft. Flares were as a rule accompanied by coronal mass ejections. Different specific features in the particle spectra behavior, possibly those related to different acceleration processes, were revealed when the events developed. The Fe/O abundance ratio in different energy intervals during the disturbed development of flareinduced fluxes has been qualitatively estimated. It has been established that ground level event (GLE) fluxes represent an individual subclass of gradual events according to the character of Fe/O variations. The manifestations of the first ionization potential (FIP) effect in the composition of SCRs during their propagation have been qualitatively described.     

Variations in the cosmic ray fluxes,modulated by the solar and terrestrial magnetic fields,and climate changes. Part 3: A time interval of 1.5 Myr,including the pleistocene

The most reliable data on a change in the intensity of cosmic rays and geomagnetic field on large time scales have been analyzed, and the relations between changes in these processes and climate during the last 1.5 Myr have been studied. An analysis indicated that the climate of the Earth is affected by changes in the Earth’s orbit parameters and geomagnetic dipole values; however, the climate responds to these changes with a delay of 10 kyr and immediately, respectively. In this case about two thirds of the effect of eccentricity on ¹⁸O is implemented via an intermediate chain: virtual axial dipole moment, changes in which can be related to changes in eccentricity. Thus, an analysis of the accumulated data on the processes, proceeding in the Earth’s atmosphere during the interaction with cosmic rays on the scales of several years to several hundreds of thousand years, indicates that the cosmophysical factor of influence on climate cannot be rejected. To make the conclusion more convincing, it is necessary to collect data for the studied time interval in a much wider region, to more accurately date samples, and to study the response of the climatic system to the external influence.     

Effect of active longitudes in cosmic ray flux modulation

Galactic cosmic rays, registered by ground-based neutron monitors, are strongly affected by the heliosphere, i.e., being subjected to solar modulation. Cosmic ray variations are closely related to different solar activity indices and IMF parameters. The longitudinal inhomogeneity of the general solar magnetic field as a star and the manifestation of this inhomogeneity in the magnetic field are considered in the work. It has been established that the longitudinal inhomogeneity of this field, with the dipole distribution of polarities along heliolongitude, mainly contributes to 27-day modulation of galactic cosmic rays.     

Cosmic ray exposure ages of chondrites,pre-irradiation and constancy of cosmic ray flux in the past

A systematic calibration of the production rate of one specific cosmic-ray-produced nuclide in chondrites, that of²¹Ne, was achieved by using four independent methods:P₂₁(1.11) = 0.507 ± 0.039, 0.302 ± 0.013, 0.312 ± 0.017and0.292 ± 0.019 (in units of 10^?8 cm³ STP/g My) based on²⁶Al-age,⁵³Mn-age,⁸¹Kr-⁸³Kr and²²Na-²²Ne methods, respectively. These production rates are all normalized to a shielding parameter ratio²²Ne/²¹Ne= 1.11 and to the chemical composition of L chondrites. The results obtained by the latter three methods are in good agreement, but they disagree in a systematic way with the²⁶Al-age calibration. Based on these results, we recommend a valueP₂₁(1.11) = 0.31 and a production rate equation:P₂₁ = 4.845 P₂₁ (1.11) F[21.77(²²Ne/²¹Ne) ? 19.32]^?, whereF = 1.00 for L and LL, andF = 0.93 for H chondrites, for the calculation of cosmic ray exposure ages on the basis of Ne concentrations. In an attempt to assess possible causes for this discrepancy, we discuss the²⁶Al half-life measurements, we evaluate effects resulting from pre-irradiation of meteorites, and we discuss the evidence regarding the constancy of the cosmic ray flux in the past, in the light of some recent astronomical observations.     

Regions of the maximal cosmic ray energy release in the atmosphere

The cosmic ray flux through the atmosphere at different levels of solar activity is simulated. The Geant program package has been used to determine the atmospheric zones where the maximal contrast of the released ray energy originates between the periods of solar minimum and maximum. The geographic coordinates and altitudes of these zones have been calculated. The results can be used to search for statistical correlations between the solar activity variations and dynamics of atmospheric transparency.     

Regional millennial trend in the cosmic ray induced ionization of the troposphere

Long-term trends in the tropospheric cosmic ray induced ionization on the multi-millennial time scale are studied using the newly released paleomagnetic reconstruction models. Spatial and temporal variations of the tropospheric ionization has been computed using the CRAC:CRII model and applying the paleomagnetic CALS7k.2 reconstruction. It has been shown that long-term variations of the tropospheric ionization are not spatially homogeneous, and they are defined not only by solar (i.e., covariant with solar irradiance) changes but also by the geomagnetic field. The dominance of the two effects is geographically separated, which makes it possible to distinguish between direct and indirect solar–terrestrial climate effects. Possible climate applications are considered.     

Annual variation detected by GPS,GRACE and loading models

Most GPS coordinate time series, surface displacements derived from the Gravity Recovery and Climate Experiment (GRACE), and loading models display significant annual signals at many regions. This paper compares the annual signals of the GPS position time series from the Crustal Dynamics Data Information System (CDDIS), estimates of loading from GRACE monthly gravity field models calculated by three processing centers (Center of Spatial Research, CSR; Jet Propulsion Laboratory, JPL; GeoForschungsZentrum, GFZ) and three geophysical fluids models (National Center for Environmental Prediction, NCEP; Estimating the Circulation and Climate of the Ocean, ECCO; Global Land Data Assimilation System, GLDAS) for 270 globally distributed stations for the period 2003-2011. The results show that annual variations derived from the level-2 products from the three GRACE product centers are very similar. The absolute difference in annual amplitude between any two centers is never larger than 1.25 mm in the vertical and 0.11 mm in horizontal displacement. The mean phase differences of the GRACE results are less than ten days for all three components. When we correct the GPS vertical coordinate time series using the GRACE annual amplitudes using the products from three GRACE analysis centers, we find that we are able to reduce the GPS annual signal in the vertical at about 80% stations and the average reduction is about 47%. In the north and the east, the annual amplitude is reduced on 77% and 72% of the stations with the average reduction 32% and 33%. We also compare the annual surface displacement signal derived from two environmental models; the two models use the same atmospheric and non-tidal ocean loading and differ only in the continental water storage model that we use, either NCEP or GLDAS. We find that the model containing the GLDAS continental water storage is able to better reduce the annual signal in the GPS coordinate time series.     

Techniques for characterizing weak transients in cosmic ray records,as measured by neutron monitor networks

The analysis of weak variations in the energetic particle flux, as detected by neutron or muon monitors, can often be considerably improved by analysing data from monitor networks and thereby exploiting the spatial coherence of the flux. We present a statistical framework for carrying out such an analysis and discuss its physical interpretation. Two other applications are also presented: filling data gaps and removing trends. This study focuses on the method and its various uses.     

Effect of snow in cosmic ray variations and methods for taking it into consideration

This paper describes a method, which makes it possible to eliminate the effect of snow cover from the neutron component of secondary cosmic radiation. For many circumpolar, high-latitude, and mountain stations, where cosmic rays are continuously registered, it is exclusively important to take the presence of snow into consideration. Comparisons are made for manual and automated measurements, which are corrected for the snow effect based on the developed algorithm. The described method was tested for a number of cosmic ray stations where considerable snow masses are accumulated during the winter period near or above a detector: Magadan, Mount Hermon, Jungfraujoch, and Nain.     

宇宙线小波分析在大地磁暴预报中的应用

利用Morlet小波变换方法对北京宇宙线台站的地面宇宙线强度在地磁暴前后的变化特征进行分析,得到: 1) 在平静期,北京宇宙线数据存在准24 h周期性的特征,且通过分析周期为12 h的Morlet小波"模",发现值稳定,且小于0.6; 2) 以90天为时间窗口,对2004年7月地磁暴前后的小波频谱变化进行详细分析,发现当发生大地磁暴时,宇宙线的静日准24 h周期被打破,其他周期的波动开始增强.进一步研究发现,周期12h的波动在大地磁暴数小时到1天左右会出现显著增强,这一现象在2001、2002和2004年期间的大地磁暴前得到验证.3) Morlet小波"模"数据的急速增大是发生地磁暴的先兆特征,当小波模变化达到一定的阈值就可能发生大磁暴.本文分析了周期为12 h时小波的模数据,对强地磁暴事件进行统计,选定阈值0.6,并通过2003年的6次大地磁暴进行预报验证,结果表明该方法不仅能够对大地磁暴事件进行预报,而且提前量满足预报需求,为基于宇宙线实测数据预报地磁暴方法提供了重要基础.     

Long-period variations in the amplitude-phase interrelation of the first cosmic ray anisotropy harmonic

The distinguished directions, dependent on the solar wind velocity and IMF line position, exist in the interplanetary space, which results in the nonuniform distribution of phases and the amplitude-phase interrelation of the first cosmic ray anisotropy harmonic. The characteristics of the first anisotropy harmonics, determined for each hour using the global survey method based on the worldwide neutron monitor network from 1957 to 2010, were used to study long-period variations in the cosmic ray anisotropy. The longitudinal distributions of the cosmic ray vector anisotropy and the interrelation between the anisotropy amplitude and phase have been obtained for each year in this time interval. The results evidently demonstrate the anisotropy variations caused by the solar magnetic and activity cycles. The anisotropy distributions at different solar wind velocities have also been studied. Periods with a specific cosmic ray anisotropy behavior are distinguished and discussed. The obtained cosmic ray anisotropy variations agree with the convection-diffusion anisotropy model.     

Some aspects of ionization and the cloud cover,cosmic ray correlation problem

A variety of searches have been made for the generation of cloud by ionizing agents: cosmic rays, radon and nuclear fall-out. None has proved successful.     

Changes in cosmic ray cut-off rigidities due to secular variations of the geomagnetic field

An analytical expression is derived for the cutoff rigidity of cosmic rays arriving at a point in an arbitrary direction, when the main geomagnetic field is approximated by that of an eccentric dipole. This expression is used to determine changes in geomagnetic cutoffs due to secular variation of the geomagnetic field since 1835. Effects of westward drift of the quadrupole field and decrease in the effective dipole moment are seen in the isorigidity contours. On account of the immense computer time required to determine the cutoff rigidities more accurately using the particle trajectory tracing technique, the present formulation may be useful in estimating the transmission factor of the geomagnetic field in cosmic ray studies, modulation of cosmogenic isotope production by geomagnetic secular variation, and the contribution of geomagnetic field variation to long term changes in climate through cosmic ray related modulation of the current flow in the global electric circuit.     

The effect of model assumptions on computations of cosmic ray induced ionization in the atmosphere

The longitudinal profile of atmospheric cascades is sensitive to the energy, mass of the primary particle and to atmospheric state. In this work are compared ionization yield functions Y for winter, summer and US standard profiles of Earth's atmosphere. The various profiles are obtained on the basis of CORSIKA 6.52 code simulations using FLUKA 2006 and QGSJET II hadronic interaction subroutines. The energy deposit of proton induced cascade processes in the atmosphere is calculated for different types of atmospheres. The ion pair production in the atmosphere and the contribution of the different shower components, precisely the electromagnetic, muon and hadronic is estimated according applied atmospheric types. In addition simulations with different hadronic interaction models GHEISHA 2002, FLUKA 2006 and QGSJET II are carried out. The ion pair production in the atmosphere and the contribution of different shower components is estimated according the assumed hadronic interaction models. The yield function Y for total ionization, respectively, for the different components is compared. The observed differences are widely discussed. General conclusion concerning the application of various atmospheric profiles and hadron interaction models is carried out.     

Extrema of long-term modulation of the cosmic ray intensity in the last five solar cycles

Modulation of galactic cosmic rays in cycles 19–23 of solar activity has been determined based on observations of their long-term variations on the ground and in the near-Earth space. The extreme values of long-term variations in cosmic rays, obtained from the data of continuous cosmic radiation monitoring on the ground and in the near-Earth space in the last five solar cycles, have been analyzed. The results are compared with the extrema in the characteristics of solar magnetic fields and the sunspot numbers in these cycles. The similarities and differences in cosmic ray modulation between different cycles are discussed.     

26Al in iron meteorites and the constancy of cosmic ray intensity in the past

Cosmic-ray-produced²⁶Al in iron meteorites has been measured by low-level γγ-coincidence counting. The²⁶Al activities, in dpm/kg, are: Aroos3.0 ± 1.0, Braunau2.6 ± 0.5. Kayakent4.6 ± 1.5, N'Goureyma4.4 ± 1.1, Okahandja3.6 ± 0.9, Treysa4.0 ± 0.5. Exposure ages based on²⁶Al/²¹Ne are in agreement, within experimental error(±20%), with those based on³⁶Cl/³⁶Ar and³⁹Ar/³⁸Ar but the ages based on⁴⁰K/⁴¹K are higher by about 50%. The difference in exposure ages is probably caused by a real change of the cosmic ray intensity in the inner solar system.     

Verification of magnetic field models based on measurements of solar cosmic ray protons in the magnetosphere

Measurements of solar cosmic ray (SCR) protons in the magnetosphere can be used to verify models of the Earth’s magnetic field. The latitudinal profiles of precipitating SCRs with energies of 1–90 MeV were measured on the CORONAS-F low-orbiting satellite during a strong magnetic storm on October 29–30, 2003. A flux of precipitating protons can remain equal to the interplanetary flux only due to a strong pitch angle diffusion that originates when the radius of the field line curvature is close to that of the particle rotation Larmor radius. The observed boundaries of the strong diffusion region can be compared with the boundaries anticipated according to the models of the magnetic field of the Earth’s magnetosphere. The adiabaticity parameter values, calculated for several instants of the CORONAS-F satellite pass based on the TS05 and parabolic models, do not always correspond to measurements. How possible changes in the model configurations of the magnetic field can allow us to eliminate discrepancies with the experiment and to explain why solar protons with energies of several megaelectronvolts penetrate deep in the Earth’s inner magnetosphere is considered here.     

Solar activity and cosmic ray variations as a factor of intensity of cyclonic processes at midlatitudes

Long-period variations in the cyclonic activity at middle and subpolar latitudes of the North Atlantic are studied on the basis of the data from the MSLP archive of the surface pressure (Climatic Research Unit, UK) for 1874–1995. It has been found that in the cold half year (the period of the most intense formation and development of extra-tropical cyclones) in the studied region, oscillations of the surface pressure with periods close to the main periods of solar activity (～80 and ～11 years) are observed. The obtained results make it possible to assume that solar activity and related variations in the galactic cosmic rays are one of the factors influencing the intensity of cyclonic processes at midlatitudes on the time scales of ～10 to ～100 years.     

Establishing an effective offset-dependent velocity model by ray tracing and its application in Kirchhoff time migration

Conventional Kirchhoff prestack time migration based on the hyperbolic moveout can cause ambiguity in laterally inhomogeneous media, because the root mean square velocity corresponds to a one-dimensional model under the horizontal layer assumption; it does not include the lateral variations. The shot/receiver configuration with different offsets and azimuths should adopt different migration velocities as they contribute to a single image point. Therefore, we propose to use an offset-vector to describe the lateral variations through an offset-dependent velocity corresponding to the difference in offset from surface points to the image point. The offset-vector is decomposed into orthogonal directions along the in-line and cross-line directions so that the single velocity can be expressed as a series of actual velocities. We use a simple Snell's law-based ray tracing to calculate the travel time recorded at the image point and convert the travel time to an equivalent velocity corresponding to a pseudo-straight ray. The double-square-root equation using such an equivalent velocity in the offset-vector domain is non-hyperbolic and asymmetrical, which improves the accuracy of the migration. Numerical examples using the Marmousi model and a wide azimuth field data show that the proposed method can achieve reasonable accuracy and significantly enhances the imaging of complex structures.