Solar modulation of galactic cosmic rays in the three-dimensional heliosphere according to meteorite data

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.     

Dynamics of the photospheric magnetic field in the vicinity of the solar equator

SOHO-MDI daily magnetic field synoptic data (a 14-year series of daily maps of the solar magnetic field intensity B available at the site ) have been used to analyze the dynamics of the photospheric magnetic field in the vicinity of the solar equator. The standard deviation s _B of the field B calculated over areas of tens of square degrees on the solar disk was taken as a basic index. An 11-year variation similar to that observed at higher latitudes is observed in the vicinity of the equator, and is similar for weak and strong fields; i.e., the solar cycle exists in the sunspot-free zone. New qualitative data support the idea that the weak background magnetic field increases toward the solar limb. This angular dependence suggests the existence of a transverse component of the background field. The magnetic fields in the vicinity of the equator were significantly different in the initial phases of Cycles 23 and 24. Annual variations of s _B were observed near the center of the solar disk. These variations are due to two factors: the annual variation of the distance from the equator to the disk center and the increase of s _B with with distance from the equator. Reliable detection of these variations is an evidence of high accuracy of the s _B estimates.     

Analysis of geomagnetic field along seismic profile P4 of the International Project POLONAISE'97

This paper presents relative secular variations of the total intensity of the geomagnetic field against a background of results of magnetic anomaly interpretation along seismic profile P4. Profile P4 crosses a Variscan folding zone in the Paleozoic Platform (PLZ), the Trans-European Suture Zone (TESZ), and the Polish part of the East European Craton (EEC). Secular geomagnetic field variations measured in 1966–2000 along a line adjacent to seismic profile P4 were analysed. The study of secular variations, reduced to the base recordings at the Belsk Magnetic Observatory, showed that the growth of geomagnetic field at the East European Craton was slower than in the Trans-European Suture Zone and the Paleozoic Platform.A 2D crustal magnetic model was interpreted as a result of magnetic modelling, in which seismic, geological and geothermal data were also used. The modelling showed that there were significant differences in the magnetic model for geotectonic units, which had been earlier determined based on deep seismic survey data. It should be noted that a fundamental change of trend of the relative secular variations was observed at the slope of the Precambrian Platform. After analysing the geomagnetic field observed along profile P4, the hypothesis that the contact between Phanerozoic and Precambrian Europe lies in Poland's territory can be proven.     

Gamma-ray curvature radiation from the polar regions of a radio pulsar with an axisymmetric magnetic field

The influence of an axisymmetric magnetic field on the intensity, spectrum, and shape of a pulse of gamma-ray curvature radiation from the polar regions of a radio pulsar is investigated. The pulsar is considered in a Goldreich-Julian model with a free-electron emission from the neutron-star surface. The influence on the curvature radiation of variations of both the curvature of the magnetic field lines and the electric field due to the nondipolarity of the magnetic field are investigated. The presence of even modest nondipolarity (less than 10%) can lead to a sharp drop in the intensity of the gamma-ray curvature radiation, while the intensity of the X-ray curvature radiation (photon energies <100 keV) is affected only weakly.     

2D geological–geophysical model of the Timok Complex (Serbia,SE Europe): a new perspective from aeromagnetic and gravity data

The study reports new aeromagnetic and gravity data for the northern part of the Timok Magmatic Complex (TMC), East Serbia. The TMC is part of the Tethyan Eurasian metallogenic zone well known for hosting large copper and gold deposits. The complex formed by continuous volcanic activity 90–78 Ma ago, that developed in roughly three phases: Turonian andesites, Santonian–Campanian andesites/basaltic andesites (both mostly volcanic) and Campanian latites/monzonites (mostly shallow intrusive). The aeromagnetic measurements included acquiring total magnetic intensity data that were corrected for diurnal variations, leveling, microleveling, calculated normal field values, calculated anomaly values of total magnetic field intensity and reduction to the pole. The gravity measurements were carried out in an irregular grid with relative gravity values obtained using a Worden gravity meter. 2D modeling reveals that the subsurface extension of the Campanian Valja Str? pluton is ten times larger than it is indicated by its surface outcrops. This implies that the area south and southeast from the pluton can be interesting in terms of finding new porphyry systems. The model indicates that this intrusive body should not be considered as a deeply dissected pluton. This sheds new light onto its potential with respect to epithermal gold mineralization, as well. The model also suggests that there are larger non-exposed bodies of Santonian–Campanian volcanics and near-surface hydrothermally altered rocks than it is inferred from geological maps. The results of our study suggest that further interdisciplinary investigations in the TMC, in particular those integrating geophysics and geology, may have potential of advancing the existing exploration models.     

Aspects on the origin of the precursory magnetic anomalies of the Mw 6.4 Aquila earthquake

An anomalous behaviour of the scaling exponent derived from the detrended fluctuation analysis (DFA) of the time series of low frequency variations of the horizontal and vertical magnetic field components has been recently reported as being observed 2 months prior to the Mw 6.3 earthquake on 6 April 2009, close to L’Aquila city, Italy. Here, we suggest a possible physical explanation of this effect based on the experience from similar measurements in Greece. In particular, for example, we compare these observations associated with Aquila earthquake with the ones of the Mw 6.6 earthquake on 13 May 1995 at Kozani-Grevena, Greece where both magnetic field variations and seismic electric signals (SES) were recorded. Almost 1 month before the latter earthquake, anomalous variations in both electric and magnetic field were detected, the time series of that were analysed by means of DFA and led to an exponent close to unity. Similarly, the calculated DFA exponent for the Aquila earthquake time series of the anomalous magnetic field variations 2 months before the main shock was also found close to unity. These results could imply that in the case of Aquila, according to the Maxwell’s laws, one should expect to observe simultaneously with the magnetic signal an associated SES activity, provided that an appropriate station to monitoring the earth’s electric field variations in the same area was available. Hence, it seems that similar underlying non-linear dynamic processes in mechanical and as well as electromagnetic sense, with features of criticality, dominated in both pre-focal areas.     

Optical spectrum variations of IL Cep A

The results of many-year uniform spectroscopic observations of the Herbig Ae/Be star IL Cep A are presented. Its Hα line has either a single or a barely resolved two-component emission profile. The Hβ emission line is clearly divided into two components with a deep central absorption. Smooth variations of the observed parameters of individual spectral lines over nine years are observed. The He I λ5876 Å line has a complex absorption profile, probably with superposed emission components. The NaI D1, D2 doublet exhibits weak changes due to variations in the circumstellar envelope. The variations observed in the stellar spectrum can be explained by either binarity or variations of the magnetic field in the stellar disk. Difficulties associated with both these possibilities are discussed.     

Integrated potential field study on the subsurface structural characterization of the area North Bahariya Oasis, Western Desert, Egypt

The present study aims mainly to delineate and outline the regional subsurface structural and tectonic framework of the buried basement rocks of Abu El Gharadig Basin, Northern Western Desert, Egypt. The potential field data (Bouguer gravity and total intensity aeromagnetic maps) carried out in the Abu El Gharadig Basin had been analyzed together with other geophysical and geological studies. The execution of this study is initiated by transformation of the total intensity aeromagnetic data to the reduced to pole (RTP) magnetic map. This is followed by applying several transformation techniques and various filtering processes through qualitative and quantitative analyses on both of the gravity and magnetic data. These techniques include the qualitative interpretation of gravity, total intensity magnetic and RTP magnetic maps. Regional–residual separation is carried out using the power spectrum. Also, the analytic signal and second vertical derivative techniques are applied to delineate the hidden anomalies. Aeromagnetic anomalies in the area reflect significant features on the basement tectonics, on the deep-seated structures and on the shallow-seated ones. Major faults and intrusions in the area are indicated to be mainly along the NE–SW, NW–SE, ENE–WSW and E–W directions. The Bouguer gravity map indicates major basement fracturing, as well as variations in the sedimentary basins and ridges and subsequent tectonic disturbances. The most obvious anomalous trends on the gravity map, based on their frequencies and amplitudes, are along the NE–SW, ENE–WSW, E–W and NW–SE trends. The main of Abu EL Gharadig Basin depositional center does not show sharp variations, because of the homogeneity of the marine rocks and the great basement depths.     

Mass and magnetic properties for 3D geological and geophysical modelling of the southern Agnew–Wiluna Greenstone Belt and Leinster nickel deposits,Western Australia

Physical property measurements provide a critical link between geological observations and geophysical measurements and modelling. To enhance the reliability of gravity and magnetic modelling in the Yilgarn Craton's Agnew–Wiluna Greenstone Belt, mass and magnetic properties were analysed on 157 new rock samples and combined with an existing corporate database of field measurements. The new samples include sulfide ore, serpentinised and olivine-bearing ultramafic host-rocks, granitoid, and felsic and mafic volcanic and volcaniclastic country rock. Synthesis of the data provides a useful resource for future geophysical modelling in the region. Several rock types in the region have sufficiently distinct physical properties that a discriminant diagram is proposed to facilitate a basic classification of rock types based on physical properties. However, the accumulation of emplacement, metamorphic, hydrothermal and structural processes has complicated the physical properties of the rocks by imposing duplicate and sometimes opposing physical property trends. The data confirm that massive sulfide and ultramafic rocks have the most distinctive mass and magnetic properties but with variability imposed by their complex history. Sulfide content imposes the strongest control on densities, but can only be identified when comprising >10 vol% of the rock. The pyrrhotite-rich Ni-sulfide assemblages generally have similar magnetic properties to the host ultramafic rocks, but can have much lower susceptibilities where the thermal history of the rocks has favoured development of hexagonal pyrrhotite over monoclinic pyrrhotite. In ultramafic rocks that contain <10 vol% sulfides, density and susceptibility are primarily controlled by serpentinisation, with olivine breaking down to serpentine and magnetite in the presence of water. Serpentinisation dramatically lowered densities and increased susceptibilities, but had limited influence on the intensity of remanent magnetisation. All ultramafic rocks contain multidomain magnetite, and most contain low coercivity grains prone to overprinting by in situ viscous remanent magnetisation or drilling-induced isothermal remanent magnetisation during extraction. Despite the low coercivities, Koenigsberger ratios of 1–20 are observed indicating that viscous remanent magnetisation aligned parallel to the present Earth field must be considered in any magnetic modelling. It is also noted that coarser-grained intrusive varieties of all rock types (e.g. granite, gabbro) show remanent magnetisation intensities 1–2 orders of magnitude greater than their extrusive equivalents (felsic and basaltic volcanics).     

Geomagnetic field reconnaissance in Kuwait

Nearly 150 measurements of the total magnetic field intensity were made in Kuwait in early 1988. Observation points are located primarily along major highways over lines varying in length from few to several tens of kilometers. Measurements were made with a proton magnetometer. Station spacing varied from nearly 1 to 5 km. Diurnal correction to the data was made possible by frequent excursions to the base station.

Preliminary analysis of the data indicates that the field intensity undulates in SW-NE direction nearly perpendicular to the regional tectonic trend. The amplitude of these variations range approximately from 30 to 90 γ over wavelengths varying nearly from 38 to 70 km. We have made a combined inversion of the data with the unpublished Bouguer gravity map of the country along a N-S profile in the central region and find that the data are reasonably well matched with predictions of a simple two-dimensional block model. The model consists of a layer overlying a half-space. The variables of the model are the thickness and density of the surface layer and the susceptibility of the basement rock. The observed variation of the magnetic field and Bouguer anomalies for the selected profile may be accounted for either by the simultaneous northward density reduction of about 0.06 g/cm³ in the surface layer and approximately 15% increase of the basement susceptibility, or else by nearly 800 m variation of the sedimentary thickness.     

Intercombinational line profiles in the UV spectra of T Tauri stars and analysis of the accretion zone

We have analyzed for the first time profiles of the SiIII 1892 Å and CIII 1909 Å intercombinational lines in HST spectra of the stars RY Tau and RU Lup. The widths of these optically thin lines exceeded 400 km/s, ruling out formation in the stellar chromosphere. Since the intensity of the Si line exceeds that of the C line, it is unlikely that a large fraction of the observed line flux is formed in a stellar wind. The observed profiles can be reproduced in the framework of an accretion shock model if the velocity field in the accretion zone is appreciably nonaxisymmetric. In this case, the line profiles should display periodic variations, which can be used to determine the accretion zone geometry and the topology of the magnetic field near the stellar surface; corresponding formulas are presented. In addition, periodic variations of the 0.3–0.7 keV X-ray flux should be observed.     

Magnetic fields of telluric currents and mapping upper portions of crust

The author proposes a method of telluric-magnetic mapping, profiling, and exploration. The profiling involves recording of short-period variations in the telluric current and the magnetic field (MTP) and an areal (MVR), similar to the above. The method can be used on any segment of the crust, especially with newly designed, highly sensitive short-period magnetometer. The magnetic fields of telluric currents are measured by means of a four-channel oscillograph controlled from a panel in which switches are incorporated. The magnetic fields of the telluric current are measured at two points, since the automatic switching arrangement permits a procedure identical with the measurements in the telluric current. Amplitudes and periods of almost sinusoidal waves are measures of the chords of the elliposidal electric and magnetic fields. Analysis of magnetic field mapping and its results are given. The author feels that the telluric-magnetic profiling should replace direct telluric voltage measurements in many regions because of its economics. It gives precise data on the structure of the sedimentary cover. Telluric-exploration will open up entirely new possibilities in permafrost zones and the method will be substantially more efficient than direct telluric measurements. — A.W. Bellais     

The Earth’s magnetic field history for the past 400 Myr

Published and new data on the Earth’s past magnetic field have been interpreted in terms of its links with the frequency of magnetic polarity reversals and with tectonic events such as plume-related eruptions and rifting. The paleointensity and reversal frequency variations show an antiphase correlation between 0 and 160 Ma, and the same tendency likely holds for the past 400 Myr. The geomagnetic field intensity averaged over geological ages (stages) appears to evolve in a linearly increasing trend while its variations increase proportionally in amplitude and change in structure. Both paleointensity and reversal frequency patterns correlate with rifting and eruption events. In periods of high rifting activity, the geomagnetic field increases (15 to 30%) and the reversals become about 40% less frequent. Large eruption events between 0 and 150 Ma have been preceded by notable changes in magnetic intensity which decreases and then increases, the lead being most often within a few million years.     

Variations of the dipole magnetic moment of the sun during the solar activity cycle

Observations of the large-scale solar magnetic field (synoptic maps) and measurements of the magnetic field of the Sun as a star (the total magnetic field) are used to determine the dipole magnetic moment and direction of the dipole field for three successive solar cycles. Both the magnetic moment and its vertical and horizontal components vary regularly during the cycle, but never disappear completely. A wavelet analysis of the total magnetic field shows that the amplitude of the 27-day variations of this field is very closely related to the magnetic moment of the horizontal dipole. The reversal of the global dipole field corresponds to a change in the inclination of its axis and occurs in a series of steps lasting one to two years rather than continuously. Before the onset of the reversal, the dipole axis precesses relative to the solar rotational axis, then shifts in a meridianal plane, reaching very low latitudes, where a substantial shift in longitude then begins. These results are discussed in connection with helioseismological data indicating the existence of oscillations with a period of about 1.3 yr and properties of dynamo processes for the case of an inclined rotator.     

Geomagnetic field on the territory of the Czech Republic for 1995.5

On the territory of Bohemia and Moravia the measurements of the vector of geomagnetic field (declination, inclination and total intensity) were carried out at 199 points of the first order in 1994–1996. All values were reduced to the epoch 1995.5 and magnetic maps were derived by means of standard computer software. A comparison of recent measurements with IGRF has shown that, in the first approximation, IGRF can be used on this territory as a reference magnetic field.     

Curvature and non-resonance Compton gamma-ray emission of a radio pulsar with a non-dipolar magnetic field

We consider the influence of a non-dipolar magnetic field on the gamma-ray emission from the polar regions of a radio pulsar. The pulsar is treated in a Goldreich-Julian model with a free flow of charge from the surface of the neutron star. When finding the intensity of the gamma-ray radiation of the pulsar tube, both curvature gamma-ray radiation from the primary electrons and non-resonance inverse Compton scattering of thermal photons from the polar cap on primary electrons are taken into account. When finding the height of the upper plate of the pulsar diode, we included only positrons created by the curvature radiation of primary electrons. We assumed that the polar cap is heated by the return positron current. The influence on the gamma-ray emission of variations in both the radius of curvature of the magnetic force lines and in the electric field due to the non-dipolarity of the magnetic field were taken into account. The presence of even weak non-dipolarity of the magnetic field leads to a sharp decrease in the intensity of the gamma-ray emission from the pulsar tube at energies 1–100 MeV, while the intensity of the inverse Compton radiation (at energies 1–100 GeV) varies only relatively weakly.     

Magnetic-field variations in the active region NOAA 10486 and their relationship to X-ray flares and coronal mass ejections

SOHO/MDI magnetograms are used to analyze the time variations in the magnetic parameters of the active region (AR) NOAA 10486, which was part of a large activity complex that passed over the solar disk from October 26 to 31, 2003, during solar cycle 23. The results are compared with X-ray flares in the AR and the parameters of coronal mass ejections associated with the AR. The time variations in the distributions of themagnetic-field strengths associated with the total magnetic flux (Fa), the flux imbalance between the northern and southern polarities (Im), the complexity of the field, as a measure of the mutual overlapping of the opposite polarities (Co), and the tilt angle of the magnetic axis (An) are considered. The time variations in the free energy accumulated in current sheets of ARs were traced using a parameter introduced for this purpose (Sh). The following results were obtained. First, the parameters Fa, Im, Co, An, and Sh quantitatively describe the current state of the AR and can be used to trace and analyze the dynamical evolution of its magnetic field. Second, variations in the magnetic-field-strength distributions and the mean values of Fa, Im, Co, An, and Sh are associated with flares and coronal mass ejections, and the variations have considerable amplitudes. Third, the parameter Sh characterizing the degree to which the magnetic field is non-potential in regions adjacent to the main neutral line increases before eruptive events, and is thus particular interest for monitoring the states of ARs in real time. Fourth, the magnetic field of the AR manifests a sort of quasi-elasticity, so that the field structure is restored after active events, on average, within 1–3 h.     

Magnetic anisotropy of hematite natural crystals: increasing low-field strength experiments

Hematite is a very abundant mineral in natural rock samples. Despite being one of the most important carriers of remanent magnetization, its magnetic anisotropy is not well understood partially due to its high coercivity and complex behavior. In particular, the field intensity beyond which the Rayleigh relation no longer holds varies from one crystal to another. This field threshold is usually less than the field used in most commercial instruments. The nonlinear behavior of low-field susceptibility may thus hinder the magnetic fabric analysis. We have carried out an intensive study of the low-field bulk susceptibility and anisotropy of magnetic susceptibility (AMS) at increasing low fields in the range of 2–450 A/m (effective value) in a collection of hematite natural crystals. Standard rock magnetic properties, X-ray diffraction, and mass spectrometry have also been determined in order to discover the parameters influencing the low-field susceptibility variations with field. The AMS principal directions, the shape of the AMS ellipsoid, and the degree of anisotropy are the parameters that can vary with different applied fields. It has been found that there is no correlation between magnetic properties like coercivity or saturation magnetization and the range in which the Rayleigh approximation is valid. However, there seems to be a correlation with the peak width determined from X-ray diffraction, suggesting that the Rayleigh region in hematite crystals is related to the spatial orientation of the physical domains within the basal plane.     

The effect of uniaxial compression in the behaviour of remanent and induced magnetizations for basaltic rocks from the western Sinai Peninsula, Egypt

Seventy oriented basaltic samples were collected from six sites from the Wadi Budra and Farsh El Azraq areas of the west-central part of Sinai. Rock magnetic properties such as Curie temperatures and hysteresis parameters, as well as microscopic observations, point to magnetite as the main carrier of the remanent magnetization. The stress sensitivity of basaltic rocks is relatively low. High stress produces an increase in the remanent and induced magnetizations perpendicular to the applied stress axis and a decrease parallel to it. The change of magnetization during stress action ranges from 1.1% to 3.5% for a stress of 100?bar. The differential total magnetic intensity field with time (within 2?years) was observed through 80 magnetic observation points set up on both sites of the basaltic sheet at the studied area. The observed temporal variations of magnetization can be interpreted as stress loading parallel to the regional stress field in the order of 50?±?20?bar, according to the stress sensitivity of the precursor basalt.     

Study on the variations of geomagnetic-field intensity during the quaternary in special reference to thermomagnetic measurements on volcanic rocks

Thermomagnetic measurements have been made on thirteen samples of Quaternary volcanic rocks of different episodes from three localities by Thellier’s method. Paleomagnetic field intensities for the three Quaternary sub-periods have been obtained: 0.62 for Early Pleistocene, 1.01 for Middle Pleistocene and 1.57 for Late Pleistocene with respect to the present magnetic field intensity. The results indicate that the geomagnetic field intensity has been increasing since Pleistocene time, and there exists a close relationship between paleomagnetic field intensity and climatic changes, i.e., the climate trends to become colder with increasing paleomagnetic field intensity, and vice versa.