Showing papers on "Earth's magnetic field published in 1968"
TL;DR: In this article, the authors investigated the low-energy electron population in the magnetosphere within the local time range ∼17 to ∼22 hours using the OGO 1 satellite and OGO 3.
Abstract: Observations of electrons of energy 125 ev to ∼2 kev with the OGO 1 satellite and of electrons of energy 40 ev to ∼2 kev with OGO 3 (by means of modulated Faraday cup detectors) are used to investigate the low-energy electron population in the magnetosphere within the local-time range ∼17 to ∼22 hours. Intense fluxes of these electrons are confined to a spatial region, termed the plasma sheet, which is an extension of the magnetotail plasma sheet discovered by the Vela satellites and is identified with the soft electron band first detected by Gringauz. The plasma sheet extends over the entire local-time range studied in this investigation, from the magnetospheric tail past the dusk meridian toward the dayside magnetosphere. In latitude it is confined to within 4–6 RE of the geomagnetic and/or solar magnetospheric equatorial plane, in agreement with observations already reported from the Vela satellites; no electron fluxes are detected high above the equator, not even very near the magnetopause. In radial distance the plasma sheet is terminated by the magnetopause on the outside and by a well-defined sharp inner boundary on the inside. The inner boundary has been traced from the equatorial region to the highest latitudes investigated, ∼40°; during geomagnetically quiet periods, it is observed at an equatorial distance of 11 ± 1 RE and appears to extend to higher latitudes along magnetic field lines. Weak or no electron fluxes are found between the inner boundary of the plasma sheet and the outer boundary of the plasmasphere. Detection (by an indirect process) of the very high ion densities within the plasmasphere gives positions for its boundary in good agreement with other determinations. During periods of magnetic bay activity, the plasma sheet extends closer to the earth; the inner boundary of the plasma sheet is then found at equatorial distances of 6–8 RE. This is most simply interpreted as the result of an actual inward motion of the plasma during a bay. In one case, it was possible to associate the beginning of this motion with the onset of the bay and to estimate an average radial speed of ∼12 km/sec, from which an electric field corresponding to ∼48 kilovolts across the magnetospheric tail was inferred. Within the plasma sheet, the electron population is characterized by number densities from 0.3 to 30 cm−3 and mean energies from 50 to 1600 ev and higher, with a strong anticorrelation between density and mean energy, so that the electron energy density (∼1 kev cm−3) and energy flux (∼3 ergs cm−2 sec−1) show relatively little variation. The lower energies and higher densities tend to occur during periods of geomagnetic disturbance. The nonobservation of electrons in regions above the plasma sheet implies an upper limit on the electron number density of 5 × 10−2 cm−3 if their mean energy is assumed to be ∼50 ev (typical of the magnetosheath) and 10−2 cm−3 if the energy is ∼1 kev (typical of the plasma sheet). At the inner boundary of the plasma sheet there is a sharp softening of the electron spectrum with decreasing radial distance but apparently little change in the electron number density. The electron energy density decreases across the inner boundary roughly as ∼exp (distance/0.4 RE) during quiet periods; during times of magnetic bay activity the energy density decreases as ∼exp (distance/0.6 RE), and there is a more complicated spatial structure of density and mean energy.
1,590 citations
TL;DR: In this article, it was shown that the geomagnetic anomalies are caused by a sequence of normally and reversely magnetized blocks that have been produced by sea floor spreading at the axes of the ridge in the Pacific, Atlantic, and Indian oceans.
Abstract: This paper summarizes the results of the three previous papers in this series, which have shown the presence of a pattern of magnetic anomalies, bilaterally symmetric about the crest of the ridge in the Pacific, Atlantic, and Indian oceans. By assuming that the pattern is caused by a sequence of normally and reversely magnetized blocks that have been produced by sea floor spreading at the axes of the ridges, it is shown that the sequences of blocks correspond to the same geomagnetic time scale. An attempt is made to determine the absolute ages of this time scale using paleomagnetic and paleontological data. The pattern of opening of the oceans is discussed and the implications on continental drift are considered. This pattern is in good agreement with continental drift, in particular with the history of the break up of Gondwanaland.
958 citations
TL;DR: In this paper, the authors compared the worldwide geomagnetic data with IMP 1 magnetic records obtained in the interplanetary space, and found that the magnetic fluctuations of the magnetospheric convective system are coherent with variations in the north-south component of the inter-planetary magnetic field.
Abstract: From the comparison of the worldwide geomagnetic data with IMP 1 magnetic records obtained in the interplanetary space, it is found that the DP 2 fluctuations, which are thought to be the geomagnetic counterpart of intensity fluctuations of the magnetospheric convective system, are coherent with variations in the north-south component of the interplanetary magnetic field. This coherence is observed irrespective of whether this component is directed northward or southward. Average time delay between the crossing of an interplantary magnetic structure across the nose of the bow shock and the associated magnetic variation on the ground is 7 minutes at the pole and 9 minutes at the midday equator. Applicability of the proposed models of the magnetospheric electric field to this phenomenon is critically examined, and the penetration of the interplanetary electric field into the magnetosphere is suggested as the origin of the DP 2 phenomenon.
440 citations
TL;DR: In this article, a probability model based on the theory of Bernouli trials was proposed to analyze variations in the lengths of geomagnetic polarity, intervals are analyzed by means of the probability that a polarity inversion will occur during one cycle of change in the geOMagnetic dipole moment.
Abstract: Variations in the lengths of geomagnetic polarity, intervals are analyzed by means of a probability model based on the theory of Bernouli trials. Polarity reversals are assumed to occur as the result of the interaction between steady oscillations of the geomagnetic dipole and secular variations of the nondipole field. The particular cycle on which a polarity inversion occurs is determined by the magnitude of the nondipole field, which is assumed to vary randomly and independently of dipole variations. The reversal properties of the geomagnetic dynamo are characterized by the single parameter p, the probability that a polarity inversion will occur during one cycle of change in the geomagnetic dipole moment. From an analysis of polarity changes during the past 10 m.y., the value of p is estimated to be 0.05. During the Permian period, it was at least two orders of magnitude smaller. The analysis suggests that within the past 10 m.y. there have occurred hitherto undiscovered short geomagnetic polarity events with durations shorter than 0.05 m.y.
312 citations
TL;DR: In this paper, it is suggested that there may be a rather continual relation between this solar structure and terrestrial responses, of which the recurring M-Region geomagnetic storms are just the most prominent example.
Abstract: Many observations related to the large-scale structure of the interplanetary magnetic field, its solar origin and terrestrial effects are discussed. During the period observed by spacecraft the interplanetary field was dominated by a sector structure corotating with the sun in which the field is predominantly away from the sun (on the average in the Archimedes spiral direction) for several days (as observed near the earth), and then toward the sun for several days, etc. The average sector appears to be a coherent entity with internal structure such that its preceding portion is more active than its following portion. Cosmic rays corotate with the interplanetary field, and there are differential flows associated with the sector pattern. Profound effects on geomagnetic activity and the radiation belts are produced as the sector pattern rotates past the earth. The solar origin of the sector pattern is discussed. The solar source may be associated with the large-scale weak background photospheric fields observed with the solar magnetograph. It is suggested that there may be a rather continual relation between this solar structure and terrestrial responses, of which the recurring M-Region geomagnetic storms are just the most prominent example.
281 citations
TL;DR: The polar substorm (DP 2) as discussed by the authors is associated with fluctuations in the magnetospheric plasma convection, and it will provide a useful means for the identification of the 'viscous-like' interaction mechanism.
Abstract: A DP 2 fluctuation has a time scale of about one hour and appears coherently all over the world. It differs from the polar substorm (DP 1) in that it is not caused by the activation of the auroral electrojet. Its current system consists of twin current vortices and a zonal part. It is associated with fluctuations in the magnetospheric plasma convection, and it will provide a useful means for the identification of the ‘viscous-like’ interaction mechanism.
280 citations
TL;DR: In this article, the authors proposed a method of selecting from all eligible velocity fields those which are of particular geophysical interest, such as the one which is most nearly a rigid rotation (westward drift) or the one that is most near a latitude dependent westward drift with m degrees of freedom.
Abstract: The motions in the Earth’s electrically conducting fluid core which are the probable cause of the geomagnetic secular variations have time scales of the order of a few centuries or less. Seismic bounds on the kinematic molecular viscosity of the core and order-of-magnitude arguments about the eddy viscosity make plausible the hypothesis that at such short periods the core motion consists of a boundary layer of Ekman-Hartmann type close to the core mantle boundary, and an interior free-stream motion where the viscosity and resistivity can be set equal to zero. This boundary-layer approximation requires that the unknown vertical length scale of the poloidal geomagnetic field deep in the core be at least as long as the 600 km horizontal length scales inferred at the surface of the core from observations above the mantle. For periods shorter than a century the Ekman and magnetic boundary layers are probably thinner than 120 km. If magnetic flux diffusion is neglected (i.e. if electrical conductivity is considered infinite) in the free stream in the core then the external geomagnetic field is completely determined by the fluid motion at the top of the free stream. Therefore the hypothesis of negligible flux diffusion in the free stream has implications for the geomagnetic secular variation, and these implications can be used as a test of whether there is any motion of a perfectly conducting core which will produce the observed secular variation. If the observed secular variation passes this test, we can write down explicitly all ‘ eligible’ velocity fields, i.e. all velocity fields at the top of the free stream in the core which are capable of producing exactly the observed secular variation. The different eligible velocity fields are obtained by different choices of an arbitrary stream function on the surface of the core. We describe a method of selecting from among all eligible velocity fields those which are of particular geophysical interest, such as the one which is most nearly a rigid rotation (westward drift) or the one which is most nearly a latitude dependent westward drift with m degrees of freedom.
276 citations
TL;DR: Magnetosphere mathematical model with electric field representing plasma flow superimposed on geomagnetic field is presented in this article, where the electric field represents plasma flow and the magnetic field represents electric field.
Abstract: Magnetosphere mathematical model with electric field representing plasma flow superimposed on geomagnetic field
220 citations
TL;DR: The Explorer 33 satellite was launched July 1, 1966 and was injected into a highly elliptical earth orbit, and the first 8 orbits of Explorer 33 (July 1 to November 11, 1966) mapped the earth's magnetosheath and magnetic tail from the western flank of the bow shock to the eastern flank as discussed by the authors.
Abstract: The Explorer 33 satellite was launched July 1, 1966 and was injected into a highly elliptical earth orbit. The Goddard Space Flight Center magnetic field experiment onboard the spacecraft consists of a triaxial fluxgate sensor with a maximum dynamic range of ±64 gammas and a sensitivity of ±0.25 gamma along each axis. Because of the initial apogee-earth-sun angle of 118° west of the sun, the first 8 orbits of Explorer 33 (July 1 to November 11, 1966) mapped the earth's magnetosheath and magnetic tail from the western flank of the bow shock to the eastern flank. This mapping of the geomagnetic tail out to 80 earth radii established that the tail extends beyond the lunar orbital distance. Explorer 33 has also found that the earth's bow shock is still a detectable boundary between the interplanetary magnetic field and the downstream magnetosheath at a geocentric distance of 75.7 earth radii. The measurements have further suggested that the cross section of the geomagnetic tail is probably not cylindrical and have shown that the magnetic field magnitude in the tail decreases with distance down the tail from the earth.
217 citations
TL;DR: Geomagnetic tail configuration and reconnection data from Explorer 33 satellite, noting skewing of field lines was collected by NASA's Explorer-33 satellite as mentioned in this paper, which is the only satellite capable of extracting geomagnetic data.
Abstract: Geomagnetic tail configuration and reconnection data from Explorer 33 satellite, noting skewing of field lines
171 citations
TL;DR: Geomagnetic field sudden impulses relation to solar wind pressure changes using Pioneer 6 measurements were analyzed in this paper, showing that the sudden impulses were correlated with the solar wind's pressure changes.
Abstract: Geomagnetic field sudden impulses relation to solar wind pressure changes using Pioneer 6 measurements
TL;DR: In this article, solar plasma observations during magnetic storms, discussing shocks and tangential discontinuities, geomagnetic variations and geomagnetworks were discussed, as well as He
Abstract: Solar plasma observations during magnetic storms, discussing shocks and tangential discontinuities, geomagnetic variations and He
TL;DR: In this article, a review on the distribution and origin of the large-scale electric field in the magnetosphere and its influence on the dynamical behavior of the magnetospheric plasma is given.
Abstract: A review is given on the distribution and origin of the large-scale electric field in the magnetosphere and its influence on the dynamical behavior of the magnetospheric plasma. Following a general discussion on the gross structure of the magnetosphere and its tail, two principal electric field systems are deduced from ground-based geomagnetic variations. One is responsible for the polar substorm, the DP 1 field, which is closely associated with the activation of the auroral electrojet. The other is responsible for the twin current vortices, the DP 2 field, and this represents the general convective system set up in the magnetospheric plasma. The origin of these magnetospheric electric fields is possibly resided in the domain of the solar wind interacting with the outer geomagnetic field. However, the mechanism, in which the energy is transferred, is still quite controversial. Several theories so far proposed are re-examined, and some modification of them are suggested to have a consistent understanding of these two types of electric fields. The effects of electric fields on magnetospheric plasma dynamics are described, such as the formation of the plasmapause, the acceleration and diffusion of energetic particles in the radiation belt.
TL;DR: In this paper, the effects of magnetic storms on the middle latitude D -region over Europe are examined using observations of transmissions over short paths of v.l.f., l.f. and h.f, which reveal pronounced effects associated with certain storms, effects which persist for several days after the recovery of the geomagnetic field.
TL;DR: In this paper, the authors improved their previous self-exciting "homogeneous" laboratory dynamo and developed a completely homogeneous dynamo that exhibits spontaneous oscillation and reversal of its magnetic field.
Abstract: WE have improved our previous self-exciting “homogeneous” laboratory dynamo1; the new dynamo is in essence completely homogeneous and exhibits spontaneous oscillation and reversal of its magnetic field.
TL;DR: In this paper, evidence is presented that suggests that geomagnetic bay disturbances occur in two stages and the onset of each stage is accompanied by a Pi 2 micropulsation.
Abstract: Evidence is presented that suggests that geomagnetic bay disturbances occur in two stages The onset of each stage is accompanied by a Pi 2 micropulsation; the fact that a Pi 2 occurs almost synchronously over the earth's surface allows the onset of this micropulsation to be used to define the onset of each stage of a bay The time lag between the onsets of the two stages ranges from about 10 to 30 minutes The delay between the two stages is suggested to be the time required for the transfer of information from the front of the magnetosphere to the region of reconnection in the magnetotail The recognition of the first stage of a bay as a precursor can facilitate high-resolution studies of auroral phenomena
TL;DR: In this paper, the authors studied the interplanetary magnetic field radial gradients between 0.81 and 1.0 AU noting microstructure, mesostructure, macrostructure and directional distribution of discontinuities.
Abstract: Interplanetary magnetic field radial gradients between 0.81 and 1.0 AU noting microstructure, mesostructure, macrostructure and directional distribution of discontinuities
TL;DR: Latitudinal variations in exosphere thermal ion composition, examining evidence of solar and geomagnetic control of ion distribution, were examined in this article, where the authors found that both solar and magnetic fields were involved in ion distribution.
Abstract: Latitudinal variations in exosphere thermal ion composition, examining evidence of solar and geomagnetic control of ion distribution
TL;DR: In this article, the authors studied the magnetic properties of four groups of Eocene and Cretaceous volcanic rocks and sediments and suggested the hypothesis that Turkey, the Arabian Shield and Africa have acted as one drifting unit since Late Mesozoic times.
TL;DR: In this article, the role of the external current responsible for the magnetospheric tail plays at quiet times in the penetration, motion, and arrival of low-energy cosmic rays is deduced from the integration of 1- to 500-Mev proton trajectories in a model magnetosphere.
Abstract: The role the external current responsible for the magnetospheric tail plays at quiet times in the penetration, motion, and arrival of low-energy cosmic rays is deduced from the integration of 1- to 500-Mev proton trajectories in a model magnetosphere. Using the Williams and Mead model, we show that protons can reach the midnight side at latitudes between 60° and 69° and the day side at latitudes between 60° and 80° by way of the tail. Protons have direct access to higher latitudes along open field lines. Thus, for latitudes above 60°, the cutoffs are lowered below the internal field cutoff values. No such lowering occurs for latitudes below 60° because the field lines in this region are not appreciably affected by the external current responsible for the tail. A daily cutoff variation, the minimum rigidity trajectories coming from the night side for any local time of arrival, is found. The directions of approach, along which the low-energy cosmic rays cross the magnetopause en route to the station, show a variation with local time. The daily variation in cutoff and approach directions are induced by axial asymmetry of the geomagnetic cavity.
TL;DR: In this article, the electron production rate q and electron density N produced by cosmic rays (CR) in the lower part of the D -region are theoretically considered and on the basis of the obtained formulas q and N are calculated from galactic CR for four geomagnetic latitudes 0°, 30°, 41°, 55° at maximum and minimum solar activity in winter and summer.
TL;DR: Temporal characteristics of geomagnetic micropulsations and related energetic auroral zone electron precipitation as function of local time were studied in this paper, where they were shown to be independent of the local time.
Abstract: Temporal characteristics of geomagnetic micropulsations and related energetic auroral zone electron precipitation as function of local time
TL;DR: Sahasrabudhe et al. as mentioned in this paper made a very extensive palaeomagnetic study of the Deccan traps using magnetic cleaning techniques and made a complete analysis of his data and the purpose of this communication is to demonstrate that the earlier results are more likely explained in terms of viscous magnetization.
Abstract: INITIAL surveys1–3 of the palaeomagnetism of the Deccan traps showed that there is an apparent decrease of palaeomagnetic inclination with altitude above sea level. This was interpreted2,4 as indicating a continuous northward movement of India during the time when the traps were being extruded. It was pointed out, however, that the observations could also be explained in terms of partial magnetic instability causing the directions to be pulled towards the present geomagnetic field. Sahasrabudhe5 has now made a very extensive palaeomagnetic study of the Deccan traps using magnetic cleaning techniques. His aim was to try to use the palaeomagnetic directions for stratigraphic purposes and he did not attempt to analyse his data for normal palaeomagnetic purposes. I have made a complete analysis of his data and the purpose of this communication is to demonstrate that the earlier results are more likely explained in terms of viscous magnetization. This conclusion leads to some consequences regarding the northward drift of India during the Tertiary.
TL;DR: Secular change examination in cislunar geomagnetic tail field gradient during summers of 1966 and 1967, using Explorer 33 and 35 results as mentioned in this paper, using Explorer 3 and 4 images.
Abstract: Secular change examination in cislunar geomagnetic tail field gradient during summers of 1966 and 1967, using Explorer 33 and 35 results
TL;DR: In this article, it was shown that magnetic merging in the neutral sheet of the geomagnetic tail takes place very near the earth (i.e., between about 10 and 30 RE) depending on the development of vacuum-like conditions immediately behind the earth.
Abstract: It is proposed that magnetic merging across the neutral sheet of the geomagnetic tail takes place very near the earth (i.e., between about 10 and 30 RE). The plasma density in the near-earth portion of the tail is usually low because the supersonic solar wind leaves a rarefied wake region extending about 30 RE behind the dipole-like magnetosphere. The merging of oppositely directed field lines occurs when the plasma density is too low to form a current sheet of sufficient strength to prevent merging. (This mechanism is self-limiting in that the plasma energy density is built up by the merging processes to be almost, but not quite, the required level.) The magnetic merging then takes place somewhat as it would in a vacuum. Merging in the neutral sheet, then, depends on the development of vacuum-like conditions immediately behind the earth. This vacuum-merging mechanism preserves the essential features of frozen-in flux that have been so successful in predicting the configuration of both the spiral interplanetary magnetic field and the extended magnetospheric tail. Magnetic merging does not appear to proceed when the plasma density is high enough to produce the currents required to prevent merging.
01 Jan 1968
TL;DR: The phenomenon of high-energy electrons impinging upon the atmosphere is now recognized to be a common one in geophysics and the most spectacular demonstration of this effect is the polar aurora, in which the luminosity produced during the excitation of air atoms and molecules by the electrons is readily visible as mentioned in this paper.
Abstract: The phenomenon of high-energy electrons impinging upon the atmosphere is now recognized to be a common one in geophysics. The most spectacular demonstration of this effect is the polar aurora, in which the luminosity produced during the excitation of air atoms and molecules by the electrons is readily visible. However, many other geophysical features are also caused by precipitating electrons since the structure of the ionosphere can be markedly affected by particle bombardment. Radio attenuation effects, particularly of the type observed by riometers in the auroral region, and radar back-scattering from inhomogeneities in the ionosphere are also an indication of electron precipitation. Some geomagnetic variations are related to the bombarding electrons, since the change in ionospheric conductivity resulting from the electron bombardment is an important factor in the localization of the current which produces magnetic variations.
TL;DR: In this article, a large universal-time variation in the low-energy electron fluxes in the northern polar region during summertime was revealed, and it was suggested that these variations are associated with the diurnal changes in the tilt of the geomagnetic axis relative to the solar wind direction.
Abstract: Particle observations by the Rice University/ONR satellite Aurora 1 have revealed a large universal-time variation in the low-energy electron fluxes in the northern polar region during summertime. The electron fluxes are highest near 1800–2000 UT, both on the night- and the day-side of the earth above ∼75° invariant latitudes, whereas a minimum in the fluxes is reached between 0600 and 1200 UT. It is suggested that these variations are associated with the diurnal changes in the tilt of the geomagnetic axis relative to the solar wind direction.
TL;DR: The geophysical and geological data in and near the Japan Arc are summarized as a contribution to the Upper Mantle Project as mentioned in this paper, which provides information about the structure and the physical processes underneath the islands of Japan, which are one of the typical island arcs.
Abstract: The geophysical and geological data in and near the Japan Arc are summarized as a contribution to the Upper Mantle Project. These up-to-date data presented here provide information about the structure and the physical processes underneath the islands of Japan, which are one of the typical island arcs. The following items are covered: topography and geology, volcanoes, gravity anomaly, earthquake seismology, explosion seismology, crustal thickness, crustal deformation, terrestrial heat flow, geomagnetic anomaly, and geomagnetic variation anomaly.