Showing papers on "Earth's magnetic field published in 1978"

Geomagnetic paleointensities from radiocarbon‐dated lava flows on Hawaii and the question of the Pacific nondipole low

Abstract: Radiocarbon ages have been published for nine basaltic lava flows on the island of Hawaii; the ages range from 2600 to somewhat older than 17,900 years B.P. By using the Thelliers' method in vacuum, geomagnetic paleointensity values were obtained from eight of the lavas; the ninth proved unsuitable. The paleointensities for the four youngest flows (2600–4600 years B.P.) yield virtual dipole moments (VDM's) that are 20% greater to more than twice the worldwide values for those times obtained by V. Bucha from archeomagnetic data. The dispersion of virtual geomagnetic poles for the eight lavas is 15.5°, appreciably larger than the average for older lava flows on Hawaii. These results contrast with the historic magnetic field in the region of Hawaii, in which both secular variation and nondipole components are very low. At about 10,000 years B.P. the measured VDM is not very different from the long-term worldwide average but differs considerably from a smooth extrapolation of Bucha's average curve. At about 18,000 years B.P. the measured VDM is very low and is associated with an unusually shallow paleomagnetic inclination for the latitude of Hawaii. These new paleointensity and paleodirectional data strongly suggest that sizable nondipole geomagnetic fields have existed in the vicinity of Hawaii at various times during the Holocene epoch and perhaps earlier.

Electron temperatures in the F region of the ionosphere - Theory and observations

Abstract: The theory and observations relating to electron temperatures in the F region of the ionosphere are reviewed. The review is divided into three basic parts. In the first part the theory concerning electron heating, cooling, and energy transport processes is reviewed, and all the relevant expressions are updated. In the second part the behavior of F region electron temperatures, as measured by satellites, rockets, and incoherent scatter radars, is discussed. This portion covers electron temperature variations with altitude, latitude, local time, season, geomagnetic activity, and solar cycle. The third part is primarily devoted to a discussion of the various attempts to compare measured and calculated F region electron temperatures.

Solar wind stream interfaces

Abstract: Results are presented for a superposed epoch analysis of discontinuous solar wind interfaces. The average time-space profiles of stream interfaces are discussed with reference to fluid properties (flow speed, pressure ridge, density, electron and proton temperatures) and kinetic properties (electron core and halo, flow speed fluctuations, electron heat flux, alpha particles). Other aspects of stream interfaces are described, such as the persistence of individual interfaces, shock associations, the sector boundaries of the interplanetary magnetic field, and sudden impulses in the geomagnetic field. Interface position is considered in terms of the observed temperature jump. A conceptual model of high-speed stream evolution is proposed.

ISEE plasma observations near the subsolar magnetopause

Abstract: The early ISEE orbits provided the opportunity to study the magnetopause and its environs only a few Earth radii above the subsolar point Measurements of complete two-dimensional ion and electron distributions every 3 or 12 s, and of three-dimensional distributions every 12 or 48 s by the LASL/MPI instrumentation on both spacecraft allow a detailed study of the plasma properties with unprecedented temporal resolution This paper presents observations obtained during four successive inbound orbits in November 1977, containing a total of 9 magnetopause crossings, which occurred under widely differing orientations of the external magnetic field The main findings are: (1) The magnetosheath flow near the magnetopause is characterized by large fluctuations, which often appear to be temporal in nature (2) Between ∼01 and ∼03R E outside the magnetopause, the plasma density and pressure often start to gradually decrease as the magnetopause is approached, in conjunction with an increase in magnetic field strength These observations are in accordance with the formation of a depletion layer due to the compression of magnetic flux tubes (3) In cases where the magnetopause can be well resolved, it exhibits fluctuations in density, and especially pressure and bulk velocity around average magnetosheath values The pressure fluctuations are anticorrelated with simultaneous magnetic field pressure changes (4) In one case the magnetopause is characterized by substantially displaced electron and proton boundaries and a proton flow direction change from upwards along the magnetopause to a direction tranverse to the geomagnetic field These features are in agreement with a model of the magnetopause described by Parker (5) The character of the magnetopause sometimes varies strongly between ISEE-1 and -2 crossings which occur ∼ 1 min apart At times this is clearly the result of highly non-uniform motions There are also cases where there is very good agreement between the structures observed by the two satellites (6) In three of the nine crossings no boundary layer was present adjacent to the magnetopause More remarkably, two of the three occurred while the external magnetic field had a substantial southward component, in clear contradiction to expectations from current reconnection models (7) The only thick (low-latitude) boundary layer (LLBL) observed was characterized by sharp changes at its inner and outer edges This profile is difficult to reconcile with local plasma entry by either direct influx or diffusion (8) During the crossings which showed no boundary layer adjacent to the magnetopause, magnetosheath-like plasma was encountered sometime later Possible explanations include the sudden formation of a boundary layer at this location right at the time of the encounter, and a crossing of an ‘inclusion’ of magnetosheath plasma within the magnetosphere (9) The flow in the LLBI is highly variable observed directions include flow towards and away from the subsolar point, along the geomagnetic field and across it, tangential and normal to the magnetopause Some of these features clearly are nonstationary The scale size over which the flow directions change exceeds the separation distance (several hundred km) of the two spacecraft

Transmission of polar electric fields to the Equator

Abstract: SEVERAL kinds of geomagnetic variations are observed simultaneously at high latitudes and in the equatorial region. These are substorms or DP-1 variations, Spq or DP-2 variations, some kinds of pulsations, and the DS-part of SSC and SI. Araki1 analysed the relationship of the preliminary reverse impulse of SC* occurring in the high-latitude and the equatorial regions and found that their occurrence in both regions is well correlated, almost simultaneous, and that the waveforms are very similar. From the characteristics of these geomagnetic variations, it seems that a horizontal electric field impressed in the polar ionosphere from the magnetosphere greatly contributes to the equatorial part of these geomagnetic variations. This electric field is generated by large scale dynamic processes in the magnetosphere such as a sudden compression by an interplanetary shock wave or a change of the magnetospheric convection, and its direction will be approximately east–west (dawn–dusk)2. To clarify the mechanism of the instantaneous horizontal transmission of the polar electric field, we have analysed the response of the ionosphere to a suddenly impressed electric field.

Geomagnetic pulsations observed simultaneously on three geostationary satellites

Abstract: Simultaneous observations of magnetic pulsations have been made by three geostationary satellites carrying similar magnetometers and acting as an azimuthal array. Autospectral and cross-spectral analysis yields coherence and phase differences between the pulsations at the satellite positions. The majority of the data fit the Kelvin-Helmholtz generation mechanism. The azimuthal wave number changes sign near noon and corresponds to propagation away from noon. Usually, the wave number is less than 10 deg per degree of longitude. Later in the afternoon, however, strong pulsations are observed with low coherence, implying large wave numbers. This suggests an instability driven by a gradient in the intensity of energetic protons, which may be expected at this local time. The data also suggest that some of the observed phase difference between the azimuthal components is due to small separations in magnetic shell, whereas this is not the case for the radial components. This implies a localized field-line resonance.

Electron density in the plasmasphere: Whistler data on solar cycle, annual, and diurnal variations

Abstract: Whistler data are used to present a statistical view of equatorial plasmaspheric electron density n/sub eq/ and associated tube electron content N/sub T/ (defined as the number of electrons in a geomagnetic flux tube of 1cm/sup 2/ crosssectional area at 1000km altitude and extending to the magnetic equator). The data were acquired between 1959 and 1973 at Byrd (Lapprox. =7), Eights (Lapprox. =4), and Siple (Lapprox. =4), Antarctica, which are within 1 hour of the same geomagnetic meridian, and from Stanford, California (Lapprox. =2). The plasmaspheric n/sub wq/ profile beyond Lapprox. =3 is dominated by variations associated with magnetic disturbances and sunsequent recovery. In the aftermath of disturbances the plasmasphere tends to be divided into an inner 'saturated' region, which is in equilibrium with the underlying ionosphere in a diurnal average sense, and an outer 'unsaturated' region, which is still filling with plasma from below. In the outer plasmasphere bond approx.3.5 R/sub E/, diurnal variations appear as relatively small effects superimposed on larger storm-associated variations. Large numbers of whistler traces (as many as 3000 in some cases) were scaled for each of several months. These data sets form the basis for approximations to n/sub eq/ profiles to form log/sub 10/more » (n/sub eq/) =aL+b. These profiles are offered for reference use in estimating plasmasphere density levels. The previously reported annual and solar cycle variations are further documented by new evidence that these effects diminish with increasing L beyond Lapprox. =3.« less

Field-aligned currents in the south polar cusp and their relationship to the interplanetary magnetic field

Abstract: The large-scale field-aligned currents (FAC) as reported earlier from the Triad magnetometer data received at College, Alaska (lijima and Potemra, 1976a, b), are also observed in the south polar region. From the analysis of vector magnetometer data of more than 230 passes of Triad that were recorded at McMurdo, Antarctica, the principal characteristics of the cusp region FAC in the dayside south polar region that have been determined are as follows: (1) The cusp region FAC (defined as the currents appearing poleward of, and adjacent to, the region 1 FAC of Iijima and Potemra (1976a)), are most often observed in the midday sector of ∼0900–1500 MLT (magnetic local time) in the south polar region. These currents generally flow into the ionosphere in the postnoon sector (∼1200–1500 MLT) and flow away from the ionosphere in the prenoon sector (∼0900–1200 MLT). The demarcation line between the prenoon cusp region FAC and the postnoon cusp region FAC scatters statistically around the magnetic noon meridian. At a given MLT the flow of the cusp region FAC is the opposite of the flow of the region 1 FAC. (2) During weakly disturbed polar geomagnetic conditions (|;AL| 0). Conversely, the postnoon cusp region FAC (flowing into the ionosphere) are observed about twice as often during periods when the interplanetary magnetic field is directed away from the sun (By > 0) as during periods when the By is negative. In contrast, the region 1 FAC show less of a systematic occurrence tendency which depends upon the polarity of the interplanetary magnetic By component. (5) There is no special preference of the polarity of the interplanetary magnetic Bz component associated with the occurrence of the cusp region FAC. We suggest that the region 1 FAC and the cusp region FAC have basically independent generators, probably in the magnetosphere, and that the cusp region FAC may be directly related to regions of the magnetosphere which mark the transitions of plasma and magnetic fields from the magnetosheath type to the internal-to-the-magnetosphere type. The more intense cusp region FAC are associated with increases of Bz in the southward direction, as determined for the northern hemisphere (Iijima and Potemra, 1976b). But the larger number of events studied here show a wide spread of FAC intensities for a given Bz, and there is not a close correlation between the intensities and Bz. There is no close correlation between the FAC intensities and the By component.

Intense electrostatic waves near the upper hybrid resonance frequency

Abstract: Plasma wave measurements using instruments on the Imp 6 and Hawkeye satellites are utilized in a study of very intense electrostatic waves near the upper hybrid resonance frequency in the region just outside the plasmapause. Studies of these electrostatic disturbances show that the events occur at local times and at magnetic latitudes varying from the equator to 50 deg, and the polarization of these waves is such that the wave electric field vector is oriented perpendicular to the geomagnetic field. In most cases the center frequency of the intense waves corresponds to an (n + 1/2) fg(-) harmonic near the upper hybrid resonance frequency. The hot distribution on function is described for a few events showing temperature anisotropy and a loss cone distribution. A possible mechanism for producing intense waves near the upper hybrid resonance frequency is suggested, and evidence which indicates that the intense electrostatic waves may be a source of nonthermal continuum radiation is given.

Anomalies in the Earth’s Magnetic Field Increase the Scatter of Pigeons’ Vanishing Bearings

Abstract: Homing pigeons were released under sunny conditions at places with large variations in the total intensity of the Earth’s magnetic field. At five out of six such places, pigeons were more scattered in their homeward orientation than at magnetically normal sites. This suggests that some aspect of the magnetic field affects either the pigeon’s sun compass or its navigational system.

Magnetic field perturbations in the dayside cleft and their relationship to the IMF

Abstract: Magnetometers on the Isis 2 satellite have been used to study large-scale perturbations in the geomagnetic field in the region of the dayside cleft (or cusp). Relatively large perturbations, in a plane perpendicular to the main field direction, are observed on most satellite passes; on the average the perturbations near noon are larger than those observed in the dawn and dusk sectors. The peak perturbations tend to lie in two relatively narrow ranges of direction, pointing approximately eastward or westward depending on the sign of By, the y component of the interplanetary magnetic field (IMF). In general, for this northern hemisphere data set, positive By corresponds to an eastward perturbation, and negative By to a westward perturbation. The invariant latitude of the perturbation is correlated with Bz, the z component of the IMF, while the magnitude of the perturbations is more strongly correlated with By than with Bz. The perturbations are discussed briefly in terms of the tilt of the field direction relative to a model field, and it is suggested that this is related to the direction of convection in the magnetosphere. On the basis of this interpretation the predominant convection direction in the cleft is approximately either eastward or westward.

Global morphology of nitric oxide in the lower E region

Abstract: Measurements of nitric oxide at 105 km by the ultraviolet nitric oxide experiment on Atmosphere Explorer C are presented. The amount of nitric oxide in the lower E region is shown to depend on latitude, longitude, and magnetic activity. Near the equator the density at the peak of the NO layer is typically about 2 x 10 to the 7th power/cu cm and varies little with longitude or magnetic activity, except during major storms. At high latitudes (up to 68 deg geographic latitude), peak densities are typically 2 or 3 times larger and much more variable. A longitudinal dependence is found in both geographic and geomagnetic coordinates, with minimum densities found near 45 deg E geomagnetic longitude and maxima near 135 deg W geomagnetic longitude. At 40 deg dip latitude the half amplitude is about 30%.

The magnetic properties of some DSDP basalts from the North Pacific and inferences for Pacific plate tectonics

Abstract: One hundred seven basalt samples from seven DSDP sites in the North Pacific studied for magnetic properties were found to have a mean magnetization of 0.005 emu/cm3, a mean susceptibility of 0.001, and a mean Koenigsberger ratio of 10. The mean remanence coercivity as measured by the mean demagnetizing field is 90 Oe. The titanomagnetite in most of these old (13–115 m.y.) and highly fractured basalts has been largely oxidized to titanomaghemite during sea floor weathering. The titanomaghemitization is manifest in an increase in Curie temperature from about 160°C to 300°–350°C and a threefold to fourfold decrease in the saturation magnetization. Although a 50% decrease in remanence intensity and susceptibility can be attributed to oxidation at one site, the relation between degree of oxidation and these two properties is obscured at most sites by magnetic grain size differences. A decrease in remanence intensity no doubt occurs but was not observed because the most highly oxidized basalt, that in thin flows and in the margins of thicker flows, is also the finest grained and therefore had a higher initial remanence intensity. Remanence coercivity, while mainly dependent on magnetic grain size, increases about 50% with oxidation. The remanence direction does not appear to be affected by oxidation. Although the remanance inclinations differ considerably from the present geomagnetic field inclination at most sites, the expected range of secular variation is such that the remanence, with the exception ofthat in Meiji Seamount, could have been acquired by the basalts at the present site latitudes. But the site paleolatitudes calculated from the remanence inclinations correspond more closely to the paleolatitudes predicted by assuming that the Pacific plate has moved northward with the motions deduced by Morgan and others from linear volcanic chains. In particular, the coincidence of the magnetic paleolatitude, 19°, measured in Meiji Seamount at the northern end of the Emperor Seamount chain, with the latitude of the island of Hawaii, supports the fundamental assumption of the Morgan model of Pacific plate motion, wherein the volcanic locus or ‘hot spot’ forming the Emperor-Hawaiian chain has remained essentially stationary with respect to the earth's axis.

Stormtime Pc 5 magnetic pulsations observed at synchronous orbit and their correlation with the partial ring current

Abstract: Stormtime Pc 5 pulsations are a class of magnetic pulsations observed at synchronous orbit most frequently during the main phase of magnetic storms. The waves are linearly polarized in a meridian plane with nearly equal compressional and transverse components. The waves usually accompany a depression in local field magnitude associated with the onset of a magnetospheric substorm. In this paper, we use local time-universal time maps of mid-latitude magnetic perturbations to study the association of these waves with the development of the partial ring current. We find that these waves occur at the local time of maximum development of the partial ring current, at or shortly after the onset of a magnetospheric substorm. These results confirm our earlier speculation based on satellite data alone that the waves are associated with substorm enhancement of the partial ring current.

Transitional field configurations and geomagnetic reversal

Abstract: Records of various geomagnetic reversals which occurred over the past 25Myr suggest that transitional field configurations are largely controlled by low-order zonal components. Given sufficient data further clarification is possible as octupole and quadrupole dominated fields are palaeomagnetically distinguishable. Moreover, because each geometry may reflect a reversal process which starts in a particular region of the core, configurational characteristics of the geomagnetic dynamo during polarity transitions are, in principle, identifiable.

A View of Solar Magnetic Fields, the Solar Corona, and the Solar Wind in Three Dimensions

Abstract: In the last few years it has been recognized that the solar corona and the solar wind are three-dimensional. The deviations from spherical or even cylindrical symmetry are first-order effects, which are important for a basic description and physical understanding of the coronal expansion. Models of coronal magnetic fields are considered along with the characteristics of large-scale solar structure, the interplanetary magnetic field, coronal holes, geomagnetic activity, cosmic rays, and polar fields of the sun. It is pointed out that the present understanding of coronal and interplanetary morphology is based on data acquired during the descending part and the minimum of the considered sunspot cycle.

Magnetic field detection is distinct from light detection in the invertebrates Tenebrio and Talitrus

Abstract: THE mechanism used by animals for geomagnetic field detection has long been discussed1. Leask2 has proposed that sensitivity to magnetic field might result from polarised light detection through optical pumping into the lowest level triplet state of (say) the rhodopsin molecule that possesses spin. Light detection, he suggests, might be a prerequisite for magnetic field detection and might result in an axial rather than a polar response in the animal. However, a unimodal reaction has been found3 with Tenebrio molitor L., the flour-beetle, in a horizontally directed magnetic field and a light field without directional features. This result was obtained when Tenebrio had been allowed to associate the geomagnetic field with the directional properties of the anisotropic light field in the culture container. The preferential direction in the horizontally directed magnetic field could be predicted from the ‘dark direction’ and from the relative humidity in the container (ref. 3, expt 43, page 429). I report here that Tenebrio and Talitrus saltator Mont., the sandhopper, can orientate in the Earth's magnetic field in complete darkness, and that in Tenebrio this orientation is essentially polar, not axial. These results are evidence that these two invertebrates do not require light for the detection of the magnetic field.

Relative importance of stars and the magnetic field for the accuracy of orientation in night-migrating birds

Abstract: In the natural geomagnetic field or a field of comparable intensity (0.46 Gauss), the vector length rm of the test series, calculated from the headings of the individual test nights, was similar in the presence and absence of stars, a slight increase under stars being observed only for the robin. The concentration ai around the selected direction was, however, strongly increased by the stars; artificial and natural ones having the same effect. In a reduced magnetic field (0.34 Gauss), no preferred heading direction was found, but again the concentration ai was greatly increased by the presence of artificial stars.

Geomagnetic field fluctuations at synchronous orbit 2. Radial diffusion

Abstract: Power spectra of geomagnetic-field variations measured at synchronous equatorial altitude (geomagnetic shell parameter about 6.6) in the magnetosphere are used to calculate the time dependence of the radial diffusion coefficient for particles in the radiation belts. The diffusion coefficients calculated are mainly applicable for relativistic electrons. The magnitudes of the derived diffusion coefficients using data only from local day observations are consistent with those reported from analyses of most particle observations and thus are slightly larger than those derived from magnetic sudden commencements. They are consistent with the diffusion coefficients calculated from power spectra of ground-based geomagnetic data measured near L = 4.

Coronal holes, solar wind streams, and geomagnetic activity during the new sunspot cycle

Abstract: We have extended our previous study of coronal holes, solar wind streams, and geomagnetic disturbances from the declining phase (1973–1975) of sunspot cycle 20 through sunspot minimum (1976) into the rising phase (1977) of cycle 21. Using daily He I 10830 A spectroheliograms and photospheric magnetograms, we found the following results: An updated Bartels display of the occurrence of holes, wind speed, and geomagnetic activity summarizes the evolution of their characteristics and interrelations as the sunspot cycle has progressed. Long-lived, low-latitude holes have become rare but remain terrestrially effective. The more common high-latitude holes are effective only when the Earth lies at a relatively high heliographic latitude in the same solar hemisphere.

Induction of auroral zone electric currents within the Alaska pipeline

Abstract: The Alaskar pipeline is a highly conducting anomaly extending 800 miles (1300 km) from about 62° to 69° geomagnetic latitude beneath the most active regions of the ionospheric electrojet current. The spectral behavior of the magnetic field from this current was analyzed using data from standard geomagnetic observatories to establish the predictable patterns of temporal and spatial changes for field pulsation periods between 5 min and 4 hr. Such behavior is presented in a series of tables, graphs and formulae. Using 2- and 3-layer models of the conducting earth, the induced electric fields associated with the geomagnetic changes were established. From the direct relationship of the current to the geomagnetic field variation patterns one can infer counterpart temporal and spatial characteristics of the pipeline current. The relationship of the field amplitudes to geomagnetic activity indices,A p, and the established occurrence of various levels ofA p over several solar cycles were employed to show that about half of the time the induced currents in the pipe would be under 1 A for the maximum response oscillatory periods near 1 hr. Such currents should be of minimal consequence in corrosion effects for even a section of the pipeline unprotected by sacrificial electrodes. Of greater interest was the result that the extreme surges of current should reach over one-hundred amperes in the pipeline during high activity.