Showing papers in "Journal of geomagnetism and geoelectricity in 1967"

The Determination of Paleo-Intensities of the Earth's Magnetic Field with Emphasis on Mechanisms which Could Cause Non-ideal Behavior in Thellier's Method

Abstract: 95 NRM-TRM curves were determined by Thellier's method from a variety of volcanic rocks. Most of them deviate from a straight line over parts of their length, sometimes so much that not even a crude estimate of paleo-intensity can be made. Some of the many possible causes of such non-ideal behavior include the effects of the sample demagnetizing field, secondary components of magnetization, mechanisms of acquisition of TRM which violate the assumptions of Thellier's method (such as nonlinearity of TRM with field), changes in the TRM spectrum induced by heating in the laboratory, and others. Where possible these mechanisms are discussed from both a theoretical and experimental standpoint, and their effects are identified in the NRM-TRM curves. In addition, diagnostic tests designed to determine quickly the suitability of a rock for intensity studies were sought. Tests tried included the comparison of heating and cooling Js-T curves, measurement of susceptibility before and after heating, and others. None were adequate. Finally, the quicker method of simply comparing the NRM and the total TRM is compared with Thellier's method for determining paleo-intensities. The latter is clearly the more informative and reliable when dealing with individual units, but the former may be useful for deriving average values of the paleo-intensity during geologic periods from large suites of volcanic rocks of varying types.

A Proposed Model for the International Geomagnetic Reference Field-1965

Abstract: A best current model of the main geomagnetic field is presented as a response to a need for an “International Geomagnetic Reference Field”. This model is described by a series of 120 spherical harmonic coefficients and their first and second time derivatives from an epoch 1960.0. It was derived from a sample of all magnetic survey data available from the interval 1900-1964 plus a recent global distribution of preliminary total field observations from the OGO-2 (1965-81A) spacecraft for epoch 1965.8. A duplicate data selection was made and the resulting field model compared with the first to help evaluate the minimum error. It was noted that the root —mean—square difference between the two models was about 30γ in the force components, 0.04 degrees in dip and 0.3 degrees in declination at the earth's surface for 1965.0.

A Portable Three-Component Magnetic Variometer

Abstract: A three-component recording magnetic variometer has been designed and constructed for field use. It can be built in a research instrument shop at low enough cost so that simultaneous recording over an array of twenty or more instruments is possible on a moderate research budget. The design is classical, the angular positions of three magnets suspended on torsion wires being recorded photographically at ten second intervals. The resolution is better than one gamma and variations of period greater than one minute are well recorded. The variometer records unattended for three weeks on power from modest batteries. A cardinal point of the design is the construction of the instrument in a long narrow tubular case of aluminum. In use it stands vertically in a hole drilled in soil so that the suspended magnets are efficiently thermostatted. In addition, first-order thermal compensation is provided. Tests of the prototype and of eight similar variometers have shown no detectable interaction between the suspended magnets, no measurable effect of temperature changes of the air above the ground, and acceptable rates of drift, and have established that the variometer is a reliable and effective instrument for field study of local conductivity anomalies.

The Westward Drift of the Earth's Magnetic Field in Historic Times

Abstract: Old records of magnetic measurements and archeomagnetic data at various places were collected to examine whether the westward drift has been a persisting feature of the earth's magnetic field and to investigate the extent to which drifting of the field has contributed to the observed secular variation.It turned out that main features of the secular variation such as maxima and minima of magnetic declination and inclination; were very likely to have drifted westwards with a velocity of about 0.36°/year over several hundred years.Comparison of the observed time variation with the spatial distribution of the present geomagnetic field suggests that the westward drift of the non-dipole field is responsible for producing a large part of the secular variation, even for such long period as 1000 years.

Wobbling Motion of the Geomagnetic Dipole Field in Historic Time During These 2000 Years

Abstract: Results of archaeomagnetic observations so far obtained and those of secular variation from the world-wide geomagnetic observatories were put together to see whether or not there exists any movement of the geomagnetic dipole field in historic time during the past 2000 years.The archaeo-secular variation thus summarized can be explained more reasonably if a wobbling movement of the dipole field was assumed to have occurred.

Study on Irreversible Change of Magnetic Properties of Some Ferromagnetic Minerals

Abstract: Magnetic minerals separated from some acidic rocks undergo an irreversible change in Curie point and saturation magnetization when they are heated in vacuum: both Curie point and saturation magnetization decrease. Microscopic observation of polished sections reveal that all rocks which show such irreversible changes contain, in addition to titanomagnetite, some amount of titanomaghemite. All the other experimental resules such as chemical, X-ray and low-temperature thermomagnetic analyses indicate that the irreversible change reflects a break down of the γ-phase titanomaghemite to the α-phase ilmenite-hematite series during heating.

Unstable Components and Paleomagnetic Evidence for a Geomagnetic Polarity Transition

Abstract: Part of a section of Miocene lavas in southeastern Oregon has been observed to possess natural remanent magnetism (NRM) superficially consistent, in both direction and intensity of magnetization, with the existence of a geomagnetic polarity transition contemporaneous with initial cooling of the lavas. Investigation of unstable magnetic components and other appropriate properties reveals, however, that the critical NRM is a function of petrological and not geomagnetic field properties. The occurrence of maghemite and unoxidized ilmenite lamellae in titanomagnetite are strongly associated with the systematic magnetic instability. The creation of high magnetic stability in the lavas concerned, by natural secondary oxidizing processes, could possibly result in convincing but totally misleading evidence for a Miocene geomagnetic polarity transition.

Non-dipole Field and Fluid Motion in the Earth's Core

Abstract: Assuming that the geomagnetic non-dipole field is created by the interaction between a strong toroidal magnetic field and convective motions, the velocity field in the earth's core is estimated. The maximum velocity amounts to 0.001cm/sec or a little smaller. A marked pair of upflow and downflow is found respectively under Africa and the Central Pacific Ocean. The well-known non-dipole low over the Pacific area may have something to do with the downflow of the core material beneath there.

Paleomagnetism of Pliocene Basalts from the Southwestern U. S. A.

Abstract: Late Pliocene basaltic lavas in New Mexico and Arizona are investigated paleomagnetically and petrographically. Detailed studies did not indicate any systematic difference in the magnetic or petrographic properties between normal and reversed rocks. Other evidence supports the idea of field reversals. The virtual geomagnetic poles determined from these lavas are grouped about the present geographic pole, which is in agreement with the paleomagnetic results for Pliocene rocks from other regions.

An Application of Oblate Spheroidal Harmonic Functions to the Determination of Geomagnetic potential

Abstract: The general theory of harmonic analysis of the potential of the Earth's main magnetic field is presented in terms of oblate spheroidal harmonic functions, treating the figure of the Earth as an oblate spheroid. It is a modification of the theory given originally by Schmidt, but removes the requirement of 48 multiplicative constants pnm and qnm. The theory is applied to Schmidt's data for epoch 1885 and for comparison the same data has been analyzed using sperical harmonic functions and treating the Earth as a sphere. Both analyses have been done both considering and ignoring the external field. Of the 48 coefficients for the external field, 18 are found to be significant at the 95 per cent confidence level and the magnitude of the external component of g10 is found to be significantly reduced from 226γ for a spherical Earth to 139γ for an oblate Earth. This reduction is shown to be theoretically necessary, and application of the theory to spherical harmonic coefficients for epoch 1965, shows that the magnitude of the external component of g10 is reduced from 82γ to 0γ.

New Emission Mechanism of Oxygen Green Line λ5577 in a Glow Discharge

Abstract: Experimental conditions under which the forbidden line of oxygen atom, 2 5577, is emitted in a low pressure glow discharge tube containing a mixture of argon and oxygen gas, have been studied. Examining the pattern of the intensity variation of the line, according to the total pressure and the mixing percent of oxygen, it was proposed that the exciting mechanism of the state 0(1S0) may be classified into two types: A) high pressure and low oxygen percentage type and B) low pressure and high oxygen percentage type. The main process of the type A mechanism is inferred to be 0+(4S)+e-0(1P)-0(1S0)+hv (2 1218), where the metastable argon atoms are supposed to be acting as powerful sources of the atomic ions 0+(4S). The type B mechanism is supposed to be the one suggested by McLennan, that is, A(3P2)+02(x39)--A(1S0)+O(1S0)+O(1D2)+0.26 ev.

Suggested Rotation of New Guinea

Abstract: Palaeomagnetic sampling has been carried out at eight sites in New Guinea. The magnetic stability has been verified by a. c. washing. The results give an increase in westerly declination with age, stretching back as far as the Cretaceous. The rotation of New Guinea during the Tertiary is suggested.

Balloon Measurement of Atmospheric Electric Potential Gradient

Abstract: On September 20, 1966 the potential gradient was measured in the altitude range of 5km to 25km over the Pacific Ocean from the coast to about 100km ESE of Honshu Island, giving the values of 9V/m to 0.7V/m. The electric field sonde consists of a pair of field antenna suspended 55m below a plastic balloon of 1000m3. The field antenna consists of a steel wire 5m in length, hanging a hollow copper sphere 30cm in diameter. The potential difference between the two antennas was measured. The result was compared with the vertical profile deduced from the conductivity-altitude profile with a constant vertical current density, both experimental and theoretical. The present measured profile is in good agreement with Gish's profile in the altitude range of 10km to 22km. Comparing the measured profiles of both Gish's and ours with the theoretical one, the decreasing rate of the former with altitude was found to be smaller than the latter, even considering the effects of the geomagnetic latitude concerned, and UT variation. Small scale changes of the measured potential gradient were compared with those of atmospheric temperature which were measured on the same electric field sonde. There were good correlations between both the changes. Near the temperature inversions the potential gradient showed very clear inverse phase changes suggesting strong concentrations of dust particles.

Dependence of Magnetic Properties on the Thermal History of Natural Polycrystalline Pyrrhotite, Fe0.89S.

Abstract: Thirty-two Specimens of virtually pure pyrrhotite were annealed at temperatures up to 600°C for periods ranging from 10minutes to several days in argon atmosphere. Magnetic properties of these specimens were determined with a magnetic balance or a ballistic magnetometer both before, during and/or after annealing. The results show that both the magnetization at 20°C in fields up to 2550 oe and the occurrence of the γ transition depends on the thermal history of the specimen. The data obtained during and after annealing strongly support the concept of variations in the degree of sublattice component order affecting the magnetic susceptibility. The degree of order seems to be high after annealing at 400°C, and it seems to be drastically reduced during annealing at 600°C. An application of the dependence of magnetic properties on the thermal history of pyrrhotite to problems in ore genesis is not yet apparent.

Irregular Type Sporadic-E Observed by Rocket Borne Gyro-Plasma Probe at a Temperate Latitude

Abstract: By a gyro-plasma probe experiment on board K-9M-21 rocket the micro-structure of the electron density profile has been measured within an error of ±3%. Irregularity of the electron density fluctuating within ±20% of its average has been detected in altitude ranges of 100km-103km and 115km-120km independent of the wake effect of the vehicle motion. This irregularity is identified with the radio scattering source of diffuse type sporadic-E on the ionogram obtained during the rocket flight.

Thermal Changes in the Magnetic Properties of an Anomalously Magnetic Mineral

Abstract: The paper decribes influences of thermal treatment of a complex natural mineral from the Magnet Cove on its magnetic properties. This mineral is characterized by an anomalously high magnetization. Its thermal dependence, specific remanent magnetization and its stability were studied in detail on this mineral. These studies resulted in the definition of some characteristics of the NRM.

The Electron Density Distribution in the Lower Ionosphere Produced through Impact Ionization by Precipitating Electrons and through Photoionization by the Associated Bremsstrahlung X-Rays

Abstract: In this paper characteristic features of the synthetic effect of a flux of precipitating mono-energy electrons are studied for the representative incident energies. The maximum rate of impact ionization produced by an electron flux of 27r X 107cm-2sec-1 is found to be about 1. 7 X 103cm-3sec-1 at about the 116 km-level for the incident electron energy E0=10 key, and about 2. 3 X 104cm-3sec1 at about the 88 km-level for Eo=100 key. On the other hand, the maximum rate of photoionization produced through the absorption of bremsstrahlung x-rays caused by the same flux is about 3. 6 X 10-2cm-3sec-1 at about 97km for E0=10 key, and about 1. 9 X 10'cm-3sec-1 at about 45 km for Eo=100 key. The consequent maximum electron density is estimated to be about 8. 4 X 104cm-3 at about 117 km for Eo=10 key, and about 3. 0 X 105cm-3 at about 90 km for Eo=100 key. In the latter case where Eo=100 key, the eletron density of the order of 103cm-3 extends to a level as low as 65 km. The associated auroral luminosity is estimated to be 0.21 kR (kilo-rayleighs) at 3914A, 0. 14 kR at 15577A, and 0. 17 kR at 26300A for Eo=10 key; and 1. 4 kR at 23914A, 0. 15 kR at 5577A, and 0.046 kR at 26300A for Eo=100 key. Estimates are also made of the total effects of a flux of precipitating electrons having an energy spectrum expressed as 27rioexp (-E0//9) at the top of the atmosphere. With io=108cm-2sec-1kev-ester-1 and S=5key, the maximum electron density is found to be about 3. 2x 105cm-3 at about 114 km. It is suggested that the electron flux of 27r X 4.5 X 104cm-2sec-1 having such an energy spectrum would be required in order to explain the observed electron density in the nighttime E layer at middle latitudes, as due to the influx of energetic electrons.

Absorption of Very Low Frequency Waves in the Whistler Mode Propagation at Low Latitudes

Abstract: Absorption of very low frequency (VLF) waves in the whistler mode of propagation at low geomagnetic latitudes of 24° and 15° have been calculated for various ionospheric conditions during sunspot maxima, average and minima. The very high absorption values of 60dB, 46dB, 22dB at 24° and 104dB, 90dB, 42dB at 15° of VLF waves (10Kc/s, 5Kc/s and 1Kc/s) for two ionospheric paths between 50-200Km height can explain the non occurrence of whistlers and VLF emissions such as chorus and hiss at low geomagnetic latitudes during day time.The absorption contributed by F-region though generally smaller than that contributed by D and E layers is never negligible and at times of high F-layer concentrations during the magnetic storms the F-layer absorption may even be dominant.The absorption of VLF waves is low at night and as such can not explain the low occurrence of whistlers during night time. However, when the angle between the magnetic field and the wave normal is taken into account it is found that the absorption index increases considerably and hence the whistler energy may not be received on the ground especially at geomagnetic latitudes below 15°.Comparing the computed values of absorption of VLF waves by Altman and Cory at 40° geomagnetic latitude and Laschy at 55° latitude with our values, for low latitudes it is found that the absorption increases rapidly as the latitude decreases which is in conformity with the results of Helliwell and Altman and Cory.

Insight into the Magnetic Mineralogy of Antarctic Rocks

Abstract: A magnetic powder technique is presented, which is considered to be phase I of a methodology being developed at the University of Pittsburgh, to ultimately relate the magnetic properties of rocks to the causitive mineralogy. The methodology, termed magnetic petrology, was suggested by an initial study of plutonic rocks from Ellsworth Land, Antarctica.Phase I, the magnetic powder technique utilizes a strained mechanically polished rock surface upon which a magnetite colloid is deposited. After washing the surface with alcohol or acetone, the magnetic minerals or magnetic phases are patterned with magnetite powder; the non magnetic components remain free of powder.

Role of Electric Field Generated in the Equatorial Electrojet Region

Abstract: Adopting an atmospheric model for the sunspot maximum day, the height variation of various ionospheric conductivities have been computed. The electric currents are calculated from yearly averaged magnetic data for the sunspot maximum period in 1958. Using the height integrated Cowling conductivity, electric fields for five selected equatorial and non-equatorial stations have been obtained from the calculated electric currents. The electric currents and electric fields thus obtained have been compared with the electric field derived from the rocket measured electrojet current density. It is shown that such comparisons give good overall agreement of the results obtained from magnetic data and the rocket measurements. The electron temparature is calculated from Joule heating considerations. The resulting electron temparature has been found to be smaller than the rocket measured values, The vertical electron drift velocity produced by the electric field in the electrojet region has been calculated and is found to be higher than the earlier calculation of Hirono and Kitamura (1956) and compares well with the drift velocity values obtained from continuity equation.

Attenuation Characteristics of Smooth Type Atmospheric Waveforms

Abstract: Quasi-sinusoidal waveforms of distant atmospherics recorded at night were Fourier analysed using an electronic digital computer to yield the amplitude spectra in the VLF range of 1-20kc/s. The relative values of attenuation coefficients, calculated from amplitude spectra have been compared with the experimental results of Hepburn and Wait's theoretical attenuation curves. The attenuation is found to be maximum at 4kc/s and minimum in the frequency range 7-12kc/s, and is in general agreement with results of Croom (1964). The attenuation is also found to increase in 12-20kc/s range, as earlier observed by Taylor and Lange (1958) and Obayashi et al (1959), and this can be explained partly by the waveguide theory (Wait, 1962). The variation of peak frequency and band width of the received atmospherics with propagation distance has also been discussed.

Magnetic Lines of Force Deformed by Motion of a Conducting Fluid (II)

Abstract: The magnetic field dragged by a constant convective motion in a conducting fluid was illustrated in the previous paper. When the interaction between magnetic fields and motions is strong, the motions distort magnetic lines of force, while the convection currents are in turn modified by the deformation of magnetic lines of force. We should therefore solve induction equation coupled with equation of motion in order to know the exact behaviors of magnetic lines of force as well as that of fluid streams. The author makes in this paper an attempt at solving the above equations for a model with a pair of convection. It turns out that the pattern of velocity streamlines is markedly distorted while the magnetic flux is deformed only slightly. Time-dependent deformations of both the stream lines and magnetic lines of force are graphically illustrated in series of figures in such a way that they can easily be compared with the results obtained on the assumption of the constant fluid motion.

Current Moments at ELF of Lightning Discharges Associated with a Mature Tropical Hurricane

Abstract: The mean spectrum of negative polarity ‘slow tail’ ELF atmospherics received during daytime from the area of a distant mature tropical storm (Hurricane Blanca, August 1966) is presented. The mean amplitude spectrum is used with established attenuation rates to calculate from zero-order mode theory the mean current moment associated with the waveform sources. It is suggested that the waveforms may be greatly controlled by intracloud lightning discharges associated with the degree of vertical development of the hurricane.

Universal Aspects of Atmospheric Electricity

Abstract: An analysis of the more universal aspects of atmospheric electricity is carried out. The simple mathematical treatment dispenses with the well established concept of a spherical condenser, and replaces it with the simpler and more physically acceptable picture of an earth immersed in a medium whose electrical conductivity increases exponentially with altitude to infinity. The effects of various large and small scale perturbations of this simple model are considered.