摘要:

From maps of the geomagnetic secular variation, the time derivative of the radial component of the magnetic intensity is extrapolated to the core‐mantle boundary. This problem is divided into two parts, the first of which is a purely geometrical extrapolation on the basis of potential theory for an insulating mantle. The effects of a finite conductivity of the mantle are to be considered in a later paper. Assuming the mantle an insulator, a quantitative description is given of the topography of the magnetic field variation at that boundary. Although the projection is carried out here in terms of circular hills and dales, it is found that the magnetic topography at the core is far better described in terms of an extensive system of long ridges radiating out from a set of focal points. Frequently, a near‐illusion of the existence of hills or valleys is brought about by neighboring ridges. A typical ridge has a half‐width of from 150 to 600 km at the core's surface, and extends over several thousand kilometers, being paralleled on each side by ridges of opposite sign. The maximum heights of the ridges frequently occur at large distances from the focal points. The integrated effects at the core are such that, for an insulating mantle, radial field intensities of 2 to 5 gauss are common, whereas intensities ranging from 5 to 15 gauss occur in the more active regions. A lower limit of the total root‐mean‐square value of the time derivative of the vertical component at the core is estimated to be 0.18 (±0.05) gaus

ISSN:0148-0227    

DOI:10.1029/JZ060i004p00377

年代:1955

数据来源: WILEY

摘要:

The authors have studied the diurnal variation of irregular geomagnetic fluctuations in moderately low latitudes using the eight dailyKnumbers (three‐hour‐range indices) for the seven years 1940–1946 and for the six observatories Alibag, Watheroo, Honolulu, Tucson, San Juan, and San Fernando. These observatories were chosen because they are fairly uniformly distributed in longitude, being at 73°, 116°, 202°, 249°, 294°, and 354° east, respectively.A local time variation, to be expected from the work of earlier investigators, is apparent also in these data. The present data indicate a minimum near sunrise and a maximum in the late evening. This diurnal variation appears to have a small seasonal change.When the local time variation is deducted from the original data for each observatory, the remainders suggest a universal time variation which exhibits a pronounced seasonal change.A hypothesis is developed to explain the nocturnal prevalence of the irregular fluctuations in terms of atmospheric turbulence in the ionosphere. The turbulent motions are regarded as hindered during the day by electromagnetic damping. It is suggested that features of the large‐scale circulation of the atmosphere may contribute to the universal t

ISSN:0148-0227    

DOI:10.1029/JZ060i004p00389

年代:1955

数据来源: WILEY

摘要:

Data from an oblique‐incidence time‐delay measurement experiment over an 1150‐km east–west path between Sterling, Virginia, and St. Louis, Missouri, are used to examine the accuracy of the transmission‐curve method of determining oblique‐incidence ionosphere characteristics from vertical‐incidence soundings. The experiment employed a pulsed sweep‐frequency ionosphere recorder at each of the endpoints and another at the midpoint of the great‐circle path. A small but consistent difference between the maximum usable frequencies (MUF) observed at the endpoint stations and the MUF determined from the vertical‐incidence soundings was found. Seasonal trends of this difference are presented. The results of the analysis indicate that the average error of the transmission‐curve‐derived MUF varies between zero and 5 per cent too low, depending on time of day and season. Random variations result in a spread of about 10 per cent between the upper

ISSN:0148-0227    

DOI:10.1029/JZ060i004p00395

年代:1955

数据来源: WILEY

摘要:

The paper shows some sweep‐frequency pulse‐transmission records obtained over a 2400‐km path during the winter of 1953–1954. Although a detailed analysis of the records has not been completed, some preliminary results are given. Among the most significant of these is observed oblique‐incidence propagation on numerous occasions at frequencies considerably above the maximum usable frequency as computed from vertical‐incidence ionospheric observations at the midpoint

ISSN:0148-0227    

DOI:10.1029/JZ060i004p00411

年代:1955

数据来源: WILEY

摘要:

The cooling of the “upper atmosphere” (region between the altitudeh0= 100 km and the altitudeh1= 380 km) after sunset was investigated under the assumptions that (a) the temperature at the altitudeh0is constant and equals 240°K, (b) the temperature gradient at the altitudeh1is equal to zero, and (c) the process of heat transfer takes place solely by conduction. Assumed initial temperature is that given by the Rocket Panel, ranging from 240°K at altitudeh0to 1250°K at altitudeh1. For the sake of simplicity, thermal conductivityKand specific heatcwere assumed constant and dependence of density ρ on temperature was ignored, the differential equation of heat conduction being solved numerically on the assumption that the density ρ and, therefore, the thermal diffusivity α =K/cρ varies with altitude but is independent of time, the variation of ρ with altitude being that given by the Rocket Panel. The computations revealed that after 2–1/2 hours the temperature has not changed at altitudes below 160 km, and that the maximum drop at altitudeh1is 440°K. From the computed temperatures at timet= 2h(2 hours), the densities were computed from formula (2) below. Computations revealed that a certain settling of the atmosphere takes place, the densities at timet= 2hbeing larger than at timet= 0 in some region, and correspondingly lower at altitudes above the upper limit of this region. Analysis of the ion density led to the conclusion that there is an appreciable increase of the ion density in theF‐layer in spite of the recombination of ions which takes pl

ISSN:0148-0227    

DOI:10.1029/JZ060i004p00421

年代:1955

数据来源: WILEY

摘要:

Evidences are quoted which show that the fading of 150‐kc waves is due to random absorption rather than random scattering from the ionosphere. On the basis of this, a statistical theory has been worked out for the relationship between phase and amplitude of a wave which has encountered random absorption on its downward passage. The predicted behaviour shows excellent agreement with experiment and yields a method for the estimation of the collisional frequency at the region where the absorption is taking place. Experimental results pertaining to 150‐kc waves at State College are described and discussed.The method has possibilities for supplementing wind‐measurement results to provide information regarding the heights of

ISSN:0148-0227    

DOI:10.1029/JZ060i004p00431

年代:1955

数据来源: WILEY

摘要:

The propagation of elastic waves in an electrically conducting solid permeated by a uniform, static magnetic field is discussed. In the case of plane wave motions, two systems of waves arise: simple uncoupled systems and a trimodal coupled system of waves. In the uncoupled case, in which polarizations are unaltered, two dispersive, complex phase velocities exist. For a weak impressed magnetic field, one of these velocities is close to the elastic wave velocity of the polarized wave in the absence of the field. The other wave, called an eddy current wave, although strongly attenuated, cannot be neglected in the solution of boundary value problems.When the theory of magnetoelastic interactions is applied to seismic motions in the conducting core of the earth, it is found that compressional waves are virtually unattenuated in the core for the pertinent values of frequency, conductivity, and magnetic intensity. It is concluded that magnetoelastic interactions are not a significant mechanism in the earth's core.

ISSN:0148-0227    

DOI:10.1029/JZ060i004p00441

年代:1955

数据来源: WILEY

摘要:

A theoretical study of the variation of the state of polarization of a vertically incident electromagnetic wave while in propagation in the ionosphere has been made on the basis of an approximate solution of the wave equations obtained by Saha, Banerjee, and Guha. It has been shown that the major axes of the polarization ellipses of both the ordinary and the extraordinary waves would lie in the N–E quadrant in the northern hemisphere and in the N–W quadrant in the southern hemisphere. A new method has been outlined for the determination of the electron density and the collision frequency in the ionized layers from the value of the tilt‐angle and the ratio of axes of the elliptic patterns.An analysis of the characteristics of the experimentally observed polarization patterns indicates that inElayer the value ofvis 1.7×106per second. They further show that the polarization of the downcoming waves corresponds to their respective reflection levels, rather than a limiting region below the

ISSN:0148-0227    

DOI:10.1029/JZ060i004p00457

年代:1955

数据来源: WILEY

摘要:

Previous work on the excitation of large‐scale oscillations in an atmosphere on a rotating globe is extended to include a unified treatment for both gravitational and thermal forcing functions and is applied to the solar and lunar semi‐diurnal pressure variation, that is,S2andL2, respectively. It is assumed that the heating is applied only at the base of the atmosphere and that the temperature gradient is constant in this region as in the actual troposphere. The solution of the problem consists of the usual Bessel's functions characteristic of a purely gravitational forcing function found by Pekeris [see 1 of “References” at end of paper], plus a particular integral found by the method of variation of parameters. The total resonant amplification is obtained for the various atmospheric models used by Jacchia and Kopal [2]. The hitherto neglected phase of the dynamical tidal oscillation is included in a treatment where complex variables are systematically employed to represent the magnitude and phase of observables. It is found that current atmospheric models favor the conclusion that thermal effects are far more important than the gravitational in producing theS2variation (≃15) as compared with Chapman's [3] 1924 conclusion that they are of nearly equal importance. However, if one assumes, as did Chapman, that eddy motion at the ground is the only heating source, then our conclusion is at odds with observed values of eddy conductivity found by Eiffel Tower measurements. A possible resolution of this paradox is the consideration of other heating sources. Balloon observations by Riehl and the analysis of Haurwitz [4]are cited in support of this po

ISSN:0148-0227    

DOI:10.1029/JZ060i004p00483

年代:1955

数据来源: WILEY

摘要:

Aspect‐sensitive radio reflections in the frequency range from 6 to 30 Mc have been regularly obtained from scattering sources located within the ionosphere at locations quite far south of the auroral zone. Observations have been made at two locations on the west coast of the United States (Stanford, California, geomagnetic latitude 43.75°, and Spokane, Washington, geomagnetic latitude 55°). With few exceptions, the echoes occur when the line of sight from the transmitter intersects a magnetic field line at perpendicular incidence at heights corresponding to those of theEandFlayers. Thus, theE‐layer echoes are obtained from areas in the immediate vicinity of the observing stations. The echoes may be detected with relatively low‐power radars during the majority of the hours of darkness on almost every night. The reflection geoinetry and the characteristics of the echoes themselves—occurrence frequency, fading rate, etc.—all suggest that the observed low‐latitude phenomenon is caused by the same general type of particle bombardment which is believed to cau

ISSN:0148-0227    

DOI:10.1029/JZ060i004p00497

年代:1955

数据来源: WILEY