摘要:

In the summer of 1966 an optical radar was operated in the vicinity of Oslo, Norway, to obtain measurements of the aerosol content of the mesosphere at times when noctilucent clouds might be present. The work was a continuation of similar experiments conducted in Alaska and Sweden in the summer of 1964. The measurements indicate that the altitude region 60–70 km contains an appreciable amount of particulate material in the summertime at high latitudes during periods of noctilucent cloud activity, as suggested by our earlier results. The observed vertical distribution of aerosols has been related to the general circulation of the upper atmosphere to produce an estimate of the meridional flux of particulate material at high latitudes. Also, improved resolution of the apparatus made it possible to observe some transient features of a noctilucent cloud: the height of the cloud varied from 75 to 73 km during the observation interval, the geometric thickness of the cloud was appreciably less than 1 km, and the optical thickness was about 10

ISSN:0148-0227    

DOI:10.1029/JB074i010p02453

年代:1969

数据来源: WILEY

摘要:

Use of the zonal harmonics series for calculating the terrestrial wave guide fields directly is described. The analysis is extended to include radio waves propagating into sea water or below the earth's surface. A sample calculation of ELF radio waves is analyzed into a direct wave and a wave that has traveled the circumference of the earth. The location of the ripples in the standing wave pattern is compared with the locations predicted by less exact but simpler mathematical models. It has been found that approximate formulas check within a few percent of the exact analysis when used to estimate positions of maxima and minima near the antipode. It is concluded that the exact analysis can be used to check various approximate formulas. Where possible the extension of the analysis to more complex models should be accomplished with the exact solution.

ISSN:0148-0227    

DOI:10.1029/JB074i010p02459

年代:1969

数据来源: WILEY

摘要:

Airborne infrared radiometer measurements of water surface temperatures at Lake Hefner, Oklahoma, show an average diurnal variation of about 1°C for late summer conditions. The lake surface, cooled by evaporation, was 0.4° to 0.9°C cooler than the water about 1 cm below the surface. Applications of an evaporation‐reducing monomolecular film reversed this gradient. The surface water temperature was 0.3°C warmer under the monomolecular layer than in the surrounding open

ISSN:0148-0227    

DOI:10.1029/JB074i010p02471

年代:1969

数据来源: WILEY

摘要:

Seismic profiler data from about 200,000 km of traverse in the South Pacific are used to develop a sediment isopach map of the area. They reveal in some detail the marginal trench sediments and the sediments of the equatorial and subantarctic zones. Recent sea‐floor spreading is indicated by an abrupt thinning of sediments near the crest of the Pacific‐Antarctic ridge. This recent cycle of spreading appears to be related to possible large‐scale vertical movements in Melanesia. Recent sea‐floor spreading explains some aspects of sediment distribution and tectonic activity but is not clearly applicable to the distribution of older sediments in the South Pacific. The sediment distribution (except near the mid‐ocean ridge) in subantarctic waters seems to depend primarily on the effects of a former more northerly location of the polar front and on modern bottom currents. Active trenches occasionally reveal trench sediments that appear to be folded near the continental slopes in profiler records when crossings are made at acute angles to the fold axes. The velocity structure of equatorial sediments is derived from sonobuoy data, and the areal extent of the Cretaceous (‘opaque layer’) reflector

ISSN:0148-0227    

DOI:10.1029/JB074i010p02477

年代:1969

数据来源: WILEY

摘要:

Calculations based on mathematical models are performed to provide improved estimates of the major element chemical abundances within the earth, Venus, Mars, Mercury, and the moon. Approximate equations of state at high pressure for the important constituents of the terrestrial planets are constructed from experimental data and theoretical relations. Bounds on the amounts of these materials present within detailed self‐consistent models of the terrestrial planets are calculated, subject to the assumption of additive partial molar volumes, and the sensitivity of the abundance calculations to variations in the primary assumptions is indicated. Representative models give calculated total Iron mass fractions of 0.38 for the earth, 0.35 for Venus, 0.26 for Mars, 0.68 for Mercury, and 0.13 for the moo

ISSN:0148-0227    

DOI:10.1029/JB074i010p02494

年代:1969

数据来源: WILEY

摘要:

Seismic‐refraction data from the ocean are combined with geological data from the shore to determine the structure of the continental margin and the continent‐ocean transition off West Africa. More than 5 km of Cretaceous‐Quaternary sediments accumulated on the continental shelf and slope as the surface of the underlying continental crust subsided. On the shelf the pre‐Mesozoic rocks consist of a 2‐ to 3‐km thickness of Cambrian‐Devonian sedimentary rocks over a crystalline Precambrian continental crust. These Paleozoic sedimentary rocks can be interpreted as a pinching out under the upper continental slope off Sierra Leone and may not extend any great distance into the South Atlantic. Layer 2 (oceanic basement) with a velocity range similar to that of the Paleozoic sedimentary rocks appears to extend all the way from the mid‐Atlantic ridge to the lower continental slope. This layer may consist entirely of post‐Paleozoic volcanies. The Cretaceous‐Quaternary embayment of the Senegal basin is separated from the less well developed embayment of Sierra Leone by a west‐southwest‐trending arch in the pre‐Mesozoic surface under the continental shelf. Mesozoic or Tertiary faulting produced the present configuration of the arch, but this faulting probably followed the zones of Paleozoic folding and faulting along the northwest limb. An anomalously high‐velocity crust, 7.0–7.3 km/sec, occurs near the Sierra Leone rise. This may be similar to the crust that occurs beneath the Bermuda rise, a crust formed by metamorphism due to the igneous activity of the many seamounts comprising the rise. This anomalous crust does not extend to the ridge flank, suggesting that the Sierra Leone rise is an in

ISSN:0148-0227    

DOI:10.1029/JB074i010p02512

年代:1969

数据来源: WILEY

摘要:

A model for colliding objects in the asteroidal belt is formulated. An integro‐differential equation describing the evolution of a system of particles undergoing inelastic collisions and fragmentation is derived and solved for steady‐state conditions. It is found that the number density of particles per unit volume in the mass rangemtom+dmisAm−adm, whereAand α are constants (provided that certain conditions are satisfied). The population index α can then be derived theoretically; for asteroids and their debris, α = 1.837, in agreement with an empirical fit to the observed distribution. Various statistical properties of the distribution can be derived from the model. It is found that, for asteroidal objects, catastrophic collisions constitute the most important physical process determining particle lifetimes and the form of the particle distribution for particles sufficiently large that radiation effects are unimportant. The lifetime of the largest asteroids is found to be of the same order of magnitude as the probable lifetime of the solar system; therefore, some of the largest asteroids may have survived since the time of creation, whereas most smaller ones have not and are collisional fragments, according to the prese

ISSN:0148-0227    

DOI:10.1029/JB074i010p02531

年代:1969

数据来源: WILEY

摘要:

This paper lends fresh support to the hypothesis that large angular displacements of the earth's rotation axis relative to the entire mantle have occurred on a geological time scale, owing to the gradual redistribution (or decay or manufacture) of density inhomogeneities within the earth by the same convective processes that are responsible for continental drift. The first of our three contributions is a pedagogic theorem that rigorously illustrates this mechanism of polar wandering for a ‘quasi‐rigid body’. That theorem states that any slow changes in shape of such a body preserve as an adiabatic invariant the solid angle traced out by its angular momentum vector as viewed from its principal axes. Thus, if the body were once set spinning about the axis with the greatest moment of inertia, it would always continue to spin almost exactly about the same principal axis no matter how that axis moves through the deforming body. The second and main contribution is our refutation of the widely accepted notion that the earth's figure shows unmistakable signs of the faster spin rate of the past. If correct, the degree of permanence of the rotation bulge so inferred by G. J. F. MacDonald (1963, 1965) and D. P. McKenzie (1966) would have been an effective impediment against any significant polar wandering of the earth as a whole. However, we show here that, after subtraction of the hydrostatic flattening, the remaining or nonhydrostatic part of the earth's inertia ellipsoid is distinctly triaxial. Such a triaxial shape, as well as the coincidence of the present rotation axis with the principal axis having the largest of the nonhydrostatic moments of inertia, is indeed to be expected of any randomly evolving, nearly spherical object without too much ‘memory’ for its past axis of rotation. Finally, we discuss briefly some statistical aspects of polar wandering on the assumption that the earth is such

ISSN:0148-0227    

DOI:10.1029/JB074i010p02555

年代:1969

数据来源: WILEY

ISSN:0148-0227    

DOI:10.1029/JB074i010p02568

年代:1969

数据来源: WILEY

摘要:

Magnetization measurements were made on a hundred‐twelve independently oriented cores drilled at twenty‐two sites distributed among six basic intrusive plugs forming part of the Monteregian Hills group in southeast Quebec. On the basis of adopted magnetization homogeneity criteria, less than 80% of the sampled cores were accepted as reliable carriers of paleomagnetic information, after af cleaning in a peak demagnetizing field of 250 oe. An analysis of the data obtained from these cores representative of sixteen sites yielded a mean direction of magnetization whose declination and inclination are, respectively, 157.4° and −59.9°. The circle of confidence about the resultant of the sixteen ‘weighted’ site means has a radius α′.95equal to 3.3°. No reliable evidence of mixed polarity in the paleomagnetic directions within any one of the six intrusives studied was found, although additional evidence was obtained to postulate at least one earth's field reversal during their formation. Combining the above mentioned data with seventy‐five previously reported core mean directions representative of sixteen sites on four other members of the Monteregian Hills group yielded a paleomagnetic pole position at 170.5°W, 71.3°N. The low angular standard deviation of the thirty‐two ‘weighted’ site means summarizing these data (7.8°) suggests that the non‐dipole component of the earth's magnetic field was less important in Cretaceous time than

ISSN:0148-0227    

DOI:10.1029/JB074i010p02570

年代:1969

数据来源: WILEY