摘要:

23 measurements in the floor of the Vema Fracture Zone show heat flow to be above normal and remarkably uniform between the active spreading centers (HF = 3.5 HFU). A simple thermal model of a transform fracture zone shows that heat flow over the fault plane should equal the means of the heat flows over the two abutting lithospheric plates. This model predicts a rather uniform heat flow between the two spreading centers.

ISSN:0094-8276    

DOI:10.1029/GL003i005p00241

年代:1976

数据来源: WILEY

摘要:

The dynamical laws which guarantee conservation of momentum and continuity of traction across a tangential slip surface are the same in an infinite, homogeneous, elastic medium which is subject to a large, uniform, compressive isotropic stress as in one which is not. It follows that many of the results from the theory of seismic faulting are applicable in this case. Any consideration which explicitly involves the concept of energy is different in the two instances, because in the former there are additional second order terms which arise in calculating the work done against the initial stress. The relative contribution of these terms to the net elastic strain energy released by a typical seismic fault appears to be no more than a few percent.

ISSN:0094-8276    

DOI:10.1029/GL003i005p00245

年代:1976

数据来源: WILEY

摘要:

The decay of147Sm to143Nd allows143Nd/144Nd to be used to trace Sm/Nd fractionation in long time‐scale geologic processes.143Nd/144Nd has been measured in terrestrial rock samples of different ages to establish the characteristics of Nd isotopic evolution in the crust and mantle. The evolution of143Nd/144Nd in the mantle indicates Sm/Nd essentially equal to that of chondrites, and implies a chondritic REE distribution for the earth. Variations in143Nd/144Nd do exist in the mantle, however, indicating Sm/Nd heterogeneity and the existence of distinct mantle reservoirs with characteristic143Nd/144Nd.143Nd/144Nd in average crustal rocks today is much lower than found in recent mantle samples and reflects their age and low Sm/Nd. Oceanic tholeiites and alkali basalt are derived from sources with Sm/Nd which has been 5‐10% greater than chondritic over the age of the earth. Alkali basalt can not be derived from mantle reservoirs which have been light REE‐enriched for long

ISSN:0094-8276    

DOI:10.1029/GL003i005p00249

年代:1976

数据来源: WILEY

摘要:

Through 1975 published measurements of228Ra in most geochemical samples have been calculated using a 6.7 year half‐life for228Ra. The currently accepted half‐life is 5.75 years and was established in 1962. Measurements as early as 1908 indicated a value of about 5.5 years, but a 1918 measurement giving a 6.7 year half‐life was adopted and remained unchallenged until 1960. Seawater228Ra activities calculated using a 6.7 year half‐life are probably no more than 4% low, and approximately 2% low on the average. Therefore, data that have appeared in the literature are not significantly altered by the new value. Diffusion coefficients derived from the distribution of228Ra in seawater are generally 8% to 20% low due to possible errors in the calculated activities and use of the wrong decay constant. Coral growth rates derived from the distribution of228Ra in modern corals are about

ISSN:0094-8276    

DOI:10.1029/GL003i005p00253

年代:1976

数据来源: WILEY

摘要:

The coupling of acoustic‐gravity waves in the main atmosphere to acoustic waves characteristic of individual minor species in the atmosphere is postulated. Such coupling would exist as a result of resonances in the response of the minor species and its likelihood depends on the mass of the atmospheric particle relative to the major species mass, the diffusion of the minor species and the direction of propagation of the main disturbance. These minor species disturbances may explain some AE‐C measurements in the thermosphere, and could possibly play a role in the distribution of minor species and their chemistry in the mesosph

ISSN:0094-8276    

DOI:10.1029/GL003i005p00257

年代:1976

数据来源: WILEY

摘要:

For use in various wind engineering applications (e.g. wind energy conversion, wind loads on structures, air pollution transport) it is desirable to have a consistent relationship by which to project height variations of both "instantaneous" (e.g. few minute average) winds and parameters of the wind speed probability distribution. The power law V2/V1= (Z2/Z1)nis often used for height projection of wind profiles, with the exponent n sometimes taken as depending on surface conditions or on atmospheric stability. The power law profile for wind speed is shown here to be consistent with observed height variation of Weibull wind speed probability distribution functions which have been found to fit observed wind speed distributions (at least above relevant threshold wind speeds). For consistency between the wind speed profiles and the height variation of the Weibull wind speed probability distributions, it is necessary only that the exponent n vary as n = a + b ℓn V1, where a and b are constants whose values depend on the reference height at which wind speed V1is measured. For a reference height of 10 m, it is found that a = 0.37 and b = −0.0881 (with V1in m/s) adequately describes both the observed height variation of wind speed and wind speed probability distributi

ISSN:0094-8276    

DOI:10.1029/GL003i005p00261

年代:1976

数据来源: WILEY

摘要:

Recent measurements of the exhaust gases in the stacks of power plants burning coal and natural gas have shown high levels of nitrous oxide. Calculations based upon the known combustion parameters of the power plants and extrapolated to the current world production of coal and natural gas indicate that combustion may be a significant source of nitrous oxide in the atmosphere. In view of the predicted increases in the combustion of fossil fuels, particularly coal, it is likely that the importance of combustion as a source of atmospheric nitrous oxide will increase. As a result of the current uncertainty regarding the size of the various sources and sinks of nitrous oxide in the atmosphere, it would appear that the question of the importance of combustion to the atmospheric nitrous oxide budget deserves further scrutiny.

ISSN:0094-8276    

DOI:10.1029/GL003i005p00265

年代:1976

数据来源: WILEY

摘要:

In late December 1975, the orbital configuration of the Atmosphere Explorer‐D satellite made possible the measurement of the winter helium bulge within a single perigee pass. Shortly after the winter solstice, the perigee of the polar orbiting AE‐D satellite crossed the equator, at which time descending and ascending portions of the orbit stretched symmetrically over the southern and northern hemispheres. The open source neutral mass spectrometer (OSS) on board AE‐D measured helium densities between the perigee (about 150 km) and altitudes of 650 km. During the time the perigee was at the equator, altitudes above approximately 550 km were located north and south at latitudes greater than 50°, Helium showed, in the winter hemisphere, a factor of 20 higher densities than at corresponding altitudes and latitudes in the southern, summer hemisphere. Absolute densities of helium agree well with previous measur

ISSN:0094-8276    

DOI:10.1029/GL003i005p00269

年代:1976

数据来源: WILEY

摘要:

The Atmosphere Explorer satellites (AE‐C, ‐D, and ‐E) were initially placed into highly elliptical orbits with perigees around 140 km and apogees of 4000 km. As a result of such an orbital geometry, measurements of neutral constituents at high altitudes represent mainly vertical changes in densities. The influence of horizontal density gradients on measurements above 400 km is small. Under geomagnetically quiet conditions, the density profiles can be used to derive scale height temperatures of the exosphere. The Open Source Neutral Mass Spectrometer (OSS) flown on all three AE‐satellites measured neutral constituents such as N2, O and N well above 400 km. The temperatures derived from scale heights show a good agreement among the constituents and the expected close correlation with the F10.7 cm solar flux. Satellites with highly elliptical orbits provide the opportunity to measure simultaneously both densities and tempe

ISSN:0094-8276    

DOI:10.1029/GL003i005p00273

年代:1976

数据来源: WILEY

摘要:

Energetic (E>1.6 MeV,>3.9 MeV) trapped electron fluxes observed at the synchronous altitude during 1974 and 1975 by an experiment aboard ATS‐6 exhibit a modulation in intensity which is correlated with the passage of sector structure boundaries of the interplanetary magnetic field past the earth. The electron fluxes reach equilibrium intensities during the time the magnetosphere is in a given IMF sector which are highest in the fall for (+) sectors and highest in the spring for (−) sect

ISSN:0094-8276    

DOI:10.1029/GL003i005p00277

年代:1976

数据来源: WILEY