摘要:

A method is described for the interpolation of deflections of the vertical from horizontal gravity gradients that can be done with considerable accuracy. From the interpolated deflections and astronomic observations, the geodetic coordinated can then be determined. The accuracy of the interpolated deflections or of the geodetic coordinates have a maximum standard error of 0.5′′ for lines 30–40 km long. The method is very efficient for the densification of deflections of the vertical where otherwise a very detailed gravity survey is required, but for geodetic coordinate determination, the procedure generally cannot be considered superior to conventional methods of establishing horizontal control. A potential application may be found, however, in photogram

ISSN:0148-0227    

DOI:10.1029/JB073i022p06869

年代:1968

数据来源: WILEY

摘要:

Ocean and laboratory data demonstrate the presence of an overshoot phenomenon in the growth of various frequency components of the wind‐generated wave spectrum. An overshoot occurs when the energy of a spectral component first grows rapidly past its eventual equilibrium valueFeand then decays back toFe. Typical growth curves from both sources of data are presented here, and their significant features are discussed. A comparison between the two sets of data leads to speculation as to the possible mechanism responsible for the overshoo

ISSN:0148-0227    

DOI:10.1029/JB073i022p06879

年代:1968

数据来源: WILEY

摘要:

The effect on the flow caused by a thin rigid radial wall that acts as a total barrier to continuous zonal motion in a heated rotating annulus has been examined. The gross effects of increases in rotation on the flow in the absence of such a barrier are greatly diminished. Measurements of total heat transfer and temperature field are compared for the two cases.

ISSN:0148-0227    

DOI:10.1029/JB073i022p06887

年代:1968

数据来源: WILEY

摘要:

The chromaticity of the scattered radiation received by a terrestrial observer from different parts of the sky during twilight has been evaluated for six different model atmospheres. The first model is free of atmospheric ozone and dust, the second one contains 0.242 atm cm of ozone but no dust, whereas the remaining four models contain both ozone and dust. The evaluation method involves rectilinear propagation (no refraction) and the single scattering of direct sunlight. The computed chromaticities for the various models are discussed in terms of certain classically observed features of the twilight, namely, the purple light (main and secondary), the increased blueness of the zenith sky during twilight, and the anti‐twilight arc and the dark segment. Contrary to G. V. Rozenberg (1963), the authors find that the main purple light phenomenon cannot be explained by single scattering in a purely molecular atmosphere; the presence of stratospheric dust is found to be essential. Although certain features of the secondary purple can be explained by primary scattering in an upper stratospheric dust layer, chromaticities based on accurate calculation of both primary and secondary scattering will be required before a selection can be made between the secondary‐scattering explanation and the upper dust‐layer explanation of the secondary purple. The increase in zenith sky blueness during twilight requires the presence of ozone in the atmosphere; dust contributes to an increased blueness at all twilight solar zenith angles. The observed chromaticities of the anti‐twilight arc and the dark segment cannot be reproduced in the model calculations and, therefore, must be produced by multiple sca

ISSN:0148-0227    

DOI:10.1029/JB073i022p06897

年代:1968

数据来源: WILEY

摘要:

A magnet assembly consisting of a magnetized bar and an unmagnetized bar was attached to a footpad of Surveyor 6 in such a manner that it would permit viewing by the television camera following the lunar landing of the spacecraft and after the assembly had made contact with the lunar surface. Results of the experiment indicate that there is a small amount of magnetic material present in the Sinus Medii and appear to support a basaltic composition. This experiment strengthens the conclusion that basaltic composition may dominate the maria units, and the basalt may be scoriaceous. In addition, the magnet experiments lend support to a volcanic origin of this mare material, and would further suggest fine particles at the time of origin, rather than subsequent pulverization by impact.

ISSN:0148-0227    

DOI:10.1029/JB073i022p06915

年代:1968

数据来源: WILEY

摘要:

The spectrum of sea level at Lord Howe Island has a broad peak at 0.006 cycle/day (period 170 days), most likely due to movement of the strong circulation pattern of the East Australian Current system relative to the island. At higher frequencies, 0.02–0.05 cpd, the spectrums at Lord Howe Island and also at two stations on the east Australian coast (Sydney and Coff's Harbour) are comparable and are an order of magnitude larger than the spectrums at Honolulu and Canton Island. It is suggested that the high values in this frequency range at the Australian stations, both coastal and island, may be due to a different feature of the circulatio

ISSN:0148-0227    

DOI:10.1029/JB073i022p06925

年代:1968

数据来源: WILEY

摘要:

Ninety‐eight observations of longshore current velocity, beach slope, and the breaker height, period, angle, crest length, and trough depth were made on an Atlantic ocean beach. Precision inshore surveys during the observation period revealed an essentially plane beach with an offshore bar parallel to the shoreline during two‐thirds of the study period. Analysis of replicate measurements of current velocity revealed no topographically‐induced non‐“uniformity” in the current and suggested that an individual determination of velocity was within about ±10 percent of the true velocity value.A linear multi‐regression analysis performed on the data resulted in the following empirical correlation, for the four strongest independent variables:V¯=‐0.170455+0.037376(α¯b)+0.031801(T¯b)+0.241176(Hbs)+0.030923(m¯)whereV¯is in meters per second,α¯bis the mean acute angle between the breaker front and the shoreline in degrees,T¯bis in seconds,Hbsis the significant breaker height in meters, andm¯is the mean beach slope in degrees. The total reduction of varianceR2forα¯bis 0.46 and forα¯bplusT¯bit is 0.53;Hbsandm¯each add 0.02 to successive values ofR2. The similarity between this equation and that obtained by Sonu et al. (1967), who used similar variables and analytical techniques, suggests that a general equation of this type may be valid for many Atlantic beaches. The present equation may be applied to values ofHbs,T¯b, andm¯falling within certain specified ranges, whenα

ISSN:0148-0227    

DOI:10.1029/JB073i022p06929

年代:1968

数据来源: WILEY

摘要:

Sixteen samples of kimberlite have been collected from deep underground in the Premier Mine at Cullinan in the Transvaal. The stability of the natural remanent magnetization of the samples has been well tested by alternating‐field demagnetization and confirmed by thermal demagnetization. The magnetization is shown to be associated with magnetite, some of which is of primary origin and some of secondary origin. The magnetite of secondary origin was formed contemporaneously with or shortly after the emplacement of the kimberlite as a result of extensive hydrothermal alteration of primary minerals. It has not been possible thus far to decide between a thermoremanent and a chemical remanent origin for the observed magnetization. Previous paleomagnetic evidence has demonstrated that the kimberlite was emplaced in Precambrian times rather than in the Cretaceous, as was previously supposed. This evidence is supported by recently published geochronological work, which suggests an age of about 1750 m.y. The paleomagnetic pole at the time of emplacement of the kimberlite is located at 51.1°N, 37.5°E withA95= 7.5°. This position is significantly different from, and lies approximately 17.5° away from, that obtained in a previous study of the post‐Waterberg diabase sills, one of which cuts across the pipe. The age difference between the kimberlite emplacement and the sill's intrusion is not thought to be ver

ISSN:0148-0227    

DOI:10.1029/JB073i022p06937

年代:1968

数据来源: WILEY

摘要:

Fifteen of the sixteen known enstatite chondrites were studied microscopically in reflected and transmitted light, and their modal compositions were determined by point‐counting techniques. Compositions of clinoenstatite, orthoenstatite, plagioclase, kamacite, taenite, troilite, oldhamite, daubreelite, niningerite, ferroan alabandite, and schreibersite were determined with the electron microprobe X‐ray analyzer. Chemical composition, mineral occurrence, and mineral composition were found to depend on degree of recrystallization of the chondrites as judged by, for example, distinctness of chondrules and coarseness of silicates. On the basis of these parameters, three groups of enstatite chondrites can be distinguished and are referred to as type I, intermediate type, and type II. Differences between types I and II are pronounced, whereas intermediate type is transitional. The suggestion of Van Schmus and Wood that type II enstatite chondrites originated from type I by reheating is reviewed in the light of the new data. It is concluded that, although many of the chemical‐mineralogical parameters of type II chondrites could be explained as being the result of reheating of type I chondrites, there are some that would require rather stringent environmental conditions during reheating. For example, lower iron and sulfur contents in type II chondrites would presumably require reheating of type I chondrites to ≥975°C, the lowest temperature at which a melt would appear in the Fe‐Ni‐S system of type I composition and at which physical separation of the liquid from the silicates could occur. Differences in Si/Mg ratios would require reheating to even higher temperatures and fractionation in an open system. Furthermore, observed differences in nitrogen and sinoite contents between type I and type II are difficult to explain unless reheating took place in a closed system, or under oxygen fugacities low enough to allow nitrogen to react with SiO2and Si to form Si2N2O. An alternative model to the one by Van Schmus and Wood is discussed; it assumes that major differences in chemical and mineralogical composition between type I and type II were essentially established before or during chondrule formation and agglomeration by, for example, igneous differentiation or fractionation during condensation from a solar nebula, and that differences in texture are due either to different cooling rates of type I and type II chondrites during and after agglomeration of chondrules or to mild reheating to temperatures ≤975°C. This model does not, however, readily explain why only enstatite chondrites of type II bulk chemical composition (i.e. low Fe, S) cooled slowly or were reheated, and why chondrites of type I composition (high Fe, S) were always quenched to temperatures low enough to prevent recrystallization and we

ISSN:0148-0227    

DOI:10.1029/JB073i022p06945

年代:1968

数据来源: WILEY

摘要:

Four heat‐flow values from the central Sierra Nevada vary systematically from 1.3 μcal/cm2sec near the crest to 0.45 μcal/cm2sec at the eastern edge of the San Joaquin Valley. Corresponding heat‐production values determined from drill cores by Harold Wollenberg and Alan Smith range from 0.9 μμcal/cm3sec (higher than the average granite) to 0.07 μμcal/cm3sec (lower than the average basalt) in these granitic and intermediate rocks. With Francis Birch and Robert Roy and their collaborators we find that heat flowqis related to surface heat productionA0byq=q0+DA0, whereq0andDare empirically determined constants (0.4 μcal/cm2sec and 10 km, respectively). This relation can be preserved under differential erosion (for which there is much evidence) only if the crustal heat sources are distributed vertically according toA(z) =A0e−z/D.q0is interpreted as the uniform contribution from the mantle. This exponential source‐distribution law forms the basis for an idealized model by means of which it is possible to reconcile the observed distributon of heat flow, surface heat producton, seismic velocities, and crustal thickness, as well as the volume of sediments attributed to post‐plutonic erosion of the Sierra and the generation of the Sierra Nevada batholith by anatexis in a great geosyncline as proposed by Paul Bateman and his associates. The model implies that in a period of remarkable activity ending in the early Tertiary the western Sierra was almost completely purged of heat‐producing elements in a time interval of th

ISSN:0148-0227    

DOI:10.1029/JB073i022p06977

年代:1968

数据来源: WILEY