摘要:

Electric field rise times have been measured for about 500 first and 500 subsequent lightning return strokes in western Pennsylvania at distances between 5 and 300 km. Risetimes to peak are almost always in the range 1 to 6 μsec. The mean risetime for 436 first strokes beyond 25 km was 3.7 μsec with a standard deviation of 1.6 μsec; the mean risetime for 480 subsequent strokes beyond 25 km was 3.0 μsec with a standard deviation of 1.1 μsec. Risetimes to peak were essentially the same for close strokes as for distant str

ISSN:0148-0227    

DOI:10.1029/JC077i003p00399

年代:1972

数据来源: WILEY

摘要:

The interactions between positive corona streamers and droplets atomized from a water and glycerin solution have been studied by means of the Lichtenberg figure technique. The results indicate that a droplet with a radius greater than approximately 50 μm can acquire charge from an interaction in which a streamer impinges on the droplet, whereas a smaller droplet is limited to indirect charging, which results from the close approach of a streamer. Droplets can acquire surface charge densities, via the mechanism of streamer impingement, that are an order of magnitude or more greater than that possible from indirect charging. Despite this fact, the effect of positive streamer‐droplet interactions on precipitation growth should derive primarily from the indirect charging mechanism because of the much greater number density of smaller droplets in a typical cloud population and because of the greater sensitivity of the growth process to perturbations at the small radius end of the spectr

ISSN:0148-0227    

DOI:10.1029/JC077i003p00407

年代:1972

数据来源: WILEY

摘要:

A new sampler for the collection of atmospheric CO2by means of molecular sieve adsorption has been developed and flown on operational USAEC balloon flights over San Angelo, Texas, (31°N) at altitudes ranging from 21 to 37 km. The total weight of this sampler and molecular sieve material is appromixately 30 kg. Depending on altitude, between 1 and 5 liters of CO2, sufficient for accurate14C measurements, were collected on each mission. Based on 24 measurements in 1968–1970, the14C data indicate the upper stratosphere has small vertical gradients at 31

ISSN:0148-0227    

DOI:10.1029/JC077i003p00412

年代:1972

数据来源: WILEY

摘要:

A conformal transformation of the equations that constitute the boundary value problem of permanent‐form finite gravity waves from thex,yplane to the velocity‐potential‐stream‐function plane is presented. After the resulting equations are given in a nondimensional form the Fourier coefficients of the solutions to this problem are determined for a representative sampling of theoretical waves of various heights at different depths of water through a numerical iterative process. A comparison of the results is made with existing Stokes first, third, and fifth order theories and withChappelear's [1961] direct numerical calculations. The approach presented has the following advantages: (a) simplification of the boundary conditions through the mapping transformation, (b) one set of coefficients to define the wave characteristics, (c) easy evaluation of the particle trajectories, and (d) a wide range of depths of water and heights of waves to which it can be

ISSN:0148-0227    

DOI:10.1029/JC077i003p00420

年代:1972

数据来源: WILEY

摘要:

In May 1966, an ocean‐botton geophysical station, OBS 3, was implanted about 160 km off the coast of San Francisco at a depth of 3903 meters. This station has been in continuous operation since then. The tidal constants at this location for a number of constituents areestimated from four years of pelagic tidal heights. The amplitudes for the most important constituents,S2,M2,N2,K1,P1, andO1, are 13.0, 54.4, 12.0, 44.2, 12.7, and 29.0 cm and their corresponding Greenwich epochs are 210.9, 226.7, 207.0, 225.4, 224.5, and 233.2 degrees respectively. For major constituents the yearly analysis of data gives stable results. The agreement is good between the average yearly tidal constants and the constants obtained from the four years of tidal heights. For major components the differences in amplitude are less than 0.2 cm. The tidal constants obtained from classical tidal analysis and those obtained from cross‐correlation of the observed tides with the noise‐free synchronous equilibrium tides agree very well. Tidal constants of theM2constituent are compared with eight different cotidal charts for the vicinity of OBS 3. The chart of Tiron et al. is in close agreement with the observations, although proof of existence of their alleged amphidromic point requires more pelagic measure

ISSN:0148-0227    

DOI:10.1029/JC077i003p00434

年代:1972

数据来源: WILEY

摘要:

The theory of wave‐induced longshore currents is extended to curved semicircular beaches. The currents are produced by the nonvanishing mean lateral thrust exerted by the waves through the divergence of their radiation stress in the surf zone. The equations are linearized and only the retarding effect of bottom friction is taken into account. The origin and influence of the various forcing terms are discussed. As a rule, the dominant forcing term is the one caused by the oblicity of incidence of the waves at the breaker line. A general solution is found for a semicircular bay of radius of curvature much greater than the width of the surf zone and linear beach slope. A specific example is worked out for a given form of the incident wave field at the breaker line, with small, but nonuniform angle of incidence and wave amplitude along that lin

ISSN:0148-0227    

DOI:10.1029/JC077i003p00444

年代:1972

数据来源: WILEY

摘要:

The application of image enhancement to improve sea‐ice depiction in satellite infrared data is investigated using Nimbus high resolution infrared radiometer (HRIR) measurements of the northern Canada‐Greenland arctic region. The results of densitometric analyses indicate that although ice boundaries can be detected in HRIR film strips by identifying relative temperature differences, quantitative interpretation of the film strips cannot be obtained even when the accompanying gray‐scale wedges are used as reference. Based on the densitometric analyses, experiments are performed to enhance the gray‐scale contrast within the temperature range of interest. Through the experimentation, an improved scheme is developed such that the data are presented in a format from which accurate quantitative information can be visually derived and in which features of significance to sea‐ice mapping are more clearly defined. Simulations of a five‐level gray‐scale depict

ISSN:0148-0227    

DOI:10.1029/JC077i003p00453

年代:1972

数据来源: WILEY

摘要:

Oxygen isotope ratios in the aragonite precipitated by the scleractinian reef‐building corals indicate that the skeletal carbonate is not in isotopic equilibrium with the sea water of the reef environment in which the corals grew. Despite this apparent isotopic disequilibrium, δ18O values are temperature dependent. The δ18O versus temperature curves for various coral genera are parallel or nearly parallel to the isotopic ‘paleotemperature scale’ established by Epstein et al. (1953) but in each case the curves are displaced toward lower18O/16O ratios at a given temperature. Regression coefficients for 44 genera have been determined. These findings suggest that if skeletal carbonate is derived from both sea‐water bicarbonate and metabolic carbon dioxide, the relative proportions contributed by each of these two sources of carbon and oxygen are essentially constant for a given genus, but are different from one genus to another. Thus it is possible that isotopic composition can indicate relative excretory efficiency and that stable isotope ratios can be of considerable value in elucidating some of the processes involved in reef coral de

ISSN:0148-0227    

DOI:10.1029/JC077i003p00463

年代:1972

数据来源: WILEY

摘要:

Penetration depth of90Sr in deep‐water sediments of Lake Superior and Lake Ontario was 8–10 cm by 1969. Detailed picture of the90Sr‐containing layer indicates that the main mechanisms of transport from lake water into sediment are (a) diffusion of90Sr in interstitial water, and (b) uptake of90Sr by solid phases in sediment. A diffusional transport model, with diffusion coefficientD= 2 × 10−6− 6 × 10−6cm2· sec−1and distribution factorK= 120 − 440 in favor of solids, gives90Sr concentrations in sediment comparable with observed values. Intensity of diffusional flux into sediment increases with greater uptake by solids (larger values ofK). In Lake Ontario, flux into sediment has been removing90Sr from lake water at the rate of 0.2–0.5% per year, during the period 1954–1969. The slowness of flux compared with the rate of90Sr removal in lake outflow (12% per year) accounts for the small amount accumulated in sediments (4–6% of90Sr in lake water) and for the lack of noticeable control of concentrations in lake

ISSN:0148-0227    

DOI:10.1029/JC077i003p00474

年代:1972

数据来源: WILEY

摘要:

Changes in the potential gradient at six observatories in Britain, Japan, and Portugal, are examined over the period 1950 to 1964. The changes follow the same pattern at all six stations. The accumulation of surface radioactive fallout, following nuclear explosions, offers a plausible causative explanation for the potential gradient variations. This explanation is supported by similarities in the variations and in nuclear testing. Further confirmatory evidence is furnished by comparing British data on the potential gradient changes and on alterations in the near‐surface ionization rate. Analytic development of this comparison enables the atmospheric environment at the two British observatories to be identified, respectively, as nucleus (pollution) dominated and relatively clean; this differentiation is confirmed by independent evidence and extended to the Japanese and Portuguese locations. The fallout accumulation considerably complicates studies of the electrode effect and of relationships between pollution and atmospheric electricit

ISSN:0148-0227    

DOI:10.1029/JC077i003p00482

年代:1972

数据来源: WILEY