摘要:

Coefficients of wind drag, sensible heat transfer, and evaporation are shown to depend on a bulk Richardson number derived from the Monin‐Obukhov length. Ratios of these transfer coefficients to their neutral values are derived from recent profile theory and compared with some overwater measurement

ISSN:0148-0227    

DOI:10.1029/JB073i008p02549

年代:1968

数据来源: WILEY

摘要:

Laboratory experiments with vortex‐stabilized arcs show that any effect the vortex may have in decreasing the deionization rate between pulses of power to the arc was too small to be measured with available apparatus. The major function of the vortex is to keep the plasma in contact with the electrodes, and a secondary function is to hold the plasma column on the shortest spacing between the electrodes. The concentration of the plasma by centrifugal action of the vortex gives only a 13% reduction in arc threshold power at the expense of a threefold increase in vortex kinetic energy. This effect is less important than previous experiments have indicated. The threshold power density of the arc is essentially a constant at 52 watts/cm3and does not change appreciably over a threefold change in vortex kinetic energy. Tests with hard sparks did not show any preference for the axis of the vortex, but sparks occurring in rapid succession, say 10 to 20 per second, tend to restrike in the same channel more often in the vortex than elsewhere. Multistroke cloud‐to‐ground lightning discharges may not show preference for a tornado axis, since, owing to the absence of electrodes, the vortex will not play the same role as in the laboratory experi

ISSN:0148-0227    

DOI:10.1029/JB073i008p02559

年代:1968

数据来源: WILEY

摘要:

‘Set‐down’ and set‐up, the negative and positive changes in mean water level due to the presence of a train of surface waves, was measured in a wave channel. Well outside the break point the experimental results are in good agreement with the theoretical relationship determined by Longuet‐Higgins and Stewart. Near the break point, where the wave height is greater than predicted by first‐order wave theory, the measured ‘set‐down’ was consistently less than theory would predict from the deep water wave height. Inside the break point the bore height was found to be a linear function of the mean water depth. In this region, the gradient of the set‐up,, was related to the beach slope tan β and the mean ratio of wave height to water

ISSN:0148-0227    

DOI:10.1029/JB073i008p02569

年代:1968

数据来源: WILEY

摘要:

Simplified models of wind‐forced motions are considered in the two‐layer circular basin ‘model Great Lake’ introduced in an earlier paper. Under summer conditions, when a thermocline is present, both a uniform, steady wind and a uniform wind varying periodically in time produce a frictionless lake response characterized by strong boundary currents and pronounced thermocline movements in the shore zone. The length scale determining the width of this shore zone is the ‘radius of deformation,’ typically three miles. Observations on Lakes Huron, Michigan, and Ontario show such motions to be present near

ISSN:0148-0227    

DOI:10.1029/JB073i008p02579

年代:1968

数据来源: WILEY

摘要:

Observations in the coastal waters off southern California have revealed significant periodic oscillations in the magnitude of the vertical thermal gradient within the seasonal thermocline. These fluctuations occur with periods of approximately 6, 8, 12, and 24 hours and appear to be closely related to the internal tides.

ISSN:0148-0227    

DOI:10.1029/JB073i008p02591

年代:1968

数据来源: WILEY

摘要:

A technique for routinely determining the velocity structure of the sediment column with an average error of less than 100/m sec during normal reflection profiling is described. An expendable passive sonobuoy is launched while the ship is underway. A variable angle reflection profile is recorded on one channel of the seismic profiler, and a vertical reflection profile is obtained on the other, providing dip and topographic corrections for the variable angle data. The velocity structure is determined by means of a modifiedT2/X2solution programmed for a digital computer. The sonobuoy system has the advantage of being free of towing noise, permitting the use of lower frequencies, which in some areas results in greater penetration than is possible with a towed array. The accuracy and reliability of the system and the problems relating to velocity gradients are discussed. The examples discussed cover a wide range of conditions and geographic locations.

ISSN:0148-0227    

DOI:10.1029/JB073i008p02597

年代:1968

数据来源: WILEY

摘要:

Interval velocity solutions from sonobuoy data reveal three major sedimentary sequences: (1) Unconsolidated sediments whose velocity increases with depth of burial and ranges from 1.6 to 2.2 km/sec; (2) semiconsolidated sediments (layer A), which probably have some velocity discontinuities, whose velocity increases with depth of burial and ranges from 1.7 to 2.9 km/sec; (3) consolidated sediments (layer β), measured in a few places, whose velocity is apparently independent of overburden and ranges from 2.7 to 3.7 km/sec. In the shallower layers, low velocities seem to be related to the deposition of clay‐sized particles by relatively swift bottom currents; high velocities, to quieter bottom conditions or the influx of much turbidite material. Except for the shallow layers, velocity‐depth functions are quite similar for the Gulf of Mexico and the Atlantic Ocean. All the curves show an increase of velocity with depth without significant velocity rever

ISSN:0148-0227    

DOI:10.1029/JB073i008p02615

年代:1968

数据来源: WILEY

摘要:

A boundary‐layer solution for steady cellular convection is applied to thermal convection within the earth's mantle. For the large Prandtl and Rayleigh numbers applicable for the mantle, each cell contains a highly viscous core, on the horizontal boundaries of the cell are thin thermal boundary layers, and on the vertical boundaries between cells thin thermal plumes drive the viscous flow. Temperature and velocity distributions applicable to the mantle are obtained. With accepted values of the Rayleigh number the theory predicts a reasonable velocity for continental drift. Predicted values for the surface heat flux are in good agreement with measurements made on the ocean floors. The thickness of the thermal boundary layer adjacent to the earth's surface varies from about 8 km in the vicinity of the vertical rise to about 60 km near the descending plume. The vertical rise has a width of about 300 km with a similar width for the descending plume. In deriving the conditions for incipient upper mantle melting from experimental data on the melting of basalt, it is shown that in the upper part of an ascending plume the mantle is likely to undergo partial melting over an extensive mushroom‐shaped area having a maximum width of about 400 km and extending to within 10 km of the surface. It appears that in the ascending plume mantle material may begin to melt over a range of temperature and pressure conditions that permit the development of a range of basaltic magma types. Thermal arguments are presented against serpentinite and in favor of basalt as the main constituent of layer 3 of the oceanic crust. The shape and characteristics of the zone of fusion suggest an explanation for the anomalous gravity and seismic observations associated with mid‐oceanic r

ISSN:0148-0227    

DOI:10.1029/JB073i008p02643

年代:1968

数据来源: WILEY

摘要:

A capillary tube model of frost and snow is used as a basis for developing equations for the temperature distribution in (1) a slab of unventilated material and (2) a slab of ventilated material. The only quantities that need to be known are the properties of ice and air and some knowledge of the density of the material. Using elementary methods of analysis, the model yields approximate results that are useful in clarifying the transfer processes for their important influences. The effects of water vapor diffusion and density stratifications are clearly demonstrated with the model.

ISSN:0148-0227    

DOI:10.1029/JB073i008p02663

年代:1968

数据来源: WILEY

摘要:

The first‐arrival data from the Lake Superior seismic experiment of 1963 have been analyzed by the method of matching structure. This method makes a proper allowance for offset and also enables one to estimate the overburden velocity from the time‐distance data alone. For the upper refractor, which lies at a depth of 7–8 km and has a velocity of about 6.7 km/sec, the resulting profile agrees well with profiles previously obtained by the time‐term method. But the profile for the Mohorovicic discontinuity disagrees sharply with that previously obtained. This disagreement is shown to be due to improper weighting of the data by the time‐term method, which causes the derived structural relief to be nearly twice the true relief and which shifts the main structure 70 km to the west. Good wide‐angle reflections from the mantle were recorded, andt2‐x2analyses yield a mean overburden velocity of 6.85 km/sec. This value should be compared with the value of 6.75 km/sec obtained by matching structure. It is emphasized that both these estimates refer to the whole of the crust, so that it is most unlikely that there is any major velocity reversal beneath the upper refractor. The mean discrepancy between depths obtained from the reflections and depths obtained from the first‐arrival refraction was 1.5 km. The only other correlatable arrival possibly indicates a reflector that rises from a depth of about 25 km under the east‐central part of the lake to about 15 km or less under its western edge and under the Keweenaw peninsula. The amplitudes of the first arrival from the upper refractor were consistent with its being a simple head wave, but the amplitudes from the mantle were at least ten times too large. The simplest explanation is that there is a velocity gradient in the upper mantle of about 5 × 10−3sec−1. It is recommended that, in the interpretation of refracted‐wave time‐distance data, the effect of offset should always be allowed for and that mean crustal velocities should be obtained from properly designed reflection spreads. More theoretical studies are needed to determine how the amplitude ofPnis affected by the earth's curvature and by vertical velocity variations on either side of the

ISSN:0148-0227    

DOI:10.1029/JB073i008p02669

年代:1968

数据来源: WILEY