摘要:

The ‘law of the wall,’ familiar from turbulent boundary layer theory, has been extended to turbulent flow along a sharp density interface. The effective gravity of such an interface is an additional independent variable, so that in nondimensional form the ‘law of the interface’ becomes a one‐parameter family of curves. A convenient label for each curve is its ‘Keulegan parameter,’ a nondimensional combination of inner variables, which also plays a role in the theory of interfacial stability. One important difference between the law of the wall and the law of the interface is that the velocity gradient at an interface is typically much less than the stress divided by the molecular viscosity. Even in the nonturbulent core of an interface the effective viscosity is appreciably higher than the molecular viscosity. This finding is explained by the presence of viscous wavelets on the interface which contribute to momentum transfer through a combination of ‘sheltering’ and the generation of an interfacial viscous boundary layer. A simple approximate theory based on these ideas reproduces the observed functional form of effective viscosity versus Keulegan parameter (a square root relationship for miscible fluids). At interfaces with free surface energy, for low relative velocities, capillarity plays an important role. Capillary‐gravity waves of minimum celerity become key agents of momentum transfer, so that effective interface viscosity comes to depend on surface tension. The second major effect of variations of effective gravity is changing hydrodynamic roughness. The extent of this influence is governed by the buoyancy flux, and it also occurs over solid walls, although this has so far been ignored in the literature. Evidence from a variety of sources now suggests that hydrodynamic ‘roughness’ is determined by the energy balance of turbulence very close to the wall. A simple approximate theory based on this postulate reproduces qualitatively the observed interface roughness changes. Bulk relationships (drag, shear, and mass transfer coefficients) for interfaces may be determined by matching inner and outer laws in the conventional manner. The most practical independent variables for the presentation of such laws appear to be a gravity to viscous force ratio (rather than Reynolds number) and a Keulegan parameter (rather than Froude number), both based on

ISSN:0148-0227    

DOI:10.1029/JC083iC05p02329

年代:1978

数据来源: WILEY

摘要:

The dry deposition of Pb, Zn, and Cd containing particles from the atmosphere was studied by comparing theory with experiment for two types of surfaces: first, smooth flat teflon plates mounted on a smooth building roof and, second, fields ofAvena fatua, wild oat grass, about 50 cm tall. Gravitational sedimentation controlled the dry deposition of these trace metals on flat surfaces, while inertial impaction was the controlling mechanism for the vegetated surfaces. Convective diffusion to the grassy surfaces controlled the deposition of particles smaller than 0.1 μ (condensation nuclei) over the grassy fields; this mechanism contributed little to total trace metal deposition. Theories for these three mechanisms were then used to construct a plot of deposition velocity versus particle diameter forAvena, The model incorporates a novel two‐step deposition process: eddy diffusion and sedimentation from the atmosphere to the grassy field followed by filtration by the grass elements. The results of the calculations compared well with literature data for the total lead deposition on fields ofAvena. Brownian diffusion was negligible, while impaction on the plant elements was responsible for nearly all of the deposition. Of these particles, about one‐fourth were brought from the atmosphere into the canopy by sedimentation; wind eddy transport was responsible for the remaining frac

ISSN:0148-0227    

DOI:10.1029/JC083iC05p02343

年代:1978

数据来源: WILEY

摘要:

There has been recent controversy over how well the Rayleigh distribution matches the observed distribution of wave heights. Most of this controversy stems from comparisons based on different definitions of the significant wave height. Once consistent definitions are used, all available data support the conclusion that the Rayleigh distribution overpredicts the heights of the higher waves in a record. Analysis of 116 hours of hurricane‐generated waves in the Gulf of Mexico permitted the empirical fitting of the data to a Weibull distribution. Statistics developed from the empirical distribution include the prediction that the highest wave in 1000 is only 0.907 times the height predicted by the Rayleigh distributio

ISSN:0148-0227    

DOI:10.1029/JC083iC05p02353

年代:1978

数据来源: WILEY

摘要:

The densities of 124 samples of seawater from stations at 35°N in the Pacific Ocean have been measured with a vibrating flow densimeter at 25°C. The measured densities were compared with those calculated from the equation of state of Millero et al. (1976b), derived for seawaters of constant relative composition. Values for the excess density Δd(excess) =d(meas) ‐d(calc) were found to be ±3.8 ± 3.0 × 10−6g cm−3from 0 to 490m, 12.5 ±4.2 × 10−6g cm−3from 490 to 1000 m,; and 17.6 ± 2.6 × 10−6g cm−3from 1000 to 5834 m. The excess densities for the deep waters are in good agreement with our earlier measurements: 16.1 ± 3.6 × 10−6g cm−3(Millero et al., 1976c). The values of Δd(excess) predicted by correcting for the increase of alkalinity (ΔAT), total carbon dioxide (ΣCO2), and dissolved silica (ΔSiO2) and nitrate (ΔNO3) in the deep waters (Brewer and Bradshaw, 1975; Millero et al., 1976c) agree with the measured values on the average to ±5.2 × 10−6g cm−3. In the deep waters the measured values of Δd(excess) are ∼6 × 10−6g cm−3higher than the predicted values. The values of Δd(excess) were also calculated by assuming that the changes in salinity due to the added solids affect the density by the same amount as changes in weight‐diluted standard seawater: 106Δd= 757ΔS(‰). The values of Δd(excess) calculated from 106Δd(excess) = 37.9ΔAT+ 72.8ΔSiO2+ 47.7ΔNO3agree with the measured values on the average to ±4.3 × 10−6g cm−3, independent of the depth. These results indicate that the density changes due to small changes in the composition of deep ocean waters can be accounted for by changes in the salinity due to the mass of added dissolved solids (ΔS(‰) = ΣMiΔni, whereMiis the equivalent or molecular weight and Δni

ISSN:0148-0227    

DOI:10.1029/JC083iC05p02359

年代:1978

数据来源: WILEY

摘要:

Synoptic data on near‐surface and near‐bottom currents for two 1‐month periods are analyzed for six stations located 3.5–7 km offshore. Tidal currents are rotary with long ellipse axes approximately parallel to the shoreline and are nearly synchronous. On the basis of amplitude the seven largest constituents of the currents were identified asM2,S2,N2,K1,O1,J1, andSO1. Maximum tidal current speed decreases with distance to the south away from the entrance to Chesapeake Bay. Near the bottom, tidal currents at spring strength decrease from 32.4 cm/s at the entrance to 8.2 cm/s at a point 22 km to the south. Near‐bottom tidal currents are incompetent by themselves to move fine sand except in the entrance area. Forty‐hour low‐pass currents are generated by winds and by sea surface slopes. They reach peak speeds near the surface of 48 cm/s in events of up to 6 days' duration. In summer a strong pycnocline inhibits downward propagation of these high‐speed surface currents. In the fall the surface currents penetrate more readily to the bottom. Winds to the south in summer generate stronger currents than winds to the north having the same speed. Seasonal variations in wind regimes and corresponding currents seem to require a strong south slope to the sea surface in summer and a very gentle slope to the north in the fall. Waves entrain the bed sediment 60–83% of the time in depths of 8–13 m. With a threshold taken at 20 cm/s, only the south‐directed low‐pass currents supplement the incompetent tidal currents so as to produce sediment transport. Threshold exceedance in 8–13 m occurs 1–2% of the time under south‐flowing low‐pass currents in summer and 3–5% of the time under southerly low‐pass currents in the fall. At 15 m the transport threshold was not reached during the observation period. A coastwise parallel stream of intermittent bed sediment transport is thus defined. The frequency of exceedance decreases to the south away from the entrance area. This decrease is consistent with the seaward bulging configura

ISSN:0148-0227    

DOI:10.1029/JC083iC05p02365

年代:1978

数据来源: WILEY

摘要:

In 1953, G. I. Taylor showed that longitudinal dispersion of matter in a pipe can be represented by a one‐dimensional dispersion equation and derived the magnitude of a coefficient to represent the effect of the shear flow. Taylor's analysis is extended to a shear flow in which the velocity vector rotates with depth but is horizontally homogeneous. We show that horizontal dispersion can be represented by a two‐dimensional equation in which a tensor coefficient represents the effect of the vertical shear. The terms in the tensor are derived for an approximation to the mean flow on the Middle Atlantic Bight of the U.S. Atlantic continental sh

ISSN:0148-0227    

DOI:10.1029/JC083iC05p02373

年代:1978

数据来源: WILEY

摘要:

A solution is presented for the electromagnetic fields radiated by an arbitrarily oriented current filament over a conducting ground plane in the case where the current propagates along the filament at the speed of light, and this solution is interpreted in terms of radiation from lightning return strokes. The solution is exact in the fullest sense: no mathematical approximations are made, and the governing differential equations and boundary conditions are satisfied. The solution has the additional attribute of being specified in closed form in terms of elementary functions. This solution is discussed from the point of view of deducing lightning current wave forms from measurements of the electromagnetic fields and understanding the effects of channel tortuosity on the radiated fields. In addition, it is compared with two approximate solutions, the traditional moment approximation and the Fraunhofer approximation, and a set of criteria describing their applicability are presented and interpreted.

ISSN:0148-0227    

DOI:10.1029/JC083iC05p02377

年代:1978

数据来源: WILEY

摘要:

Multistation electric field change measurements have confirmed earlier findings that lightning ground strokes in the Hokuriku winter storms generally lower positive charge to earth. Only one out of eight flashes involved the ‘normal’ negative strokes commonly found in summer storms. The mode of discharge appears to favor the continuing current type: eight out of twelve strokes to ground were followed by a continuing current. Despite the ‘abnormal’ stroke polarity, the Hokuriku storms appear to exhibit a normal dipolar structure (positive charge uppermost), although the dipole is apparently severely tilted in the direction of the wind shear. A crude estimate of charge height based upon one negative cloud‐to‐ground flash and one positive flash locates the negative charge below the positive charge in a cloud system whose bases are at 400 m and radar tops are at 7.5 km. The reason for the occurrence of dominantly positive return stroke flashes in these winter storms rema

ISSN:0148-0227    

DOI:10.1029/JC083iC05p02385

年代:1978

数据来源: WILEY

摘要:

Previous studies of the effect of water vapor on the destruction of ozone in the stratosphere perturbed by NOxor ClX pollutants did not include temperature feedback effects (i.e., they assumed a fixed temperature profile). These studies indicated that if an increase in stratospheric water vapor concentration were induced (perhaps as a result of an increase in the temperature of the tropical tropopause caused by a change in stratospheric ozone), there would be a significant further reduction in total ozone. Our results from using a one‐dimensional transport kinetics model with a fixed temperature profile confirm these earlier findings. However, when the temperature profile is allowed to change as the species concentrations change, the sensitivity of total ozone to changes in water vapor abundance is greatly reduced. In the case of an NOxinjection at 20 km there is even a reversal of sign such that an increase in stratospheric water vapor leads to an ozone increase relative to the case with no change in water vapo

ISSN:0148-0227    

DOI:10.1029/JC083iC05p02395

年代:1978

数据来源: WILEY

摘要:

Stratospheric aerosol measurements have been made by laser radar at São José dos Campos (23°S, 46°W) since July 1970. From 1970 to 1974 the measured scattering ratios for the 20‐km layer were similar to those reported for other locations. A large increase was observed in April 1975, 6 months after the eruption of Volcán de Fuego in Guatemala. This delay in the transport of the Fuego dust to our latitude is interpreted as being due to the inhibition of southward eddy transport during the southern summer by the mean meridional circulation. A maximum monthly average scattering ratio of 1.28 measured at a wavelength of 5890 Å was observed at 20 km in August 1975. Since early 1976 the 20‐km scattering ratio has oscillated around a value of about 1.15, but the integrated columnar backscattering coefficient above 17 km, indicative of the total stratospheric dust loading, has increased by about 40%. Scattering from the upper stratosphere, at heights above 30 km, was observed in the southern springs of 1971, 1972, and 1973. There appears to be some evidence that the dust responsible for this scattering was of extraterrestri

ISSN:0148-0227    

DOI:10.1029/JC083iC05p02403

年代:1978

数据来源: WILEY