摘要:

Neon, argon, and krypton were measured in an air sample collected between 43.6‐ and 62.3‐km altitude with a rocket‐borne cryogenic air sampler. Concentrations of these noble gases in this high‐altitude air sample, as determined by isotope‐dilution mass spectrometry, were identical to their concentrations in dry surface air, within experimental error limits of several per mille. These experimental results confirm expectations that the atmosphere is very well mixed up to, and within, the lower mesosphere, having no observable degree of gravitational separation. The results also establish that air sampling by intake through a simple normal shock diffuser at supersonic speeds and condensation at low temperatures provides undifferentiated samples and permits the quantitative recovery of the noncondensable tr

ISSN:0148-0227    

DOI:10.1029/JC075i033p06731

年代:1970

数据来源: WILEY

摘要:

A successful flight of a recoverable payload designed to collect particles from a noctilucent cloud was made on August 1, 1968, at 0410 local daylight time (0910 UT), from Fort Churchill, Canada. Photographs obtained by project observers at Thompson, Canada, 400 km south‐west of Churchill, showed that the noctilucent cloud was over the launch site at the time of flight. Electron microscope examinations of collecting surfaces exposed above 60 km showed about 6000 particles/cm2of a certain type on surfaces facing the flight direction. Few of these particles were found on nonflight control surfaces. Most of the particles range in size from 0.1–0.2 μ and do not exhibit features suggesting that any liquid was associated with them. The shape of these particles is generally equant, often rod‐like, subrounded to rounded; the particles are moderately dense to electrons, show internal structure, and have occasional protuberances. Considerable variation of particle concentration was observed from one flight surface to the next. Flight surfaces show some damage from aerodynamic heating. Thus, caution is necessary in applying these findings pending confirmatory sounding rocket flights through noctilucent clouds. Evidence from this flight, from previous rocket and satellite flights, and theoretical studies suggests that the noctilucent cloud particles are uplifted from lower altitudes and could have a terrestrial as well as cosmic

ISSN:0148-0227    

DOI:10.1029/JC075i033p06736

年代:1970

数据来源: WILEY

摘要:

On August 1, 1968, a rocket flight above Fort Churchill, Canada, collected cosmic dust in the mesosphere and in the upper atmosphere. The rocket was launched at 0410 LT (0910 UT) during the presence of a weak noctilucent cloud display. Several collectors were exposed between 60‐ and 113‐km altitude. The collectors in our module provided the following results: (1) A low number of penetration holes was recorded; (2) 100 particles/mm2were collected on the surfaces in the size range between 0.1 and 0.25 μ diameter. These results are interpreted in two ways: (1) as noctilucent cloud particles, leading to a particle number density of about 0.1 particles/cm3in the noctilucent clouds; and (2) as noncloud particles collected preferably between 60‐ and 70‐km altitude. Fluxes were calculated and have the followin

ISSN:0148-0227    

DOI:10.1029/JC075i033p06751

年代:1970

数据来源: WILEY

摘要:

The drag coefficient of the sea surface has been measured with a telemetering thrust anemometer on a stable platform. The mean value for 32 runs,C10= 1.35 × 10−3± 0.34 × 10−3is believed to be representative of open‐sea conditions. No significant variation of the drag coefficient with wind speeds from 7 to 16 m/sec is detected. Downwind‐vertical quadrature spectra are consistently negative between 0.

ISSN:0148-0227    

DOI:10.1029/JC075i033p06758

年代:1970

数据来源: WILEY

摘要:

Spectra of air pressure and wind were obtained that cover a frequency range from 10−4to 102Hz during both day and night with and without a corn crop. The pressure spectra were very similar to those previous workers obtained by different methods under different conditions. The spectral density for pressure decreased with approximately the −6/3 power of frequency for all conditions from about 108to 10−3μbar2/Hz over the entire frequency range. The corn crop had no obvious effects on the spectra, but the magnitude of the curves was strongly correlated with surface wind speed, at least for frequencies higher than 10

ISSN:0148-0227    

DOI:10.1029/JC075i033p06771

年代:1970

数据来源: WILEY

摘要:

By using known results on the radiation stress associated with gravity waves, the total lateral thrust exerted by incoming waves on the beach and in the nearshore zone is rigorously shown to equal (E0/4) sin 2θ0per unit distance parallel to the coastline, whereE0denotes the energy density of the waves in deep water and θ0denotes the waves' angle of incidence. The local stress exerted on the surf zone in steady conditions is shown to be given by (D/c) sin θ per unit area, whereDis the local rate of energy dissipation andcis the phase velocity. These relations are independent of the manner of the energy dissipation, but, because breaker height is related to local depth in shallow water, it is argued that ordinarily most of the dissipation is due to wave breaking, not to bottom friction. Under these conditions the local mean longshore stress in the surf zone will be given by (5/4)ρumax2ssin θ, where ρ is the density,umaxis the maximum orbital velocity in the waves,sis the local beach slope, and θ is the angle of incidence. It is further shown that, if the friction coefficientCon the bottom is assumed constant and if horizontal mixing is neglected, the mean longshore component of velocity is given by (5π/8)(s/C)umaxsin θ. This value is proportional to the longshore component of the orbital velocity. When the horizontal mixing is taken into account, the longshore currents observed in field observations and laboratory experiments are consistent with a friction coefficient of abo

ISSN:0148-0227    

DOI:10.1029/JC075i033p06778

年代:1970

数据来源: WILEY

摘要:

The profile of the longshore current, as a function of distance from the swash line, is calculated by using the concept of radiation stress (introduced in an earlier paper) together with a horizontal eddy viscosity μeof the form μe= ρNx(gh)1/2, where ρ is the density,xis the distance offshore,gis gravity,his the local mean depth, andNis a numerical constant. This assumption gives rise to a family of current profiles whose form depends only on the nondimensional parameterP= (Π/2)(sN/αC), wheresdenotes the bottom slope, α is a constant characteristic of breaking waves (α ≑ 0.41), andCis the drag coefficient on the bottom. The current profiles are of simple analytic form, having a maximum in the surf zone and tending to zero at the swash line. Comparison with the laboratory experiments of Galvin and Eagleson (1965) shows remarkably good agreement if the drag coefficientCis taken as 0.010. The theoretical profiles are insensitive to the exact value ofP, but the experimental results suggest thatPnever exceeds a critical val

ISSN:0148-0227    

DOI:10.1029/JC075i033p06790

年代:1970

数据来源: WILEY

摘要:

The problem of tsunami generation is treated by a numerical method utilizing the governing hydrodynamic equations of motion and continuity and a time‐dependent description of bottom motion. The ground‐motion model preserves the essential features of a real seismic event, including both horizontal rupture and vertical displacement with associated time scales. The vertical bottom displacement is coupled through the continuity equation to surface water elevation, and a finite difference scheme follows the development of the wave system. An example, the Alaskan Good Friday earthquake of 1964, is shown in some detail, and computations are compared with observations. The approach appears to be capable of accurate description of tsunami generation, limited only by uncertainties in tectonic input. It is also capable of accurate propagation calculations, limited by computer s

ISSN:0148-0227    

DOI:10.1029/JC075i033p06802

年代:1970

数据来源: WILEY

摘要:

A turbulent buoyant jet operating in a linearly stratified fluid is investigated. By requiring similarity forms for the velocity, density difference, and shear stress and by adopting an integral representation of the governing equations, the rate of entrainment of ambient fluid into the plume is found to be an explicit function of the dependent variables. The entrainment is a function of the Reynolds stress, the form of the similarity profiles, and the local mean densimetric Froude number. The Reynolds stress term is shown to be related to the constant obtained if the entrainment rate is assumed to be proportional to the mean centerline velocity. A critical parameter of the analysis is the ratio of the form of the velocity profile to the form of the density difference profile. Values of this parameter near unity seem most appropriate. Numerical solutions are compared with experimental results to suggest values for the Reynolds stress term.

ISSN:0148-0227    

DOI:10.1029/JC075i033p06818

年代:1970

数据来源: WILEY

摘要:

Data illustrating seasonal changes in temperature and salinity profile beneath an annual sea ice cover are presented. The water column heat loss is about 15% of the latent heat extracted for ice growth. Time series temperatures (measured over one month with a thermistor chain depending from the ice sheet) indicate penetrative convective plumes as a probable mechanism for profile changes and are tentatively related to laboratory studies.

ISSN:0148-0227    

DOI:10.1029/JC075i033p06836

年代:1970

数据来源: WILEY