摘要:

Analytical solutions to the cloud charge screening‐layer model of Brown et al. are obtained for planar, cylindrical, and spherical cloud geometries. Two specifications of the negative ion concentrationn−at the surface of a positively charged cloud, representing upper and lower approximations to the actual supply of ions, are employed: (1)n−=n0= constant, and (2)n−decays with timetapproximately as (1 + αt)−1, where α is constant. The latter form forn−comes from a model that allows for space charge divergence outside the cloud but ignores ionization and recombination. In mksa units the maximum (saturation) space charge is found to be (4/e2) (ε0E0/λ0), wheree= 2.718 …, ε0is the permittivity of air,E0is the initial cloud electric field, and λ0is the mean free path of ions in an uncharged cloud (typically, λ0= 10 meters). The surface electric field when the cloud particles first become saturated isE0/e2, and the final depth of the saturated layer is λ0/4. If the relaxation time of the surface electric field for the first case is τ (typically 40 sec), then the relaxation time for the second case is 1.94 τ. The screening‐layer formation time (i.e., the time required for the surface screening‐layer charge density to be withine−1of its saturation value) is 0.49 τ in the first case and 0.67 τ in the second. Brown et al. obtained numerical solutions for the field and screening charge density as a function of time and depth for the special case of a flat layer cloud withn−=n0at the surface. The agreement between their results and ours for t

ISSN:0148-0227    

DOI:10.1029/JC077i018p03187

年代:1972

数据来源: WILEY

摘要:

Measurements of total air‐earth current and conduction current in conditions of fair weather reveal the existence of a component current of charges to earth caused by the mechanical effects of local air movements; this mechanical‐transfer current is of the same magnitude as the conduction current and almost entirely governs the diurnal variation of the total air‐earth current. The interpretation of variations of total current in terms of global atmospheric electrical conditions is therefore open to grave doubt. New evidence of the influence of the electrode effect at a land station within the austausch region supports the notion of a mechanical‐transfer current, and some characteristics of total air‐earth currents in precipitation are explained using the same concept. The use and performance of an exposed plate as a receiver of air‐earth current i

ISSN:0148-0227    

DOI:10.1029/JC077i018p03196

年代:1972

数据来源: WILEY

摘要:

Atmospheric CO was measured with the aid of instrumented aircraft operating in the vicinity of the tropopause and in the lower stratosphere. In confirmation of previous measurements the CO mixing ratio was found to decrease above the tropopause. From the observed gradients the size of the stratospheric CO sink can be calculated. Above the mixing region adjacent to the tropopause the CO mixing ratio assumes a new constant value of about 0.04 ppm. The stratospheric CO value is interpreted as the balance between the production by oxidation of hydrocarbons (e.g., methane) and the consumption by reaction with OH radicals. The steady‐state CO mixing ratio and the OH radical concentration required to provide the observed stratospheric CO sink are in satisfactory agreement with a recent model by McConnell et al. (1971

ISSN:0148-0227    

DOI:10.1029/JC077i018p03204

年代:1972

数据来源: WILEY

摘要:

Wind and current observations made over the continental shelf off Oregon in the summer of 1969 are compared. It is demonstrated that the wind and current are related at periods longer than 2 days. The wind and current data are both filtered to suppress variations of diurnal and higher frequencies. The current behaves similarly to the wind when the wind varies slowly. The amplitude of the current fluctuations seems to depend on the stratification of the water. The current is roughly parallel to the local bottom contours.

ISSN:0148-0227    

DOI:10.1029/JC077i018p03215

年代:1972

数据来源: WILEY

摘要:

Laboratory fogs were generated under controlled and reproducible conditions in a 600‐meter3chamber and seeded with aerosols of various compounds that form organic surface films at air‐water interfaces. The fogs were programmed through several slow expansions and compressions to assure adequate time to permit the coating of the fog drops with a surface film and to avoid nucleation on aerosols of the surface active material. Visibility characteristics and droplet data were obtained for both seeded and control fogs. Cetyl alcohol stabilized fogs significantly during compressions and periods of constant pressure. This observation was substantiated by measurements of visibility, drop size, drop concentration, and liquid water content of the fogs. The cetyl alcohol, a linear molecule, formed tightly packed surface films around the fog drops, which inhibited the transport of water molecules across the water‐drop‐air interface and thereby appreciably retarded the evaporation rate of the fog droplets. Oleyl alcohol, a nonlinear molecule, formed fluid surface films that did not retard evaporation or alter fog visibility. The data suggest that droplet growth on treated nuclei can be retarded but that under the controlled conditions of these experiments fog formation was not significantly altered by the chemical seeding. It is concluded that additional experiments designed to limit natural fog formation with evaporation retardants are not warranted. In the natural atmosphere the release of organic compounds from human activity may cause inadvertent cloud and fog stabilization; the determination of the chemistry and physics of this process represents an important and relatively unexplored area of environmental

ISSN:0148-0227    

DOI:10.1029/JC077i018p03221

年代:1972

数据来源: WILEY

摘要:

Field observations were made of wave‐induced nearshore circulations and meandering longshore currents on an undulatory surf‐zone bed, under the action of uniform incident waves. Circulations were associated with normal‐wave incidence; meandering currents were associated with oblique‐wave incidence. The transport in the observed circulations generally agreed with Bowen's (1967) linear theory based on the concept of radiation stress (Longuet‐Higgins and Stewart, 1962, 1964), provided that a friction coefficientC= 0.014 was assumed. The longshore current near the shore line moved from a shoal to a depression as predicted, but this movement was also directed from an area of high waves to one of low waves, which is different from the case of a circulation driven by nonuniform breaker heights on the bar. Spilling breakers over a shoal underwent greater energy dissipation than plunging breakers in the rip current. Observed streamlines were narrow in the outflow and broad in the inflow, a characteristic that was probably associated with a nonlinear mechanism arising from a steep depression in the rip channel, as previously explained by Arthur (1962). These circulations were pulsational, unlike the circulations of a steady‐state solution. Occasional strong outflows at beat frequencies caused water to escape from the circulation. For a given surf‐zone undulation, breaking over the inner bar was essential to the formation of a circulation, and the intensity of breaking, controlled by tide, corresponded with a proportionally stronger circulation. Thus, circulations were generally stronger during low tide than during high tide. Low rip‐current velocities at high tide fluctuated with incoming swells, whereas high velocities at low tide tended to fluctuate at surf beat frequencies. In proportion to increasing rip velocities, the rip pulsation tended toward lower intervals. Mean surface slopes caused by wave set‐up and set‐down agreed with trajectories of neutral‐density balls released in the circulation. Meandering currents associated with oblique‐wave incidence could be explained as a combined effect of circulation cells and p

ISSN:0148-0227    

DOI:10.1029/JC077i018p03232

年代:1972

数据来源: WILEY

摘要:

Entrainment of relatively cold low‐salinity water by the Gulf Stream and subsequent formation of a cold filament adjacent to the northern edge of the Gulf Stream were frequently observed during a series of combined ship and aircraft surveys conducted north‐eastward of Cape Hatteras between October, 1968, and May, 1969. Particularly well‐defined entrainment was observed during mid‐May, 1969 when a band of surface water 10 to 15 km wide and 40 meters thick was observed to reach from the continental shelf to the northern edge of the Gulf Stream. Transport seaward from the outer shelf is of the magnitude 104m3/sec. Failure to observe entrainment during some of the flights agrees with the discontinuous nature of the cold filament adjacent to the northe

ISSN:0148-0227    

DOI:10.1029/JC077i018p03248

年代:1972

数据来源: WILEY

摘要:

Concentration‐time models for90Sr in the Great Lakes deal with transient concentrations of a radionuclide in a chain of mixed lakes and in a chain of periodically stratified lakes. In the model, the lakes receive time‐dependent input of90Sr from atmosphere and land (0–10% of annual deposit in the land drainage basins). Removal of90Sr from lake water is by outflow and decay. In the five Great Lakes computed concentrations of90Sr rise from nil (assumed) in 1953 to a maximum in 1964–1965, followed by a gradual decline until 1969. Computed concentrations are comparable to the range of reported values. However, a closer agreement between the model and reported concentrations requires the rates of input in 1962–1964 to be higher than the mean, as well as the rates of removal to be faster (by 6–8%) than the removal by decay and mean outflow. Seasonal stratification of the lakes has virtually no effect on mean annual concentrat

ISSN:0148-0227    

DOI:10.1029/JC077i018p03256

年代:1972

数据来源: WILEY

摘要:

This brief report predicts the variation of surface temperature induced by a plane progressive irrotational linear water wave when a thermal boundary layer exists. The following conclusions are drawn. (1) When the wave period is sufficiently small (≲3 sec), the amplitude of the wave‐induced temperature fluctuation is proportional to the wave amplitude and to the square root of the wave period. This result is in perfect agreement with experiments that, however, are by no means definitive. (2) Surface temperature maximums lead wave crests by one‐eighth of a period when the average surface temperature is less than the bulk water temperature; surface temperature minimums lead wave crests by one‐eighth of a period when the average surface temperature exceeds that of the wate

ISSN:0148-0227    

DOI:10.1029/JC077i018p03265

年代:1972

数据来源: WILEY

摘要:

Aircraft temperature data are presented that contain evidence of convective plumes filled with relatively cool air. It is suggested that this phenomenon occurs when warm unstable air moves over a cool irrigated area.

ISSN:0148-0227    

DOI:10.1029/JC077i018p03270

年代:1972

数据来源: WILEY