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Abstract
About 700 cases of wind direction meander occurred in a three-year period during onshore flow at a Long Island coastal site. Most appeared to be caused by internal gravity waves but some by roll vortices. Each case was documented with respect to date, time, wind speed, wind direction and stability, and described by duration, number of waves, angular amplitude and period. Hourly wind data for the same years were examined to determine the frequency of onshore flows.
Most meander cases occurred in spring and summer, at low to moderate wind speeds and with stable conditions over the ocean. Duration varied from 4 to 438 min and averaged 94 min. The number of half-waves per case varied from 4 to 63 and averaged 10. Frequency varied from 0.3 to 30 with a mean of 4 waves per hour. Mean angular amplitude ranged from 4 to 68 and averaged 14°. Maximum amplitudes as large as 125° occurred. Results were compared to σy data from oil-fog smoke diffusion experiments. Calculations show that horizontal dispersion caused by a combination of meander and turbulent diffusion can be more than 30 times greater than that caused by diffusion alone and averaged 4 times greater. However, meander with angular amplitudes greater than 3° occurred only 15% of the time during onshore flow even though the air over the ocean was stable 59% of the time. Thus, the presence of significant meander cannot be assumed for diffusion calculations, although diffusion measurements indicate that minor meanders are frequent during stable conditions.
Abstract
About 700 cases of wind direction meander occurred in a three-year period during onshore flow at a Long Island coastal site. Most appeared to be caused by internal gravity waves but some by roll vortices. Each case was documented with respect to date, time, wind speed, wind direction and stability, and described by duration, number of waves, angular amplitude and period. Hourly wind data for the same years were examined to determine the frequency of onshore flows.
Most meander cases occurred in spring and summer, at low to moderate wind speeds and with stable conditions over the ocean. Duration varied from 4 to 438 min and averaged 94 min. The number of half-waves per case varied from 4 to 63 and averaged 10. Frequency varied from 0.3 to 30 with a mean of 4 waves per hour. Mean angular amplitude ranged from 4 to 68 and averaged 14°. Maximum amplitudes as large as 125° occurred. Results were compared to σy data from oil-fog smoke diffusion experiments. Calculations show that horizontal dispersion caused by a combination of meander and turbulent diffusion can be more than 30 times greater than that caused by diffusion alone and averaged 4 times greater. However, meander with angular amplitudes greater than 3° occurred only 15% of the time during onshore flow even though the air over the ocean was stable 59% of the time. Thus, the presence of significant meander cannot be assumed for diffusion calculations, although diffusion measurements indicate that minor meanders are frequent during stable conditions.
Abstract
A study of the atmospheric transport and diffusion climatology of the United States east and Gulf coasts was conducted to aid in planning and site selection for potentially polluting installations. This paper presents selected results from an extensive statistical study. Regular hourly observational data were obtained from 30 coastal stations from Maine to Texas and analyzed in terms of conditions important to emission transport and diffusion. The 30 stations included four pairs with one of each pair at a greater distance from the coast than the other but near the same latitude.
For each station, wind directions were classified into eight groups with reference to orientation of the local coastline. For some studies, fewer classes were desirable and these were combined into three groups—onshore, alongshore and offshore. Wind speeds were divided into four classes. A stability class for each observation was computed by a modified Pasquill method. This gave eight classes which were combined into three—unstable, neutral and stable—for some studies. Diffusion ratings ranging from very good to very poor were derived from combinations of wind speed and stability classes. Finally, the joint frequency distributions of wind direction and diffusion rating were calculated for each station. Data were then classified by season, time of day, wind direction, wind speed, stability class and combinations of these variables, and the percent of hours in each subgroup determined.
Onshore winds were least frequent along the New England and Mid-Atlantic coasts except from Cape Cod to New York City and along the west coast of Florida. Onshore winds were most frequent along the east coast of Florida and the Texas coast. Poor diffusion conditions occurred most frequently from the Carolinas to the Florida east coast and along the northern Gulf Coast. At all stations, diffusion conditions were better during the day than at night. Among the paired stations, the more inland had a greater frequency of poor diffusion hours than the one nearer the coast.
Abstract
A study of the atmospheric transport and diffusion climatology of the United States east and Gulf coasts was conducted to aid in planning and site selection for potentially polluting installations. This paper presents selected results from an extensive statistical study. Regular hourly observational data were obtained from 30 coastal stations from Maine to Texas and analyzed in terms of conditions important to emission transport and diffusion. The 30 stations included four pairs with one of each pair at a greater distance from the coast than the other but near the same latitude.
For each station, wind directions were classified into eight groups with reference to orientation of the local coastline. For some studies, fewer classes were desirable and these were combined into three groups—onshore, alongshore and offshore. Wind speeds were divided into four classes. A stability class for each observation was computed by a modified Pasquill method. This gave eight classes which were combined into three—unstable, neutral and stable—for some studies. Diffusion ratings ranging from very good to very poor were derived from combinations of wind speed and stability classes. Finally, the joint frequency distributions of wind direction and diffusion rating were calculated for each station. Data were then classified by season, time of day, wind direction, wind speed, stability class and combinations of these variables, and the percent of hours in each subgroup determined.
Onshore winds were least frequent along the New England and Mid-Atlantic coasts except from Cape Cod to New York City and along the west coast of Florida. Onshore winds were most frequent along the east coast of Florida and the Texas coast. Poor diffusion conditions occurred most frequently from the Carolinas to the Florida east coast and along the northern Gulf Coast. At all stations, diffusion conditions were better during the day than at night. Among the paired stations, the more inland had a greater frequency of poor diffusion hours than the one nearer the coast.
Abstract
Dispersion and deposition of ragweed pollen released naturally from circular area sources of four sizes (5–27 m in diameter) and artificially from point sources were studied at Brookhaven National Laboratory. Concentrations were measured by wind-impaction samplers mounted on 20° radii at four heights (0.5–4.6 in) and four or five distances from the sources to a maximum of 69 m. Deposition was measured by greased microscope slides on the ground. Differences in dispersion patterns between point and area sources are analyzed. Normalized centerline concentrations, cross-wind integrated concentrations, plume widths, plume heights and mass flux are presented as functions of distance and related to source size and meteorological variables. Deposition data are also related to distance and source size. Most deposition velocities ranged from 2–6 cm sec−1 but values close to area sources were much greater. Loss of airborne particles between sampling circles is compared to deposition over the same distances. Results are compared to those of previous dispersion and deposition studies and to theory.
Abstract
Dispersion and deposition of ragweed pollen released naturally from circular area sources of four sizes (5–27 m in diameter) and artificially from point sources were studied at Brookhaven National Laboratory. Concentrations were measured by wind-impaction samplers mounted on 20° radii at four heights (0.5–4.6 in) and four or five distances from the sources to a maximum of 69 m. Deposition was measured by greased microscope slides on the ground. Differences in dispersion patterns between point and area sources are analyzed. Normalized centerline concentrations, cross-wind integrated concentrations, plume widths, plume heights and mass flux are presented as functions of distance and related to source size and meteorological variables. Deposition data are also related to distance and source size. Most deposition velocities ranged from 2–6 cm sec−1 but values close to area sources were much greater. Loss of airborne particles between sampling circles is compared to deposition over the same distances. Results are compared to those of previous dispersion and deposition studies and to theory.
Abstract
Pollen transport and dispersion from generalized area sources was studied by 29 flights to distances of 100 km and heights of 3 km using an aircraft-mounted isokinetic sampler. Tree pollens and ragweed pollen served as tracers. Four types of flights were made to study various aspects of pollen transport: 1) ascents over a fixed location to investigate vertical distribution; 2) flights over a source-free area to document change of concentration with distance, 3) east-west flights along Long Island to study the influx of pollen from the mainland with westerly winds; and 4) vertical ascents and horizontal flights during sea breeze flows to determine their effect on pollen concentrations.
It was found that large quantities of pollen are transported in orderly fashion from their source regions but pollen often travels in large, discrete clouds. Pollen is transported to Long Island from the mainland in some quantity. Sea breeze flows greatly decrease low-level concentrations but pollen is carried aloft at the sea breeze front and recirculated in the return flow aloft. Vertical distribution is reasonably well related to lapse rate although secondary concentration peaks which often occur below elevated inversions cannot be explained by the data obtained.
Abstract
Pollen transport and dispersion from generalized area sources was studied by 29 flights to distances of 100 km and heights of 3 km using an aircraft-mounted isokinetic sampler. Tree pollens and ragweed pollen served as tracers. Four types of flights were made to study various aspects of pollen transport: 1) ascents over a fixed location to investigate vertical distribution; 2) flights over a source-free area to document change of concentration with distance, 3) east-west flights along Long Island to study the influx of pollen from the mainland with westerly winds; and 4) vertical ascents and horizontal flights during sea breeze flows to determine their effect on pollen concentrations.
It was found that large quantities of pollen are transported in orderly fashion from their source regions but pollen often travels in large, discrete clouds. Pollen is transported to Long Island from the mainland in some quantity. Sea breeze flows greatly decrease low-level concentrations but pollen is carried aloft at the sea breeze front and recirculated in the return flow aloft. Vertical distribution is reasonably well related to lapse rate although secondary concentration peaks which often occur below elevated inversions cannot be explained by the data obtained.
