Climatology of Transport and Diffusion Conditions along the United States Atlantic and Gulf Coasts

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.