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<br />blocking ridge is to ascend the blocking topography. A plume of seeding <br />material approaching the ridge may have portions of its material trapped <br />in the lower layers while other portions are caught in the ascending <br />airflow and transported over the ridge. With valley channeling the <br />oncoming airflow may be channeled by the surrounding walls of the main <br />valley, yet, interacting with the airflow from minor tributary valleys. <br />In this case, a plume of seeding material may be trapped and channeled <br />in the valley but with portions of it escaping the top of valley due to <br />mechanical and convective turbulence and stability. With the isolated <br />or singular mountain, a substantial portion of the oncoming airflow is <br />forced to diverge and flow around the obstacle instead of over it. A <br />plume of seeding material may be affected in the same manner but with <br />portions of the material ascending the summit of the mountain. <br />All three terrain types may be found in the western United States. <br />In Colorado, the Eagle River Valley and Climax-Leadville area located <br />in the Central Rocky Mountains and the San Juan Mountains in southern <br />Colorado are good examples of all three types. The Elk Mountain area <br />of southern Wyoming is a good example of a singular mountain. <br />The previous discussion indicated that the spatial distribution of <br />a particulate plume over mountainous terrain is affected by numerous <br />variables, e.g., <br /> <br />iI <br /> <br />--+ -+ -+ -+ <br />C(r) = f(Q,w ,T ,h ,V,H,Z,A,f,U(z),U ,S,K.,t T) <br />s ssg 1, <br /> <br />These variables can be categorized under the four previous <br />principal headings as follows: <br /> <br />2-2 <br /> <br />~ <br /> <br />Source characteristics <br />Q,w ,T ,h <br />s s s <br /> <br />Depletion mechanisms <br /> <br />Gravitational settling <br />Precipitation scavenging <br />Surface impaction <br />Electrostatic attraction <br />Adsorption <br />Coagulation <br />Chemical interaction <br />Ultraviolet decomposition <br />Resuspension and redeposition <br /> <br />v <br /> <br />Atmospheric motions <br /> <br />Mean flow Turbulence <br />-+ -+ <br />f,U(z),U ,T S,K.,t <br />g 1 <br /> <br />Boundary Conditions <br />-+ <br />Z,H,A <br /> <br />A schematic illustration of these various parameters and the role <br />they play in transport and dispersion over irregular terrain is shown <br />in Fig. 2-1. <br /> <br />~, <br /> <br />16 <br />