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<br />Page 28 <br /> <br />2. Transport and Diffusion Missions <br /> <br />The release of SF6 will be from either the ground or from an <br />aircraft. The ground release sites are expected to be one of the <br />places where a highway crosses the Black Hills or along a highway <br />crest northwest of Payson. Aircraft releases will be along either <br />the 55 or 60 n.mi. DME arc from the Winslow VORTAC between <br />radials appropriate for a wind direction to carry the tracer <br />material towards Happy Jack. The determination of the <br />appropriate radials will be made by the aircraft scientist in <br />the instrumented aircraft. <br /> <br />For ground releases the aircraft will proceed to a position <br />over the foothills west of Happy Jack for a number of passes <br />perpendicular to the wind direction at a series of <br />finely-stepped altitudes to document the vertical extent and <br />cross-sectional shape of the plume at that location. The <br />aircraft will then proceed to the Happy Jack region for a <br />similar series of crosswind passes and altitude steps. <br /> <br />For aircraft releases the plume will approach the target area <br />in a zig-zag pattern, possibly rising in altitude. The <br />instrumented aircraft will fly a series of finely-stepped <br />altitudes parallel to the wind from Happy Jack to either the <br />