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e VII. TREATMENT DESIGN ..e A. Targeting As noted in section VI, seeding effects are directed at a designated target area (fig. 6-1). To simplify operational procedures, seeding effects are directionally targeted whenever possible on Hell Hole Reservoir, which is in the east-central part of the target area. This target point serves only as an operational aid. If there are no clouds suitable for seeding upwind of Hell Hole Reservoir but there are suitable clouds upwind of other parts of the target area, those clouds are seeded. B. Experimental Unit Declaration 1. -Summary In order for an experimental unit to be declared, a number of condi- tions must be satisfied. The conditions are shown in a flow chart in figure 7-1. First, the project must not be under suspension for any reason related to potential weather hazards in the region (section VII-F). Second, the required instrumentation shown in table 7-1 must be func- tioning. Assuming that these two requirements are met, the Operations Director determines on the basis of the available data whether or not the weather situation justifies launching aircraft to investigate the clouds in the area. The decision to launch is based mainly on radar observations and cell motion criteria and on the anticipated duration of the conditions (table 7-2). After launch, the aircraft sample convective cells in the formation zone to determine whether their si ze and "seedabil ity" sati sfy the criteria of table 7-2. If they do so, and if a final check shows all required instruments are still functioning, an experimental unit is declared. The following sections discuss the various steps in the process. 2. PET Criteria It is required that in the region where the preclassification is con- ducted, i.e., the formation zone, that the radar detect no echo. However, echoing cloud will exist downwind of this region which will provide the information on PET classification. . The appropri ate PET must be present. If there are echoes on the radar, they must have been categorized as Cl or C2 echoes by the seeding coordi- nator. The Cl and C2 echo categories are identified by evaluating the character and coverage of radar reflectivity in the American River Basin. If a pattern of convective elements exists as individual cells or clusters of cells which covers more than one-half of the area affected, the PET is classified as C2. The PET is classified as Cl if the pattern covers less than one-half the area. Coverage refers to the region of convective activity, not the entire area of the American River Basin. If the char- acter of the echo indicates that convection is likely but the echo appears somewhat homogeneous, soundings will be used to evaluate stability. If 23