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3. 1994 FACILITIES AND INSTRUMENTATION 3.1 Seeding Sites Two high-altitude seeding sites will be used. One will be the HAS (High Altitude Site) used in 1991 at an elevation of 2500 m. The other seeding site will be the AHS (Aspen Hills Site) about 5 km south of HAS at 2350 m elevation. Each site will be equipped with a Desert Research Institute (DRI) remote-controlled AgI generator, a remote-controlled propane dispenser and a remote-controlled mass flow controller for dispensing SF6 tracer gas. Each site will have automatic measurements of wind speed, direction, air temperature and relative humidity. The HAS will be equipped with a Rosemount icing detector for SLW observations. These and other sites to be mentioned are shown on Fig. 1. Three valley AgI generators will be used during some T &D experiments. They will be located by NA WC (North American Weather Consultants), the firm which conducts the Utah operational seeding program. NA WC will site these generators with the intention of targeting the "upwind highway" where Plateau-top sampling of AgI will be concentrated. The upwind highway refers to that portion of Highway 31 which parallels the west edge of the Plateau top. It extends from the intersection of Highways 31 and 264 to the RRS site 6.5 km further south. Simulated seeding will be conducted by releasing SF 6 gas from the mouth of Birch Creek Canyon during some experiments. The specific release site is not shown on Fig. 1, but it will be near the 2000 m contour about 2.5 km east of the Project H.Q. This site was used a few times during the 1991 program. Some nighttime (non-aircraft) investigations of AgI releases from this site may be conducted. 3.2 Cloud Physics Aircraft The instrumented NOAA King Air C-9Q aircraft used in 1991 will again be available. The aircraft will be equipped to monitor ice particles (2D-C probe), cloud droplets (FSSP probe), AgI (NCAR IN counter), SF6 gas concentration (fast-response analyzer), horizontal position (GPS and Loran-C), liquid water content (King probe) and state parameters. Horizontal winds will be calculated from some of these measurements. The aircraft will be based at the Provo Airport about 75 km northwest of RRS. A special Federal Aviation Administration waiver has been requested for 1994 to permit in-cloud, IFR (instrument flight rules) sampling to within 300 m of the highest terrain within 8 km of the flight path (the normal vertical restriction is 600 m). Aircraft sampling during 1991 was done under such a waiver. This low-level sampling will allow measurements of ground-released plumes near the mountainous terrain. The aircraft would often be unable to penetrate the ground-released plumes with normal vertical terrain separation. 3.3 Instrumented Van An instrumented four-wheel drive 3/4 ton van will be equipped to monitor ice particles with a vane-mounted 2D-C probe above the van which will keep the probe pointed into the resultant wind. A nearby anemometer will measure wind speed to determine the 2D-C's strobe rate. Silver iodide IN will be measured with an NCAR acoustical ice nucleus counter (hereafter NCAR IN counter) and SF6 gas with a fast-response analyzer. Other van measurements will include horizontal position with a GPS, air temperature, relative humidity and pressure. An aircraft-type Rosemount icing detector will monitor the presence of SLW. The concept of using a vane-mounted 2D-C probe was briefly tested in 1991. However, a head-on collision rendered the probe inoperable for most of the field season. While only limited 2D-C observations were obtained along the upwind highway, they showed the concept was practical. It is expected that wind-blown snow will contaminate measurements of falling ice particles along windier portions of the highway. The extent of this potential problem must be determined by experience. 4