WMOD00290 - Laserfiche WebLink

Home Browse Search

4. SPECIFIC EXPERIMENTS TO BE ATTEMPTED 4.1 General Aspects of the 1994 Field Program Synoptic weather information will be available at the Project HeadqUarters at Skyline Resort (H.Q. on Fig. 1). Based on forecasts and nowcasting of the local weather, and the types of experiments previously conducted, a decision will be made just before each aircraft missiOli concerning the type of experiment to be attempted. Aircraft missions will be restricted to daylight hours for reasons of safety. Observations of AgI will be made routinely with NCAR IN counters near the head of Birch Creek Canyon (the RRS site) and at the TAR site. The van will repeatedly sample along the upwind highway using an NCAR IN counter and fast-response SF6 detector. The aircraft will carry similar detectors to monitor AgI IN and SF6 above the Plateau. Tracer gas will be collected with syringe samplers at the RRS and TAR for later analysis. Each syringe sample will integrate outside air over a 0.5 h period. When valley-released AgI is not detected on top the Plateau, van sampling will be done within Fairview Canyon and along the Sanpete Valley floor to determine how high and where the material in question is being transported. Observations during 1991 indicated that during stable conditions the AgI pooled in a shallow layer near the valley floor, and was sometimes funneled up-valley. Modeling suggests that in some cases the valley-released tracer material was limited to a surface layer less than 100 m thick which moved toward the west. Tracer gas releases will normally be limited to aircraft missions to minimize costs. Gas releases will be made at 30 kg h-1 from the mouth of Birch Creek Canyon with no other material being released from that site, or from the two high-altitude sites (18 kg h-1 per site) to "tag" co-released propane plumes or AgI plumes. A variety of additional supporting measurements will be made to allow for later evaluation of the meteorological conditions under which T &D is adequate and those under which it is inadequate, realizing that these conditions will vary for different types of generator sites. The supporting observations primarily will be of airflow and atmospheric stability. They will include rawinsonde releases from the upwind valley during aircraft missions; continuous Doppler acoustic sounder measurements from the Plateau top; and wind, temperature and moisture observations from automatic weather stations at the Mount Pleasant Airport, well up Birch Creek and Fairview Canyons, and on the Plateau top at RRS and TAR. In addition, the RRS radiometer will indicate when SLW is present over the Plateau, to document periods when T&D to cloud levels is desirable. Moreover, the radiometer's time history is a good indicator of convection. Ka-band radar cloud tops will also suggest passage of convective bands and other cloud structure of interest. The network of 9 recording precipitation gauges will be maintained over the Plateau, primarily in support of the direct detection experiments to be discussed. However, these measurements are of general interest concerning storm evolution which will be related to the T &D of seeding agents. 4.2 Transport and Dispersion Experiments The T &D monitoring approaches used in 1991 were generally successful and will be repeated during 1994 with some modifications. Sampling of plumes will be done at the two mountain observatories (RRS and TAR), by the instrumented van driven primarily along the upwind highway, and by the instrumented aircraft flying above the Plateau top's west and east edges. Aircraft sampling can detect plumes along the entire Plateau provided vertical transport is sufficient. However, aircraft sampling is practical only a fraction of time that surface sampling can be conducted. In practice, usually one and sometimes two missions per day can be flown, during daylight hours, with no more 8