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6.3 New Instruments and Observational Approaches A number of new instruments and observational approaches were developed and deployed during the NOAAlUtah AMP. For example, the mobile microwave radiometer (Huggins 1992, 1995, 1996; Wetzel et al. 1996) provided a useful new way to map SL W over a mountain barrier. This approach is particularly important when it is recognized that safety concerns often prevent instrumented aircraft from flying low enough to monitor the orographic cloud SL W field in the region where most snow particles grow. -- Truck-mounted NCAR counters and SF 6 detectors were used in tracking plumes up and over the Plateau. One truck carrying plume detection equipment also had a vane-mounted 2D-C laser probe on a mast above it. The vane kept the probe pointed into the resultant wind as the truck was driven along the Plateau top, while the 2D-C strobe rate was controlled by an anemometer. Tower-mounted 2D-C probes, also pointed into the wind by vanes, provided similar ice particle observations at fixed locations (Super and Holroyd - 1997).. Use of vane-moun..ted 2D-C probes provided a new and more accurate means of observing ice crystals caused by seeding. As it became available, GPS (Global Positioning System) equipment was used to record truck and aircraft positions. Super (1993) reported on testing of an automated, self-antifreeze-rechargirig, recording precipitation gage in a winter mountain environment. The gage was shown to be as accurate as the conventional Belfort Universal gage which requires manual service and chart reduction. Two methods of estimating AgI ice nuclei concentrations effective at cloud temperatures sampled by aircraft were discussed by Super and Holroyd (1994). One method used tracer gas concentration measurements while the other was based on NCAR counter observations. Both methods were compared with the preferred, but often unavailable, approach of directly observing resulting ice particle concentrations with a laser probe. The methods were found to provide reasonable first approximations for the AgI aerosol and cloud conditions sampled by the study. , The tracking of AgI and SF 6 tracer gas with instruments on aircraft and ground vel1icles was important in many of the reported studies. The sometimes maligned NCAR acoustical ice nucleus counter was shown to closely approximate AgI observations made by the "standard" CSU Cloud Simulation Laboratory (DeMott et al. 1995). Of course, the counter must be in good condition and must be maintained by someone knowledgeable in its proper operation. Several past applications used faulty NCAR counters or insufficiently trained counter operators. The three NCAR counters used during the Plateau experiments were often cross compared and found to be in good agreement. Considerable effort was expended into calibrating and comparing fast response SF 6 detectors during the field programs. Known concentrations ofthe gas were injected into the detectors at frequent intervals. Like NCAR counters, these instruments also require significant maintenance and knowledgeable operators. The CSU laboratory studies by DeMott et al. (1995) provided a new calibration of the NA WC AgI generator. It demonstrated that improvements had been made since the last calibration 'because warmer temperature ice particle yields were significantly enhanced. Beside the generator calibration with the standard AgI-NH4I-acetone-water solution used in Utah, one was made with a solution also containing sodium iodide and paradichlorobenzene. . This latter solution was expected to produce a condensation- freezing ice nuclei. Laboratory tests showed that ice crystal production rates were much faster with the latter solution. The results imply that an order of magnitude increase in ice crystal formation could be 26