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1128 JOURNAL OF APPLIED METEOROLOGY VOLUME 27 TABLE I, Ground seeding experiments, Max, Angle Plume Panel Upper wind levels Init, plume height average potent. in Fig, (km) width deg, (m) from temp. (K) Date Times Site above (1986) (MST) no.* 2 4 acou teth inst span crest AgI ice aye span 5 Feb 1701-1743 5 90 70 X 294 2 10 Feb 1121-1500 2 g a 3,3-4 7 96 400 X 288 4 12 Feb 1200-1352 3 h b 3,2-4 3.4-5 18 39 400 X 295 5 14 Feb 1140-1530 6 m c 3.2-4 16 30 800 X 300 7 24 Feb 1600-1851 I a d 3,5-7 15 27 500+ X 307 3 27 Feb 0825-1151 I b e 3,5-6 18 70 300,700 X 302 5 7 Mar 0834-1152 8 f f 3,3-5 16 24 700 X 305 4 8 Mar 0854-1150 4 g 3,6-7 27 51 600 X 306 9 14 Mar 1148-1415 6 j h 3,6-7 7 41 500+ X 298 3 14 Mar 1520-1810 7 k 3.6-7 3,2-3 X X 298 2 19 Mar 1052-1248 2 e j 3,3-4 3,1-2 10 31 500+ X 295 4 20 Mar 1025-1227 2 c k 3,7-8 3.3-5 6 33 700+ X 298 5 20 Mar 1251-1425 I d I 3,7-8 3.3-6 26 32 800+ X 298 5 24 Mar 1012-1410 7 I 3,2-4 3,0-1 13 38 11 00+ X 307 4 median 15 38 500+ * Seeding site: No, Latitude Longitude Altitude I 39003'49" 108005'58" 2914 m 2 39003'59" 108006'17" 2694 m 3 38059'50" 108006'32" 3018 m 4 38057'08" 108010'25" 2615 m 5 39001'56" 108003'28" 3246 m 6 39001'10" 107059'52" 2978 m 7 38059'27" 107056'04" 2515 m 8 38031'46" 108041'08" 2641 m with the same solution (Garvey 1975) showed an out- put of7 X 1014 ice nuclei g-I, effective at -20oC, for the light wind conditions typical of the release sites during these experiments. The unit was portable, so it could be transported by helicopter or by an over-snow vehicle to isolated operating sites. Airborne seeding was performed using an Aero Sys- tems solution burner installed on the instrumented aircraft. This unit burned a 2% by weight solution of AgI complexed with NH4I [typical of most of the tests for airborne units in Garvey (1975)] at an approximate consumption rate of 80 g AgI h -I . Calibration tests at CSU indicated an output of approximately 1 X 10 IS ice nuclei g-I effective at -20oC. It should be noted that photodeactivation of the type of AgI used in these experiments is not believed to be significant. The same AgI complex was used in the field observations reported by Super et al. (1975), who demonstrated that it did not significantly lose its ice nucleating ability, as monitored by an NCAR acous- tical ice nucleus counter, even after 2 to 3 h of exposure to sunlight. b, Aircraft instrument system A Rockwell 690A Turbo Commander was used as the primary instrument system platform. This aircraft was certified for flight into known icing conditions and had sufficient performance to allow repeated in-cloud passes under most storm conditions. The instrumen- tation package consisted of a microcomputer-con- trolled data acquisition system and sensors to measure aircraft heading and air speed, pressure, temperature, moisture, liquid water, ice nuclei, cloud particles and position. The last was obtained using a Texas Instru- ments Model 9100 Loran C Navigator system. Al- though operating in a marginal signal reception area (i.e., the "intercontinental gap"), position accuracy was generally quite good. Only one instance of a temporary signal loss that lead to known large errors was encoun- tered during the 20 flights reported on here. As dis- cussed by Super et aI. (198,8), absolute differences from a known location were generally < 1.0 km and relative differences were usually <0.5 km. The NCAR acoustical ice nucleus counter was used for the detection of the edges of the plumes of AgI in a manner similar to that described by Super et al. (1988). An earlier version of the instrument was de- scribed by Langer (1973). Air from outside the aircraft cabin was drawn at about 10 L min -1 through pre- conditioners to add water vapor and cloud condensa- tion nuclei to the sample prior to injection into a 17 L cloud chamber refrigerated to near -20oe. The IN were made detectable by the growth of ice crystals around them in the supercooled cloud. The crystals made an audible click when they passed through an