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826 JOURNAL OF APPLIED METEOROLOGY VOLUME 27 (- -50C). It also shows crystals from the center of the 10 dBZ region probably initiated around 2.8 km (-9.50C). At the point of echo formation (4 dBZ), the predicted crystal was a 554 ILm column with a fallspeed of 0.55 m S-I. At the point where a 10 dBZ echo was first observed (to + 19) the predicted crystal was a rimed column with a major axis of 1 004 ~m and a fallspeed of 1.1 m S-I. The slope of the 10 dBZ echo contour implied a particle fallspeed of 1.25 m s- I. The final calculated crystal fallspeed was 1.13 m S-I. The speed of the radar echo was measured at 10.2 m S-I between 2055 and 2111 UTe. At the point where the 10 dBZ contour reached the surface, the echo was 20.8 km downwind of the seeding location. By com- parison the calculated trajectory terminated 16 km downwind of the SLCP. The crystal moved at an av- erage speed of 8.1 m s- I. An x-z plot of radar echo and the calculated crystal trajectory illustrate this dif- ference in Fig. II. Points of equivalent times of the radar echo path and crystal trajectory are shown. In general, there was good agreement between radar echo evolution and predictions for fallout time of a crystal originating at the SLCP at -70e. The crystal was predicted to fall out in 33 min, nearly identical to the radar results. However, the downwind distance traveled differed by 5 km. This may have been due to errors in the calculated wind field (see sec. 4a), since mean echo motion was observed to be approximately 2 m S-l faster than the mean predicted crystal hori- zontal velocity. 6. Summary and conclusions The diagnostic method for targeting during airborne seeding experiments of the Sierra Cooperative Pilot Project was described in this paper. During aircraft seeding operations, this technique was used operation- ally to direct aircraft to the appropriate seeding location in the cloud in order to target effects to a specific ground location. The area of effect on the ground was also estimated. The methods used were data-interactive, so 5.0 4.0 E ~ 3.0 I- :I: c> 2.0 W :I: +2 . +6 . +10 . . 1.0 Terro;n _ 0.0 o that the latest possible information concerning the local wind fields and cloud liquid water content could be incorporated into the targeting calculations. The pa- rameterizations were simple, designed for operational expediency. The total time required to perform the targeting calculations and direct the aircraft to the seeding location was usually under 3 min. Three evaluations of the targeting technique were presented. These studies include comparisons of I) predicted wind fields with those measured by aircraft; 2) ice particle growth rates within seeded cloud regions with predicted growth rates; and 3) radar echo evolution within seeded cloud regions with predicted particle tra- jectories. The diagnosed wind fields over the Sierra Nevada were found to generally correspond to aircraft mea- surements of wind speed and direction within the lower atmosphere (<5000 m) upwind of the crestline. Errors in the u- and v-components of the wind were generally <4 m S-l over the 100 km domain upwind of the crest. Exceptions were noted in regions of strong vertical shear and/or when the barrier jet core extended far into the foothills. In these cases, narrow regions of more significant errors (4-10 m S-I) were observed. These regions of large error were generally above (shear) or west (barrier jet) of the primary region where seeding was conducted. The displacement of predicted fallout locations due to misrepresentation of the wind fields within the region affected by seeding was less than 10 km from the target in nearly all cases, and often less than 5 km. Comparison of predicted ice particle habits and growth rates with those measured within seeded regions of storms were made during 11 storm systems. Ice par- ticles were sampled by aircraft 4-81 min after seeding. Particle habits and growth rates used in the targeting parameterization generally agreed with measurements taken in the temperature range -80 to -l30e. At warmer temperatures, particle growth rates were gen- erally overestimated. Habits were typically thick col- umns, plates or rimed particles rather than the expected needle. The reason for the discrepancy appeared to be +20 +14 [) +:~_...~-l +26 · · · . +2V~ y~ +24 _ _-- ---+2S~ 1 10 15 DISTANCE ALONG ECHO PATH (km) 20 Seeding Location FIG. II. Comparison of calculated crystal trajectory and radar echo development in the X-Z plane. Dots connect calculated crystal position and echo at equivalent times. The radar echo contour represents 5 dBZ. Vertical dashed line represents seeding curtain. , ',.