| OCR Text |
Show periods of seeding effect at Rabbit Ears Pass for those times when sufficient upper wind data were available to compute travel times. The ice nucleus count (Figure 100) at Rabbit Ears Pass first increased significantly shortly after 0600 MST, indic-ating the breakup of the inversion noted on the Mt. Harris 03 44 MST sounding (Figure 86) and the subsequent arrival of seeding material in the target area. In-phase pulsing of precipitation rate at Rabbit Ears began following the 0630-0700 Agl release and was spectacularly evident during the steadiest wind regime (see Figure 99a-d), from 1130 MST to 1430 MST. After 1430 MST, the cloud layer deepened (Figure 88) and the precipitation rate traces became more complicated, as would be expected, since the deepening of the moist layer probably resulted from large scale lifting with resulting destabilization, thus producing an increase in the convective precipitation component. Much less pulsing is noted in the Buffalo Pass precipitation rate trace. The relative amplitudes of the total 1 cph precipitation component at selected target area ridge stations for two differ e nt time segments of this operational period are shown in Figures 101 and 102. These figures can be interpreted as follows: The amplitudes result from the total 1 cph precipitation component, i. e. , natural plus seeded component. (1) (2) If there exists a significant positive 1 cph seeding effect and it is exactly out of phase with a natural 1 cph component of a similar magnitude, near zero amplitude may result. On the other hand, an in-phase condition of two such 1 cph components would yield very high amplitude. Thus, caution is necessary in interpretation of these figures. (3) Differences in amplitude for stations falling within the computed area of seeding effect compared to stations outside the area of effect yield the most valuable clues to inference of seeding effects. When comparing station amplitudes in Figures 101 and 102· with reference to station location with respect to computed area of seeded precipitation (Figures 90, 92, and 94), amplitudes within the area of seeding effect are noticeably higher than those outside the area. This means one of two things, (1) that ther2 was a positive 1 cph seeding effect in phase with a natural 1 cph component, or (2) that there was a negative 1 cph seeding effect out of phase with a natural 1 cph component. Reference to the computed times of occurr· ence of seeding effect in relation to the Rabbit Ears precipitation rate trace in Figure 101 gives a strong indication that the seeding effect was positive. Figure 103 gives the amplitude of the Rabbit Ears 1 cph component when (1) the major seeding effect was north of the site, (2) the major seeding effect 168 |
