OCR Text |
Show nuclei count was 11 per liter. The sounding and wind profile taken near the release site are presented in Figure 49. If it is assumed that cross-wind and downwind diffusion rates should be the same, predictions of (cross-wind) plume dimensions from a standard diffusion model such as the Pasquill-Gifford form (Turner, 1969) can be applied to the ( downwind) dispersion of a seeded track. Applying the Pasquill-Gifford plume- spread curves in this case, a standard deviation of nuclei distribution across the plume (cr value) of 900m would be predicted after 17km of downwind travel. A reasonable plume width is 4 cr, giving a predicted width of 3. 6 km which compares favorably -yrith the measured 4. 3 km. On 28 March 1969, a series of six lines 15. 5 km in length was released in a continuous pattern (multiple aircraft passes perpendicular to wind vector) at 9, 000 ft. MSL. The release period was from 1422 to 1459 MST. The sounding and wind profile measured at nearby Mt. Harris are presented in Figure 50. The lithium stearate tracer was released only on the first pass, or line, of this test. The plots in Figures 51-53 ar£ not corrected for the one minute lag time of the counter system. The following three tracks are presented: Track 4; 9, 000 ft. MSL, 1451 MST (Figure 51); Track 5; 9, 500 ft. MSL, 1451 MST (Figure 52); and Track 6; 9, 5 00 ft. MSL, 1515 MST (Figure 5 3). First of all, note that the tracks at the higher level (9, 500 ft. MSL) display a more uniform concentration of material than the tracks at the release height. Also, the measured peak concentration on any of the tracks is 40 liter- 1 . However, the counter system time constant causes some smoothing of the nuclei counts, From the records of tracks 5 and 6 at 9, 500 ft. MSL, it can be concluded that under the conditions of this test (winds at release level of 30 knots), line sources released at approximately five minute intervals will provide nearly uniform treatment of the horizontal dimension of a volume. Figure 54 presents the record of the nuclei counter and the flame photometer located on the surface at Rabbit Ears Pass, 45 km from the release line at' 9, 500 ft. MSL. The time of arrival is in precise agreement with the measure! wind at the release level. The period of above background nuclei count spans 45 minutes and the peak count is 67 liter- 1 , in agreement with the aircraftdati The bulk of the lithium tracer signal, with the exception of two spurious pulsei at 1440 MST, occurs over a 25 minute period even though only a single five minute line was released. This spreading along the mean wind vector is sig· nificant. It indicates that the intermixing of the individual lines of release in· dicated by the aircraft tracing data are real. Figure 55 shows a track through a line release on 2 April 1969 at 10, 000 ft. MSL five minutes after the release. A twelve second averaging period was used on the nuclei count data. After this short travel time a plume of nearly 3 km width is indicated, with a peak nuclei count of 83 liter-1. This indicates that serious overseeding is not probable even five minutes after the release, 84 |