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Show The release plane was, on several occasions, followed by the tracer aircraft and the lithium tracer, which is quite visible, was observed to spiral away from the aircraft in a large vortex. The vortex was estimated to be 20 m in radius at a distance of 20-30 m behind the releasing aircraft. Another revealing test was conducted o:n 21 March 1969. A multiple pass source consisting of seven lines at 12, 000 ft. MSL was released from 14031438 MST. The radiosonde and measured upper level winds are presented in Figure 56. Figure 57 shows the nuclei trace taken at 1420 MST at the time the fourth line release was in progress. Even after such a short time the individual lines appear to be merging. The line is characterized by spikes; these are probably due to elements of the diffusive processes and not individual source lines, because there are more peaks than lines released to that time, The peak nuclei count is 180 liter-1 on this track. Figures 58a and b present the results of a track 15 minutes later at the release level of 12, 000 ft. MSL. The release of the seventh and last line was in progress. The estimated positions of the seven lines are indicated and the peak counts are generally 80 liter- 1 , except for line No. 3 where the count reached 180 liter- 1. Line No. 1 is approximately 16 km from the release line. If the next most stable category from neutral in the Pas quill-Gifford model is used, the 4 a plume width after this travel distance would be predicted to be 2. 4 km. This compares to an observed width of 1. 6 km indicated for line No. 1. Some of the later lines are apparently wider than the first line. Figure 59a shows a track at 1501 MST five hundred feet above the release level. The maximum count at this level is only 20 liter- 1 ; vertical diffusion for this case was apparently quite slow. Compare the wind profile at the time of the sonde (1243 MST) to the wind profile at 1543 MST (Figure 56). They show that there was a definite change at levels below 13, 000 ft. MSL and indicate a possible inversion formation at this level. A separate experiment which was part of the Skywater I series was conducted on 25 March 1968. The temperature stratification and wind structure at the time of the test are shown in Figure 60. The lapse rate was near neutral except for a small inversion layer near 13, 000 ft. MSL. The release was made just above this stable layer. Two line sources of 1OOg of silver iodide were released perpendicular to the flow ten minutes apart; the first at 1507. 5 MST on a SSE heading from the Hayden beacon and the second from 1517-1520. 5 MST on the complementary heading. These are depicted in Figure 61. The projected locations of these lines were computed for thirty minute intervals based on the 25 knot winds at release level. The projected locations of the first line source are shown with light solid lines. The aircraft tracks are shown by a heavy solid line and the portions of track where nuclei count above background was found are referenc by circles; those portions of the nuclei count data from the track are plotted 11 the figure. 92 |
