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SEPTEMBER 1996 REYNOLDS 1445 5000 4500 td ttl 4000 3500 g 1 E Ol 3000 TT . .0; t :r: l ACFT 2500 I! . ~ ACFT 2000 t 1500 t 1 m/s JVL: 1000 .10000 -5000 0 5000 10000 15000 Distance from JVL (m) FIG. 13. Rawinsonde-derived vertical velocities for 17 March, showing a well-defined lee-wave pattern that influenced the transport of SF6 on this day. Locations of aircraft sampling altitudes over the valley and ridge passes are annotated. sampling port of the aircraft and the registration of SF6 on the analyzer. This was accounted for in the analysis of these data but is not in the figures of SF6 plumes shown in this paper. Plume intercept times were com- piled and identified for whether the plume originated from site 7 or 9 if simultaneous releases were made. Statistics were compiled on each plume, and parame- ters tabularized for the site of origin and whether it was sampled on the valley, the ridge, or the downwind flight track. These results are discussed in the following sec- tions. 1) V ALLEY TRACK PLUME INTERSECTIONS Table 3 lists a total of 31 valley interceptions of the SF6 plume from site 7 made by the aircraft. The mean distance from site 7 to the valley intercept was 13 kIn. At this distance, the plume age varied dependent on wind speed. On average, the plume was approximately 15 min downwind of the release point but varied from 10 min on 17 February to 27 min on 19 March. For flights made in IFR conditions, the highest con- centrations of SF6 at 2500 m and above were found on 5 February. Unfortunately, temperatures were too warm at the release site to initiate seeding. This day, along with 16 March, had the most liquid water at and above 2500 m. The fewest plume interceptions were on 17 March. Only one plume intercept was observed on the valley track. Winds were near 25 m s -Ion this day and may have caused the plume to move almost hori- zontally from the release altitude of 2200 m since very little SF6 was found in the valley either. It should be mentioned that when winds exceeded 25 m s -1 , aircraft operations were aborted. If the average SF6 concentration is plotted against the SF6 intercept altitude (Fig. 10) for all plume intercepts on aU experimental days, it is apparent that concentra- tions peak at the release altitude and falloff dramatically above and below this altitude. Fifty-five percent of the passes made along the valley track at 2500 m showed no SF6. Almost all passes made below 2400 m along the valley track showed SF6 above background levels. It is important to note the horizontal dimensions of the plume to determine whether dispenser density is sufficient to cover the target area. On average, the plume is about 130 or 3 kIn wide over the valley. This is very close to the dispersion rate used in the opera- tional targeting model (section 4) and similar to the average dispenser seperation. There is a tendency for the plume to be wider at plume interceptions made near the release altitude. This would indicate that the plume centerline remains near the release altitude, with the plume becoming narrower both above and below this elevation. Thus, at 2500 m the aircraft is probably sam- pling near the top of the plume over the valley as the frequency of plume intersection drops off dramatically and the plume width narrows. Table 4 summarizes the valley plume interceptions from site 9. Site 9 SF6 releases could not be made until 17 February due to equipment problems. Thus, many of the plume interceptions were made on VFR flights at altitudes below 2500 m. The mean distance from site 9 to the plume intercept was almost 18 kIn. This 5-kIn difference compared to site 7 is a result of site 9 being TABLE 7. Sulfur hexaflouride plume characteristics from site 7 as observed by aircraft for downwind track. Plume width Dist. site 7 Max SF6 Avg SF6 AIt Temp Avg LWC Wind speed Wind direction Date Pass C) (lan) (lan) (ppt) (ppt) (m) CC) (g m-3) (m S-I) ("1') 9 March 15 26 15 31 58 25 2471 3.1 0.00 10 197 9 March 16 28 15 30 45 21 2475 2.9 0.00 5 215 16 March 11 1 1 38 14 8 2606 0 0.25 NA NA 16 March 16 7 5 36 23 11 2597 -0.3 0.33 6 196 16 March 18 16 10 33 23 9 2598 0.4 0.20 13 227 Average 16 9 34 33 15 2549 1.2 0.16 8 209