RADIOACTIVITY AND POTENTIAL VORTICITY 94, 41 39 447 — — RB57 SAMPLES — , . 4 é —_ I ! | ro | tf yd | | i) mn ho ~“ RB5S7 SAMPLES oy 31 —- i] Oo ALTITUDE, 1000 FT 208. Fig. 9—-Flight paths of WB50 aircraft along vertical cross section shown in Fig. 8. Total beta activities in disintegrations per minute per standard cubic foot. April 21 (18Z) to April 22 (01Z), 1963. tained from the sample. By comparing the average slopesto the activities a conversion factor was calculated. This permits oneto estimate the activity directly from the slope of the continuous radioactivity trace at any point on the flight path, It is worth noting that the samples in the layer were taken near the boundaries where the slopes were smaller than those at the center of the layer. Dilution of the activity by mixing with the tropospheric air is implied by these smaller slopes along both boundaries. Figure 11 illustrates the potential-vorticity distribution and the %Sr activity as did Fig. 6. It also includes two values at the center of the layer (21,500 and 24,000 ft), These values were calculated from the slope of the accumulation traces. As before, the numerical correspondence is remarkable especially when allowances are made for theflight path during the time of sampling. In this case we have proof that the radioactivity extends to the 19,000-ft level, with the concentrations at 21,000 ft almost as large as at 28,000 and 34,000 ft. This supports the concept of tropopause folding with transport rather than diffusion as the predominant mode of transfer, Furthermore, the split in the potential-vorticity tongue at 20,000 ft is confirmed by the accumulated