Dispersion and deposition of fallout from nuclear testing @ B. E. Moroz er av. direction of the '*’Cs deposition pattern is significantly 265 the meteorological input data. HYSPLIT air masstrajectories (Fig. 6) clearly illustrate the significant wind shear, which is inconsistent with the assertion that wind shear further to the north than the Yamamotoet al. (2008) data. However, the deposition patterns resulting from the alternative '*’Cs activity-size distributions given in Table 1 (Fig. 4) shift the HYSPLIT fallout pattern closer to that reported in Yamamotoet al. (2008) and clearly indicate that the predicted '°’Cs deposition is very sensitive to the estimated fraction of '°’Cs on particles greater than 50 was minimal (Shoikhetet al. 1998; Imanakaet al. 2005). Although the estimated peak '*’Cs deposition density predicted by HYSPLIT in the vicinity of Dolon (Table 9) is slightly closer to that measured by Yamamoto et al. (2008) (corrected for decay) for the alternative particle-size distributions than for the MI distribution, the HYSPLIT maximum deposition density near Dolon is still much lower than the maximum pom. As discussed earlier, and shown in Table 1, the distribution used for the Marshall Islands simulations assumed only about 20% ofthe '*’Cs activity on particles greater than 50 jzm, while the alternate distributions assumea largerfraction of '°’Cs on particles of diameter greater than 50 ym. As shown in Fig. 5, where the activity on various size groups of particles is plotted separately, the HYSPLIT simulation indicates that most of the particles depositing in the vicinity of Dolon, and particularly along the axis of the fallout pattern, to be greater than 50 jm in diameter, while the particles further from the centerline were generally less than 50 ym. However, even assuminga greaterfraction of '°’Cs activity on large particles, the HYSPLIT pattern still deviates from the axis of the Yamamoto data and is much broader, presumably reflecting the wind shear present in measured by Yamamoto et al. (2008) (corrected for decay). However, this is to be expected since, as a result of the predicted wind shear, the HYSPLIT fallout is spread over a wider area compared to the Yamamoto et al. (2008) soil data and, thus, is diluted. Wesurmise the shift of the HYSPLIT pattern to the north, compared to the measurements of Yamamotoetal. (2008), to be a result of wind shear in our meteorological data and other limitations of those data. However, it may also partly reflect the fact that the '°’Cs activity-size model used in HYSPLIT simulations is too crude and may not be apportioned to give enoughofthe total '*’Cs activity on the larger particles that deposit closer to the 5 to 30 um 35 to 60 um 78.0° E 79.5° E 81.0°E 78.0°E 79.5° E 81.0°E T T T T T T 51.4°N - = 51.4°N 51.0°N F - 51.0°N Dolon@ 50.6°N Dolon@ — 50.6°N | | | | | | T T T T T T 51.4°N F 4 = 51.4°N 51.0°N F 4 — 51.0°N Dolon® 50.6°N , Dolon @ i iar" F I 78.0°E 79.8° E 65 to 90 um 81.0°E 78.0°E — 50.6°N 1 J 79.5° E 81.0°E 95 to 150 um Fig. 5. HYSPLIT-predicted fallout patterns of different particle sizes at the Semipalatinsk Test Site in Kazakhstan following event 1 (29 August 1949).