Dispersion and deposition of fallout from nuclear testing @ B. E. Moroz Er AL. Table 4. Comparison of wind speed and direction at time of detonation at the Enewetak test site for the 7 April 1951 (GMT) Dogtest. DNA (1979) HYSPLIT Altitude Wind speed Wind direction Wind speed Wind direction 1,524 3,048 4,572 6,096 7,620 9,144 10,668 12,192 13,716 15,240 16,764 48 35 38 35 19 50 47 53 42 35 50 80 80 70 30 300 280 230 220 280 310 340 45 27 21 19 19 23 37 45 45 32 19 81 57 35 22 134 298 266 259 262 275 288 (m) (km h~') (deg) (km h~') (deg) 261 Nevada Test Site: Upshot-Knothole Harry Upshot-Knothole Harry was a 32 kt fission device detonated on 19 May 1953 at the NTS. The Harry test was simulated using the HYSPLIT model with the purpose of comparing deposition patterns and fallout arrival times to published data (Becket al. 1990; Beck and Anspaugh 1991) as well as with the meteorological modeling results of Cederwall and Peterson (1990). Particle sizes and release heights for the Harry simulation closely followed those selected by Cederwall and Peterson (1990). Trajectory endpoint calculations and fallout pattern plots produced by Cederwall and Peterson (1990) indicated two diverging air masses at approximately H+10 h downwind. At lower altitudes, particles were shownto deposit at latitudes between the northern border of New Mexico and Denver, CO, while Table 5. Comparison of wind speed and direction at time of detonation at the Enewetak test site for the 24 May 1951 (GMT) Item test. DNA (1979) Altitude (m) 1,524 3,048 4,572 6,096 7,620 9,144 10,668 12,192 13,716 15,240 16,764 Wind speed (km h~') 26 8 14 14 19 16 14 13 — — — Wind direction (deg) 90 90 260 290 250 360 250 280 — — — HYSPLIT Wind speed (km h~') 21 16 11 13 19 23 18 13 11 11 11 Wind direction (deg) 103 114 50 2 147 352 318 280 278 310 345 Other sources of weather observations from this region are largely conjectural, but may have included data collected from passing ships at sea and aircraft. Comparisons with the actual wind data from the test site (DNA 1979) and the model-predicted wind data at the test site resulted in only sporadic agreement between the two. Furthermore, Kistler and Kalnay (2000) indicated that upper-air rawinsonde observations were inconsistent and very few in the tropics during this time period resulting in reanalysis forecasts of poor quality. For these various reasons, the meteorological input data used for HYSPLIT simulations, solely based on the NCAR/NCEPreanalysis model, did not often reproduce downwind meteorological conditions accurately enoughto predict trajectories of the radioactive debris clouds with strong certainty. De- particles aloft deposited further to the south at latitudes between Cedar City, UT, and Albuquerque, NM. Using this information, two separate simulations were performed, each modeling the respective bottom and top halves of the debris cloud. The particle sizes used in the simulation ranged from 5 to 1,000 um in diameter (Table 7). Deposition parameters in our Harry simulations differed from those used by Cederwall and Peterson (1990). Cederwall and Peterson (1990) chose a fixed deposition velocity of 0.005 ms | to represent a range of values for various radionuclides and modeled only washout, not rainout, assuming that precipitation removed only airborne material below the radioactive debris cloud. As stated previously, in applying HYSPLIT, the deposition velocity was assumedto be only attributed to gravitational settling. Also, both below-cloud and incloud wet deposition processes were simulated. It should be noted that the model used by Cederwall and Peterson (1990) incorporated a washout coefficient dependent on precipitation rate; in contrast, in the HYSPLIT model, the rainout coefficient is dependent upon the precipitation rate and the washoutcoefficient is independentofit. Results. The fallout patterns and fallout arrival times resulting from the Harry simulation agree reasonably well with those reported by Cederwall and Peterson (1990), but there are some noticeable differences. Fig. 3 shows that at H+12 h, the HYSPLIT-predicted debris indicating which tests could have impacted the Marshall Islands and which likely did not, particularly for years spite these limitations, the simulations proved useful for cloud had entered Colorado and New Mexico and by H+ 18 h the debris cloud had reached Denverin the north and crossed into New Mexico much further south. The fallout pattern produced by HYSPLIT appears to agree with the estimated centerline of the plume produced by with no actual monitoring data (Beck et al. 2010). Cederwall and Peterson (1990). However, the patterns Simulations were also useful for interpolating between actual monitoring data for atolls that were not surveyed. disagree in some locations. Cederwall and Peterson’s pattern is broader north to south. Furthermore, the