Fallout deposition in the Marshall Islands @ H. L. Beck er av. 133 direction. For example, at Rongelap in the northern shown in Table 1 of Simon et al. (2010a), we believe those 45 tests deposited local or regional fallout primarily only on thetest site atolls of Bikini and Enewetak and on the open ocean outside of the area of the Marshall Islands. This conclusion is based on our analysis of available monitoring and meteorological data, as well as corroboration by data in unpublished reports. Fig. 1 shows an example of calculated directions of travel of air masses as they moved away from the nuclear test site, clearly illustrating the fallout moving away from the Marshall Islands. The air-mass trajectories were reconstructed using the NOAA-HYSPLIT model and archival meteorological data. Using the HYSPLIT model one can determine whether air masses likely moved towards or away from the inhabited atolls of the Marshall Islands. In the absence of actual measurements, this type of analysis helped confirm our conclusions on which tests likely deposited fallout on the inhabited atolls. Marshall Islands, estimated TOAsvaried from as short as 6 h for Bravo to about 80 h for Nectar and Zuni. Conversely, at Majuro in the southern Marshall Islands, TOAsvaried from about 36 h for King to about 140 h for Yoke. The shortest TOA wasabout4 h for Bravo fallout at Ailinginae and the longest TOA was about 170 h (>1 wk) for Union fallout at Kili Island. The TOAestimates tend to be conservative in that, as illustrated by both auto-monitor and gummed film data, the fallout at some atolls often continued over many hours or days. Since gummed film data represented the deposition for a 24-h interval, our estimates of the initial TOAs are uncertain to about +12 h if only based on those data. Although the initial TOA can be determined more precisely from the auto-monitor data which recorded data every 6 h, in many cases, the fallout arrived over a period of many hours to many days with no specific peak. For other tests, the TOA could only be crudely estimated based on whether fallout occurred prior to an airplane survey or between repeated surveys. Fallout time-of-arrival (TOA) Estimates were made of the TOAoffallout for each test at each atoll. These estimates, expressed in hours post-detonation, are presented in Table 6. Times of arrival varied considerably depending on the distance of For tests with little actual data, the fallout and TOA were estimated from the HYSPLIT model. As discussed in a companion paper in this issue (Moroz et al. 2010), the each atoll from the test site, wind speed, and wind 160° E 180° 160° W Trajectory Start Heights 13km 15km 30°N a 17km @ 19-24km oO + 30°N Enewetak: Atoll 10°N 4 10°N 0 500 1000km -———_——_ 0 10°SF wt 120°E 140°E 500 1000 mi = 10°S y4 is‘ 160° E : te. cri 2 eR ! 180° 160° W Fig. 1. Upper level air mass trajectories moving W and NE away from Bikini Atoll (i.e., away from Marshall Islands, shown as gray shaded area) duringthe first 39 h following the Poplar detonation as derived from archival meteorological data and simulated with the NOAA-HYSPLIT model for the day of the Hardtack I Poplar test (7/12/58, 9.3 Mt explosive yield). Note: trajectory symbols represent 3-h intervals.