Meteorological modeling of radioiodine transport and deposition within the continental United States.

A meteorological transport and deposition interpolation model has been employed to estimate radioiodine deposition remote from the Nevada Test Site between points of observed deposition. The movement of the radioactive cloud across the United States is obtained from wind trajectories at various quasi-constant levels up to the top of the initial radioactive cloud. This model deals primarily with depositions beneath the passing cloud that are associated with precipitation. The fraction of radioiodine scavenged was inferred from a relationship derived statistically from fallout at locations having wet deposition. Therefore, estimation of deposition at locations between fallout observations is possible wherever precipitation occurred under the cloud. These estimates use very detailed historical records of precipitation available for virtually every county in the United States. Because significant dry and wet depositions also occur in areas that are not beneath the cloud, interpolation methods, such as kriging, are used to estimate fallout between the radioactivity observation locations. Ground-level radioactivity measurements are required for these alternative methods. Such observations are validated before being used, often by the use of supplementary low-level trajectories.