268 Health Physics The type of meteorological data provided by most reanalysis models makes 1t difficult to model wet deposition Atmospheric models may incorporate simplifying assumptions for wet deposition, as does the HYSPLIT model, or may disregard the wet removal process altogether Wet deposition can be a large contributor to fallout under conditions of precipitation and can often lead to localized pockets of elevated radioactivity Thus, to accurately model fallout through computer simulation, a refmed wet deposition model would be needed in conjunction with accurate precipitation data The assessment offallout deposition m the Marshall Islands discussed m a companion paper (Beck et al 2010) 1s a good example ofretrospective modelmg ofthe dispersion and deposition of fallout usmg the HYSPLIT model HYSPLIT predictionsoffallout deposition can be used for supplementing existing ground-based fallout measurement data, particularly when no ground-based fallout measurement data are available In such cases, HYSPLITcan beused to indicate whether or notfallout might have occurred at a particular location and provide, at mmimum, crude estrmates of the magnitude of the deposited activity This, m itself, can be a very valuable asset for the reconstruction of past fallout events Acknowledgments—This work was supported by the Intra-Agency agree mentbetween the NabonalInsbtute of Allergy and Infectious Diseases and the National Cancer Institute, NTATD agreement #¥2 Al $077 and NCT agreement #¥3-CO $117 The authors are mdebted to Roland Draxler and Barbara Stunder of the NOAA AmResources Laboratory m Silver Spring, MD,for thew vallngness and generosity m providmg mstruction and information about the operation and theory of the HYSPLIT madel (http ready arl noaa gow/HYSPLIT php) REFERENCES Anspaugh L, Church B Fhstoncal estimatesof external expo sure and collective external exposure from testing at the Nevada Test Site through Hardtack TI, 1988 Health Phys 5235-51, 1986 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