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At the onset of the Fukushima Nuclear Power Plant (FNPP) event, it was
decided that development of advisory ocean forecast products was to proceed
even though there was no initial actionable information on ocean or
atmospheric radionuclide composition or release rates. This decision
resulted in the evolution of a two-phase program. The first phase was ocean
model forecasting of an idealized plume of water released in and around the
FNPP area. The second phase began once numerical estimates of atmospheric
wet deposition of radionuclides on the ocean surface began to arrive.
As the event progressed, limited geospatial information derived from ocean
measurements at selected stations in the region close oﬀshore from the FNPP
site were received from MEXT and TEPCO. These were used as “ground truthing”
guidance on the modeled plume time- dependent estimates of radionuclide
activity. These data were not part of the input data for the forecast
Two separate unverifiable model data sets of atmospheric wet deposition
radionuclide deposition fuxes were received over the course of the event and
were used in the production of plume forecast products. A third veriﬁable
data set was received near the end of the event and was used in the
development of ocean tracer forecast products, but not by the
particle-density based plume estimates.