Mapping Nuclear Fallout Using the Weather Research & Forecasting (WRF) Model

There are many models that attempt to predict transport & dispersion (T&D) of particulate matter in the sensible atmosphere. The majority of these existing models are unable to incorporate atmospheric processes such wet deposition through scavenging and cloud condensation nuclei (CCN) formation. To this end, the numerical weather prediction (NWP) model known as the Weather Research & Forecasting with Chemistry (WRF/Chem) Model is studied to determine its suitability as a potential tool for predicting particulate T&D following an atmospheric nuclear detonation. This is done by modifying relevant modules, originally designed to predict the settling of volcanic ash, such that a stabilized cloud of nuclear particulate is initialized within the model. This modified code is then executed for various atmospheric test explosions and the results are qualitatively and quantitatively compared to historical dose-rate contour data contained in DNA-1251-EX. The same simulations were also performed using the offline (NWP wind flow separately applied) Hazard Predication Assessment & Capability (HPAC) Model and Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) Model. By comparison, using WRF/Chem for particulate tracking allows for the incorporation of important meteorological processes inline with dispersion processes and leads to more realistic fallout pattern with effects of the fallout coupled back into the numerical weather forecast