125 HYDRODYNAMIC MODELS APPLIED TO THE PACIFIC OCEAN RADIOLOGICAL SCENARIO Some brief comments on the hydrodynamic models which were used to calculate ocean circulation to be used in Pacific Ocean radiological scenario are given below (references where full details are provided are included). XI-1. DESCRIPTION OF THE JCOPE2, JAPAN COASTAL OCEAN PREDICTABILITY EXPERIMENT JCOPE2 was developed by the Japan Agency of Marine-Earth Science and Technology [XI-1]. It is based on one of the world community models, Princeton Ocean Model. Open boundary conditions are obtained from a global scale circulation model with lower resolution, using a one-way nesting procedure. JCOPE2 consists of 23 vertical levels and spatial resolution is about 9 km. The model is driven by wind stresses, plus heat and salt ?uxes. The wind stress and heat ?ux field are calculated from the 6 hourly National Centers for Environmental Prediction (NCEP) Global Forecast system data using bulk formulae. The salinity at the surface is restored to the monthly mean climatology with a timescale of 30 days. The output of JCOPE2 is used for ship routing of oil tankers, fishery and drilling ships. Some examples of applications are described in Refs. [XI-2–4]. It has also been applied to simulate the dispersion of Fukushima Daiichi NPP accidental releases in the Pacific [XI-5–8]. XI-2. NTUA, NATIONAL TECHNICAL UNIVERSITY OF ATHENS The NTUA model is a general deterministic model which solves the full Navier–Stokes equations for transient, 3-D turbulent ?ow and utilizes an Eulerian approach. The turbulence model adopted for the present study is the renormalization group k ? ?. Additional processes and equations which are relevant are also included in the model: density variation with salinity (salinity is computed by solving an additional transport equation), expressions for describing wind-induced currents, etc. The finite-volume method was implemented for the numerical solution of the system of equations. The above model is implemented in the Computational Fluid Dynamics code PHOENICS (Parabolic, Hyberbolic, or Elliptic Numerical Integration Code Series). At solid walls, such as the coast, the sea bottom or any other solid, wall functions are used. Grid- independency runs were also performed to obtain grid-independent results. To ensure convergence, relaxation of the false time step type was used for all other variables; and linear for pressure. The false time step used was equal to the ?uid average residence time in the smallest cell in the domain [XI-9–11]. XI-3. NCOM, NAVY COASTAL OCEAN MODEL NCOM is a numerical model used to produce surface currents and temperature, mixed layer depth, current and thermohaline profiles in global scale [XI-12]. NCOM is a free surface, primitive-equation model with a curvilinear horizontal grid. Horizontal resolution varies from 19.5 km near the Equator to 8 km in the Arctic, with mid-latitude resolution of about 1/8° latitude (?14 km). The hybrid sigma/z vertical schemes are adopted with 19 terrain following sigma levels in the upper 137 meters, and 21 fixed thickness z?levels extending to a maximum depth of 5500 m. NCOM extends from the Arctic Ocean to the coast of Antarctica and from the open ocean over the shelf break to near-shore regions. The present daily model run consists of