Validation Test Report for OCEANS 1.0: The 1/40 Global, Reduced Gravity NRL Layered Ocean Model

Abstract

Abstract : The components of OCEANS 1.0 are described in this report. They consist of the marginally eddy-resolving 1/4 deg global, reduced gravity NRL (Naval Research Laboratory) Layered Ocean Model (NLOM) and the Pacific West Coast (PWC) model. The reduced gravity version of NLOM is capable of accurately depicting the large-scale oceanic circulation, but there are a few exceptions. The version of NLOM described here is wind-forced only, with no assimilation of altimeter or infrared frontal data. Thus, it cannot be expected to produce accurate hindcasts of sea surface height or upper layer velocities in regions dominated by mesoscale flow instabilities. Maps are provided to show the relative importance of direct wind forcing (deterministic) versus flow instabilities (nondeterministic). NLOM has mixed success in hindcasting sea level variations when compared to observed tide gauges; however, some of its highest correlations are at stations within the PWC domain. A comparison between observed and NLOM simulated drifting buoys has also been made. Ensemble forecasts of four model simulations generally produce an average simulated track that is closer to the observed drifter than any single simulation. However, the model cannot consistently beat a persistence forecast due to the large amount of nondeterminism in the upper layer velocity fields. NLOM will also provide boundary conditions for the PWC model. Two PWC simulations were run, one using climatologically wind-forced NLOM boundary conditions and one using climatologically wind-forced NLOM boundary conditions. The latter case showed improved sea level correlation over the former case. Satellite altimetry assimilation and a refinement in the boundary condition implementation should further improve the results.