Prototype Ocean OSSE

Prototype Ocean OSSE
A prototype Gulf of Mexico ocean Observing System Simulation Experiment (OSSE), that follows the complete set of procedures developed for the atmosphere, has been developed at the Ocean Modeling and OSSE Center OMOC, a joint center involving the Atlantic Oceanographic and Meteorological Laboratory (AOML), the Rosenstiel School for Marine and Atmospheric Science (RSMAS)of the University of Miami (UM), and the Cooperative Institute for Marine and Atmospheric Studies (CIMAS). It includes:
  1. the Nature Run (NR) – performed by a free running state-of-the-art ocean general circulation model;
  2. the Data Assimilation System (DAS) – consisting of the Forecast Model (FM), which is different from the NR model and is coupled to a Data Assimilation (DA) procedure;
  3. a toolbox to simulate realistic synthetic observations from the NR.

The models used for NR and DAS/FM in the OMOC prototype OSSE are fraternal twin models, based on the Hybrid Coordinate Ocean Model HYCOM, which allows flexibility in several model attributes. Specifically, the OMOC twin models have substantially different configurations with different physics and truncation errors, hence called fraternal twins. The NR is performed at 0.04° resolution while the FM is configured on a 0.08° Mercator mesh that consists of every other grid point of the NR mesh to introduce additional truncation errors. More details and the DA procedure are given in Halliwell et al. (2014). A rigorous evaluation comparing OSSEs to reference Observing System Experiments (OSEs) demonstrated that the OSSE system produces valid impact assessments without requiring calibration. Please go here to see details of the OSSE system validation.


Six-year (2005-2010) mean fields of SSH, SST, and SSS from experiments NR and unconstrained FM are compared to each other and to mean fields of SSH obtained from the CNES (Centre National d’Etudes Spatiales) mean dynamic topography derived from altimetry and mean fields of temperature and salinity from the Navy GDEM3 (Generalized Digital Environment Model) ocean climatology (Carnes, 2009). The mean patterns of all variables produced by the two experiments are similar to each other and to the climatological mean patterns. This similarity demonstrates that both the NR and FM produce statistically realistic climatological structure as required for a valid OSSE system. (Note: For a bigger view please click on the figure.) 


Carnes, M., 2009. Description and evaluation of GDEM-V3.0. Naval Research Laboratory Tech. Rep. NRL/MR/7330-09-9165, 21pp.
Halliwell, G.R., A. Srinivasan, V.H. Kourafalou, H. Yang, D. Willey, M. Le Hénaff and R. Atlas, 2014. Rigorous Evaluation of a Fraternal Twin Ocean OSSE System for the Open Gulf of Mexico. J. Atm. Ocean. Techn. 31(1):105-130, doi:10.1175/JTECH-D-13-00011.1.