NOAA-AOML/UM-RSMAS Ocean Modeling and OSSE Center (OMOC)
|OMOC Research Projects:
Ocean OSSE Validation
Validation of the OMOC prototype ocean OSSE system is done through a rigorous evaluation procedure that compares OSSEs to reference Observing System Experiments (OSEs). The free-running Nature Run (NR) and the Data Assimilation System (DAS) with the Forecast Model (FM) are used (see here). The OSE assimilates real observations, while the OSSE assimilates synthetic observations sampled from the NR. Assimilated datasets from actual observations include along-track measurements of SSH anomaly (SSHA) from three altimeters: Jason-1, Jason-2, and Envisat, with respect to the mean dynamic topography field, all obtained from the Archiving, Validation, and Interpretation of Satellite Oceanographic (AVISO) data center. SST from the satellite-derived Multi-Channel Sea Surface Temperature (MCSST) product, in-situ measurements collected by ship and surface buoys, and in-situ measurements collected by surface drifters, were all obtained from the USGODAE server and used for assimilation. Subsurface measurements include XBT profiles collected from ships that were also obtained from the USGODAE server. Subsurface measurements also include airborne AXBT, AXCTD, and AXCP profiles collected by the NOAA WP-3D hurricane research aircraft on nine flight days between 8 May and 9 July 2010 (Shay et al., 2011). A set of synthetic observations identical to the above actual observations were sampled from the NR. To each observation type, realistic errors are added. Instrument and other local random errors are added to each individual observation using a random number generator that assumes a Gaussian probability density distribution.
Flow chart of OSSE system validation. Blue arrows denote assimilation of real and synthetic observation into the coupled Forecast and DA systems (the OSEs and OSSEs). The black arrows point to the statistical comparisons performed between modeled and observed fields. (Note: For a bigger view please click on the figure.)
Seven experiments that compare OSSEs to reference OSEs are analyzed. The OSE experiments are evaluated by comparing actual airborne profiles to the same profiles extracted from the DAS simulations. The OSSE experiments are evaluated by comparing synthetic airborne profiles simulated from the NR with realistic errors added to the same synthetic profiles extracted from the DAS simulations. Experiment OSE1 assimilates all real observations while OSE2 denies the WP-3D profiles for evaluation purposes, and OSE3 further denies two of the three altimeters (Jason-2 and Envisat). Experiments OSSE1, OSSE2, and OSSE3 are performed that are identical except for assimilating synthetic observations. For comparison to unconstrained simulation results, experiment DAFREE is used. The comparisons of OSSEs to reference OSEs demonstrated that the OSSE system produces valid impact assessments without requiring calibration. For more details please refer Halliwel et. al. (2014).
EXAMPLE OF STATISTICAL EVALUATION OF THE EXPERIMENTS
All temperature values measured between 0 and 250m for OSE (top left) and OSSE (top right) experiments, and H20 for OSE (bottom left) and OSSE experiments (bottom right). The blue, red and black lines are for OSE2 (OSSE2), OSE3 (OSSE3) and DA-FREE respectively. (Note: For a bigger view please click on the images.)
Halliwell, Jr., G. R., A. Srinivasan, V. Kourafalou, H Yang, D. Willey, M. Le Hénaff, and R. Atlas, 2014. Rigorous evaluation of a fraternal twin ocean OSSE system in the open Gulf of Mexico. J. Atm. Ocean. Techn. 31(1):105-130, doi: 10.1175/JTECH-D-13-00011.1.
Shay, L. K., B. Jaimes, J. K. Brewster, P. Meyers, E. C. McCaskill, E. Uhlhorn, F. Marks, G. R. Halliwell, Jr., O-M Smedstad, and P. Hogan, 2011. Airborne ocean surveys of the Loop Current complex from NOAA WP-3D in support of the Deep Water Horizon oil spill. In Monitoring and Modeling the Deepwater Horizon Oil Spill: A Record-Breaking Enterprise, Liu et al., Eds., AGU Monograph Series, 131-151.