OSE/OSSE Evaluation of the Impact of Targeted P3 Airborne Ocean Observations Obtained in Response to the Deepwater Horizon Oil Spill

Efforts to forecast the spreading of oil from the Deepwater Horizon oil spill require high-quality ocean nowcasts and forecasts of circulation in the Gulf of Mexico. Given that enhanced observational coverage for data assimilation is critically important for improving ocean model products, an emergency decision was made to fly P3 hurricane research aircraft missions to deploy AXBTs, AXCTDs, and AXCPs in grid patterns over the eastern Gulf of Mexico. Nine missions were flown between 7 May and 9 July 2010 to resolve mesoscale ocean features associated with the Loop Current, the detaching warm ring (eddy Franklin), and associated cyclones. To justify the continuation of these missions, efforts have commenced to use both OSEs and OSSEs to quantify their impact on ocean nowcasts and forecasts in the Gulf of Mexico. To perform an initial quick-turnaround evaluation, the 0.04° HYCOM Gulf of Mexico nowcast-forecast system is being used to perform an OSE. Twin experiments are being run, one with all observations assimilated and the other with all observations except P3 assimilated. Evaluation will involve comparing these two experiments along with comparing ocean forecasts initialized by these two experiments. Key evaluation metrics will include error reduction with respect to observations that were not assimilated and error reduction between trajectories of actual surface drifters and synthetic surface drifters advected by the model fields. Longer-term evaluation efforts will involve OSSEs using ocean models with different resolution and different data assimilation procedures to determine if the evaluation results are robust and also to design more optimal targeted observational strategies.