Regionally Enhanced Global (REG) Data Assimilation (DA)

We discuss a data assimilation technique that prepares a global analysis and multiple limited area analyses by a single computational process. The technique computes a high-resolution global analysis increment, which it then uses to update both the global and limited area background state estimates. The main advantages of the technique are a reduction of the complexity and maintenance cost of the data assimilation computer codes, a lower overall computational cost of data assimilation, and potentially more accurate global and limited area analyses and forecasts. We have already developed a prototype data assimilation system by implementing the technique on the operational model and data assimilation computer codes of the U.S. Navy. In this talk, we present the results of analysis/forecast experiments with a reduced resolution version of the prototype system for different choices of the background state estimates. The results suggest that REG DA leads to a 1-3% average reduction of the forecast errors in the 5-day forecast range for NAVGEM and the 3-day forecast range for COAMPS.