EMC’s Data Assimilation Priorities
Figure L-1. Two forecast examples for Hurricane Ivan generated with the 2005 version of the NCEP Global Ensemble Forecast System. The ensemble in figure L-1a indicates a case with relatively small track uncertainty while that in figure L-1b shows a case with large uncertainty. Such information can be critical in emergency management applications. Overprotection can be avoided in the first, while increased vulnerability can be indicated in the second case.
igure L-2. Track error of (solid lines) and spread around the ensemble mean forecast (dashed lines) for 8/23-10/1 2004 Atlantic storms with the then operational (blue) and since implemented (red) versions of the NCEP Global Ensemble Forecast System. The closely matching error and spread curves indicate an ensemble forecast system that is statistically reliable for tropical storm prediction applications.
Figure L-3. NCEP global ensemble mean (green) and Global Forecast System (GFS, red) tropical storm track forecast errors (nm) averaged over the 2005 Atlantic Hurricane season. The error in the ensemble mean track is lower than that in the high resolution single forecast at all lead times. Of interest, the computational cost of generating either the lower resolution ensemble or the higher resolution single forecast is similar. (Courtesy of Dr. James Goerss, U. S. Navy.)
ESMF and the Common Modeling Structure
The ESMF is a multi-agency project to develop both a model superstructure and infrastructure. The superstructure is defined as a set of standards that allow new components to be coupled together with minimal impact on remaining components. Components may be defined as complete models (e.g. ocean model) or parts of a complete model (e.g. dynamics, physics, or parts of each). The infrastructure is a set of portable, reusable utility routines that can be used across different models.
Both superstructure and infrastructure must be flexible enough to allow evolution of NCEP’s models and general enough to accommodate both global and regional models and data assimilation modules for each application. It must also accommodate both primary and secondary models, some of which could originate from other parts of NOAA or from outside NOAA. ESMF-compatible code should be easily transferable to NCEP operations, given the high degree of modularity and portability standards inherent with ESMF.
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