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Improved Surface Temperature Analysis
Within the Eta 3DVar System
Background:
- Eta forecasts initialized with the GFS 3DVar analysis were found to be superior to Eta forecasts initialized with the Eta 3DVar analysis
- Assimilation of surface temperature in the Eta 3DVar shown to account for nearly all of the forecast degradation
- It appears that the Eta 3DVar is handicapped by being cast in the step-mountain framework, because Eta is not terrain following, it is difficult to cleanly limit the vertical influence of surface data
- Surface temperatures overland were turned off as a temporary fix since September 2003
- Anisotropic covariances with vertical stability dependence cast in a terrain following coordinate (at least near the surface) is been the long-term goal