The spring 2000 Global Data Assimilation Upgrade Package
BELL, R.S. ; Li, D. ; Ingleby N.B. ; Renshaw, R.
Global 3d-Var (Lorenc et al 2000) has been our operational data assimilation system since March 1999. A successful series of change were made during 1999 (Bell et al, 1999) to build on the initial success of the system. This paper describes a further set of revisions to the global data assimilation system which were implemented on 16th May 2000. In brief the changes involve: Use of Observed rather than retrieved radiance from TOVS/ATOVS; Revised background error covariance model; Use of model background at correct observation time. The package of changes was tested over two periods from 6th-29th June 1999 and from 26th Nov-26th Dec 1999, each change having first been proven individually. The results of the objective verification were very favourable with improvements in the composite skill score of 1.0 in the June case and 0.6 in the December case. This equates to about 1.8 points (1.7%) on the new Index.
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