"In an earlier Office Note (86), experimental results were presented comparing the relative efficiencies of implicit and explicit integration methods in four-dimensional assimilation. Those experiments were simulations, in the sense that the asynoptic "observations" that were assimilated were generated by the model itself. The main conclusion was that the adjustment of the model to the inserted data proceeds more slowly in the implicit than in the explicit model, but not enough to offset the implicit method's economic advantage. We have repeated those experiments using real VTPR data. This Note presents the results of the later experiments in terms of a further comparison of explicit versus implicit methods. Beyond this comparison, the experiments yield insight into four-dimensional assimilation generally, and it is primarily for this reason that we document the results in this Note"--Introduction.

National Weather Service (NWS)

United States