Abstract:

Temporally distributed deterministic and stochastic excitation of the tangent linear forecast system gov-
erning forecast error growth and the tangent linear observer system governing assimilation error growth is 
examined. The method used is to determine the optimal set of distributed deterministic and stochastic 
forcings of the forecast and observer systems over a chosen time interval. Distributed forcing of an unstable 
system addresses the effect of model error on forecast error in the presumably unstable forecast error 
system. Distributed forcing of a stable system addresses the effect on the assimilation of model error in the 
presumably stable data assimilation system viewed as a stable observer. In this study, model error refers 
both to extrinsic physical error forcing, such as that which arises from unresolved cumulus activity, and to 
intrinsic error sources arising from imperfections in the numerical model and in the physical parameter-
izations.