Data assimilation for high-resolution limited-area models

The present status of development of data assimilation techniques for high resolution limited area models is reviewed and various candidates for a new generation of a data assimilation system are compared. It is concluded that data assimilation based on 3-dimensional or 4-dimensional variational techniques is the most promising approach. Further investigations are needed, however, to find out whether variational data assimilation is feasible over ``limited'' model integration areas or whether global/hemispheric model integration areas have to be introduced for high resolution limited area data assimilation purposes. The main problem in this connection is the rapid propagation of forecast errors on a global or at least hemispheric atmospheric scale within a time-scale of a few days.