The DAO GEOS-3 data assimilation system (DAS) has been operational for over a year in support of the NASA Terra satellite. A number of DAO staff members have been devoted for the past few years to develop this system from its GEOS-1 origins. We have made considerable improvement from its dynamical core to its physical packages and analysis system. A forth order dynamical core replaced the GEOS-1 second order core; a state-of-the-art land surface model was implemented; the physical-space statistical analysis system substituted the optimal interpolation system of GEOS-1; an off-line complex quality control and an on-line adaptive quality control are in place; a forecast bias estimation procedure has been implemented; and an interative retrieval algorithm can now be used to handle the vast amount of satellite data, replacing the need to use third-parties pre-computed retrievals.

The GEOS-3 DAS represents not only a scientifically large improvement from its GEOS-1 antecedent but it also matured enormously in its software quality and modernization. The GEOS-3 DAS is largely FORTRAN-90; it has an MPI general circulation model; and it is about to replace its multitasked analysis system by an MPI version of it.

In this presentation we will give an overview of the current state of the DAO Terra GEOS-3 DAS.