GEOS Forward Processing

The GEOS FP Atmospheric Data Assimilation System (GEOS ADAS) uses an analysis
developed jointly with NOAA’s National Centers for Environmental Prediction (NCEP), which
allows the Global Modeling and Assimilation Office (GMAO) to take advantage of the
developments at NCEP and the Joint Center for Satellite Data Assimilation (JCSDA). The
GEOS AGCM uses the finite-volume dynamics (Lin, 2004) integrated with various physics
packages (e.g, Bacmeister et al., 2006), under the Earth System Modeling Framework (ESMF)
including the Catchment Land Surface Model (CLSM) (e.g., Koster et al., 2000). The GSI
analysis is a three-dimensional variational (3DVar) analysis applied in grid-point space to
facilitate the implementation of anisotropic, inhomogeneous covariances (e.g., Wu et al., 2002;
Derber et al., 2003). The GSI implementation for GEOS FP incorporates a set of recursive filters
that produce approximately Gaussian smoothing kernels and isotropic correlation functions.
The GEOS ADAS is documented in Rienecker et al. (2008). More recent updates to the model
are presented in Molod et al. (2011). The GEOS system actively assimilates roughly 2 ´ 106
observations for each analysis, including about 7.5 ´ 105 AIRS radiance data. The input stream
is roughly twice this volume, but because of the large volume, the data are thinned
commensurate with the analysis grid to reduce the computational burden. Data are also rejected
from the analysis through quality control procedures designed to detect, for example, the
presence of cloud.
To minimize the spurious periodic perturbations of the analysis, GEOS FP uses the Incremental
Analysis Update (IAU) technique developed by Bloom et al. (1996).