Event Type:

Applied Mathematics and Computation Seminar

Date/Time:

Friday, January 23, 2009 - 04:00

Location:

Gilkey 113

Event Link:

Guest Speaker:

Dacian Daescu

Institution:

Portland State University

Abstract:

The equations of the forecast sensitivity to observations and to the background estimate in a four dimensional variational data assimilation system (4DVAR DAS) are derived from the first order optimality condition in unconstrained optimization. Estimation of the impact of uncertainties in the specification of the error statistics is considered by evaluating the sensitivity to the observation and background error variances.

A continuation approach is introduced to analyze and develop adjoint-based methods for observation impact estimation in variational data assimilation. High-order accurate measures consistent to nonlinear 3DVAR/4DVAR analysis schemes are derived and issues related to the practical implementation are discussed. The potential use of the observed-minus-analysis increments to observation impact estimation is further investigated. Results are presented with the NASA/GMAO GEOS-5 DAS and idealized 4DVAR experiments with a shallow-water model.