4DVAR Assimilation of ADCP Data with the Navy Coastal Ocean Model using the Cycling Representer Method
Abstract
40-variational assimilation (4DVAR) is used to combine ADCP velocity observations with the Navy Coastal Ocean model (NCOM) to obtain an optimal solution that minimizes a cost function containing the weighted squared errors of velocity measurements, initial conditions, boundary conditions, and model dynamics. However, in order to converge to the global minimum of this cost function,the ocean model (and its adjoint) must be linear. Ocean models, especially those that are designed to resolve baroclinic and mesoscale processes, are typically highly-nonlinear and must be linearized. Tangent linearization is a linearization method that is performed by expanding the nonlinear dynamics about a background field using the first order approximation of Taylor's expansion. The accuracy and stability of this tangent linearized model (TLM) is a very sensitive function of the background accuracy, the level of nonlinearity of the model, complexity of the bathymetry, and the complexity of the flow field. Therefore, in high-resolution coastal domains, the TLM is only going to be stable for a relatively short period 0! time. In this paper, assimilation experiments are performed in a high-resolution Mississippi Bight coastal domain The TLM of NOOM for this domain is only accurate for about 1 day. The representer method is used to solve this highly nonlinear, weak-constraint, 4DVAR problem. However, due to the shortage...
Document Details
- Document Type
- Technical Report
- Publication Date
- Jan 30, 2008
- Accession Number
- ADA476547
Entities
People
- Gregg A. Jacobs
- Hans E. Ngodock
- Scott Smith
Organizations
- United States Naval Research Laboratory