The prediction/correction cycle of the 4d Var. algorithm ...
The gradient (of the cost function, J with respect to the initial conditions) vector
The analytical expression for the 4d Var. gradient which has to be evaluated in the algorithm...
- + Indirect observations (including ones with a non-linear forward model) can be used
- + Efficient enough for global solution
- + Dynamical consistency
- + Can infer much knowledge about the system, including regions upstream of observations
- + Can analyse growing structures
- - Expensive to development and run
- - Adjoint coding is needed