Parallel-in-Time 4D-Var: Experiments with Simple Models

In four-dimensional variational data assimilation (4DVAR) the majority of the wall clock time is spent calculating the tangent-linear and adjoint. Recent work, by others, indicates that it may be possible to construct at 'time-parallel' version of 4DVAR, in which the full assimilation window is broken down into a nubmer of shorter assimilation windows - each run in parallel.

In this presentation, we showresults of experiments in which observations are assimiliated using 3DVar, 4DVar, and parallel-in-time 4DVARr, for the Lorenz 96 model and for a simple Quasi-Geostrophic model. Results will show differences in wall clock time and forecast skill from 3DVAR, 4DVAR, and parallel-in-time 4DVAR assimilation.