Incremental Linear Normal Mode Initialization in Four-Dimensional Data Assimilation

Abstract

A five-day data assimilation experiment is described in which linear normal mode initialization is used to suppress the transient gravity waves. The initialization is performed on increments to the model fields resulting from the insertion of data. The scheme is well behaved and is found to produce analyses which are similar to those produced by a scheme in which the more usual nonlinear normal mode initialization is used. The incremental linear scheme, however, is found to maintain a much stronger meridional circulation in the tropics than the nonlinear scheme. An examination of the noise characteristics shows that the incremental linear scheme allows a higher level of transient gravity wave activity.