Moist Singular Vectors and African Easterly Waves

The ECMWF moist singular vector (MSV) package and forecast system has been used to extend our theoretical understanding of African easterly waves (AEW), concentrating on the role played by diabatic processes and non-normal mode structures.

Here the structure and growth mechanisms of non-developing AEWs from early in summer 2006 are presented and compared to those of more non-linear developing waves later in the monsoon season. The usefulness of MSVs in indicating the predictability of mature easterly waves is assessed and the extent to which the temporal development of these MSVs are found in the full forecast model are examined.

The work contributes to building a strong framework of understanding in which the observations resulting from the AMMA Special Observing Periods in summer 2006 may be considered. They help to determine whether MSVs targeted on West Africa are suitable for perturbations to initial conditions for ensemble prediction schemes and to determine what the elements of a new observing strategy may be.