The Interannual and Intraseasonal Variability of African Easterly Wave Activity

This study focuses on the nature and causes of interannual and intraseasonal variability of African easterly wave (AEW) activity. The motivation for this work is to improve our understanding of the characteristics and causes of variability of AEWs and how the two-way interaction of weather and climate is manifested over West Africa.

In the first part of the work, new metrics for AEW activity have been developed based on an Empirical Orthogonal Function approach. This approach is shown to effectively capture the structure and evolution of AEWs and is able to emphasize different AEW characteristics. The commonly used AEW index, eddy kinetic energy, is also incorporated to provide an alternate measure of the wave activity for comparison.

The second half of the research will analyze how the variability of AEW activity is manifested in changes in AEW characteristics and also how these vary in association with the large-scale environment. Three key factors regarding AEW variability will be investigated: the environment, the character of the convection coupled to the waves, and the triggering mechanism proposed by Thorncroft et al. (2008). The variation of the environment, for example, the jet and moisture supply, can significantly impact the nature of AEWs. In addition, the extent to which the convection is coupled to the waves has a strong impact on the characteristics of AEWs with respect to intensity and phase speed. Lastly, particular emphasis will be given to how the large-scale environment such as that provided by the MJO and equatorial modes modulates the AEW genesis and activity.

While this research is currently conducted with ECMWF Interim reanalysis data, a comparison with other reanalysis datasets will be made to evaluate the robustness of the key findings.