The role of African Easterly Wave Variability in North Atlantic Cyclogenesis

African easterly waves (AEWs) are an integral part of the West African and tropical Atlantic climate. They modulate daily rainfall over West Africa during the monsoon and can impact downstream tropical cyclogenesis (Hopsch et al., 2010). They are also implicated in the generation and transport of large quantities of mineral dust from North Africa to the Caribbean (Jones et al., 2004) and which can modify the West African monsoon and interact with the development of tropical cyclones (Jury and Santiago, 2010). Furthermore, 85% of 'major' hurricanes (category 3 and above on the Saffir Simpson scale) in the Atlantic develop from AEWs (Landsea, 1993) which in turn drives economic and insured losses on the eastern seaboard of the United States (Lott and Ross, 2006). Despite their importance, the detailed aspects of AEW genesis and evolution are not well understood. In particular, our understanding of the processes that influence whether or not an AEW will develop near the west coast of Africa and spawn a tropical cyclone is poor. The aim of this project is to improve our understanding of the physical processes that enhance and suppress hurricane development associated with AEWs and their interaction with the large-scale environment This is addressed firstly by getting a better understand of the key atmosphere and ocean interactions that govern the AEW evolution over the Atlantic, as well as the interactions between dynamics and convection at intraseasonal and shorter timescales. Secondly, by determining information about the statistics of the AEWs in the Tropical Atlantic which are important for downstream cyclogenesis and prediction, such as the variability of their number and intensity. The specific scientific points we are investigating are:

(i) AEW spatial distribution and variability at various timescales, and how the structure of AEWs can encourage cyclogenesis.

(ii) the role of the African Easterly Jet in AEW propagation and development in the context of the large scale environment. The role of dry air (either advected in from the mid-latitudes or the Saharan Air Layer (SAL)) is of significant interest here.

(iii) the effects of SST anomalies and large scale modes of convection on intraseasonal and interannual timescales in influencing AEW variability, cyclogenesis and possible landfall. It is hoped this work will aid the creation of an enhanced seasonal forecast scheme for Atlantic cyclones, the results of which could be made available to the wider scientific and business community.