The Interaction between Mesoscale Convective Systems and African Easterly Waves

The role of African Easterly Waves (AEWs) in initiating and modifying Mesoscale Convective Systems (MCSs), and the upscale role of the MCSs on AEWs is currently not well understood. Here we investigate this interaction from a mesoscale perspective in order to understand this two-way interaction. Schwendike and Jones (2010) studied the two-way relationship between convection and its environment over West Africa and the Atlantic using a convection-allowing simulation. We take a similar approach, expanding on their results by examining multiple MCSs, and with a specific focus on their relationship with the AEW. This focus is motivated by Laing et al. (2008), who showed that MCSs regularly travel at different speeds relative to the AEW and are present in all phases of the AEW, although more prevalent in the northerlies and the trough, than the southerlies and the ridge. It is therefore likely that MCSs interact with AEWs in different ways at different stages during their lifetime.

We track multiple MCSs in convection-allowing WRF simulations as they propagate through or with AEW envelopes. We characterize the AEW-MCS relationship as those moving slower, faster, or with the AEW, and by what phase of the AEW the MCS is present in. We examine how MCSs affect their environment, relating this back to concurrent changes in the AEW. This is carried out using PV, moisture, and thermodynamic budgets. In addition, we examine how the varying phases of AEWs modify the environment to initiate or modulate each MCS. For this we examine how the AEW adjusts the thermodynamic, moisture, and shear prior to and during the MCS lifetime. The aim is that this work will provide a detailed model of AEW-MCS interaction based on a broad set of MCS-AEW interactions.