Moisture Sensitivity of the African Easterly Wave-African Easterly Jet and Convection Systems

The growth and propagation of African easterly waves (AEWs) remains an active area of research partly due to the complex role of moisture in AEW-convection interactions. The goal of this study is to understand how environmental moisture plays a role in driving the growth and propagation of the AEW-convection system and how that role relates to the AEW-African easterly jet and AEW-West African Monsoon systems. Moisture sensitivity experiments were performed with the Model for Prediction Across Scales-Atmosphere (MPAS-A) in a novel regional and convection-permitting configuration. We found that in a moister environment, diabatic heating at the center of the AEW that is associated with coupled convection is shallower, ultimately weakening the wave amplitude. Energetics from the AEW-AEJ system are limited in a moister environment as the AEJ strengthens yet narrows, and shifts northward limiting interaction with the monsoon, convection from the ITCZ, and the wave-convection system. The more intense monsoonal flow in a moister environment can instigate the decoupling between convection and AEW as deep convection is more likely in the wave ridge rather than in the trough region. The westward translation of the wave is mainly determined by the mean flow. In a moister environment, the mean zonal flow is weaker and as a result, the westward translation speed of the wave due to mean flow advection is slower than in the other experiments. There is a small contribution to the westward translation from propagation highlighting the relevance of deep convection in AEW westward translation. The implications of this work are that more moisture, all else being equal, does not necessarily favor wave and convection growth driven by moisture. Moisture-sensitivity experiments like these cannot be directly related to climate studies (for example, the role of temperature and anthropogenic sources are not being considered here), but could inform potential differences in future, more moist climate states. The results are instead meant to help elucidate the role of moisture and convection in the African mean state, AEW growth, and genesis to enable better evaluation of weather and climate models in the tropics.