| Abstrakt: |
The growth and propagation of African easterly waves (AEWs) remains an active area of research, especially for those that become tropical cyclones (TCs). This is partly due to the complex role of moisture, realized through AEW‐convection interactions. The goal of this study is to understand how environmental moisture plays a role in influencing the growth and propagation of a case of an AEW‐convection system, that became a TC and how that role relates to the West African Monsoon System. Moisture sensitivity experiments were performed in a regional and convection‐permitting novel configuration. It is found that in a moister environment, diabatic heating associated with convection coupled to the wave is shallower, ultimately, weakening the wave amplitude. Energetics are reduced in a moister environment as the African easterly jet strengthens, yet narrows, and shifts northward limiting interaction with the monsoon 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 ridge rather than in the trough region. Over western Africa, more continuous rainfall over the Guinea Highlands can inhibit phase locking with the AEW. 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. While the mean flow advection dominates the translation, further differences in phase speed arise from differences in convection within the wave. Plain Language Summary: African easterly waves (AEWs) which can serve as tropical cyclone (TC) precursors, remain an active area of research. This is in part due to the complicated interactions between the waves, clouds, and water vapor. Although we have learned that the further development of TC precursors coupled with cloud systems can benefit greatly from water vapor, we still have unanswered questions such as: would more water vapor in the atmosphere allow for more favorable interactions between the TC precursor and cloud systems that ultimately lead to a stronger and more efficient TC formation? A high‐resolution weather and climate model was used to perform a set of moisture‐varying experiments to evaluate the moisture dependency of a historic event of an AEW that became a TC. We found that more moisture can intensify the West African Monsoon system, but shifts the African easterly jet (the source of energy for AEWs) further north inhibiting wave growth over land. More moisture affects how fast the wave propagates both through the changes in the background flow and partly to those within the cloud‐system structure. More moisture results in less favorable types of clouds close to the wave, which weakens the system. Key Points: More moisture narrows and shifts the African easterly jet poleward, reducing the kinetic energy available to the African easterly waveIn a moister environment, more deep convection occurs but its phasing with the wave becomes sub‐optimal for intensificationMoisture reduces wave translation over land, leading to convection phase locking with the Guinea Highlands rather than with the wave itself [ABSTRACT FROM AUTHOR] |
