Improving Understanding and Prediction of Atlantic Tropical Cyclogenesis

知识优势：这项研究的目标/任务是：(A)对与非洲东风波有关的两个热带气旋案例进行6-7天的云解模拟：其中一个发展成飓风，另一个没有发展成飓风；(B)探索这两个风暴的可预测性；(C)研究不同环境条件和内部动力学在确定不同热带气旋的成因和演变情景中的作用。将讨论以下三个研究问题：(1)当相关的空中预警系统仍位于西非上空时，这两个技术控制系统在多大程度上是可预测的？(2)撒哈拉空气层(SAL)、AEW和对流产生的涡旋(CGV)对大西洋热带气旋的形成有什么影响？(3)低层冷异常转化为暖心涡的过程是什么？气旋的成因是自下而上还是自上而下？假设：(A)大气环流通过伸展为深层对流和旋转的组织提供必要的准平衡上升运动；(B)热带气旋的生成自下而上通过涡旋热塔、向内的位涡通量汇合和通过CGV合并的高层增长；以及(C)垂直切变、干侵入和与SAL相关的稳定气团的汇聚决定了环流是否可以发展为具有飓风强度的热带气旋。为了验证/解决上述假设/问题，首席调查员将使用最精细网格分辨率为1公里的天气研究和预报(WRF)模式来模拟TC系统。然后，将进行集合积分，用随机扰动或西非上空的现场观测初始化，以检查误差增长特征和来自AEW的TC成因的可预报性。将进行诊断分析和预算计算，以澄清AEW的三维结构和演变，以及SAL与TCS的关系，并研究CGV的高层增长和热力学转换。SAL和AEW对热带气旋生成的影响将通过敏感性模拟来研究，方法是利用分段位涡反演技术改变它们在模式初始条件中的大小和分布。广泛影响：该项目的成功完成将提高对来自AEW的大西洋TC成因的理解和预测，特别是SAL与大西洋风暴的相互作用。结果可能有利于大西洋飓风的业务5天预报，并改进疏散规划和减灾，从而促进沿海地区的生命和财产保护。此外，该项目将支持研究生教育，并产生同行评议的期刊出版物和会议报告。

Intellectual merit: The goals/tasks of this research are to (a) perform 6-7 day cloud-resolving simulations of two tropical cyclone (TC) cases associated with African Easterly Waves (AEWs): one of which developed into a hurricane and the other did not; (b) explore the predictability of the two storms; and (c) examine the roles of different environmental conditions and internal dynamics in determining the different TC genesis and evolution scenarios. The following three research questions will be addressed: (i) To what extent are the two TCs predictable when the associated AEWs were still located over West Africa? (ii) What are the effects of the Saharan Air Layer (SAL), AEWs and convectively generated vortices (CGVs) on Atlantic TC genesis? (iii) What are the processes accounting for the transformation of low-level cold anomalies to a warm-cored vortex? Does TC genesis from AEWs occur from the bottom upward or the top downward? It is hypothesized that (a) AEWs provide the necessary quasi-balanced upward motion for the organization of deep convection and rotation via stretching; (b) TC genesis occurs from bottom up through vortical hot towers, inward potential vorticity flux convergence and upscale growth through CGV mergers; and (c) vertical shear, dry intrusion and convergence of the stable air mass associated with the SAL determine whether or not AEWs could develop to TCs with hurricane intensity. To validate/address the above hypotheses/questions, the Principal Investigator will simulate the TC systems using the Weather Research and Forecast (WRF) model with the finest grid resolution of 1 km. Then, ensemble integrations, initialized with random perturbations or with field observations over West Africa, will be carried out to examine the error growth characteristics and the predictability of TC genesis from AEWs. Diagnostic analyses and budget calculations will be performed to clarify the three-dimensional structures and evolution of the AEWs, and the SAL in relation to the TCs, and to study the upscale growth of CGVs and the thermodynamic transformation. The effects of the SAL, and AEWs on TC genesis will be investigated through sensitivity simulations by modifying their magnitudes and distributions in the model initial conditions with the piecewise potential vorticity inversion technique. Broad impacts: Successful completion of this project will improve understanding and prediction of Atlantic TC genesis from AEWs, particularly the interaction of the SAL with Atlantic storms. Results may benefit the operational 5-day prediction of Atlantic hurricanes, and improve evacuation planning and disaster reduction, thereby facilitating the protection of life and property in the coastal regions. In addition, this project will support graduate education and generate both peer-reviewed journal publications and conference presentations.