Improving Understanding and Prediction of Atlantic Tropical Cyclogenesis

知识价值：本研究的目标/任务是：(a)对两个与非洲东风波（AEWs）有关的热带气旋（TC）进行6-7天的云分辨模拟：其中一个发展为飓风，另一个没有；(b)探讨两场风暴的可预测性；(c)研究不同的环境条件和内部动力在确定不同的TC发生和演化情景中的作用。将解决以下三个研究问题：(i)当相关的预警系统仍位于西非上空时，两个预警系统在多大程度上是可预测的？（ii）撒哈拉空气层（SAL）、AEWs和对流涡旋（CGVs）对大西洋TC形成的影响是什么？（iii）低层冷异常向暖核涡旋转变的过程是什么？由AEWs形成的TC是由下向上还是由上向下？假设(a) AEWs通过伸展为深层对流和旋转的组织提供了必要的准平衡上升运动；(b)涡状热塔由下向上形成，位涡通量向内辐合，CGV并合向高档增长；(c)垂直切变、干侵入和稳定气团的辐合决定了预警系统能否发展成具有飓风强度的tc。为了验证/解决上述假设/问题，首席研究员将使用天气研究与预报（WRF）模型模拟TC系统，网格分辨率最高为1公里。然后，利用随机扰动初始化或西非地区的野外观测进行集合积分，以检验AEWs的误差增长特征和TC发生的可预测性。通过诊断分析和预算计算，阐明AEWs的三维结构和演化，以及与tc相关的SAL，研究cgv的高级化生长和热力学转变。利用逐段位涡量反演技术，通过灵敏度模拟，通过修正模式初始条件下SAL和AEWs的大小和分布，研究了它们对TC形成的影响。广泛的影响：该项目的成功完成将提高对来自预警系统的大西洋TC成因的理解和预测，特别是SAL与大西洋风暴的相互作用。研究结果可用于大西洋飓风5天预报的操作，改进疏散规划和减灾工作，从而促进沿海地区生命财产的保护。此外，该项目将支持研究生教育，并产生同行评审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.