Intraseasonal Variability of the West African Monsoon

麦登-朱利安涛动（MJO）调节大西洋的热带气旋和东风波，为提前几周预测大西洋飓风活动增强提供了可能。该项目将解决几个主要的悬而未决的问题：(i)北半球夏季MJO影响大西洋的遥相关途径，（ii）一旦MJO建立遥相关，西非和大西洋的降水实际上是如何由MJO发起的，（iii） MJO调节非洲东风波的机制，以及（iv）这些东风波如何反馈影响MJO。将使用一系列模型来理解MJO影响大西洋和西非的远相关途径，包括非发散正压涡度方程、球体上的过滤浅水模型和大气环流模型。由于假设MJO首先引发了苏丹达尔富尔地区的对流异常，因此将使用几种观测产品（如云档案用户服务（CLAUS）亮度温度、热带降雨测量任务（TRMM）和全球降水气候学项目（GPCP）降水）来记录西非降水作为MJO相位函数的时间演变。本文将使用原始方程模型验证由MJO驱动的达尔富尔地区强烈的加热变化对西非和大西洋的东风波活动幅度的调节，并验证MJO相关的非洲东风急流结构变化显著影响东风波增长的假设。此外，将在卫星和再分析数据集中研究mjo相关的东风波变率对西非和大西洋柱综合季节内水分收支的影响。这项工作的更广泛影响具有教育意义，并有可能改善我们对大西洋热带气旋活动增强期的中期预测前景。

The Madden-Julian Oscillation (MJO) modulates tropical cyclones and easterly waves in the Atlantic, providing the potential for prediction of enhanced Atlantic hurricane activity a couple of weeks in advance. This project will address several major outstanding questions: (i) the teleconnection pathway by which the MJO affects the Atlantic during boreal summer, (ii) how west African and Atlantic precipitation is actually initiated by the MJO once the teleconnection is established, (iii) the mechanism by which the MJO modulates African easterly waves, and (iv) how these easterly waves feed back to influence the MJO.A hierarchy of models will be used to understand the teleconnection pathways by which the MJO affects the Atlantic and west Africa, including the non-divergent barotropic vorticity equation, a filtered shallow water model on a sphere, and an atmospheric general circulation model. Because it is hypothesized that the MJO first initiates convection anomalies over the Darfur region of the Sudan, several observational products (e.g. Cloud Archive User Service (CLAUS) brightness temperature, Tropical Rainfall Measuring Mission (TRMM) and Global Precipitation Climatology Project (GPCP) precipitation) will be used to document the time evolution of precipitation in west Africa as a function of MJO phase. A primitive equation model will be used to test the hypothesis that strong heating variations over the Darfur region forced by the MJO modulate the amplitude of easterly wave activity in west Africa and the Atlantic, and test the hypothesis that MJO-related structural changes in the African easterly jet significantly affect easterly wave growth. Further, the impact of MJO-related easterly wave variability on the column-integrated intraseasonal moisture budget in west Africa and the Atlantic will be examined in satellite and reanalysis datasets. The broader impacts of this work are educational and in the potential to improve our prospects for medium range prediction of periods of enhanced Atlantic tropical cyclone activity.