Intraseasonal Variability of the West African Monsoon

马登-朱利安振荡（MJO）调制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性。该项目将解决几个主要的未决问题：（i）在北方夏季，MJO影响大西洋的遥相关路径，（ii）一旦遥相关建立，西非和大西洋降水实际上是如何由MJO引发的，（iii）MJO调制非洲东风波的机制，以及（iv）这些东风波如何反馈影响MJO。一系列模式将用于理解MJO影响大西洋和西非的遥相关路径，包括非辐散正压涡度方程，球上的过滤浅水模式和大气环流模式。由于假设MJO首先在苏丹达尔富尔地区引发对流异常，因此将使用几种观测产品（例如云档案用户服务（CLAUS）亮温、热带降雨测量使命任务（TRMM）和全球降水气候学项目（GPCP）降水）记录西非降水随MJO阶段变化的时间演变。一个原始方程模型将被用来测试的假设，即强烈的加热变化在达尔富尔地区迫使的MJO调制的东风波活动在西非和大西洋的振幅，并测试的假设，MJO相关的结构变化在非洲东风急流显着影响东风波的增长。此外，MJO相关的东风波变率对列综合季节内水分收支在西非和大西洋的影响将在卫星和再分析数据集检查。这项工作的更广泛影响是教育性的，并有可能改善我们对大西洋热带气旋活动增强时期的中期预测前景。

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.