A Modeling Study of Easterly Waves and Their Intraseasonal Variability in the East Pacific

东风波（EWs）是一种在低纬度地区由东向西传播的波浪形大气扰动，其脊槽大小约为1,000公里。在大部分热带地区，EWs是重要的天气制造者，在飓风发展中起着关键作用。大部分的研究都集中在非洲EWs上，它们沿着萨赫勒地区的东风气流向西传播，穿过北大西洋。这些波的成因通常用急流的不稳定性来解释，特别是东风急流，然而在热带东太平洋也发现了类似的ew，那里的大尺度流动特征非常不同。赤道东太平洋存在东太平洋气旋的一种解释是，它们起源于非洲气旋，在与非洲东风急流相关的过程中形成，随后跨越大西洋和加勒比海传播到东太平洋。虽然有一些证据支持这一理论，但PI之前的工作（见AGS-1347738）表明，尽管热带东太平洋地区与萨赫勒地区之间存在明显差异，但东太平洋地区也可能形成EWs。该项目验证了东太平洋ew主要由中美洲山脉下风地形扰动的高级增长引起的假设。PI的数值模拟表明，当中美洲地形变平时，EW活动急剧减少，但这些模拟是粗糙的，因为地形的去除对该地区的气象学有各种显着影响，包括平均流量，云量和降水。在这里进行的模拟将使用“轻推”技术来约束背景流，尽管地形和其他因素发生了变化，以便在现实环境中对特定强迫机制产生的波浪进行更集中的研究。这项工作将在允许对流的配置中使用天气研究与预报（WRF）模型。这项工作还将讨论背景流的季节内振荡对EWs的调制。额外的工作使用诊断技术，包括涡度和能量收支来研究观测数据中的电子波产生和传播。由于EWs在热带气象学和飓风发生中的关键作用，这项工作具有社会意义。如果在东太平洋发现的EWs起源于非洲偏东急流，那么它们可能比由中美洲地形局部产生的EWs更容易预测，因此这项工作的结果对业务预报具有潜在的影响。考虑到季节内振荡的较长前置时间，由季节内振荡调制电子束活动也具有实际意义。此外，该项目为研究生提供支持和培训，从而为该研究领域的未来劳动力提供支持。

Easterly waves (EWs) are wavelike atmospheric disturbances with a ridge-to-trough size of roughly 1,000km which propagate from east to west at low latitudes. EWs are important weather makers in much of the tropics and play a critical role in hurricane development. Much of the research has focused on African EWs, which along the easterly jet over the Sahel and propagate westward over the North Atlantic. The genesis of these waves is often explained in terms of jet instabilities particular to the easterly jet, yet similar EWs are found in the tropical eastern Pacific where the large-scale flow characteristics are very different. One explanation for the presence of EWs in the eastern equatorial Pacific is that they originated as African EWs, formed through processes associated with the African easterly jet, and subsequently propagated across the Atlantic and the Caribbean to reach the eastern Pacific. While there is some evidence to support this theory, previous work by the PI (see AGS-1347738) suggests that EWs can form in the tropical eastern Pacific despite the clear differences between this region and the Sahel.This project tests the hypothesis that east Pacific EWs are largely caused by upscale growth of topographically-generated disturbances downwind of the mountain ranges of Central America. Numerical simulation by the PI have shown that EW activity is dramatically reduced when the Central American topography is flattened, but these simulations were crude as the removal of topography has a variety of dramatic effects on the meteorology of the region including mean flow, cloudiness and precipitation. Simulations to be performed here would use a "nudging" technique to constrain the background flow despite modifications to topography and other factors so that a more focused study of wave generation by specific forcing mechanisms can be performed in a realistic setting. The work would use the Weather Research and Forecasting (WRF) model in a convection-permitting configuration. The work would also address the modulation of EWs by intraseasonal oscillations of the background flow. Additional work uses diagnostic techniques including vorticity and energy budgets to study EW generation and propagation in observational data.The work has societal relevance due to the key role of EWs in tropical meteorology and hurricane genesis. If EWs found in the eastern Pacific originated in the African easterly jet they may be more predictable than if they are generated locally by Central American topography, thus the results of this work have potential implications for operational forecasting. The modulation of EW activity by intraseasonal oscillations is also of practical interest given the long lead times of intraseasonal oscillations. In addition, the project provides support and training for a graduate student, thereby providing for the future workforce in this research area.