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

东风波（EWs）是一种由东向西传播的低纬度波动性大气扰动，其脊到槽的尺度约为1,000公里。 EWS是热带地区重要的天气制造者，在飓风发展中发挥着关键作用。 大部分的研究集中在非洲的EWS上，它们沿着萨赫勒上空的东风急流向西传播到北大西洋上空。 这些波的成因往往解释在射流不稳定性，特别是东风射流，但类似的EW被发现在热带东太平洋的大尺度流动特征是非常不同的。 赤道东太平洋存在EW的一种解释是，它们起源于非洲EW，通过与非洲东风急流相关的过程形成，随后传播穿过大西洋和加勒比海到达东太平洋。 虽然有一些证据支持这一理论，但PI先前的工作（见AGS-1347738）表明，尽管该地区与萨赫勒地区存在明显差异，但东太平洋EW可以在热带东太平洋形成。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的影响，包括平均流量，云量和降水。 这里进行的模拟将使用一种“轻推”技术来限制背景流，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和预报（WRF）模型。 这项工作还将解决调制的EWs的季节内振荡的背景流。 额外的工作使用诊断技术，包括涡度和能量收支研究EW生成和传播的观测data.The工作具有社会意义，由于在热带气象学和飓风成因的关键作用EW。 如果发现在东太平洋的EW起源于非洲东风急流，他们可能是更可预测的，如果他们是由中美洲地形本地产生的，因此这项工作的结果有潜在的影响业务预报。 由于季节内振荡的提前时间较长，季节内振荡对EW活动的调制也具有实际意义。 此外，该项目还为一名研究生提供支持和培训，从而为这一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.