Convection and Balanced Tropical Dynamics

该项目研究了热带对流的基本动力学，即在热带积云中发现的与强降水相关的翻转运动，它与嵌入其中的大尺度水平大气环流相互作用。这项工作的重点是非洲东风波（AEWs）内部对流的演变，这是一种波长为2000至2500公里的热带波扰动，起源于西非，向西传播到热带北大西洋。预警在热带风暴和飓风的形成中起着关键作用，因此特别令人感兴趣。这项工作是基于初步发现，表明一系列气象关系可能导致大雨的发展。一是在对流层中层（比如600mb）的气旋涡度（一种测量水平环流中气旋旋转或切变强度的方法）可以产生较高的温度和较低的温度，从而减少了该水平附近潮湿对流的不稳定性。对流层中部不稳定性的减少导致了积云的底部重质量通量剖面，其中云内的大部分上升运动发生在对流层的中低层。底部重质量通量剖面反过来又导致对流输出静态能量的效率降低，这就需要更强的对流来维持能量输出。同时，较低的不稳定性导致对流区通过水分准平衡过程变湿（部分结果来自AGS-1148594下的研究），因此湿度的增强和更剧烈的翻转运动都有助于降雨的增强。通过T-PARC/TCS-08 （Thorpex太平洋亚洲区域运动/热带气旋运动实验）和PREDICT（热带云系统低气压前调查）的现场活动数据，初步研究了这些关系。本文所做的工作进一步验证和探索了从中层涡度到对流降水的因果关系链，并考虑了更强的对流反过来影响中层涡度和大尺度环流的机制。这项工作是通过检查观测数据（包括来自实地活动、卫星和再分析产品的数据）和构建代表假设关系的简单模型来进行的。如上所述，在预警系统中导致对流降水发展的过程具有实际和科学意义，因为它们可能导致大西洋飓风登陆。更具体地说，这项工作的重点是热带风暴形成的早期阶段，这是热带气旋预报中最困难的挑战之一。该项目还促进了国际科学合作，因为它涉及与智利和克罗地亚的合作者合作，并在一个为西班牙裔服务的机构开展工作。此外，该项目还为一名研究生和一名本科生暑期实习生提供支持和培训，从而为该研究领域的未来劳动力提供支持。

This project studies the fundamental dynamics through which tropical convection, meaning the overturning motion found in tropical cumulus clouds and associated with intense precipitation, interacts with the larger-scale horizontal atmospheric circulation in which it is embedded. The work focuses on the evolution of convection within African easterly waves (AEWs), tropical waves disturbances with wavelengths of 2,000 to 2,500km which originate over West Africa and propagate westward over the northern tropical Atlantic. AEWs are of particular interest as they play a key role in the formation of tropical storms and hurricanes. The work is based on preliminary findings suggesting a chain of meteorological relationships that can lead to the development of heavy rain. One is that cyclonic vorticity (a measure of the strength of cyclonic rotation or shear in the horizontal circulation) at a mid-tropospheric level (say 600mb) can produce warmer temperatures above and colder temperatures below that level, reducing moist convective instability around the level. This reduction in mid-tropospheric instability leads to a bottom-heavy mass flux profile in the cumulus clouds, in which most of the ascending motions within the clouds occur at low to middle levels of the troposphere. The bottom-heavy mass flux profile in turn leads to a reduction in the efficiency of convection for exporting static energy from the convecting region, which requires stronger convection to maintain the energy export. Meanwhile, lower instability leads to moistening of the convecting region through a process referred to as moisture quasi-equilibrium (a result derived in part from research under AGS-1148594), so that both enhanced moisture and more vigorous overturning motions contribute to intensification of rainfall. Preliminary work suggesting these relationships was performed using field campaign data from T-PARC/TCS-08 (Thorpex Pacific Asian Regional Campaign/Tropical Cyclone Motion experiment) and PREDICT (Pre-Depression Investigation of Cloud Systems in the Tropics). Work performed here further tests and explores the proposed chain of causality from mid-level vorticity to convective precipitation, and also considers mechanisms through which more vigorous convection in turn affects the mid-level vorticity and large-scale circulation. The work is conducted through both examination of observational data, including data from field campaigns, satellites, and reanalysis products, and the construction of simple models representing the hypothesized relationships.As noted above, processes leading to the development of convective precipitation in AEWs are of practical as well as scientific interest given that they can lead to landfalling Atlantic hurricanes. More specifically, the work focuses on the early stages of tropical storm genesis, which is among the most difficult challenges in tropical cyclone forecasting. The project also fosters international scientific collaboration, as it involves work with a collaborators in Chile and Croatia, and the work is performed at a Hispanic-serving institution. In addition, the project provides support and training for a graduate student and an undergraduate summer intern, thereby providing for the future workforce in this research area.