Convection and Balanced Tropical Dynamics

对流和平衡热带动力学

• 批准号: 1546698
• 负责人: David Raymond
• 金额: $ 52.17万
• 依托单位: New Mexico Institute of Mining and Technology
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-08-01 至 2020-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1546698&HistoricalAwards=false
• 关键词: Convection; Balanced; Tropical; Dynamics

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.

这个项目研究热带对流的基本动力学，热带对流是指在热带积云中发现的与强降水有关的翻转运动，通过它与嵌入其中的更大规模的水平大气环流相互作用。这项工作的重点是非洲东风波(AEW)内对流的演变，即起源于西非并在热带大西洋北部向西传播的波长为2,000至2,500公里的热带波扰动。AEW特别令人感兴趣，因为它们在热带风暴和飓风的形成中发挥着关键作用。这项工作是基于初步发现，即可能导致暴雨发展的一系列气象关系。其一是，在对流层中层(比方说600毫巴)的气旋涡度(衡量水平环流中气旋旋转或切变的强度)可以在该层以上产生较暖的温度，在该层以下产生较冷的温度，从而减少该层周围的潮湿对流不稳定。对流层中层不稳定性的这种减弱导致了积云中质量通量分布的下沉，其中云内的大部分上升运动发生在对流层的中低层。底部-重质量通量分布反过来导致对流从对流区输出静态能量的效率降低，这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一种被称为水分准平衡的过程(这是根据AGS-1148594进行的研究的部分结果)使对流区增湿，因此增加的湿度和更猛烈的倾覆运动都有助于加强降雨。利用T-PARC/TCS-08(Thorpex太平洋亚洲区域活动/热带气旋运动实验)和预测(热带云系低气压前调查)的现场活动数据进行了初步工作，揭示了这些关系。这里的工作进一步检验和探索了所提出的从中层涡度到对流降水的因果链，并考虑了更强烈的对流反过来影响中层涡度和大尺度环流的机制。这项工作既是通过检查观测数据，包括来自现场活动、卫星和再分析产品的数据，也是通过建立代表假设关系的简单模型来进行的。如上所述，导致AEW对流降水发展的过程具有实际和科学意义，因为它们可能导致登陆大西洋飓风。更具体地说，这项工作侧重于热带风暴形成的早期阶段，这是热带气旋预测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，而这项工作是在一个为拉美裔服务的机构进行的。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，从而为这一研究领域的未来劳动力提供支持。