Hadley Cell and Subtropical Jet: Dynamics and Tracer Transport

哈德利环流和亚热带急流：动力学和示踪剂传输

基本信息

批准号：
1902409
负责人：
Darryn Waugh
金额：
$ 56.8万
依托单位：
Johns Hopkins University
依托单位国家：
美国
项目类别：
Standard Grant
财政年份：
2019
资助国家：
美国
起止时间：
2019-06-01 至 2024-05-31
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1902409&HistoricalAwards=false
关键词：
Hadley Cell Subtropical Jet Dynamics

项目摘要

The Hadley Cells (HCs, one for each hemisphere) are planetary overturning circulations in which air rises in deep cumulus clouds near the equator and subsides over the subtropics to either side. The subsidence favors clear skies and promotes the hot, dry conditions found in regions like the Sahara, the Kalahari, and the Southwestern United States. Model simulations of future climate change consistently show an expansion of the HCs, by perhaps a degree of latitude over the 21st century. Recent studies show evidence that HC expansion has already taken place and is greater than model simulations would suggest. HC expansion has clear implications for water resources and is thus a topic of practical as well as scientific interest.Beyond their impact on the climate of the tropics and subtropics the HCs play an important global role through their transports of moisture, energy, angular momentum, and chemical constituents. The angular momentum transport of the HCs is responsible for the subtropical jets (STJs) which occur at the outer edge of the HC in each hemisphere. Beyond the STJs there are eddy-driven jets (EDJs), which owe their existence to the north-south temperature contrast of the middle latitudes and the associated weather patterns. The expansion of the HCs is expected to cause the EDJs and STJs to shift poleward, meaning to higher latitudes in each hemisphere. But these expectations are not quite met. There is a robust association between the expansion of the HC, the EDJ, and the poleward edge of the subtropcal dry zone in each hemisphere. On the other hand, HC expansion has at best a weak effect on STJ latitude, contrary to expectations based on the dynamical connection between HCs and STJs. Also, measures of the width of the subtropics based on satellite observations of outgoing longwave radiation do not show the expected signature of HC expansion. The dynamical implications of these discrepancies are examined in this project, as well as their consequences for future climate change.A further issue addressed here is the role of the HCs, STJs, and EDJs in the transport and planetary-scale distribution of radiatively and chemically active trace gases. In particular, a better understanding of this transport is important for understanding the distribution of methane, the hydroxyl radical, and ozone depleting substances relevant to the ozone hole. Previous research suggests a role for the latitude of the Northern Hemisphere EDJ in regulating tracer transport into the Arctic, and there are also indications that transport from the northern mid-latitudes into the northern tropics and the Southern Hemisphere is sensitive to characteristics of the HC and the STJ. These linkages are addressed here in a suite of simulations from models at varying levels of complexity. In addition, transport estimates differ widely among simulation from different models, and models also tend to overestimate the length of time for which tracers remain in the atmosphere. These differences and their dynamical causes are examined using simulations from models participating in the Chemistry-Climate Model Initiative, a coordinated international effort to produce simulations with a common protocol that can be directly compared.The work has broader impacts due to the water resource implications of dry zone expansion, as noted above. The work on tracer transport is also of societal interest due to the role of long-range tracer transport in determining local air quality, and for understanding potential obstacles to the recovery of the ozone hole. In addition, the project promotes workforce development by providing support and training for two graduate students. The students are encouraged to participate in various forms of outreach, including outreach to K-12 schools and adult education classes at Johns Hopkins.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

Hadley细胞（HCS，每个半球一个）是行星倾覆的循环，其中空气在赤道附近的深云云中升起，并将亚热带放在两侧。沉降有利于晴朗的天空，并促进了撒哈拉沙漠，卡拉哈里和美国西南部等地区发现的炎热干燥条件。对未来气候变化的模型模拟始终显示出HCS的扩展，这可能是21世纪的一定程度。最近的研究表明，HC扩展已经发生，并且比模型模拟所暗示的要大。 HC扩展对水资源具有明显的影响，因此是一个实践和科学兴趣的话题。它对他们对热带气候和亚热带的影响HCS通过其水分，能量，角度，角度动量和化学成分发挥了重要的全球作用。 HCS的角动量转运是导致每个半球HC外边缘发生的亚热带喷气机（STJ）。除了STJ之外，还有涡流驱动的喷气机（EDJ），它们的存在归功于中纬度的南北温度对比和相关的天气模式。 HCS的膨胀有望导致EDJ和STJ向极移，这意味着每个半球的纬度更高。但是这些期望还没有得到满足。每个半球的HC，EDJ的膨胀和下层干区的极边缘之间存在牢固的关联。另一方面，HC扩展充其量对STJ纬度的影响较弱，这与基于HCS和STJ之间的动态联系的期望相反。同样，基于外向长波辐射的卫星观测值的亚热带宽度的测量并未显示HC膨胀的预期特征。这些差异的动态含义在该项目中进行了研究，以及它们对未来气候变化的后果。此处进一步解决的问题是HCS，STJ和EDJS在辐射和化学活性痕量气体的运输和行星尺度分布中的作用。特别是，更好地理解这种传输对于理解与臭氧孔相关的甲烷，羟基自由基和臭氧耗尽物质的分布很重要。先前的研究表明，北半球EDJ的纬度在调节示踪剂转运到北极的纬度中发挥了作用，并且也有迹象表明，从北部中期进入北部热带地区的运输，南半球对HC和STJ的特征敏感。这些链接以不同级别的复杂性级别的模型中的一系列模拟来解决。此外，在不同模型的模拟中，传输估计值在仿真之间差异很大，并且模型还倾向于高估示踪剂保留在大气中的时间长度。这些差异及其动力学原因是使用参与化学气候模型倡议的模型的模拟来检查的，这是一项协调的国际努力，以产生可以直接比较的共同协议的模拟。由于上述干旱地区扩展的水资源含义，其作品具有更大的影响，如上所述。由于远程示踪剂运输在确定当地空气质量方面的作用以及了解臭氧孔恢复的潜在障碍，因此示踪剂运输的工作也具有社会利益。此外，该项目通过为两名研究生提供支持和培训来促进劳动力发展。鼓励学生参加各种形式的外展活动，包括在约翰·霍普金斯（Johns Hopkins）举行的K-12学校和成人教育课程。该奖项反映了NSF的法定任务，并被认为是值得通过基金会的知识分子和更广泛影响的评估审查标准通过评估来获得支持的。