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| Hadley Cell and Subtropical Jet: Dynamics and Tracer Transport | |
| 项目编号 | 1902409 |
| Darryn Waugh | |
| 项目主持机构 | Johns Hopkins University |
| 开始日期 | 2019-06-01 |
| 结束日期 | 05/31/2022 |
| 英文摘要 | 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. |
| 资助机构 | US-NSF |
| 项目经费 | $567,995.00 |
| 项目类型 | Standard Grant |
| 国家 | US |
| 语种 | 英语 |
| 文献类型 | 项目 |
| 条目标识符 | http://gcip.llas.ac.cn/handle/2XKMVOVA/211261 |
| 推荐引用方式 GB/T 7714 | Darryn Waugh.Hadley Cell and Subtropical Jet: Dynamics and Tracer Transport.2019. |
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