| 项目编号: | 1515960
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| 项目名称: | Zonal Asymmetries in the Low-Latitude Hydrological Cycle over a Broad Range of Climates |
| 作者: | William Boos
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| 承担单位: | Yale University
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| 批准年: | 2014
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| 开始日期: | 2015-07-15
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| 结束日期: | 2017-08-31
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| 资助金额: | USD435083
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| 资助来源: | US-NSF
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| 项目类别: | Standard Grant
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| 国家: | US
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| 语种: | 英语
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| 特色学科分类: | Geosciences - Atmospheric and Geospace Sciences
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| 英文关键词: | subtropic
; hydrological cycle change
; zonal-mean circulation
; world
; dryland
; change
; project
; seasonal cycle
; midlatitude region
; sea surface temperature
|
| 英文摘要: | Broadly defined, the subtropics extend from the poleward side of the rainy equatorial belt to the midlatitude region of the westerly winds, and are generally characterized by subsidence and dry conditions. Yet the subtropics are also home to the world's monsoon systems, including the Asian, West African, and North and South American monsoons, and are thus characterized during the monsoon seasons by strong east-west contrasts between regions of heavy rainfall and neighboring drylands. Given the substantial portion of the world's population inhabiting the subtropics, it is of interest to understand how the strong hydrologic contrast between monsoon regions and drylands will change in response to changes in global mean temperature. Climate model projections of 21st century climate change generally suggest that such contrasts will intensify, but there is little quantitative agreement from one model to another on the magnitude of the intensification. And while several mechanisms have been proposed to account for the intensification, a generally accepted theory for the behavior is still lacking.
This project examines changes in the subtropical hydrological contrasts by considering changes in the zonally asymmetric component of the subtropical atmospheric circulation, including the asymmetric vertical mass flux which is upward over monsoon regions and downward over the drylands. This approach differs from previously work which emphasizes the zonal-mean circulation (e.g. the widening of the Hadley cell and the subtropical belts) and explanations in terms of energetics, atmospheric stability, and increased moisture content. It is based on preliminary work using a simpled idealized climate model in which ocean heat flux covergence is imposed over a patch of the subtropics to induce locally warmer sea surface temperatures and enhanced precipitation, which further induces subsidence and dry conditions to the west. Based on the results of these experiments, three hypotheses are posed: 1) The increase in tropopause height that occurs as global mean climate warms enhances the vertical mass flux in stationary circulations, thereby increasing zoanl asymmetries in precipiation; 2) zonal sea surface temperature gradients decreases as global mean climate warms, weakening stationary circulations and the hydrological contrasts they induce; and 3) the mechanism in hypothesis 2 applies over land, only with surface air equivalent potential temperature playing the role of sea surface temperature, so that the land surface water budget plays a role. The research agenda consists of an examination of the seasonal cycle and interannual variability of subtropical asymmetric circulations in present-day climate from observations and simulations, followed by an examination of future climate simulations from an archive of climate models, all guided by the results of the simple idealized model.
The broader impacts of the work come from the substantial portion of the world's population inhabiting the subtropics and the potential impacts of hydrological cycle change on agriculture, water resources, and other necessities of life. The development of a robust theoretical and conceptual understanding of hydrological cycle change would have significant benefit for improving confidence in model projections of future climate change and for guiding future model development. The project also supports and trains a postdoctoral research associate and a graduate student, thereby providing for the future workforce in this research area. The project also supports education and outreach to local high school students. |
| 资源类型: | 项目
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| 标识符: | http://119.78.100.158/handle/2HF3EXSE/94041
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| Appears in Collections: | 影响、适应和脆弱性
气候减缓与适应
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| Recommended Citation: | |
William Boos. Zonal Asymmetries in the Low-Latitude Hydrological Cycle over a Broad Range of Climates. 2014-01-01.
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