Zonal Asymmetries in the Low-Latitude Hydrological Cycle over a Broad Range of Climates

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项目编号	1515960
	Zonal Asymmetries in the Low-Latitude Hydrological Cycle over a Broad Range of Climates
	William Boos
主持机构	Yale University
项目开始年	2015
	2015-07-15
项目结束日期	2018-06-30
资助机构	US-NSF
项目类别	Standard Grant
项目经费	435083(USD)
国家	美国
语种	英语
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.
来源学科分类	Geosciences - Atmospheric and Geospace Sciences
文献类型	项目
条目标识符	http://119.78.100.173/C666/handle/2XK7JSWQ/68287
专题	环境与发展全球科技态势
推荐引用方式 GB/T 7714	William Boos.Zonal Asymmetries in the Low-Latitude Hydrological Cycle over a Broad Range of Climates.2015.