Deuterium Excess of Water Vapor in the Atmospheric Boundary Layer

大气边界层水蒸气氘过量

• 批准号: 1520684
• 负责人: Xuhui Lee
• 金额: $ 46.75万
• 依托单位: Yale University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-06-15 至 2019-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1520684&HistoricalAwards=false
• 关键词: Deuterium; Excess; Water; Vapor; Atmospheric

This research explores using water vapor isotope observations for attributing the sources of water vapor to remote source regions, local influences, and transport in the atmospheric boundary layer (ABL). The ABL is the lowest ~1 km of the atmosphere and is a large reservoir of atmospheric water. The ABL water pool supports convective cloud formation. Condensation in clouds depletes vapor from the ABL. Entrainment or turbulent diffusion at the top of the ABL, transports vapor to the upper atmosphere. While both these processes deplete moisture from the ABL, new vapor enters this layer from land evapotranspiration and advection of moisture from remote source regions. Understanding how water moves between the ABL, the land, and the upper atmosphere is essential for accurate prediction of precipitation processes and for climate modeling. Deuterium and oxygen-18 are stable isotopes of hydrogen and oxygen. This study will use "deuterium excess" (d-excess) of water vapor, a measure of the relative abundance of the deuterium and oxygen-18 isotopes of water, to track the movement of water among the three pools and to identify contributions of local land and remote oceanic sources to the ABL vapor. A fundamental premise of the project is that both remote water sources and local ABL processes will imprint influences on vapor d-excess, but at very different time scales. The investigators postulate combined use of the analytical tools appropriate for these different time scales will unravel local influences from those originating from water transport from outside of the local domain. The proposal conceptualizes that the local hydrological cycle is composed of three pools of water (terrestrial water, vapor in the ABL, and vapor in the free atmosphere) and that exchanges among these pools will leave distinct signatures on the d-excess temporal variations. The research methodology consists of data analyses and ABL modeling. The experimental data are hourly observations made with laser-based instruments in 11 climate zones in North America and in Asia. An isotopic land surface model will quantify local evapotranspiration effects on temporal variations in vapor d-excess. Equilibrium boundary layer calculations and large-eddy simulations will be used to infer d-excess signal of the vapor in the free atmosphere and the entrainment influence on the ABL d-excess. Trajectory analysis will identify contributions from remote source regions. The project will contribute to capacity-building in isotope hydrology and in boundary-layer meteorology. Despite the recent explosive growth of laser-based vapor isotope measurements, current ability to interpret water transport processes with these measurements remains preliminary. The project could transform the field from descriptive to quantitative. Hands-on modules, designed from large-eddy simulation data and a simplified one-dimensional ABL model, will enhance classroom learning on ABL and isotopic principles. These modules will form the basis of an open online course on ABL techniques. A new data website will promote sharing of high-frequency vapor isotope data. As the volume of laser-based measurement continues to grow, a centralized data depository will facilitate investigations that transcend disciplinary and geographic boundaries.

本研究探索利用水蒸气同位素观测将水蒸气来源归因于远程来源区域、局部影响和大气边界层 (ABL) 中的传输。 ABL 是大气层最低的~1 公里处，是大气水的一个大水库。 ABL 水池支持对流云的形成。云中的凝结会消耗 ABL 中的蒸汽。 ABL 顶部的夹带或湍流扩散将蒸汽输送到高层大气。虽然这两个过程都会消耗 ABL 中的水分，但新的蒸汽会通过陆地蒸散和来自远程源区域的水分平流进入该层。了解水如何在大气层、陆地和高层大气之间移动对于准确预测降水过程和气候建模至关重要。氘和氧 18 是氢和氧的稳定同位素。这项研究将使用水蒸气的“氘过量”（d-过量）（衡量水中氘和氧 18 同位素的相对丰度）来跟踪三个水池之间的水运动，并确定当地水的贡献。陆地和偏远海洋来源的 ABL 蒸气。 该项目的一个基本前提是，偏远的水源和当地的 ABL 过程都会对水蒸气过量产生影响，但时间尺度却截然不同。研究人员假设，结合使用适合这些不同时间尺度的分析工具，将揭示来自当地域外的水运输对当地的影响。该提案提出，当地水文循环由三个水池组成（陆地水、ABL 中的水蒸气和自由大气中的水蒸气），这些水池之间的交换将在 d-excess 时间变化上留下明显的特征。研究方法包括数据分析和 ABL 建模。实验数据是利用激光仪器在北美和亚洲 11 个气候区每小时进行的观测数据。同位素地表模型将量化局部蒸散对水汽过量时间变化的影响。平衡边界层计算和大涡模拟将用于推断自由大气中蒸汽的d-excess信号以及夹带对ABL d-excess的影响。轨迹分析将识别来自远程源区域的贡献。该项目将有助于同位素水文学和边界层气象学的能力建设。尽管基于激光的蒸气同位素测量最近出现爆炸性增长，但目前利用这些测量解释水传输过程的能力仍处于初步阶段。该项目可以将该领域从描述性转变为定量。根据大涡模拟数据和简化的一维 ABL 模型设计的实践模块将增强 ABL 和同位素原理的课堂学习。这些模块将构成 ABL 技术开放在线课程的基础。新的数据网站将促进高频蒸气同位素数据的共享。随着基于激光的测量量持续增长，集中式数据存储将促进超越学科和地理界限的调查。