Deuterium Excess of Water Vapor in the Atmospheric Boundary Layer

本研究探讨利用水汽同位素观测资料，将水汽来源归因于远源区域、局地影响及大气边界层输送。ABL是最低的~1公里的大气层，是一个大型的大气水水库。ABL水池支持对流云的形成。云中的凝结使大气边界层中的水汽减少。大气边界层顶部的卷吸或湍流扩散将水汽输送到高层大气。虽然这两个过程消耗的水分从ABL，新的蒸汽进入这一层的土地蒸散和平流的水分从遥远的源区。了解水如何在大气边界层、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），一种衡量水的氘和氧-18同位素相对丰度的方法，来跟踪水在三个水池中的运动，并确定当地陆地和远程海洋来源对ABL蒸气的贡献。 该项目的一个基本前提是，远程水源和本地ABL过程都会对蒸汽d过量产生影响，但时间尺度非常不同。研究人员假设，结合使用适合于这些不同时间尺度的分析工具，将从本地域以外的水运输产生的影响中揭示本地的影响。该建议概念化的地方水文循环是由三个水池（陆地水，在ABL的蒸汽，在自由大气中的蒸汽），这些池之间的交流将留下不同的签名的d-过量的时间变化。研究方法包括数据分析和ABL建模。实验数据是在北美和亚洲的11个气候带用激光仪器进行的每小时观测。一个同位素陆面模式将量化当地蒸散对水汽d过量随时间变化的影响。平衡边界层计算和大涡模拟将被用来推断d-过量信号的蒸汽在自由大气中的ABL d-过量的卷吸的影响。轨迹分析将查明来自偏远源区的贡献。该项目将有助于同位素水文学和边界层气象学方面的能力建设。尽管最近爆炸性增长的激光为基础的蒸汽同位素测量，目前的能力来解释水的运输过程与这些测量仍然是初步的。该项目可以将该领域从描述性转变为定量。实践模块，从大涡模拟数据和简化的一维ABL模型设计，将加强ABL和同位素原理的课堂学习。这些模块将构成ABL技术开放式在线课程的基础。一个新的数据网站将促进高频蒸汽同位素数据的共享。随着基于激光的测量量的不断增长，集中的数据存储将有助于超越学科和地理界限的调查。

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.