Collaborative Research: Testing Controls on Source, Sink, and Lifetime of Atmospheric Water with Numerical Tags and Stable Isotope Ratios

H2O很容易被识别为水的化学式，但这个简单的公式掩盖了这样一个事实，即并不是所有的氢原子都是相同的。地球上的一小部分水可以更准确地称为HDO，其中D代表氢，这是一种较重的氢同位素，其中原子核包含一个中子和一个质子。同样，一些水分子含有18O，这是一种氧的同位素，由于添加了两个中子，比普通氧更重。这些较重的水与普通的H2O有一个微妙但重要的区别：它们蒸发更慢，更容易凝结，比起汽相，它们更喜欢固体和液体。当水从陆地或海洋表面蒸发时，水蒸气中的较重同位素略有耗尽，每一次降雨从云中落下时，留在大气中的水蒸气略轻于降雨出来的水。降水对重同位素的去除表明，水蒸气和降水中重同位素的丰度为理解水文循环及其与环境条件的关系提供了重要线索。这一领域的研究结果是有希望的，但由于可能影响同位素组成的众多因素，这些结果变得复杂。其中包括降水发生地点的温度，产生降水的云的高度，水蒸气蒸发的海洋上空的相对湿度，以及雨滴在干燥空气中降落时较轻同位素的蒸发。此外，对水同位素的大部分研究都是基于同位素组成与与物理机制(例如，降雨区域的温度)有关的变量之间的相关性。这些相关性可以提供相当多的信息，但这些相关性本身并不能确定因果关系。本奖项下的工作旨在建立与同位素组成相关的物理机制与水蒸气和降水的实际组成之间的直接因果关系。这项研究是利用共同体地球系统模型(CESM)进行的，在该模型中，对同位素组成的机制及其影响是确切知道的。CESM已经配备了模拟物理过程，以确定较重和较轻同位素的比例，它还跟踪水蒸气在模拟大气中循环时的同位素组成。该项目开发了一种新的“水标记”功能，允许模拟的水蒸气记录有关蒸发条件的信息，例如蒸发的地点和时间，以及是否通过云层处理。这些信息也被转移到水蒸气凝结时产生的降水中。标签信息可以直接与同位素组成相比较，从而允许直接评估由标签所代表的物理条件和过程的影响。一些模拟使用数据同化系统(称为DART)来确保模拟的气候和环流准确地反映真实世界的气候和环流。其他工作使用一维能量平衡模型，该模型提供了一个降低复杂性的环境，以开发新的想法和测试假设。由于水同位素作为气候和水文循环功能的窗口被广泛使用，该工作具有更广泛的科学影响。例如，冰川冰芯中的同位素比率被用来估计冰期和间冰期暖期之间的温差，从而为理解当前的气候变化提供了一个有价值的参考点。这里开发的水标记算法将提供给CESM的全球用户社区，为用户提供一个强大的工具来解释同位素数据并将其应用于各种研究问题。此外，该奖项支持的研究人员通过一个专注于德克湖青年中心的项目开展教育推广活动，该中心是盐湖谷一个收容定罪后青年的设施。外展包括臭氧生物指示器花园，展示臭氧污染的危害，臭氧污染是盐湖谷的一个常见问题。惩教机构的教育机会已被证明可以减少再次犯罪。这一裁决反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

H2O is instantly recognizable as the chemical formula for water, but this simple formula masks the fact that not all hydrogen atoms are alike. A small fraction of the water on earth could be more accurately called HDO, where D stands for deuterium, the heavier hydrogen isotope in which the nucleus contains a neutron as well as a proton. Likewise, some water molecules contain 18O, an isotope of oxygen which is heavier than ordinary oxygen by the addition of two neutrons. These heavier forms of water share a subtle but important difference from ordinary H2O: they evaporate more sluggishly and condense more readily, preferring the solid and liquid phases to the vapor phase. When water evaporates from the land or ocean surface the vapor is slightly depleted of the heavier isotopes, and each time rain falls from a cloud the water vapor remaining in the atmosphere is slightly lighter than the water that rained out. The removal of heavier isotopes by precipitation suggests that the abundances of heavier isotopes in water vapor and precipitated water contain important clues for understanding the hydrological cycle and its connections to environmental conditions. Results of research in this area are promising but they are complicated by the numerous factors that can influence isotopic composition. Among these are the temperature at the location where the precipitation occurred, the height of the cloud that produced the precipitation, the relative humidity over the ocean where the water vapor evaporated, and the evaporation of lighter isotopes from raindrops as they fall through dry air. Moreover, much of the research on water isotopes is based on correlations between isotopic composition and variables relevant to physical mechanisms (temperature in the region of rainout, for instance). These correlations can be quite informative but correlations by themselves cannot definitively establish causality.Work under this award seeks to establish direct, causal relationships between the physical mechanisms relevant to isotopic composition and the actual composition of water vapor and precipitated water. The research is conducted using a model, the Community Earth System Model (CESM), in which the mechanisms and their influence on isotopic composition are known exactly. CESM is already equipped to simulate the physical processes that determine the ratio of heavier to lighter isotopes, and it also tracks the isotopic composition of water vapor as it circulates in the simulated atmosphere. This project develops a new "water tagging" capability which allows simulated water vapor to record information about conditions under which it evaporated, for instance where and when it evaporated and whether it was processed through clouds. This information is also transferred to the precipitation produced when water vapor condenses. The tag information can be directly compared to isotopic composition, allowing the influence of the physical conditions and processes represented by the tags to be directly assessed. Some simulations use a data assimilation system (known as DART) to ensure that the simulated climate and circulation accurately represent their real-world counterparts. Additional work uses a one-dimensional energy balance model, which provides a reduced-complexity setting to develop new ideas and test hypotheses.The work has scientific broader impacts due to the widespread use of water isotopes as a window on the functioning of climate and the hydrological cycle. For instance isotope ratios in glacial ice cores have been used to estimate temperature differences between ice ages and interglacial warm periods, thus providing a valuable point of reference for understanding current climate change. The water tagging algorithms developed here will be made available to the worldwide user community of CESM, providing users with a powerful tool for the interpretation of isotope data and its application to a variety of research questions.In addition, researchers supported under this award conduct educational outreach through a program focused on the Decker Lake Youth Center, a facility housing post-conviction youth in the Salt Lake Valley. The outreach involves ozone bioindicator gardens which demonstrate the hazards of ozone pollution, a common problem in the Salt Lake Valley. Educational opportunities in correctional facilities have been shown to reduce recidivism.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.