Collaborative Research: Intercomparison of Atmospheric Water Vapor Isotope Measurements from Mauna Loa, Hawaii and Implications for Characterizing Subtropical Humidity

水的稳定同位素化学是探测大气水循环的有力工具，并已被用于推进我们对地球仪周围水蒸气动力学的理解。直到最近，测量水蒸气的同位素比率仍然是一个耗时费力的过程，但光谱技术的进步现在允许自动化，实时，几乎连续地测量水蒸气中的18 O/16 O和2 H/1H（或D/H）比率。此外，在高分辨率地球红外发射光谱遥感方面取得的进展，现在可以绘制全球大气氘丰度图。这些新技术对气候研究非常有前途，但我们并不完全了解这些新测量中的偏差，也不知道这些新技术的测量结果如何相互比较，以及与更传统和劳动密集型的质谱技术（包括真空瓶收集和低温捕获）进行比较。在气候研究中充分发挥新的水汽同位素光谱测量方法的潜力之前，必须进行仪器验证和相互比较。研究员将在位于夏威夷莫纳罗亚山的美国国家海洋和大气管理局观测站使用三种不同的激光传感器和两颗不同的卫星对水蒸气同位素进行测量，并将对现场收集的样品采用传统的质谱技术进行验证。本研究的目的是比较不同的测量技术，以评估这些新的测量技术的保真度，并提供控制亚热带太平洋湿度的过程的新数据。这套全面的测量将于2008年10月12日至24日在夏威夷科纳举行的AGU查普曼会议“大气水蒸气及其在气候中的作用”期间进行。该项目的机会是在PI与工业界、NASA喷气推进实验室（JPL）、布鲁塞尔自由大学和巴黎航空服务局的同事之间最近的讨论中出现的。正在为该项目提供一些重要的资源，而这笔赠款的费用很少或没有。时机似乎是偶然的，因为几位参与的科学家正计划在夏威夷参加查普曼会议，而其他资源恰好在同一时间可用。大气水蒸气同位素的测量提供了关于地球的重要信息？的水文循环，和新技术的承诺，以扩大我们的理解使用和这种测量的局限性。该项目将首次对不同的地面和卫星技术进行相互比较，从而有助于为利用这些新技术进行气候研究奠定基础。这项研究的结果将用于更好地了解水汽同位素气候学研究的最佳系统配置，并确定新兴遥感技术的偏差。此外，该项目的数据将有助于通过提供来自干旱的亚热带海洋中部地点的水同位素的第一次连续测量来限制亚热带大气水循环的模型。这一相互比较项目的结果将对更广泛的大气水蒸气同位素研究人员具有重要意义，因为他们开始利用一系列新的遥感和激光技术。莫纳罗亚山顶的低湿度条件将测试基于表面的光谱技术的局限性，并为了解仪器在极端但气候重要条件下的可靠性提供坚实的基础。研究结果将通过出版物和在国家会议上的演讲传播，并将为美国和欧洲的算法和仪器开发提供信息。该项目将通过将研究生纳入实地方案和数据分析来促进研究生的培训。在项目的第一周，喷气推进实验室的科学家将向来自新墨西哥州大学和科罗拉多大学的学生介绍水同位素测量技术和算法。在该计划的第二周，学生将参加查普曼会议，PI将邀请其他参加会议的研究生加入他们的行列，无论是在会议开始之前，还是在会议与会者计划实地考察莫纳罗亚实验室期间，这也将包括关于这个项目的演示。此外，该项目将促进与工业界（Picarro和洛斯加托斯）以及与红外大气探测干涉仪仪器有关的欧洲同事的伙伴关系。

Project SummaryThe stable isotope chemistry of water is a powerful tool for probing the atmospheric water cycle and has been used to advance our understanding of water vapor dynamics around the globe. Until recently, measuring water vapor isotope ratios was a time-consuming and laborious process, but advances in spectroscopic techniques now allow automated, real-time, nearly continuous measurements of the 18O/16O and 2H/1H (or D/H) ratios in water vapor. In addition, advances in remote sensing of Earth's infrared emission spectrum at high resolution now allow the atmospheric deuterium abundance to be mapped globally. These new technologies are very promising for climate studies, but we do not fully understand the biases in these new measurements, nor do we know how measurements made with these new technologies compare with one another and with the more traditional and labor-intensive mass spectrometric techniques involving vacuum flask collection and cryogenic trapping. Before the full potential of the new spectroscopic methods for water vapor isotope measurements can be realized in climate research, a program of instrument validation and intercomparison must be performed. The PIs will make measurements of water vapor isotopologues at the NOAA observatory at Mauna Loa, Hawaii using three different laser-based sensors and two different satellites, which will be validated against traditional mass spectrometry techniques applied to samples collected on site. The goal of this study is to compare the different measurement techniques in order to assess of the fidelity of these new measurement technologies and to provide new data on the processes that control the humidity of the subtropical Pacific. This comprehensive set of measurements will be made from October 12-24, 2008, in conjunction with the AGU Chapman Conference "Atmospheric Water Vapor and its Role in Climate", which will be held in Kona, Hawaii. The opportunity for this project has emerged from recent discussions between the PIs and colleagues from industry, NASA's Jet Propulsion Lab (JPL), Université Libre de Bruxelles, and Service d'aéronomie in Paris. A number of important resources are being made available for this project at little or no cost to this grant. The timing seems to be fortuitous as several of the scientists involved are planning to be in Hawaii for the Chapman conference, and the other resources happen to be available at the same time. Intellectual Merit Measurements of atmospheric water vapor isotopologues provide important information about the Earth?s hydrologic cycle, and new technologies promise to expand our understanding of the use and limitations of such measurements. The project will help to establish the foundation for climate studies using these new technologies by providing the first intercomparison between different ground and satellite-based techniques. The results of this study will be used to better understand optimal system configurations for climatological studies of water vapor isotopes and determine biases in emerging remote-sensing technologies. Moreover, the data from this project will help to constrain models of the subtropical atmospheric water cycle by providing the first continuous measurements of water isotopologues from an arid subtropical mid-ocean site. Broader Impacts The results of this intercomparison project will be important for the broader community of atmospheric water vapor isotope researchers as they begin to make use of the new array of remote sensing and laser-based techniques. The low humidity conditions atop Mauna Loa will test the limitations of the surface-based spectroscopic techniques and provide a sound footing for understanding the reliability of the instruments under extreme but climatologically important conditions. The results will be disseminated via publications and presentations at national conferences and will inform algorithm and instrument development in the United States and in Europe. The project will promote the training of graduate students by including them in the field program and data analysis. During the first week of the program, JPL scientists will make informal presentations to the students from University of New Mexico and Colorado University on water isotope measurement techniques and algorithms. During the second week of the program, the students will participate in the Chapman Conference, and the PIs will invite other graduate students attending the conference to join them in the field, either before the conference begins, or during the planned field excursion to the Mauna Loa Lab by conference attendees, which will also include a presentation about this project. In addition, this project will foster partnerships with industry (Picarro and Los Gatos) and with European colleagues associated with the Infrared Atmospheric Sounding Interferometer instrument.