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，已被用来促进我们对全球水汽动力学的理解。直到最近，测量水蒸气同位素比率还是一个费时费力的过程，但光谱技术的进步现在可以自动、实时、几乎连续地测量水蒸气中的18O/16O和2H/1H(或D/H)比率。此外，在高分辨率遥感地球红外发射光谱方面的进展，现在可以在全球范围内绘制大气中的氚丰度图。这些新技术对气候研究非常有希望，但我们并不完全了解这些新测量中的偏差，我们也不知道使用这些新技术进行的测量彼此之间以及与更传统的、劳动密集型的质谱学技术(包括真空瓶采集和低温捕获)之间的比较。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比对程序。PIS将在夏威夷莫纳罗亚的NOAA天文台使用三个不同的激光传感器和两个不同的卫星测量水蒸气同位素，并将与现场收集的样品应用的传统质谱学技术进行验证。这项研究的目的是比较不同的测量技术，以评估这些新测量技术的保真度，并提供关于控制副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 Chapman会议“大气水汽及其在气候中的作用”的同时进行。这个项目的机会来自于PIS与工业界、NASA喷气推进实验室(JPL)、布鲁克塞尔自由大学和巴黎罗诺米服务机构的同事最近的讨论。正在为这一项目提供一些重要的资源，而这笔赠款的费用很少，甚至完全不需要。这一时机似乎是偶然的，因为参与其中的几位科学家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。大气水汽同位素的智能测量提供了有关地球-S水文循环的重要信息，新技术有望扩大我们对此类测量的使用和局限性的理解。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蒸气同位素气候学研究的最佳系统配置，并确定新兴遥感技术中的偏差。此外，该项目的数据将有助于限制亚热带大气水循环的模型，因为它将首次连续测量来自干旱的亚热带海洋中部地点的水同位素。更广泛的影响这一相互比较项目的结果将对更广泛的大气水汽同位素研究人员具有重要意义，因为他们开始利用新的一系列遥感和激光技术。莫纳罗亚山顶部的低湿度条件将测试基于地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。结果将通过出版物和在国家会议上的陈述进行传播，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他们的培训。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大学和科罗拉多大学的学生做关于水同位素测量技术和算法的非正式演讲。在该计划的第二周，学生将参加查普曼会议，国际和平研究所将邀请其他参加会议的研究生到现场加入他们的行列，要么在会议开始之前，要么在会议参与者计划的实地考察期间加入他们的行列，其中还将包括关于这个项目的陈述。此外，该项目还将促进与工业界(皮卡罗和洛斯加托斯)以及与红外大气探测干涉仪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.