The 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.
