Aircraft measurements of water vapor heavy isotope ratios in the marine boundary layer and lower troposphere during ORACLES

Abstract. This paper presents the water vapor heavy isotope ratio measurement system developed for aircraft in-situ measurements and used in the NASA ObseRvations of Aerosols above CLouds and their intEractionS (ORACLES) project. The resultant dataset collected, which includes measurements of specific humidity and the heavy isotope ratios D / H and 18O / 16O, is also presented. Aircraft sampling took place in the southeast Atlantic marine boundary layer and lower troposphere (equator to 22° S) over the months of Sept. 2016, Aug. 2017, and Oct. 2018. Isotope measurements were made using cavity ring-down spectroscopic analyzers integrated into the Water Isotope System for Precipitation and Entrainment Research (WISPER). The water concentration and isotopic data accompanied a suite of other variables including standard meteorological quantities (wind, temperature, moisture), trace gas and aerosol concentrations, radar, and lidar remote sensing. From an isotope perspective, the 300+ hours of 1 Hz in-situ data at levels in the atmosphere ranging from 70 m to 6 km represents a remarkably large and vertically resolved dataset. This paper provides a brief overview of the ORACLES mission and describes how water vapor heavy isotope ratios fit within the experimental design. Overviews of the sampling region and WISPER system setup are presented, along with calibration details, measurement uncertainties, and suggested data usage. Characteristics in the spatial variability of the study region over the three sampling periods are highlighted with latitude-altitude curtains. A number of individual tropospheric profiles are presented to illustrate the fidelity with which a series of different hydrologic processes are captured by the observations. The curtains and profiles demonstrate the dataset’s potential to provide a comprehensive perspective on moisture transport and isotopic content in this region. Readers interested in a quick reference to data usage and uncertainty estimation can consult the beginning of section 5. Data for the Sept. 2016, Aug. 2017, and Oct. 2018 sampling periods can be accessed at https://doi.org/10.5067/Suborbital/ORACLES/P3/2016_V2 , https://doi.org/10.5067/Suborbital/ORACLES/P3/2017_V2 , and https://doi.org/10.5067/Suborbital/ORACLES/P3/2018_V2 , respectively (see references for ORACLES Science Team, 2020 – 2016 P3 data, 2017 P3 data, and 2018 P3 data).