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Title: Investigating the source, transport, and isotope composition of water vapor in the planetary boundary layer

Increasing atmospheric humidity and convective precipitation over land provide evidence of intensification of the hydrologic cycle – an expected response to surface warming. The extent to which terrestrial ecosystems modulate these hydrologic factors is important to understand feedbacks in the climate system. We measured the oxygen and hydrogen isotope composition of water vapor at a very tall tower (185 m) in the upper Midwest, United States, to diagnose the sources, transport, and fractionation of water vapor in the planetary boundary layer (PBL) over a 3-year period (2010 to 2012). These measurements represent the first set of annual water vapor isotope observations for this region. Several simple isotope models and cross-wavelet analyses were used to assess the importance of the Rayleigh distillation process, evaporation, and PBL entrainment processes on the isotope composition of water vapor. The vapor isotope composition at this tall tower site showed a large seasonal amplitude (mean monthly δ18Ov ranged from –40.2 to –15.9 ‰ and δ2Hv ranged from –278.7 to –113.0 ‰) and followed the familiar Rayleigh distillation relation with water vapor mixing ratio when considering the entire hourly data set. However, this relation was strongly modulated by evaporation and PBL entrainment processes at timescales ranging frommore » hours to several days. The wavelet coherence spectra indicate that the oxygen isotope ratio and the deuterium excess (dv) of water vapor are sensitive to synoptic and PBL processes. According to the phase of the coherence analyses, we show that evaporation often leads changes in dv, confirming that it is a potential tracer of regional evaporation. Isotope mixing models indicate that on average about 31 % of the growing season PBL water vapor is derived from regional evaporation. However, isoforcing calculations and mixing model analyses for high PBL water vapor mixing ratio events ( > 25 mmol mol–1) indicate that regional evaporation can account for 40 to 60 % of the PBL water vapor. These estimates are in relatively good agreement with that derived from numerical weather model simulations. This relatively large fraction of evaporation-derived water vapor implies that evaporation has an important impact on the precipitation recycling ratio within the region. In conclusion, based on multiple constraints, we estimate that the summer season recycling fraction is about 30 %, indicating a potentially important link with convective precipitation.« less
 [1] ;  [1] ;  [2] ;  [3] ;  [1] ;  [1] ;  [4] ;  [5] ;  [1] ;  [1] ;  [6]
  1. Univ. of Minnesota, St Paul, MN (United States). Dept. of Soil, Water, and Climate
  2. Univ. of Minnesota, St Paul, MN (United States). Dept. of Soil, Water, and Climate; United States Dept. of Agriculture - Agricultural Research Service, St. Paul, MN (United States)
  3. Yale Univ., New Haven, CT (United States). School of Forestry and Environmental Studies; Nanjing Univ. of Information, Science and Technology, Nanjing (China). Yale-NUIST Center on Atmospheric Environment
  4. Purdue Univ., West Lafayette, IN (United States). Earth, Atmospheric, and Planetary Sciences
  5. Yale Univ., New Haven, CT (United States). School of Forestry and Environmental Studies
  6. Univ. of Minnesota, St Paul, MN (United States). Dept. of Bioproducts and Biosystems Engineering
Publication Date:
OSTI Identifier:
Accepted Manuscript
Journal Name:
Atmospheric Chemistry and Physics (Online)
Additional Journal Information:
Journal Name: Atmospheric Chemistry and Physics (Online); Journal Volume: 16; Journal Issue: 8; Journal ID: ISSN 1680-7324
European Geosciences Union
Research Org:
Univ. of Minnesota, St Paul, MN (United States).
Sponsoring Org:
USDOE Office of Science (SC); Minnesota Corn Research and Promotion Council; US National Science Foundation; University of Minnesota Supercomputing Institute (MSI) for Advanced Computational Research
Country of Publication:
United States
54 ENVIRONMENTAL SCIENCES deuterium excess; carbon-dioxide; tall tower; summer precipitation; wavelet transform; hydrologic-cycle; surface humidity; eddy covariance; United States; New England