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Deuterium excess in subtropical free troposphere water vapor: Continuous measurements from the Chajnantor Plateau, northern Chile
Author(s) -
SamuelsCrow Kimberly E.,
Galewsky Joseph,
Sharp Zachary D.,
Dennis Kate J.
Publication year - 2014
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1002/2014gl062302
Subject(s) - troposphere , water vapor , atmospheric sciences , plateau (mathematics) , deuterium , supersaturation , mixing ratio , environmental science , climatology , subtropics , chemistry , geology , meteorology , physics , mathematical analysis , mathematics , organic chemistry , quantum mechanics , fishery , biology
Water vapor measured continuously by cavity ring‐down spectroscopy from July 2012 to March 2013 on the hyperarid Chajnantor Plateau, northern Chile (elevation = 5080 m, pressure ≈ 550 hPa), has a mean deuterium excess ( d ‐excess = δD − 8* δ 18 O) of 46‰ ± 5‰ and frequently exceeds 100‰ at low water vapor mixing ratios ( q ≤ 500 ppmv). These measurements provide empirical support for theoretical predictions of free troposphere d ‐excess. The d ‐excess measured at this site can be understood in terms of supersaturation with respect to ice at relative humidities between 100% and 130%, followed by mixing with moist midtropospheric or lower tropospheric air en route to the plateau. The d ‐excess measured at Chajnantor is consistent with predictions for d ‐excess in the upper troposphere from isotope‐enabled general circulation models and with high vapor saturation over ice in cloud‐resolving and microphysical models.