Comparison of atmospheric hydrology over convective continental regions using water vapor isotope measurements from space

[1] Global measurements of the 500–825 hPa layer mean HDO/H2O ratio from the Tropospheric Emission Spectrometer (TES) are used to expose differences in the dominant hydrologic processes in the Amazon, north Australian, and Asian monsoon regions. The data show high regional isotopic variability and numerous values unexpected from classical Rayleigh theory. Correlation analysis shows that mixing with boundary layer air, enhanced isotopic fractionation during precipitation, and subsiding air parcels contribute to intraseasonal isotopic variability. These local controls explain only 8–30% of total regional variance, which suggests that the isotopes are primarily indicators of moist processes that occur upstream. Seasonal trajectory analysis demonstrates that Rayleigh distillation in a Lagrangrian framework underestimates the observed isotopic depletion during the monsoons and suggests substantial recycling of water within or below clouds. The trajectory results for the dry seasons reveal that subsiding air parcels periodically introduce isotopically depleted air into the north Australia and Asian monsoon regions, whereas vigorous low-level convection over the Amazon basin acts to quickly enrich and moisten dry subsiding air. The analysis indicates variations in the strength of convective detrainment into the lower to middle troposphere over all regions, which, during the dry seasons of the north Australian and Asian monsoon regions, correlate with increases in relative humidity. This study shows that isotopic measurements provide unique diagnostics of mechanisms that control the seasonal sources of water and that these provide a refined understanding of the differences in the characteristics of hydrologic budgets in these monsoonal regions.