Joint Seminar: The Drunkard's Search: Constraining lower-tropospheric mixing with stable isotopologues of water vapor

The stable isotopic composition of atmospheric water vapor is a sensitive recorder of mixing processes, and to the extent that quantitative, observational constraints on lower‐tropospheric mixing are important for improved understanding of the links between clouds, precipitation and circulation systems, the analysis of water vapor isotopic composition can provide an independent means for generating such constraints. Recent field studies from the subtropical North Pacific (Mauna Loa, Hawaii) and from the subtropical Southeast Pacific (Chajnantor Plateau, northern Chile) illustrate the utility of such measurements. In both sites, in-situ measurements of water vapor isotopic composition are merged with soundings and with satellite measurements to show an inverse relationship between the estimated inversion strength (EIS) and water vapor export from the marine boundary layer into the free troposphere. The relationship between EIS and water vapor transport is found to be exponential across EIS values ranging from 0 to 15.6 K. We show positive relationships between EIS, cloud fraction, and the mixing diagnostic δDv−δDr and negative relationships between EIS and the observed mixing ratios and water vapor δD values, all of which are consistent with an inverse relationship between inversion strength and water vapor export from the marine boundary layer. Inverse modeling of the isotopic data using a simple process model provides additional constraints on the average mixing ratios at both sites derived from the marine boundary layer.
The extension of this analysis to isotopically-enabled GCMs may provide a useful framework for evaluating the representation of lower-tropospheric mixing in climate models, and how those mixing processes may change as the climate warms.




13:30 h


Bundesstr. 53, room 022/023
Seminar Room 022/023, Ground Floor, Bundesstrasse 53, 20146 Hamburg, Hamburg


Joe Galewsky, University of New Mexico


Bjorn Stevens

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