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Process-evaluation of tropospheric humidity simulated by general circulation models using water vapor isotopic observations: 2. Using isotopic diagnostics to understand the mid and upper tropospheric moist bias in the tropics and subtropics

Risi, Camille and Noone, David and Worden, John and Frankenberg, Christian and Stiller, Gabriele and Kiefer, Michael and Funke, Bernd and Walker, Kaley and Bernath, Peter and Schneider, Matthias and Bony, Sandrine and Lee, Jeonghoon and Brown, Derek and Sturm, Christopher (2012) Process-evaluation of tropospheric humidity simulated by general circulation models using water vapor isotopic observations: 2. Using isotopic diagnostics to understand the mid and upper tropospheric moist bias in the tropics and subtropics. Journal of Geophysical Research, 117 (D5). Art. No. D05304. ISSN 0148-0227. http://resolver.caltech.edu/CaltechAUTHORS:20150508-161624459

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Abstract

Evaluating the representation of processes controlling tropical and subtropical tropospheric relative humidity (RH) in atmospheric general circulation models (GCMs) is crucial to assess the credibility of predicted climate changes. GCMs have long exhibited a moist bias in the tropical and subtropical mid and upper troposphere, which could be due to the mis-representation of cloud processes or of the large-scale circulation, or to excessive diffusion during water vapor transport. The goal of this study is to use observations of the water vapor isotopic ratio to understand the cause of this bias. We compare the three-dimensional distribution of the water vapor isotopic ratio measured from space and ground to that simulated by several versions of the isotopic GCM LMDZ. We show that the combined evaluation of RH and of the water vapor isotopic composition makes it possible to discriminate the most likely cause of RH biases. Models characterized either by an excessive vertical diffusion, an excessive convective detrainment or an underestimated in situ cloud condensation will all produce a moist bias in the free troposphere. However, only an excessive vertical diffusion can lead to a reversed seasonality of the free tropospheric isotopic composition in the subtropics compared to observations. Comparing seven isotopic GCMs suggests that the moist bias found in many GCMs in the mid and upper troposphere most frequently results from an excessive diffusion during vertical water vapor transport. This study demonstrates the added value of water vapor isotopic measurements for interpreting shortcomings in the simulation of RH by climate models.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1029/2011JD016623DOIArticle
http://onlinelibrary.wiley.com/doi/10.1029/2011JD016623/abstractPublisherArticle
http://onlinelibrary.wiley.com/doi/10.1029/2011JD016623/suppinfoPublisherSupporting Information
ORCID:
AuthorORCID
Risi, Camille0000-0002-8267-453X
Frankenberg, Christian0000-0002-0546-5857
Additional Information:© 2012 American Geophysical Union. Received 26 July 2011; revised 28 December 2011; accepted 30 December 2011; published 6 March 2012. We thank Debra Wunch, Vanessa Sherlock, Nicholas Deutscher, David Griffith, Paul Wennberg, Kimberly Strong, Sabine Barthlott, Frank Hase, Omaira García, Dan Smale, Emmanuel Mahieu, Justus Notholt, Thorsten Warneke and Geofrey Toon for their roles in acquiring the ground-based remote-sensing data and developing the retrievals, for making the data available, for helping with the data processing and for their useful advice to develop the rigorous model-data comparison methodology used in this paper. We thank David Sayres for providing in situ and aircraft data. We also thank Debra Wunch, Vanessa Sherlock, Nicholas Deutscher, Paul Wennberg and Kimberly Strong for detailed comments on the manuscript. Level-1b data of MIPAS have been provided by ESA. The ACE mission is supported mainly by the Canadian Space Agency. We thank the Anderson Group at Harvard University for providing ICOS and Hoxotope in situ aircraft data. We acknowledge all FTIR activities as in P1. The mid-infrared FTIR retrievals have been performed in the framework of the project MUSICA (http://www.imk-asf.kit.edu/english/musica), which is funded by the European Research Council under the European Community's Seventh Framework Programme (FP7/2007–2013)/ERC grant agreement 256961. We thank Omaira García who was in charge of the FTIR activities at Izaña. We thank all SWING2 members for producing and making available their model outputs. SWING2 was supported by the Isotopic Hydrology Programme at the International Atomic Energy Agency (more information on http://people.su.se/∼cstur/SWING2). We thank Françoise Vimeux for discussions. This work was supported by NASA Energy and Water-cycle Study (07-NEWS07-0020) and NASA Atmospheric Composition program (NNX08AR23G). We thank anonymous reviewers for their constructive comments.
Funders:
Funding AgencyGrant Number
Canadian Space Agency (CSA)UNSPECIFIED
European Research Council (ERC)FP7/2007– 2013
NASA07-NEWS07-0020
NASANNX08AR23G
Subject Keywords:general circulation models; process-based evaluation; relative humidity; water isotopes
Record Number:CaltechAUTHORS:20150508-161624459
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20150508-161624459
Official Citation:Risi, C., et al. (2012), Process-evaluation of tropospheric humidity simulated by general circulation models using water vapor isotopic observations: 2. Using isotopic diagnostics to understand the mid and upper tropospheric moist bias in the tropics and subtropics, J. Geophys. Res., 117, D05304, doi:10.1029/2011JD016623.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:57392
Collection:CaltechAUTHORS
Deposited By: Jason Perez
Deposited On:11 May 2015 23:20
Last Modified:06 Apr 2017 23:13

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