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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/acp-2016-964
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
08 Nov 2016
Review status
A revision of this discussion paper was accepted for the journal Atmospheric Chemistry and Physics (ACP) and is expected to appear here in due course.
Testing chemistry-climate models' regulation of tropical lower-stratospheric water vapor
Kevin M. Smalley1, Andrew E. Dessler1, Slimane Bekki2, Makoto Deushi3, Marion Marchand2, Olaf Morgenstern4, David A. Plummer5, Kiyotaka Shibata6, Yousuke Yamashita7,a, and Guang Zeng4 1Department of Atmospheric Science, Texas A & M, College Station, Texas, USA
2LATMOS, Institut Pierre Simon Laplace (IPSL), Paris, France
3Meteorological Research Institute, 1-1 Nagamine, Tsukuba, Ibaraki 305-0052, Japan
4National Institute of Water and Atmospheric Research (NIWA), Lauder, New Zealand
5Canadian Centre for Climate Modelling and Analysis, Environment and Climate Change Canada
6School of Environmental Science and Engineering, Kochi University of Technology
7National institute for Environmental Studies (NIES)
aNow at: Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokohama, Japan
Abstract. Climate models predict that tropical lower stratospheric humidity will increase as the climate warms, with important implications for the chemistry and climate of the atmosphere. We analyze the trend in 21st-century simulations from 12 state-of-the-art chemistry-climate models (CCMs) using a linear regression model to determine the factors driving the trends. Within CCMs, the long-term trend in humidity is primarily driven by warming of the troposphere. This is partially offset in most CCMs by an increase in the strength of the Brewer-Dobson circulation, which tends to cool the tropical tropopause layer (TTL). We also apply the regression model to individual decades from the 21st century CCM runs and compare them to observations. Many of the CCMs, but not all, compare well with observations, lending credibility to their predictions. One notable deficiency in most CCMs is that they underestimate the impact of the quasi-biennial oscillation on lower stratospheric humidity. Our analysis provides a new and potentially superior way to evaluate model trends in lower stratospheric humidity.

Citation: Smalley, K. M., Dessler, A. E., Bekki, S., Deushi, M., Marchand, M., Morgenstern, O., Plummer, D. A., Shibata, K., Yamashita, Y., and Zeng, G.: Testing chemistry-climate models' regulation of tropical lower-stratospheric water vapor, Atmos. Chem. Phys. Discuss., https://doi.org/10.5194/acp-2016-964, in review, 2016.
Kevin M. Smalley et al.
Interactive discussionStatus: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
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RC1: 'Review', Anonymous Referee #1, 07 Dec 2016 Printer-friendly Version 
AC1: 'Reply to RC1', Kevin Smalley, 20 Mar 2017 Printer-friendly Version Supplement 
 
RC2: 'Review', Anonymous Referee #2, 15 Jan 2017 Printer-friendly Version 
AC2: 'Reply to RC2', Kevin Smalley, 20 Mar 2017 Printer-friendly Version Supplement 
Kevin M. Smalley et al.
Kevin M. Smalley et al.

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Short summary
This paper explains a new way to evaluate model trends in lower stratospheric water vapor. We use a multivariate linear regression to predict 21st century lower stratospheric water vapor within 12 chemistry climate models using tropospheric warming, the brewer dobson circulation, and the quasi-biennial oscillation as predictors. This methodology produce strong fits to simulated water vapor, and potentially represents a superior method to evaluate model trends in lower stratospheric water vapor.
This paper explains a new way to evaluate model trends in lower stratospheric water vapor. We...
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