Revisiting Southern Hemisphere polar stratospheric temperature trends in WACCM: The role of dynamical forcing
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2017
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American Geophysical Union
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Abstract
The latest version of the Whole Atmosphere Community Climate Model (WACCM), which includes a new chemistry scheme and an updated parameterization of orographic gravity waves, produces temperature trends in the Antarctic lower stratosphere in excellent agreement with radiosonde observations for 1969-1998 as regards magnitude, location, timing, and persistence. The maximum trend, reached in November at 100hPa, is -4.42.8Kdecade(-1), which is a third smaller than the largest trend in the previous version of WACCM. Comparison with a simulation without the updated orographic gravity wave parameterization, together with analysis of the model's thermodynamic budget, reveals that the reduced trend is due to the effects of a stronger Brewer-Dobson circulation in the new simulations, which warms the polar cap. The effects are both direct (a trend in adiabatic warming in late spring) and indirect (a smaller trend in ozone, hence a smaller reduction in shortwave heating, due to the warmer environment).
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©2017. American Geophysical Union. All Rights Reserved.We thank W.J. Randel and two anonymous reviewers for their comments, which have resulted in an improved paper. The National Center for Atmospheric Research (NCAR) is sponsored by the U.S. National Science Foundation (NSF). N. Calvo acknowledges partial support from the European Project 603557-STRATOCLIM under program FP7-ENV.2013.6.1-2 and from the Spanish Ministry of Economy and Competitiveness through the PALEOSTRAT (CGL2015-69699-R) project. R.R. García was supported in part by NASA grant X09AJ83G; and D.E. Kinnison was supported in part by NSF Frontiers in Earth System Dynamics grant OCE-1338814. WACCM is a component of NCAR's CESM, which is supported by the NSF and the Office of Science of the U.S. Department of Energy. Computing resources were provided by NCAR's Climate Simulation Laboratory, sponsored by NSF and other agencies. This research was enabled by the computational and storage resources of NCAR's Computational and Information Systems Laboratory (CISL). The ozone and temperature data used in this study are available from the references cited; model output has been stored at NCAR and is available from the authors.