On the lack of stratospheric dynamical variability in low-top versions of the CMIP5 models
We describe the main differences in simulations of stratospheric climate and variability by models within the fifth Coupled Model Intercomparison Project (CMIP5) that have a model top above the stratopause and relatively fine stratospheric vertical resolution (high-top), and those that have a model top below the stratopause (low-top). Although the simulation of mean stratospheric climate by the two model ensembles is similar, the low-top model ensemble has very weak stratospheric variability on daily and interannual time scales. The frequency of major sudden stratospheric warming events is strongly underestimated by the low-top models with less than half the frequency of events observed in the reanalysis data and high-top models. The lack of stratospheric variability in the low-top models affects their stratosphere-troposphere coupling, resulting in short-lived anomalies in the Northern Annular Mode, which do not produce long-lasting tropospheric impacts, as seen in observations. The lack of stratospheric variability, however, does not appear to have any impact on the ability of the low-top models to reproduce past stratospheric temperature trends. We find little improvement in the simulation of decadal variability for the high-top models compared to the low-top, which is likely related to the fact that neither ensemble produces a realistic dynamical response to volcanic eruptions. © 2013. American Geophysical Union. All Rights Reserved.
Charlton-Perez, AJ; Baldwin, MP; Birner, T; Black, RX; Butler, AH; Calvo, N; Davis, NA; Gerber, EP; Gillett, N; Hardiman, S; Kim, J; Krüger, K; Lee, YY; Manzini, E; McDaniel, BA; Polvani, L; Reichler, T; Shaw, TA; Sigmond, M; Son, SW; Toohey, M; Wilcox, L; Yoden, S; Christiansen, B; Lott, F; Shindell, D; Yukimoto, S; Watanabe, S
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