On the lack of stratospheric dynamical variability in low-top versions of the CMIP5 models
Journal of Geophysical Research: Atmospheres
American Geophysical Union
This is the final version of the article. Available from the American Geophysical Union via the DOI in this record.
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.
We acknowledge the World Climate Research Programme’s Working Group on Coupled Modelling, which is responsible for CMIP, and we thank the climate modeling groups for producing and making available the model output listed in Table 1. For CMIP the U.S. Department of Energy’s Program for Climate Model Diagnosis and Intercomparison provides coordinating support and led development of software infrastructure in partnership with the Global Organization for Earth System Science Portals. A.J.C.-P. and L.J.W. were supported by an National Centre for Atmospheric Science CMIP5 grant. M.P.B. was funded by NSF under the US CLIVAR program and the Office of Polar Programs. T.B. and N.A.D. acknowledge support by the U.S. National Science Foundation. The research efforts of R.X.B., B.A.M. & Y.-Y.L. were conducted under support by the U.S. Department of Energy, Office of Biological and Environmental Research, Award No. DE-FOA- 000024 and by the National Science Foundation Grant, ARC-1107384. N.C. was supported by the Spanish Ministry of Science and Innovation (MCINN) through the CGL2008-05968-C02-01 project. E.P.G. was supported by the National Science Foundation. The work of M.T. and K. K. contributes to the BMBF joint research project MiKlip within the project ALARM through the grant 01LP1130B. The work of S.C.H. was supported by the Joint DECC/Defra Met Office Hadley Centre Climate Programme (GA01101). We also acknowledge the European Commission’s 7th Framework Programme, under Grant Agreement number 226520, COMBINE project which supplied some data not available from the CMIP5 archive. We also thank Gerard Devine (NCAS-CMS) for help with accessing and parsing meta-data information from the models.
Journal of Geophysical Research Atmospheres, Vol. 118, pp. 2494 - 2505