Stratosphere-troposphere coupling and annular mode variability in chemistry-climate models

Edwin P. Gerber, Mark P. Baldwin, Hideharu Akiyoshi, John Austin, Slimane Bekki, Peter Braesicke, Neal Butchart, Martyn Chipperfield, Martin Dameris, Sandip Dhomse, Stacey M. Frith, Rolando R. Garcia, Hella Garny, Andrew Gettelman, Steven C. Hardiman, Alexey Karpechko, Marion Marchand, Olaf Morgenstern, J. Eric Nielsen, Steven PawsonTom Peter, David A. Plummer, John A. Pyle, Eugene Rozanov, John F. Scinocca, Theodore G. Shepherd, Dan Smale

Research output: Contribution to journalArticlepeer-review

Abstract

The internal variability and coupling between the stratosphere and troposphere in CCMVal-2 chemistry-climate models are evaluated through analysis of the annular mode patterns of variability. Computation of the annular modes in long data sets with secular trends requires refinement of the standard definition of the annular mode, and a more robust procedure that allows for slowly varying trends is established and verified. The spatial and temporal structure of the models annular modes is then compared with that of reanalyses. As a whole, the models capture the key features of observed intraseasonal variability, including the sharp vertical gradients in structure between stratosphere and troposphere, the asymmetries in the seasonal cycle between the Northern and Southern hemispheres, and the coupling between the polar stratospheric vortices and tropospheric midlatitude jets. It is also found that the annular mode variability changes little in time throughout simulations of the 21st century. There are, however, both common biases and significant differences in performance in the models. In the troposphere, the annular mode in models is generally too persistent, particularly in the Southern Hemisphere summer, a bias similar to that found in CMIP3 coupled climate models. In the stratosphere, the periods of peak variance and coupling with the troposphere are delayed by about a month in both hemispheres. The relationship between increased variability of the stratosphere and increased persistence in the troposphere suggests that some tropospheric biases may be related to stratospheric biases and that a well-simulated stratosphere can improve simulation of tropospheric intraseasonal variability.

Original languageEnglish (US)
Article numberD00M06
JournalJournal of Geophysical Research Atmospheres
Volume115
Issue number18
DOIs
StatePublished - 2010

ASJC Scopus subject areas

  • Geophysics
  • Forestry
  • Oceanography
  • Aquatic Science
  • Ecology
  • Water Science and Technology
  • Soil Science
  • Geochemistry and Petrology
  • Earth-Surface Processes
  • Atmospheric Science
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science
  • Palaeontology

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