2004: Stratosphere–troposphere coupling in a relatively simple AGCM: The role of eddies

• Main Authors: Edwin P. Gerber, Lorenzo M. Polvani
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: polar night
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.574.2608; http://www.columbia.edu/~lmp/paps/gerber+polvani-JCLIM-2009.pdf

The impact of stratospheric variability on the dynamical coupling between the stratosphere and the tro-posphere is explored in a relatively simple atmospheric general circulation model. Variability of the model’s stratospheric polar vortex, or polar night jet, is induced by topographically forced stationary waves. A robust relationship is found between the strength of the stratospheric polar vortex and the latitude of the tropo-spheric jet, confirming and extending earlier results in the absence of stationary waves. In both the clima-tological mean and on intraseasonal time scales, a weaker vortex is associated with an equatorward shift in the tropospheric jet and vice versa. It is found that the mean structure and variability of the vortex in the model is very sensitive to the amplitude of the topography and that Northern Hemisphere–like variability, with a realistic frequency of stratospheric sudden warming events, occurs only for a relatively narrow range of topographic heights. When the model captures sudden warming events with fidelity, however, the exchange of information both upward and downward between the troposphere and stratosphere closely resembles that in observations. The in-fluence of stratospheric variability on variability in the troposphere is demonstrated by comparing integra-tions with and without an active stratosphere. A realistic, time-dependent stratospheric circulation increases the persistence of the tropospheric annular modes, and the dynamical coupling is most apparent prior to and following stratospheric sudden warming events. 1.