HR: 11:35h
AN: A12A-06 INVITED     [Abstracts]
TI: Extratropical Stratosphere-Troposphere Dynamical Coupling: Perspectives from a Simple AGCM
AU: * Kushner, P J
EM: paul.kushner@utoronto.ca
AF: Department of Physics, University of Toronto, 60 St. George St., Toronto, On M5S 1A7 Canada
AB: As evidence grows that stratospheric conditions might signficantly influence the tropospheric circulation, many questions remain about the dynamics of this influence. A useful tool for beginning to answer these questions is a class of relatively simple atmospheric general circulation models (AGCMs) that use highly idealized model "physics" and are capable of simulating realistic extratropical stratosphere-tropospohere eddy-mean-flow interactions. In this talk, two sets of simple-AGCM calculations are described that lend insight into the time dependence of strat-trop coupling on 10-100 day and on climate timescales. In the first set, transient stratosphere-troposphere coupling events are stimulated using wave-activity pulses that are initiated in the troposphere, propagate into the stratosphere, and return with some delay into the troposphere. These calculations show that the initial stratospheric state can exert significant control on the delay of the return signal. In the second set of calculations, a long-term tropospheric circulation response is stimulated by stratospheric cooling. When the model is run without a seasonal cycle, the troposphere responds strongly but takes several hundred days to fully equilibrate. When the model is run with a seasonal cycle, the troposphere responds more weakly, but so does the stratosphere, so that the ratio of the stratospheric response to the tropospheric response remains approximately constant with and without a seasonal cycle. These and other results demonstrate that the eddy-drag responses in the stratosphere and troposphere are highly coupled and serve to dampen, not amplify, the imposed thermal perturbation. Taken together, both sets of calculations leave open several questions, including the issue of what ultimately controls the timescale of the downward propagation of stratosphere-to-troposphere signals and of the long-term tropospheric adjustment.
UR: http://individual.utoronto.ca/paul\_kushner
DE: 3362 Stratosphere/troposphere interactions
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting