12th Conference on Middle Atmosphere

Wednesday, 6 November 2002: 2:35 PM
Dynamical response of the troposphere and stratosphere to radiative equilibrium changes in a simple global circulation model
Masakazu Taguchi, University of Washington, Seattle, WA; and D. L. Hartmann
A series of numerical experiments with a simple global circulation model are performed to investigate to what extent planetary wave-mean flow interaction increases the response of the troposphere and stratosphere to forcing by the greenhouse-gas increase and ozone depletion.

The model used here is a 3D global primitive model with a resolution of T21L42, which also includes simplified physical processes such as Newtonian thermal relaxation toward a perpetual winter condition. Control runs are redone under the same conditions as in a previous study (Taguchi et al. 2001), and perturbation runs are carried out by imposing changes of the radiative equilibrium state in the stratosphere. One of the imposed temperature change fields mimics the change by doubled CO2. It is characterized by stratospheric cooling with negative meridional and vertical gradient of the temperature change, which also includes warming in the tropical upper troposphere. The set of control and perturbation runs are repeated for different values of amplitude of a sinusoidal surface topography to examine role of forced planetary waves in the dynamical response.

Preliminary simulations have shown that, while the dynamical response is small for no planetary wave forcing, it can be large for large wave forcing and act to increase the imposed cooling in the high-latitude lower stratosphere. This suggests a possibility that atmospheric composition changes trigger positive feedback between radiative and dynamical processes to induce the observed lower stratospheric cooling.

Supplementary URL: