HR: 0800h
AN: A31A-0049    [Abstracts]
TI: The Evolution of Stratospheric Dynamics and Thermal Structure in the Presence of a Weak Surface Temperature Gradient
AU: * Korty, R L
EM: korty@mit.edu
AF: Massachusetts Institute of Technology, 77 Massachusetts Avenue Room 54-1611, Cambridge, MA 02139 United States
AB: The dynamic response of the stratosphere to a weak pole-to-equator surface temperature gradient is examined in order to assess the ease with which polar stratospheric clouds might have formed during warm climates in the geologic record. This study uses a general circulation model with a resolved middle atmosphere to analyze the changes in the general circulation during warm climates and their effects on the residual mean circulation in the winter stratosphere. While the eddy kinetic and potential energies of the entire atmosphere decrease markedly when the surface temperature gradient is weakened, the eddy energy in the stratosphere remains largely unchanged. This is partially attributable to the relative stability of the amount of energy in the largest stationary eddies, but the dynamic response of the lower stratosphere also contributes by altering the refractive index for vertically propagating waves. The pole-to-equator gradient in the height of the tropopause lessens as the surface temperature gradient decreases, limiting the depth to which the polar stratospheric vortex penetrates. The resulting adjustment of the lower stratospheric meridional temperature gradient produces winds in thermal wind balance that are considerably lighter in the lower stratosphere than in present observations. This allows energy in some shorter stationary eddies to propagate vertically into the stratosphere, ensuring that the residual mean circulation of the winter stratosphere remains strong. The convergence of the Eliassen-Palm Flux in the stratosphere is larger in the simulations with a weak surface temperature gradient than in those with a contemporary one. Temperatures during the polar night remain as far from radiative equilibrium values in simulations using the weak surface temperature gradient as in simulations using a present one.
DE: 3334 Middle atmosphere dynamics (0341, 0342)
DE: 3344 Paleoclimatology
DE: 3319 General circulation
DE: 1620 Climate dynamics (3309)
DE: 0342 Middle atmosphere--energy deposition
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting