Abstract
The dynamical effect of the stratosphere on the troposphere is investigated in a series of numerical experiments with a simple global circulation model under a perpetual winter condition. One control simulation (CS) and four degraded stratosphere simulations (DS) are performed for three values of topographic amplitude h0 of 0, 500, and 1000 m to examine the role of forced planetary waves. In DS, the thermal relaxation rate is increased only in the stratosphere to give poor simulations there. A comparison of the tropospheric circulation between CS and DS reveals the stratospheric effect on the troposphere, or tropospheric response to the stratospheric degradation.
The numerical experiments demonstrate that the tropospheric response to the stratospheric degradation depends on h0. The response is weak for h0 = 0 and 500 m but remarkably strong for h0 = 1000 m. The response is projected onto the dominant mode of variability, or annular variability, which is the model counterpart of the Arctic Oscillation, in different ways depending on h0. The response is essentially projected onto the annular variability for h0 = 0 and 1000 m. The climatological states shift toward negative (positive) polarity of the mode for h0 = 0 m (1000 m), characterized by positive (negative) anomalies of geopotential height in high latitudes. The response is almost independent of the annual variability for h0 = 500 m. A diagnosis based on the transformed Eulerian mean equations shows that the change of the wave driving in the stratosphere can explain the tropospheric response in part, suggesting that the downward control is a mechanism at play.
Corresponding author address: Dr. Masakazu Taguchi, Dept. of Atmospheric Sciences, University of Washington, Box 351640, Seattle, WA 98195-1640. Email: taguchi@atmos.washington.edu
