HR: 0800h
AN: A31A-0018    [Abstracts]
TI: Sensitivity Of The Low Frequency Variability Of The Atmosphere To The Surface Friction In An Idealized Model
AU: * Chen, G
EM: gchenpu@mit.edu
AF: MIT, Program in Atmospheres, Oceans, and Climate, Cambridge, MA 02139, United States
AB: The low frequency variability of the atmosphere can play an important role in the climate response to external forcing. The persistence of the jet vacillation can often vary with the latitudinal shift of the climatological mean jet. We study the sensitivity of the low frequency variability of surface westerlies associated with the poleward shift of surface westerlies when the surface friction is reduced in the Held and Suarez model (1994, BAMS). In spite of the longer frictional damping scale, the westerlies are less persistent, as the barotropic shear of zonal flow gets stronger and shears out the jet vacillation. We further examine this mean flow modification from the viewpoint of the zonal mean momentum balance in both the equilibrated response and instantaneous response to a change in surface friction. Additionally, a simple shallow water model of upper troposphere is constructed, suggesting that the effect of the mean flow on eddies, possibly through changes in eddy phase speeds, may be important in generating this low frequency vacillation.
DE: 1620 Climate dynamics (0429, 3309)
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting