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gfdl's home page > gfdl on-line bibliography > 1981: Journal of the Atmospheric Sciences, 38(2), 270-280
On the role of large-scale transient eddies in the maintenance of the vorticity and enstrophy of the time-mean atmospheric flow
| Holopainen, E. O., and A. H. Oort, 1981: On the role of large-scale transient eddies in the maintenance of the vorticity and enstrophy of the time-mean atmospheric flow. Journal of the Atmospheric Sciences, 38(2), 270-280. |
| Abstract: The global distribution of the forcing of time-mean flow due to large-scale, horizontal Reynolds stresses is determined from upper wind statistics for the period 1968-73. The role of this forcing in the maintenance of the vorticity and enstrophy of the time-mean flow is discussed. |
| The most striking effect of transient eddy stresses is the tendency to shift the subtropical maxima in the time-mean flow and the associated vorticity patterns poleward. However, significant longitudinal variations in forcing occur, also. Calculations of the dominant terms in vorticity budgets of the North Pacific Low, the North Atlantic Low, and the Siberian High, which may be called the centers of action of wintertime circulation at sea level in the Northern Hemisphere, are presented. In all three cases, transient eddies are found to be important in maintaining the centers against the dissipative action of surface friction. |
| In terms of the enstrophy budget, the hemispheric and global-mean effects of transient eddies on the mean flow are small, both in December-February and June-August. In the Northern Hemisphere, where the results are most reliable, the eddies are weakly dissipative with a time scale on the order of several months. |
| When separating the time-mean flow into the contributions from the axisymmetric component and from the stationary disturbances, it is found that the transient eddy stresses tend to maintain the axisymmetric mean flow, but to weaken the stationary disturbances. There are significant latitudinal variations in the enstrophy forcing of the stationary disturbances. Thus eddy forcing is an important factor in maintaining the enstrophy of stationary disturbances in the extratropics, while it tends to destroy their enstrophy in the tropics. |