On the Role of Large-Scale Transient Eddies in the Maintenance of the Vorticity and Enstrophy of the Time-Mean Atmospheric Flow

Abstract

Abstract The global distribution of the forcing of the time-mean flow due to large-scale, horizontal Reynolds stresses (u′ u′, v′ v′, u′ v′) 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 he called the centers of action of winter-time 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 ef...