Transient Eddy Forcing of the Time-Mean Flow as Identified by Geopotential Tendencies

Abstract

The forcing of the time-mean flow by transient eddies is examined within the framework of a quasi-geostrophic equation relating the geopotential tendency to the convergence of transient eddy transports of heat and vorticity. The forcing functions of this equation are computed using observed circulation statistics for the wintertime Northern Hemisphere, and solutions are sought for the three-dimensional structure of geopotential and temperature tendencies associated with eddies of different time scales. In general, the geopotential tendencies associated with vorticity fluxes are of the same sign within a given atmospheric column; whereas the polarity of the geopotential tendencies associated with heat fluxes in the lower troposphere is opposite to that in the upper troposphere. The geostrophic wind tendencies associated with synoptic-scale eddies with periods between 2.5 and 6 days are strongest in the vicinity of the oceanic storm tracks. The enhanced poleward heat transports by active disturbanc... Abstract The forcing of the time-mean flow by transient eddies is examined within the framework of a quasi-geostrophic equation relating the geopotential tendency to the convergence of transient eddy transports of heat and vorticity. The forcing functions of this equation are computed using observed circulation statistics for the wintertime Northern Hemisphere, and solutions are sought for the three-dimensional structure of geopotential and temperature tendencies associated with eddies of different time scales. In general, the geopotential tendencies associated with vorticity fluxes are of the same sign within a given atmospheric column; whereas the polarity of the geopotential tendencies associated with heat fluxes in the lower troposphere is opposite to that in the upper troposphere. The geostrophic wind tendencies associated with synoptic-scale eddies with periods between 2.5 and 6 days are strongest in the vicinity of the oceanic storm tracks. The enhanced poleward heat transports by active disturbanc...