Feedbacks between the isentropic slope and wave generation at tropospheric levels and implications for stratosphere/troposphere coupling

Extratropical tropospheric variability is investigated during Northern Hemisphere winter in the context of feedbacks between the meridional slope of the isentropic surfaces and the generation of eddy activity in the lower troposphere. The results reveal that at mid-high latitudes, periods of anomalously large tropospheric eddy heat fluxes (and thus wave generation) are preceded by anomalously steep isentropic surfaces in the free troposphere, and followed by anomalously poleward eddy momentum fluxes near the tropopause. The lag between the isentropic slope and wave generation is consistent with our theoretical understanding of baroclinic instability. The lag between the eddy fluxes of heat and momentum suggests that variability in the momentum fluxes is driven in part by variability in wave generation near the Earth’s surface. The forcing of tropospheric wave generation by variations in the isentropic slope are applied to the dynamics of stratosphere/troposphere coupling. Periods of anomalous wave driving at stratospheric levels are associated with an anomalous downward flux of mass over polar latitudes that extends to tropospheric levels. The anomalous mass fluxes act to flatten isentropic surfaces throughout the mid-high latitude troposphere and are accompanied by a reduction in wave generation at the surface. The results provide observational support for robust linkages between variability in the stratospheric mass circulation, the slope of the tropospheric isentropes, and the generation of eddies in the lower troposphere. They do not provide a complete explanation for the observed linkages between stratospheric variability and the anomalous wave fluxes of momentum at the tropopause level.